Latin Name: Lymantria dispar L.
Common Names: Gypsy Moth, European Gypsy Moth
The import of the gypsy moth to North America can be blamed on an unhealthy silkworm population. After the American Civil War (around 1869), there was a shortage of cotton from the southern states. Also the silk industry was battling a "wilt" disease in the larvae that produce silk. These two problems caused a major supply problem in the supply of fibre within the US. Thinking that he could produce a healthy insect and a commercial source of silk, an American naturalist imported some European gypsy moth egg masses. His hope was to cross the vigorous gypsy moth with the ailing silkworm and produce a hybrid that would meet the needs of the industry. The experiments were unsuccessful and, some of the egg masses were lost. Thus began the spread of the gypsy moth through the eastern US.
Since 1889, various control programs have been used off and on. The gypsy moth still managed to spread to Ontario and Quebec. In 1971, male moths were captured in Nova Scotia and New Brunswick.
Although this insect has not yet caused significant defoliation in our NS forest stands, it continues to impact the urban forest and forest industry. Currently the western region of Nova Scotia has been identified as infested with gypsy moth and is regulated by the Canadian Food Inspection Agency.
The gypsy moth has one generation per year. The larvae hatch in May. The tiny (2mm) larvae crawl away from the egg mass and after much tasting, choose a suitable host. First instar larvae can go up to one week without food. Between the first and third instar, the larvae feed from dawn to mid-morning and then seek shelter from the heat of the day under bark or in ground cover. As the larva grows, its behaviour changes. The fourth to sixth instars feed at night from sunset to sunrise but if the population density increases, the larva will feed both day and night. When mature, the larvae are 30-65mm in length and very hairy. The head has yellow markings and the body is slate-coloured with light stripes along the back. Starting just after the head, there are five pairs of blue spots followed by six pairs of red spots down the back. These coloured spots are the characteristic that distinguishes the gypsy moth larvae from any other large, hairy larvae.
The larva stage lasts approximately 40 days from egg-hatch to pupation. The female will take a few more days to reach pupation than the male. There are usually five instars in the male larvae and six instars in the female larvae. If food supply is reduced, the number of instars the larvae have will increase, allowing it to feed for a longer period of time.
Once mature, the larvae wander around for several hours in search of a shady, protected spot to pupate, usually in a hollow or at the base of the tree. Pupation lasts approximately two weeks.
The moths begin to emerge in July and August. The males emerge first, about five days ahead of the females. The males have brown forewings with darker brown markings (male wingspan: 2.5 - 3.8cm) while the larger females have whitish forewings marked with dark wavy lines (female wingspan: 5.0 - 6.4cm). The males are strong fliers and, unlike most of our NS moths, they fly during the day. The females have very heavy bodies and even though they have well developed wings, they do not fly. They crawl up a tree and attract the male by means of a pheromone .
After mating the female lays her eggs in a shady spot, usually on the under side of a branch or in a crack in a tree. Egg masses are oblong and can range in size from 1.3 - 5.1cm. The size of the egg mass is affected by the population density and the food supply. If the food supply is good and the population is low, egg masses will be larger. On average, there are 400-500 eggs per mass. The egg mass is covered in a layer of buff-coloured hairs that protect the egg mass from water loss and make them unappetizing to birds.
The larvae develop within the egg for 4 - 6 weeks and then remain in the egg until they hatch in late spring. Gypsy moth eggs require a period of cold before they will hatch.
Gypsy moth larvae are aggressive feeders. There are 485 recorded plants/trees that the larvae will attack. The preferred tree species are oak, poplar, apple, and birch. The older larvae have been observed on hemlock, pine, and spruce.
The larvae feed on the foliage. Crowns can appear thin in the early summer. Although hardwood trees can usually re-leaf, continuous years of defoliation can weaken and cause tree mortality. When populations are high, large quantities of frass and cast skins can be seen on the ground at the base of the host tree.
The gypsy moth is parasitized in the egg stage and the larva stage by several species of flies and wasps. Also, there are many birds that feed on the larvae, including the blue jay and the black-capped chickadee. These natural control will help to limit a small population but will not control a large infestation.
Destroying egg masses is one way that homeowners can help to control this insect on their property. Once an egg mass is identified, scrape it from the tree and drop it into a dish of vegetable oil and leave it for a couple of days. Make certain that all of the mass is treated. It usually will not come off the tree in one lump but will break into pieces.
A fungus disease and a virus disease infect the gypsy moth in the larval stage. These diseases are more prevalent when populations are high. There is research being done on artificially introducing these diseases into the gypsy moth population as a form of biological control.There is a synthetic pheromone that attracts the male moth. In small populations, traps baited with pheromone can help to control the population by catching the male before he has a chance to mate. This method requires a complete saturation of the area with traps. There are also biological and chemical insecticides available for use on gypsy moth.
CAUTION: Read and follow the instructions on the label when using any control agent. Proper application and use of recommended personal protective equipment are essential for the safe use and effectiveness of any pesticide.DISCLAIMER: Control options are suggestions only. Actions taken for pest control are the sole responsibility of the applicator in full compliance with any Federal, Provincial or Municipal Acts, Regulations or Bylaws.