GYPSY MOTH IN NEW HAMPSHIRE —1991 



Dr. Siegfried Thewke 



T 



he gypsy moth, Lymantria 

 dispar L, is native to Europe and 

 is a pest there as much as it is 

 in the United States. In 1868 or 

 1869, a Mr. L. Trouvelot living in 

 Medford, Massachusetts, imported 

 some eggs of this pest for pur- 

 poses of experimentation. There 

 was a small but active silk industn,' 

 in the country at the time and he 

 was using native silk moths in his 

 experiments. Historical records 

 show that either some eggs or 

 gypsy moth larvae were blown out 

 of the window of the room he was 

 experimenting in and escaped. He 

 informed the authorities of the 

 escape after trying to eradicate it 

 on his own. The stage was now set 

 for establishment of the gypsy 

 moth in the United States. Local 

 control commissions were estab- 

 lished to combat it in the New 

 England States and quarantines 

 were enacted to contain it. Ad- 

 vance of this pest was not to be 

 stopped however, primarily be- 

 cause of mass transportation of 

 people and goods. Today the GM 

 can be found throughout the 

 country with major concentrations 

 of it still in the northeast. 

 The most frequently asked 

 question about this pest when it 

 has been doing its work in an area 

 is, "when will the cycle end?" 

 People have noticed that there are 

 periods of concentrated activity by 

 the GM followed by periods of 

 relative inactivity. This does seem 

 to be the case, as our records 

 dating from 1934 to 1981 show 

 cycles occurring every 7 to 10 

 years. The present defoliation was 

 begun by GM survivors of the last 

 onslaught over ten years ago when 

 nearly 2 million acres were 

 affected. A general description of 

 how the cycle works is as follows: 

 survivors of the collapse or rapid 

 population decline build up their 

 numbers season by season. 

 Parasites, predators and diseases 

 also build up but at a slower rate, 

 not quite keeping up. As the GM 

 population approaches the 5th to 

 7th season, people begin to notice 

 the pest is back again. By this 

 time the GM population is quite 



large and considerable acreages 

 are being affected. I^rge numbers 

 of caterpillars competing for the 

 same food source create a stress 

 situation. As caterpillars become 

 stressed, biological control agents 

 begin to take their toll. Ultimately 

 the GM population collapses and is 

 again reduced to a very low level - 

 to begin again. 



Control of GM can be accom- 

 plished by use of biological and/ 

 or chemical insecticides/agents. 

 Many times members of the public 

 have complained that no birds or 

 insects are being used to help kill 

 this defoliator. This is clearly not 

 the case at all. After the GM was 

 introduced into the United States, 

 a massive foreign exploration 

 program was instituted in 1905 to 

 look for and send to the United 

 States organisms that kill this pest. 

 Between 1905 and 1914, two 

 species of parasitic flies and four 

 species of parasitic wasps were 

 found and are now established and 

 working in this countn,-. In 1922- 

 1923 two additional species of 

 parasitic flies were imported. 

 During the last 25 years, over 

 211,000 individuals of approxi- 

 mately 78 species have been 

 imported as agents against the 

 gypsy moth. Gypsy moth cater- 

 pillars are also subject to attack by 

 various diseases. One of these is 

 known as "wilt" and is a virus 

 quite specific to this pest. One can 

 see this virus in action by looking 

 for GM caterpillars hanging in an 

 inverted "X^ posture, attached to 

 vertical surfaces or from under 

 tree branches or twigs. These [ 

 break open when touched or I 

 AU 



jostled and release a brown liquid 

 which contains more of the virus. 

 Fungi also play a part in control. 

 Kntomophaga niaimaiaa is a fun- 

 gus that had been imported into 

 the country many years ago, but 

 had not been seen working until 

 two to three years ago. This fun- 

 gus — along with the virus — was 

 responsible for the great reduction 

 of GM in North Conway/Conway 

 in 1990. Parasites, predators and 

 diseases take quite a toll of the 

 g>'psy moth. The work of these 

 agents is not always seen by many 

 people but certainly is important in 

 the control of this pest. 



The gypsy moth defoliated 

 approximately 133,000 acres in 

 1990. Defoliation in New Hamp- 

 shire in 1991 extends from Wolfe- 

 boro to Alton, over to Plymouth, 

 and from Holdemess down the 

 center of the state through 

 Concord to Manchester and Nash- 

 ua. Part of the defoliation also 

 goes over to Hillsborough. There 

 are other pockets of defoliation, 

 mostly extending eastward toward 

 the coast. Most of the defoliation 

 however, is in the central portion 

 of the state. The extent of the 

 defoliation for 1991 will not be 

 known until survey flights and 

 mapping have been completed. 

 Dr. Siegfried E. Thewke is State 

 Entomologist for the New Hamp- 

 shire Department of Agriculture. 

 He's Director of the Division of 

 Plant Industry, State Lab. Bldg., 

 1Mb. D. Hazen Drive, Concord, 

 NH 03301: telephone (603) 

 271-2561. ^ 



Contact your local newspaper 

 to run a press release 



on the theme 



'Fall is for Planting." 



A pess release is 



informative 



to the public and it's always 



good to have your name 



mentioned as a professional 



in the area. 



—Tina Sawtelle 



GUST/SEPTEMBER 1991 23 



