The Gypsy Moth in Connecticut RECEIVED 1. Defoliation 1975-1980 JANi3^u 2. Review of Biological C®flforcrodtes By John P. Anderson and Ronald M. Weseloh 197S 63,411 acres 1976 9,809 acres 1977 0 acres in 0 towns 1978 4,680 acres 1979 8,589 acres 1980 381,868 acres in 131 towns TOWNS IN WHICH NOTICEABLE DEFOLIATION OCCURRED IN CONNECTICUT DURING 1975-1 980. BULLETIN 797 • THE CONNECTICUT AGRICULTURAL EXPERIMENT STATION NEW HAVEN • APRIL 1981 i a Digitized by the Internet Archive in 2011 with funding from LYRASIS members and Sloan Foundation http://www.archive.org/details/gypsymothinconneOOande The Gypsy Moth in Connecticut 1. Defoliation 1975-1980 2. Review of Biological Control Studies By John F. Anderson and Ronald M. Weseloh Although the first gypsy moth, Lymantria dispar (L. )1, was collected in Connecticut in 1905 (Britton 1906), extensive defoliation (> 1000 acres) did not occur until 1938 (Friend 1945). Outbreaks covering thousands of acres began in the 1950s (Turner 1963a), with the most extensive ones developing in the early 1970s (Anderson and Gould 1974). Gypsy moth popu- lations declined in the late 1970s, but increased sub- stantially in 1980. Early methods of controlling gypsy moths relied upon ground spraying of infested trees with chem- ical pesticides and procedures such as egg mass de- struction (Hitchcock 1974). Aerial spraying of some infested forest land with chemical pesticides began in the 1950s and continued through 1971. State regu- lations now prohibit the aerial application of chem- ical pesticides to forests and require written release statements from all land owners subject to aerially applied chemical sprays for agricultural purposes or biological sprays aerially applied to woodlands. Citi- zens still rely upon methods used decades ago to cope with gypsy moth infestations, although insec- ticide formulations have changed. This publication documents defoliation from 1975 through 1980 and reviews the Station's biological con- trol investigations. An earlier publication described Connecticut outbreaks from 1969 through 1974 (An- derson and Gould 1974) and another recent publica- tion reported the history, life cycle, and methods of control of the gypsy moth in Connecticut (Anderson 1980). Effects of defoliation on tree mortality and forest succession in Connecticut were examined in a series of papers (Turner 1963b, Stephens 1963, 1971, Stephens and Hill 1971, Stephens and Waggoner 1970, 1980). 1 Lepidoptera: Lymantriidae Connecticut Agricultural Experiment Station Bulletin 797 Defoliation, 1975-1980 Annual defoliation data document duration of out- breaks and caterpillar dispersal, and may assist in relating gypsy moth feeding to tree mortality and for- est succession. These data may also assist in pre- dicting caterpillar dispersal and the length of future outbreaks. The location, intensity, spread, and du- ration of gypsy moth outbreaks during 1975-1980 are reported. Methods used were essentially those reported by Anderson and Gould (1974). Aerial defoliation sur- veys were made in early July of each year. Intensity of defoliation and its magnitude were recorded on a topographic survey map with a scale of 1 : 125,000. Acreage defoliated within each town was calculated by using a modified acreage grid.- Defoliation cate- gories used were: 10-25%, 26-50%, 51-75%, and 76-100%. Table 1 shows the intensity of defoliation recorded by county and the total for the state for each year. Total defoliation for each town is shown in Tables 3-10. Figures 1-5 illustrate the location and intensity of defoliation for 1975, 1976, 1978, 1979 and 1980 (no defoliation occurred in 1977). 1975 Gypsy moth defoliation totalled 63,411 acres, 57,569 acres less than in 1974 (Fig. 1). Out- breaks were recorded in 37 towns in five counties. Windham County recorded the largest acreage of de- foliation (43,374 acres) and was the only county to experience an increase from 1974. The Town of Can- terbury had 11,397 acres affected. Brooklyn and Pom- fret had 5,000 to 6,000 acres defoliated. The intensity of defoliation was 75% or less in all areas. 1976 Defoliation totalled 9,809 acres, 53,602 acres less than in 1975 (Fig. 2). Caterpillars were abundant in 25 towns within the three eastern coun- ties of Tolland, Windham and New London. Popu- lation densities had declined to nondefoliation lev- els in Litchfield and Hartford Counties. Defoliation was less than 2,000 acres in each town. Defoliation was most extensive again in Windham County, al- though it totalled slightly less than 6,000 acres. The intensity of defoliation was 75% or less in all areas. This was the fifth year in succession that total defolia- tion had declined significantly from the year before. 1 977 For the first time since 1949, gypsy moths caused no defoliation. 1978 Outbreaks in six towns in Tolland and Windham Counties resulted in 4,680 acres being de- foliated (Fig. 3). Defoliation in each town was less than 2,000 acres, and 390 acres were completely de- foliated. 1979 Defoliation totalled 8,589 acres, an in- crease of 3,909 from the year before (Fig. 4). It oc- curred in three towns in Windham County. In Thomp- son, 7,292 acres were affected. Most of the acreage was defoliated 26-50%, although 700 acres were nearly completely defoliated. 1980 Gypsy moth defoliation totalled 381.868 acres in 131 towns, 373,279 acres more than the year before (Fig. 5). It was recorded in all eight counties, but was most extensive in the western counties of Fairfield, Litchfield, Hartford, and New Haven. Five towns (Thompson, Burlington, Stamford, Oxford, and Voluntown) had 10,000-15,000 acres defoliated. An- other 22 towns had 5,000-10,000 acres defoliated. A total of 110,877 acres was 75-100% defoliated, the larg- est amount ever recorded in that category. An ad- ditional 120,802 acres were 51-75% defoliated. Fall cankerworms, Ahophila pometeria (Harris), were abundant in some areas of New Haven, Fairfield and Hartford counties. Origin, geographical spread and duration of out- breaks The cyclic nature of gypsy moth outbreaks in Connecticut is evident in the figure. When the state 800,000 600,000 400,000 200,000 1950 1980 Total forest acreages defoliated and aerially sprayed (shaded area) in Connecticut since 1950. Acreage defoliated from 1970-1972 includes defoliation by the elm spanworm. (Data to 1962 from Turner (1963a); data from 1969 to 1974 from Anderson and Gould (1974)). as a whole is considered, dense caterpillar popula- tions feeding over large acreages of woodland recurred at eight- to ten-year intervals and persisted for five or six years. If this trend continues, large acreages will be defoliated in the early 19S0s. The significant increase in defoliation in the 1970s was due not only to the presence of the elm spanworm, but also to the fact that for the first time, outbreaks originated in southwestern Connecticut and subsequently spread through central portions of the state. The 19S0 out- break in large part had similar origins, and, although " Forestry Suppliers, Inc., Jackson, Miss. The Gypsy Moth in Connecticut Table 1. Intensity of defoliation by county in Connecticut, 1975-1980. Acres/Percent Defoliation County Year 10-25 26-50 51-75 76-100 Total Defoliation County Acreage Litchfield 1975 1976 1977 1978 1979 1980 ,673 5,772 507 18,369 25,057 25,974 2,180 75,172 607,168 Hartford 1975 1976 1977 1978 1979 1980 1,595 6,162 312 14,644 17,160 28,197 1,907 66,183 480,128 Tolland 1975 1976 1977 1978 1979 1980 1,867 2,340 973 3,075 1,443 1,673 4,513 3,075 3,783 268,848 Windham 1975 1976 1977 1978 1979 1980 13,926 19,539 12,448 5,954 1,248 7,683 507 17,000 39 1,365 234 8,190 390 672 897 43,374 5,993 3,003 8,589 29,133 332,740 Fairfield 1975 1976 1977 1978 1979 1980 9,633 22,269 35,412 29,952 97,266 422,031 New Haven 1975 1976 1977 1978 1979 1980 4,758 19,617 31,239 25,545 81,159 399,016 Middlesex 1975 1976 1977 1978 1979 1980 3,861 10,725 3,744 312 1 8,642 248,028 New London 1975 1976 1977 1978 1979 1980 8,714 312 1,677 10,530 2,489 234 234 195 11,437 741 1,677 10,530 63,411 9,809 0 390 4,680 672 8,589 0,877 381,868 448,576 State Totals 1975 1976 1977 1978 1979 1980 27,775 312 1,677 62,595 16,729 9,263 1,248 7,683 87,594 18,907 234 1,365 234 120,802 Connecticut Agricultural Experiment Station Bulletin 797 the defoliation was caused almost entirely by gypsy moths, fall cankerworms were abundant locally. Gypsy moth outbreaks crash naturally from epi- zootics of the nuclear polyhcdrosis virus and insuffi- cient quantities of food for the caterpillars (Camp- bell 1963, Doane.1970). Although causes of outbreaks are less understood, the immigration of large num- bers of wind blown caterpillars into an area may be a source of inoculum. In Connecticut, outbreaks tend to move in a northeasterly direction (Anderson and Gould 1974). The 1975 and 1976 outbreaks appear to have been extensions of those in previous years. The 1978 and 1979 outbreaks in northeastern Con- necticut may have originated de novo, or they could have arisen from outbreaks occurring in 1978 in near- by Massachusetts towns (USDA, APHIS defoliation map). The 1980 outbreak in western Connecticut may have had its origin in Dutchess, Putnam and West- chester Counties, New York where defoliation occurred in 1978-1980 (USDA, APHIS defoliation map). Cater- pillars probably blew into Connecticut from New York in the spring of 1978 and 1979 to contribute to the outbreak in 1980. However, part of the 1980 outbreak may have been due to increases in indigenous popu- lations. Infestations along the Connecticut River in Middlesex and Hartford Counties are substantially removed from inoculum sources in New York and some may have originated de novo. The sudden appear- ance of the 1980 outbreak in western Connecticut was similar to that of the elm spanworm-gypsy moth outbreaks of a decade before (Anderson and Gould 1974). It is likely that areas to the east of presently infested locations (Fig. 5) will be defoliated in 1981 and the following years, as in the early 1970s. The colonization by the gypsy moth of vast acre- ages of woodland to the west and southwest of Con- necticut during the past three decades (Campbell 1979) has influenced, and will probably continue to influence, gypsy moth populations in the state. All towns in Connecticut and towns in eastern New York were known to be infested in 1952. By 1974, the gypsy moth had spread throughout most of New York, much of Pennsylvania, and all of New Jersey. With pre- vailing winds coming from the southwest, caterpil- lars developing in outbreaks in these areas to the west (particularly in southeastern New York and in north- ern New Jersey) may spread into Connecticut as they apparently did in 1978 and 1979. We therefore believe that outbreaks will continue to occur at fre- quent intervals and, at times, will encompass vast areas of the state's woodland. The duration of outbreaks was determined by cal- culating the number of consecutive years of defolia- tion within town boundaries for the period 1969-1977. Data were compiled from Tables 3-10 and from An- derson and Gould (1974). The mean number of con- secutive years of defoliation was 2.9 ± 1.6 SD years per town, with a range of 1 to 8 years. Analysis of towns within specific counties revealed that outbreaks persisted longer in the eastern counties. In the four western counties (Litchfield, Hartford, Fairfield and New Haven), outbreaks averaged 1.8 to 2.8 years. In contrast, outbreaks in the eastern counties (Tolland. Windham, New London and Middlesex) averaged 3 to 4.4 years (Table 2). Toble 2. Duration of town outbreaks arranged by County, 1969-1977. County X duration (consecu- tive years) of defoliation per town Litchfield Hartford Tolland Windham Fairfield New Haven Middlesex New London 2.6 ± 1.2 2.2 ± 0.9 4.0 ± 1.4 4.4 ± 2.4 1.8 ±0.5 2.8 ± 1.0 3.0 ±0.8 3.5 ±2.0 The less persistent outbreaks in western Connecti- cut reflect the inclusion of elm spanworm defoliation data. Outbreaks of this insect in western Connecticut lasted only 1 or 2 years (Kaya and Anderson 1974). The data from the eastern counties are more repre- sentative of gypsy moth infestations. Thus, gypsy moth outbreaks usually last 3-4 years within a town and may persist as long as 8 years, but some also col- lapse after only 1 year. (Since outbreaks from one year to the next within a town will vary in size and location, the number of successive years of defoliation within a given locale of a particular town will often be smaller than that reported here for town out- breaks. ) Table 3. Noticeable defoliation by town in Middlesex County, 1975-1980. No defoliation was ex- perienced during 1975-1979. Acres/year Town Town Name 1980 Acreage Chester 1 17 10,176 Clinton 1,365 11,008 Cromwell 8,640 Deep River 468 9,088 Durham 702 14,912 East Haddam 36,864 East Hampton 429 23,552 Essex 624 7,808 Haddam 1,755 29,888 Killingworth 7,293 23,040 Middletown 1,053 27,392 Middlefield 8,412 Old Saybrook 1,365 1 1,712 Portland 1,677 15,168 Westbrook 1,794 10,368 The Gypsy Moth in Connecticut Table 4. Noticeable defoliation by town in Litchfield County, 1975-1980. No defoliation was experienced during 1976-1979. Table 6. Noticeable defoliation by town in New London County, 1975-1980. No defoliation was experi- enced during 1977 and 1979. Acres/year Acres /year Town Town Town Name 1975 1980 Acreage Town Name Bozrah 1975 467 1976 1978 1980 Acreage Barkhamsted 3,744 24,960 12,800 Bethlehem 1,170 12,608 Colchester 156 31,100 Bridgewater 1,677 10,432 East Lyme 1,245 78 22,272 Canaan 2,340 21,376 Franklin 1,985 12,800 Colebrook 21,120 Griswold 78 78 24,064 Cornwall 350 1,950 29,952 Groton 78 24,512 Goshen 195 29,184 Lebanon 1 17 35,904 Harwinton 8,736 20,096 Ledyard 25,920 Kent 234 31,680 Lisbon 1,01 1 78 10,560 Litchfield 7,683 36,672 Lyme 1 17 21,120 Morris 3,783 12,032 Montville 31 1 28,096 New Hartford 9,535 24,512 New London 4,672 New Milford 2,613 41,126 North Stoningtor i 36,032 Norfolk 1,131 29,888 Norwich 661 17,344 North Canaan 1,248 12,544 Old Lyme 2,528 156 17,344 Plymouth 7,800 14,336 Preston 20,032 Roxbury 3,276 16,896 Salem - 19,136 Salisbury 78 1,092 38,720 Sprague 2,217 8,576 Sharon 1,090 355 38,592 Stonington 78 27,238 Thomaston 1,716 7,680 Voluntown 195 1,677 10,452 25,408 Torrington 3,705 25,600 Waterford 622 23,488 Warren Washington 662 819 17,920 24,768 3,744 Watertown 2,028 19,072 Winchester 195 21,760 Woodbury 4,407 23,552 Table 7. Noticeable defoliation hv frown in Hnrf-fnrH Cnuntv 1975- 1980. No c lefoliation was experienc ed during 1976- 1979. Acres/year Town Table 5. Noticeable defoliation by town in Fairfield Town Name 1975 1980 Acreage County, 1975-1980. No i defoliation was ex- perienced d uring 1975-1979. Avon 6,201 1 5,040 Berlin Bloomfield 2,184 1,482 17,280 Acres/yi Jar 16,896 Town Bristol 2,925 17,024 Town Name 1980 Acreage Burlington Canton 14,976 6,981 19,584 16,000 1 1,136 Bethel 1,794 10,880 East Granby 1 17 Bridgeport 39 11,200 East Hartford 1,053 11,584 Brookfield 1,248 12,672 East Windsor 17,152 Danbury 3,393 28,160 Enfield 428 2,769 21,632 Darien 897 9,536 Farmington 4,680 18,368 Easton 5,616 18,432 Glastonbury 2,808 33,600 Fairfield 3,900 19,584 Granby 1 ,206 4,875 26,432 Greenwich 6,123 32,384 Hartford 1 17 1 1,776 Monroe 3,276 16,896 Hartland 273 780 22,080 New Canaan 5,226 14,812 Manchester 39 17,408 New Fairfield 2,613 16,512 Marlborough 1 5,040 Newtown 9,399 38,643 New Britain 312 8,512 Norwalk 1,014 17,728 Newington 312 8,448 Redding 7,059 20,608 Plainville 1,404 6,336 Ridgefield 6,240 22,400 Rocky Hill 8,896 She 1 ton 2,847 20,096 Simsbury 6,201 22,080 Sherman 5,031 15,040 Southington 3,081 23,616 Stamford 10,842 24,640 South Windsor 312 1 8,240 Stratford 741 1 1 ,968 Suffield 663 27,584 Trumbull 1,989 15,040 West Hartford 1,014 14,208 Weston 8,853 13,312 Wethersfield 234 8,320 Westport 1,092 14,336 Windsor 351 19,968 Wilton 8,034 17,152 Windsor Locks 312 5,888 Connecticut Agricultural Experiment Station Bulletin 797 Table 8. Noticeable defoliation by town in Tolland County, 1975-1980. No defoliation was experienced during 1977-1979. Acres/year Town Town Name 1375 1976 1980 Acreage Andover 9,984 Bolton 1,092 9,920 Columbia 13,952 Coventry 897 23,872 Ellington 1,362 272 351 22,144 Hebron 24,000 Mansfield 895 28,928 Somers 1,633 1 17 195 18,368 Stafford 389 624 38,512 Tolland 234 1,713 507 25,856 Union 311 19,136 Vernon 1 17 1 1 ,904 Willing ton 78 584 22,272 Table 9. Noticeable defoliation by town in Windham County, 1975-1980. No defoliation was ex- perienced during 1977. Acres/year Town Town Nome 1975 1976 1978 1979 1980 Acreage Ashford 39 25,792 Brooklyn 5,563 545 18,368 Canterbury 11,397 506 25,600 Chaplin 895 39 741 12,672 Eastford 428 6,825 18,304 Hampton 4,317 233 1,716 16,192 Killingly 1,129 1,168 195 32,000 Plainfield 856 272 507 2,379 27,328 Pomfret 5,990 1,401 507 25,984 Putnam 2,178 233 546 273 1 2,864 Scotland 2,568 156 11,7 16 Sterling 39 1,716 17,408 Thompson 1 17 1,482 7,292 14,274 31,168 Windham 4,435 389 17,920 Woodstock 4,007 623 273 624 819 39,424 Table 10. Noticeable defoliation by town in New Haven County, 1975-1980. No defoliation was experi- enced during 1975-1979. Town Name Ansonia Beacon Falls Bethany Branford Cheshire Derby East Haven Guilford Hamden Madison Meriden Middlebury Milford Naugatuck New Haven North Branford North Haven Orange Oxford Prospect Seymour Southbury Wallingford Waterbury West Haven Wolcott Woodbridge Acres/year Town 1980 Acreage 1,872 3,968 1,326 6,472 3,861 1 3,440 156 17,856 7,254 2 1 , 1 20 1,053 3,392 351 8,064 819 30,464 7,176 21,120 2,730 23,232 858 15,360 3,315 11,520 351 15,240 2,730 10,368 1,170 13,504 390 17,1 12 702 13,440 1,911 1 1 ,264 1 0,608 21,120 6,123 9,152 2,340 9,408 6,162 26,176 624 25,472 3,315 18,432 468 6,784 8,034 13,184 5,460 12,352 Biological Control Investigations In Connecticut, the importance of attempting to con- trol the gypsy moth through biological means was recognized by Britton as early as 1906. Significant early work included experiments with a Calosoma (Carabidae) beetle and the discovery of diseased caterpillars ( Britton 1907 ) . The Station and the USDA collaborated in attempts to establish parasites, and by 1931, Britton ( 1931 ) reported that nine parasites were established in Connecticut. Beginning in the 1950s, microorganisms, such as the nuclear polyhe- drosis virus ( NPV ) that causes wilt disease, ' and insect parasites or predators were investigated in great detail. The parasites are various species of Hymenop- tera in the superfamilies of Ichneumonoidea or Chal- cidoidea, or flies from the family Tachinidae. Their immatures develop within gypsy moths of various stages and the adults are free-living. The only pred- ators studied were the large ground beetles belong- ing to the genus Calosoma. Additional control studies were carried out with the gypsy moth sex attractant (pheromone). Nuclear polyhedrosis virus The nuclear poly- The Gypsy Moth in Connecticut hedrosis virus (NPV) is the dominant natural enemy during gypsy moth outbreaks. It appears to have been accidentally introduced into North America from Europe. Britton (1907) reported finding diseased caterpillars in Connecticut in 1906. No experimental studies were carried out until the 1950s. Wallis ( 1957, 1962) began studying the relationship between epi- zootics and environmental stresses and found that most egg masses in the field were contaminated with the virus. Doane began his extensive studies in the 1960s. His significant findings were: (1) determina- tion of the relative susceptibility of larvae to a Con- necticut strain of NPV (Doane 1967a, b), (2) dem- onstration of transovum transmission by means of con- taminated egg surfaces and hair of the egg mass (Doane 1969, 1970, 1971b, 1975), (3) determination that NPV-killed-first-instar larvae are the major source of inoculum for transmission of NPV to other larvae within the same generation, (4) demonstration of the importance of debris mats (silk webbing, larval exu- viae, pupal cases, and dried cadavers) as a source of intergeneration NPV contamination in the field, ( 5 ) development of a method of forecasting epizootics by measuring the virus load in overwintering egg masses (1971b), and (6) development of the modi- fied density-dependent hypothesis, which explains, in part, the frequency and duration of gypsy moth out- breaks by taking into account the amount of virus in the environment (Doane 1976). Bacterial pathogens Two bacterial pathogens have been studied extensively. One is the naturally oc- curring Streptococcus faecalis Andrewes and Horder and the other is the commercially available Bacillus thuringiensis Berliner (Bt). Doane (1970) reported S. faecalis as a primary pathogen capable of reach- ing epizootic levels under field conditions. Its mor- phological, biochemical and serological characteris- tics as well as its effects on larvae were described by Doane and Redys ( 1970 ) . Subsequently, Doane (1971a) suggested the disease be called "brachyosis" because of the shrunken, shortened appearance of infected larvae. Ground-application tests by Doane ( 1971a ) showed that outbreaks of this disease could be produced in populations in the field and that de- foliation of trees could be prevented, even in dense populations. A method of producing the bacterium in the laboratory was described. Experiments to determine the effectiveness of Bt against the gypsy moth were begun in the early 1960s and continued periodically for about a decade. Doane and Hitchcock (1964) obtained inconclusive results with aerially-applied Thuricide 90T, a liquid suspen- sion. The same formulation, however, protected foliage when applied from the ground with a mistblower (Doane 1966). The addition of boric acid to Bt for- mulations enhanced its effectiveness in laboratory and field tests (Doane and Wallis 1964, Doane 1965); commercial formulations containing Bt and boric acid have not been developed. When commercial formu- lations containing a more potent strain of Bl became available, further tests were made. Dunbar and Kaya (1972) showed that high rates of Bt (e.g., 0.4 pint Thuricide HPC/gallon of spray) applied with a mist- blower were required to reduce gypsy moth popula- tions to low levels. Aerial tests demonstrated that Bt reduced larval numbers and gave foliage protection, but large numbers of larvae survived and egg masses were often more numerous in the following genera- tion (Dunbar et al. 1973, Kaya et al. 1974). Laboratory culture of the gypsy moth and its par- asites The gypsy moth and its natural enemies were difficult to rear in the laboratory prior to the mid- 1960s because of the necessity of supplying large quantities of oak, apple, or other leaves for the larvae to feed on. This difficulty was overcome when Leo- nard and Doane (1966) developed an artificial wheat germ diet containing linolenic acid that was suitable for rearing larvae to adulthood. The authors also re- ported that disinfecting the surface of eggs with sodium hypochlorite greatly reduced mortality from disease, particularly NPV. These developments great- ly enhanced the research effort on the gypsy moth which was to follow. Parasites and pathogens could finally be studied and produced in large quantities with a minimum of effort spent on rearing the cat- erpillars. Hatchable eggs from the field are not conveniently available during part of the year, and despite sur- face disinfection, virus disease continues to be a prob- lem. Hoy ( 1977 ) began a program to genetically se- lect a nondiapausing strain of the gypsy moth while at the Station in 1974. By selecting and rearing only those larvae which developed without diapause, a nondiapausing, essentially disease-free strain was de- veloped in about eight generations. Using this strain it should be possible to rear host specific natural enemies in large quantities at any time of the year. Weseloh has attempted to rear the parasite, Apan- teles melanoscelus Ratzeburg, in artificial culture me- dia. Parasite eggs aseptically dissected from hosts and placed in heat deactivated sterile host hemolymph hatch and will develop to the late first instar before dying. When perfected, this approach may result in a more efficient means of culturing the insect. Exotic parasite introduction and establishment The gypsy moth parasite introduction program in North America began in 1905 when the USDA and the State of Massachusetts introduced natural enemies from Europe and Asia where the gypsy moth is a na- tive insect. Collaborative efforts between the USDA and The Connecticut Agricultural Experiment Station resulted in the introduction into Connecticut of a num- ber of natural enemies. Species introduced and their status are shown in Table 11. Ten insect parasites and one predator from Europe and Asia are estab- lished in the State. Connecticut Agricultural Experiment Station Bulletin 797 Table 11. Insect parasite and predator species introduced into Connecticut for the control of the gypsy moth. Year first released or Host stage recovered in Establishment Species Family attacked Connecticut status Reference Monodontomerus aereus Walker Torymidae Pupae 191 1 Established Britton, 1916 Compsilura concinnata (Meigen) Tachinidae Small-large larvae Larvae and pupae 1912 Established Britton, 1916 Calosoma sycophanta L. Carabidae 1914 Established Britton, 1916 Anastatus disparis Ruschka Eupelmidae Eggs 1917 Established Britton, 1921 Ooencyrtus kuvanae (Howard) Encyrtidae Eggs 1921 Established Britton, 1922 Apanteles melanoscelus (Ratzeburg) Braconidae Small larvae 1922 Established Britton, 1923 Blepharipa pratensis (Meigen) Tachinidae Larvae 1922 Established Britton, 1923 Brachymeria intermedia (Nees) Chalcididae Pupae 1963 Established Dowden, 1969 Phobocampae unicinctus (Gravenhorst) Ichneumonidae Small larvae Unknown Established Personal observation Exorista larvarum (L.) Tachinidae Larvae Unknown Established Personal observation Parasetigena silvestris (Robineau- Tachinidae Larvae Unknown Established Personal observation Desvoidy) Apanteles fulvipes (Holiday) Braconidae Larvae 1922 Not established Britton, 1923 Exorista segregata (Rondani) Tachinidae Larvae 1963 Not established Dowden, 1969 Apanteles porthetriae Muesebeck Braconidae Larvae 1965 Not established Dowden, 1969 Exorista vossica Mesnil Tachinidae Larvae 1968 Not established Dowden, 1968 Rogas indiscretus Reardon Braconidae Larvae 1968 Not established Dowden, 1968 Brachymeria lasus (Walker) Chalcididae Pupae 1979 Not established Weseloh and Anderson, (in preparation) Coccygomimus disparis (Viereck) Ichneumonidae Pupae 1979 Not established Weseloh and Anderson, (in preparation) Of the 10 gypsy moth parasites presently estab- lished in North America, only one, Brachymeria in- termedia ( Nees ) , was not known to be established by 1930. This parasite had been released in North America periodically from 1911 to 1927 (Dowden 1935), but there were no reports that it had become established except for Burks' ( 1960 ) publication of the recovery of one adult from a pupa of Cacoecia collected in Massachusetts in 1942. More releases were made by the USD A in 1963. Leonard (1966) recovered this parasite from gypsy moth pupae in five Connecticut towns in 1965, thereby confirming its establishment in North America. Leonard suggest- ed that B. intermedia maintained itself at low popu- lation levels following its early release in North America and that its appearance in 1965 was not a result of the 1963 release. The incidence of para- sitism in 1966 was less than 5% (Leonard 1967), al- though 4 years later, Doane (1971c) reported a para- sitization rate of 51% from one locality. More recently, two exotic pupal parasites from Ja- pan, Brachymeria lasus (Walker) and Coccygomimus disparis (Viereck), have been released in Windham and Fairfield counties (Weseloh and Anderson, ms. submitted). There is no evidence that either has be- come established (overwintered successfully and par- asitized gypsy moths in succeeding years). Both were shown to have multiple generations each year, thus suggesting their need for alternate hosts when gypsy moth pupae are not present. Field cage evaluation of exotic parasites An- derson et al. (1977) used field cages to study a prom- ising but unestablished exotic parasite. Rogas indis- cretus Reardon, a parasite of Lymantria obfuscata Walker in India, was selected because it readily parasitized gypsy moth larvae in the laboratory and was thought to have only one generation a year in India. Studies showed that this species, which orig- inally had been colonized in the laboratory in the 1960s and reared in various laboratories before being placed in field cages, produced three generations per year and overwintered successfully. Adult emergence the following year was synchronized with the ap- pearance of small gypsy moth larvae. The data show that the limiting factor for successful establishment in North America of this strain of R. indiscretus is the availability of suitable alternate hosts. Field cages were also used to evaluate the over- wintering potential of Brachymeria lasus and Coccy- gomimus disparis (Weseloh and Anderson, ms. sub- mitted). There was no evidence that B. lasus could overwinter, but C. disparis successfully overwintered as an immature stage in greater wax moth, Gallcria mellonella (L. ), pupae. It had four generations per year. So, like R. indiscretus, it requires suitable al- ternate hosts to survive in the field. These studies The Gypsy Moth in Connecticut 9 demonstrate the effectiveness of field cages for evaluating the potential for establishment of exotic- parasites. Inundative release of parasites Few efforts have emphasized inundative releases of parasites al- ready established. VVeseloh and Anderson ( 1975 ) reared and released 1000-7000 adults and cocooned immatures of Apanteles mclanoscelus per 4 ha plot in three towns over 2 years ( 1973-74 ) in both low and high density gypsy moth infestations. In all cases, % parasitism of caterpillars collected in five release plots was significantly greater (up to 40%) than in eight check plots. Hoy (1975b) released a triple hybrid of A. mclan- oscelus from France, Yugoslavia, and Connecticut in three plots ( 6000/plot ) in 1974 under conditions simi- lar to the above and also obtained significantly great- er % parasitism in the test plots than in three check plots. This triple hybrid had a greater fecundity in laboratory tests than did the Connecticut strain re- leased, but no evidence in the field showed it to be more effective in parasitizing larger numbers of cat- erpillars. These releases suggest that A. melanoscelus has the potential to become a more effective parasite. The development of an efficient rearing procedure would aid greatly in improving its usefulness. Behavior of natural enemies Studies of the behavior of natural enemies have relevance in under- standing parasite effectiveness and other aspects of their ecology. Diel periodicities of parasites were investigated by Weseloh (1972b, 1976b). All para- sites studied (Ooencyrtus kuvanae (Howard); Ble- pharipa pratensis (Meigen); Parasetigena silvestris (Robineau-Desvoidy); and the hyperparasite, Brachy- meria compsilurae (Crawford), which attacks tachinid parasites) were active during daylight hours. O. ku- vanae females were also seen to oviposit on gypsy moth egg masses until around 2 a.m. Weseloh ( 1977a ) found that courtship behavior in Apanteles melanoscelus was similar to that of other ichneumonoids. Old males did not mate readily, but old females were as receptive as young ones to young males. Environmental conditions under which females were not disturbed easily when contacted by males were conducive to mating. A sex-pheromone in A. melanoscelus and A. liparidis (Bouche) was found to be produced in paired glands on the female's ab- domen (Weseloh 1976d, 1980b). Doane and Schaefer ( 1971b ) showed that adults of Calosoma sycophanta (L. ) are strong and capable fliers, thus enhancing their dispersal. Responses of O. kuvanae to abiotic environmental factors were studied by Weseloh (1971). This parasite oriented to low relative humidities at moderate tem- peratures but to high relative humidities at high tem- peratures. Females were negatively geotactic in both dark and light. Their preferred temperature was be- tween 20 and 30°C. The parasites were positively phototactic under almost all conditions tested. This species appears to have broad behavioral responses to abiotic environmental factors, which may explain its wide distribution in the field. Adults responded to white- and blue-colored sticky panels that reflect wavelengths of light between 500 and 600 nm (Wese- loh 1972c). This response may indicate that the para- site disperses upward toward openings in the forest canopy. A study of comparative responses of other parasites in humidity and temperature gradients (Weseloh, 1979b ) demonstrated that Brachymeria intermedia, B. lasus, and B. sp. (the last two not established in North America) preferred dryer air and higher tem- peratures than the other gypsy moth parasites tested, including Apanteles melanoscelus and Compsilura con- cinnata, and the hyperparasites Eurytoma appendi- gaster (Swederus) and Gelis tenellus (Say). B. inter- media is known to prefer sunny areas. The responses to humidity and temperature would be compatible with such a microhabitat preference. Because the pref- erences of B. lasus and B. sp. were similar to those of B. intermedia, it seems likely that their field mi- crohabitat preferences and their impact on gypsy moth populations will be similar. Indeed, parasitization in the B. lasus release plots was highest in pupae col- lected from sunny locations (Weseloh and Anderson, ms. submitted). Parasite responses to different microhabitats in the field were also investigated. Parasetigena silvestris at- tacked tethered hosts more readily on the exposed trunks of trees, no matter what the height, than hosts placed under burlap bands or on leaves (Weseloh 1974a). Compsilura concinnata, on the other hand, preferred tethered hosts on leaves (Weseloh, ms. in preparation). Ooencyrtus kuvanae oviposited in egg masses without respect to height or aspect on tree trunks, but did not attack eggs placed in a sunny clearing (Weseloh 1972a, d). Adults were caught most often on sticky panels near the top of trees, probably while they were dispersing. Apanteles mel- anoscelus adults were caught on sticky panels most often at 4 m above ground level and above, probably due to responses to tree foliage. Brachymcria inter- media was found predominantly in sunny areas, such as the edges of clearings (Doane 1971e) and tops of trees (Weseloh 1972d). Parasite host selection and interrelationships with hosts have been investigated in a number of studies. Parasetigena silvestris attacked parasitized hosts as readily as unparasitized ones in field studies, but did not lay eggs on tethered, dead, freeze-dried eater- pillars unless these were moving in the wind. Most probably, this parasite responds to host shape and especially movement. No evidence for response to host chemicals (kairomones) was found (Weseloh 1976b). Apanteles melanoscelus was studied extensively. This 10 Connecticut Agricultural Experiment Station Bulletin 797 parasite examined and oviposited more often in non- parasitized larvae than in parasitized hosts, but su- perparasitism was common when host numbers were restricted. Supernumerary parasitoid larvae were elim- inated by active combat if all were first instars, but larger larvae eliminated younger ones by more sub- tile means (Weseloh 1976a). Apanteles melanoscelus recognized gypsy moth larvae as hosts by their hairi- ness and a Iipid-soluble kairomone on their integu- ment (Weseloh 1974b). Females responded specifi- cally to gypsy moth silk, using their antennae to examine areas where silk was laid down. Silk re- tained its activity when heated, when held 1 week at room temperature, or when placed in non-polar solvents, but water deactivated it by dissolving an active substance. Extracts and smears of the silk glands were active, especially when presented with water- deactivated silk. Results show that there is on gypsy moth silk a water soluble, stable kairomone(s) that influences the parasite's behavior and enables it to more readily find host larvae. Response of A. mel- anoscelus decreased when it was continually exposed to the silk kairomone. This habituation occurred over about 15-20 minutes. The response to silk is inti- mately associated with the response to hosts; para- sites habituated to one (silk or hosts), had decreased responses when subsequently presented with the oth- er. Habituation to silk insures that the parasite does not remain unduly active (for long periods) when in the presence of silk (Weseloh 1980a). If this kairomone can be identified it may be use- ful for manipulating A. melanoscelus in the field, es- pecially in conjunction with mass-releases (Weseloh 1976e, 1977b). Parasite diapause An understanding of diapause is important in rearing parasites, evaluating their over- wintering capabilities, and in understanding their biology. Weseloh ( 1973a ) found that diapause in Apanteles melanoscelus is terminated by exposure of field-collected cocoons to 5°C for eight or more weeks. Different photoperiod lengths after chilling are unim- portant. Induction of diapause is dependent on pho- toperiod. Older parasite larvae inside the host are most sensitive to photoperiod and almost always enter diapause when reared at photophases of less than 16 hrs. Hoy ( 1975a ) expanded this work by investigating diapause induction in various strains of A. melanosce- lus. Strains from France (F) and Yugoslavia (Y), which had been reared for many generations in lab- oratory culture, and their hybrid (F X Y) had a critical photophase of 12.5-13.5 hr light/day. In con- trast, a Connecticut strain (C) had a critical photo- phase of 16-17 hr. The triple hybrid's (FxYxC) critical photophase was 15 hr. Strain differences in diapause intensity were maintained under natural day- length conditions in June. Hoy's work shows that the diapause response is genetically controlled and that it can be changed by genetic manipulations, includ- ing inadvertent laboratory selection. Evaluation of parasite effectiveness The ef- fectiveness of parasites is an important but difficult matter to assess. Some progress has been made by comparing sampling procedures for parasites, the pred- ator Calosoma sycophanta, and the gypsy moth (We- seloh 1972a, 1973b, 1974c). The £ parasitism of eggs by Ooencyrtus kuvanae (which ranged from 10-60*) was negatively correlated with egg mass size in some but not all locations sampled. Adult numbers of Apan- teles melanoscelus and Blcpharipa pratensis were negatively correlated with immature parasite numbers and gypsy moth larval numbers; however, the sam- pling procedure may have been monitoring adult ac- tivity rather than numbers. The abundance of C. sycophanta adults was not correlated with larval num- bers or gypsy moth abundance. The number of generations per year of parasites can affect their ability to reproduce on hosts. Hitch- cock (1959) found that percent parasitism of gypsy moth egg masses by O. kuvanae did not change throughout the fall, which suggested that this para- site had only one generation in the late summer and fall. Hitchcock (1972) showed that O. kuvanae has two generations in summer but eggs laid after September 1 did not produce adults. He also docu- mented that the parasite successfully oviposits in the spring in egg masses laid the previous year. More recently, Weseloh (1976c) found that A. mel- anoscelus is not synchronized properly with its host. Adults, as measured by sticky panel catches and r< parasitism of laboratory reared hosts exposed weekly in the field, were most abundant in mid to late June when most gypsy moth larvae were 4th instars or larger. In laboratory studies, 4th instars were much less acceptable hosts than earlier instars because of their long body hairs and vigorous defensive move- ments. Thus, most second generation A. melanoscelus must attack instars which are too large for them, resulting in low parasitism rates in June although most A. melanoscelus adults are present at this time. Hyperparasites Hyperparasites annually destroy up to 99% of A. melanoscelus larvae overwintering in cocoons. Many A. melanoscelus cocoons also fall prey to predators. Van Sickle and Weseloh (1974) found that hidden cocoons were attacked more readily than exposed ones and that percent hyperparasitism in- creased as the season progressed. More recently, Weseloh (1978a) found that at least 13 species of hyperparasites attacked A. melanoscelus cocoons. Eu- rytoma appendigastcr, the most abundant species, at- tacked cocoons on tree trunks more often than those on tree leaves. Other species usually did not exhibit the same degree of preference for cocoons on trunks because E. appendigastcr destroys the immature stages of other hyperparasite species when eggs of both spe- The Gypsy Moth in Connecticut 11 cies were laid within the same A. melanoscelus co- coon (Weseloh 1979a). Protecting A. melanoscelus from hyperparasites might result in a substantial increase in numbers of parasitized gypsy moth caterpillars. One approach was to cross an A. melanoscelus strain from India with the strain established in North America. The Indian strain has a thick "halo" of silk surrounding its cocoon, a possible protection against hyperpara- sites; but it does not have a photoperiodically-induced diapause and so would not likely become established in North America. The "halo" trait is genetically con- trolled and could probably be transferred to the North American strain (Weseloh 1978b). Field and labora- tory experiments by Weseloh (ms. submitted) showed, however, that cocoons with the "halo" were as sus- ceptible to hyperparasites as those without. Careful screening of imported parasites can also be helpful in preventing the introduction into North America of new hyperparasites. Weseloh et al. ( 1979 ) found that an imported egg parasite, Anastatus kash- mirensis (Mathur), from India also attacks A. mela- noscelus and Rogas indiscretus, usually to a greater extent than they do gypsy moth eggs. Therefore, A. kashmirensis was judged too dangerous for release. Effects of insecticides on natural enemies It has long been recognized that pesticides also influ- ence beneficial insects. Several studies have examined the effects of pesticides on natural enemies of the gypsy moth. Doane (1968a) reported that egg para- sitism by Ooencyrtus kuvanae was greater outside than within plots treated with Gardona® (2-chloro-l- ( 2,4,5-trichlorophenyl ) vinyl dimethyl phosphate ) , but the difference was not attributed to a direct effect of the insecticide on the parasite. Tachinids and sar- cophagids were found to be reduced significantly in Dylox® (2,3 dimethyl (2,2,2-trichloro-l-hydroxyethyl) and Gardona®-treated plots in comparison to untreated and Sevin® (1-naphthyl N-methylcarbamate ) treated plots (Doane and Schaefer 1971a). Calosoma frigidum Kirby and C. sycophanta were susceptible to residues of Sevin. The three insecticides did not directly affect birds, although the available food (insects) was de- pleted and bird activity altered. The effects of Bt sprays on natural enemies were evaluated by Doane and Hitchcock (1964), Dunbar et al. (1973), and Kaya et al. (1974). In general, the spray applications had no apparent adverse ef- fects on small mammals, birds, predaceous insects or parasites, and may have increased the activity of Apanteles melanoscelus. When the new insecticide Dimilin® (l-(4-chloro- phenyl)-3-(2,6-difluorobenzoyl)-urea) was recognized to be effective against the gypsy moth (Granett and Dunbar 1975), studies were initiated to evaluate its effect on Apanteles melanoscelus. These authors found that the parasite within the gypsy moth host was af- fected by the insecticide. Granett and Weseloh (1975) showed that Dimilin-treated leaves fed to parasitized gypsy moth caterpillars killed A. melanoscelus larvae during their 2nd-3rd larval molt but not later in de- velopment. Granett et al. (1976) then reported that properly timed sprays of Dimilin could minimize ef- fects on the parasite and still be effective against the gypsy moth. Two juvenile hormone analogues were lethal to Ooencyrtus kuvanae at 100 ppm (Granett et al. 1975). Apanteles melanoscelus survived treatments, although development took longer. Gypsy moth sex pheromone Work at the Sta- tion on the gypsy moth sex pheromone began in 1961 when Doane published his field results with a ma- terial known as gyplure. Later studies on mating behavior revealed that only virgin female moths with the abdominal sex pheromone gland exposed (call- ing females) attracted males downwind (Doane 1968b); mated females did not call and did not attract males. Copulation usually lasted about 1 hr, but only about 8 minutes was necessary for sperm to be successfully transferred. In the presence of pheromone and at close range, males oriented to females visually. Doane also investigated mating behavior in coop- eration with other scientists. They observed that males would touch wings when arriving simultaneously near a "calling" female, causing one of the males to leave the area (Doane and Carde 1973). Apparently, this mechanism prevents aggregation of males near any one receptive female, thereby insuring a greater num- ber of successfully-mated females. In a related study, males were found to respond to pheromone-baited traps mainly from 11:00 a.m. to 3:00 p.m. (Carde et al. 1974). With the goal of improving sampling procedures for gypsy moth males, Granett ( 1973 ) developed a large- capacity pheromone trap using the synthesized pher- omone, disparlure, which caught more moths than the normal, sticky-coated survey traps. He was able to relate the number of captured males to pupal density and length-of-time-to-mating of receptive females (a measure of mating potential). Therefore, these traps might be useful in estimating population size as well as detecting moths (Granett 1974). The possible use of disparlure in controlling the gypsy moth was explored in a number of tests. An olefin hydrocarbon, 2-methyl-cis-7-octadecene, in the female's pheromone gland was discovered and shown to depress numbers of males caught in traps; how- ever, it seemed to increase male searching behavior (Carde et al. 1973, 1975). When tested in the field along with the pheromone as a "confusant," the pher- omone, in contrast to the olefin, inhibited males from finding females. Granett and Doane (1975) sprayed microencapsulated disparlure into relatively small plots from the ground using a mistblower. The pheromone disrupted mating even at high populations. This sug- 12 Connecticut Agricultural Experiment Station Bulletin 797 gests that ground application in small plots may be useful for further testing of the confusion method; other pheromone batches, however, did not give such promising results. Station scientists have also been involved in inves- tigations of the ( -t ) enantiomer of disparlure, which may be the actual pheromone. By testing racemic disparlure (which contains equal quantities of the ( + ) and ( — ) optical isomers, or enantiomers) and various analogues of the pheromone, Carde et al. (1977a) demonstrated that only the ( + ) enantiomer was attractive. In field tests, the ( + ) enantiomer was shown to initiate long range orientation better and to be more effective at trapping males than was the racemic mixture (Carde et al. 1977b). Finally, Carde et al. ( 1978 ) compared three methods of synthesizing the ( + ) enantiomer and found them equivalent in at- tractancy in field tests. The ( + ) enantiomer of dispar- lurc is now used extensively in survey and detection work. Summary Extensive studies have been and are continuing to be carried out on natural enemies in an attempt to better understand their biology, behavior, and interrelationships with their hosts; to improve their effectiveness; and to establish new exotic species. We conclude with two of Britton's observations (1906): There ore several species of parasitic Hymenoptera, Diptcra and predaceous insects that attack . . . the gypsy moth . . ., and they are also devoured by birds, toads and other insectivorous animals. But all of these working together do not control the pest. He says further of importations, . . . parasites may not be able to thrive, or even to live, in this country, but it is an experiment worth trying, and we certainly hope for much benefit from it. Our experimentation will continue. References Cited Anderson, J.F. 1980. The gypsy moth. Front. Plant. Sci. 32(3): 1-8. 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Behavioral changes in Apanteles melano- scelus females exposed to gypsy moth silk. Environ. Entomol. 9:345-349. Weseloh, R.M. 1980b. Sex pheromone gland of the gypsy moth parasitoid, Apanteles melanoscelus: Revaluation and ultra- structural survey. Ann. Entomol. Soc. Am. 73:576-580. Weseloh, R.M. and J.F. Anderson. 1975. Inundative release of Apanteles melanoscelus against the gypsy moth. Environ. Entomol. 4:33-36. Weseloh, R.M., W.E. Wallner, and M.A. Hoy. 1979. Possible deleterious effects of releasing Anastatus kashmirensis, a facultative hyperparasite of the gypsy moth. Environ. Ento- mol. 8:174-177. Acknowledgements We thank George Schuessler, Robert Moore, Carol Lemmon and Peter Trenchard for participating in the defoliation sur- veys. We are grateful to Chester Airport for their assistance in conducting the surveys and Rose Ann Scala for preparing the map overlays used in this bulletin. 15 About the maps The following maps show the location and the intensity of defoliation experienced in Connecticut during 1975-1980. Although Table 1 shows four categories of defoliation, the 10-25% and 26-50% categories have been combined on the maps for this period. 16 17 SUFFIELD ENFIELD SOMERS I'l'iMl'MiN ; GRANBY/ W|N0S0R i LOCKS EAST WINDSOR ELLINGTON I 7 WINDSOR gl — ^ ml 1 °B Si; MFIELD #/ SOUTH WINDSOR/ TOLLAND VERNON UL.la, , EASTFORD \ PUTNAM POMFRET EAST \ MANCHESTER \pOLTON ' HARTFORD MANSFIELD | CHApUN J HAMPTON ) BROOKLYN ' CANTER PUINFIELD COLUMBIA NEWING\ TON, GUSTONBURY HEBRON lltl SCOTLAND \ LEBANON JR0CKY HILL I CROMWELL ' VIARLBOROUGH PORTLAND) MIDDLETOWN MIDDLE- v^J FIELD EAST HAMPTON COLCHESTER EAST HADDAM I SALEM FRANKLIN BOZRAH I NORWICH FK DURHA * \ t HADDAM MONTVILLE NEW / MADISON? CHESTER y% LYME EAST \ WATERFORD % tv/sEYMOUR WOODBRIDGE V^ \ BETHEL \ y monroY \^Q^A V---'"^REDDING V/^\ / SHELTON %JPERBX/ -J-r— RIDGEFIELD 1 T?l A TDTU^ \ ^ ORANGE 1 , J J — iJLs^ f y\ \ s^\^ \ east°n \ TRUMBULL \^ J ^~~-~~—A \/ \ WESTON \ , y / f MILFORD Lr~ "\ '> — -^STRAT- ) y? r \ WILTON \ f V \ \ford I r\r~J ^RIDGEPORTj JL ^ S' \ \y \ FAIRFIELD y^K NEW I SH \ \ CANAAN J ( \ \ 1 \ WESTPORT S STAMFORD \ / NORWALK 1 , SLs—'^^' NEW HAVEN JNORTH HAVEN NORTH "EAST JSRANFORD HAVEN / WEST \ HAVEN BRS'JPCF: DARIEN GREENWICH 23 Fig. 4 Defoliation. 1979 10 - 50% 51 - 75% 76 - 100% 24 25 Fig. 5 Defoliation, 1980 10 - 50% 51 - 75% | 76 - 100% w University of Connecticut Libraries 39153028928432