Biology of the Gypsy Moth in British Columbia

Eggs | Larvae (caterpillars) | Pupa | Adults

It is very important to be familiar with the biology of the gypsy moth (Lymantria dispar) in order to understand how this insect can be managed. The following description of the gypsy moth life cycle has been reproduced from the Canadian Forest Service Forest Pest Leaflet 75 Gypsy Moth.

The life cycle of the gypsy moth is similar to many other moths. It has one generation per year and is characterized by four distinct stages: egg, larva (caterpillar), pupa and adult.

It overwinters in the egg stage, usually surviving winter in northern locations under a protective layer of snow. The gypsy moth can tolerate temperatures as low as - 30° C provided these conditions do not persist for several days. The female adult gypsy moth lays all of her eggs in a single, off colored egg mass that resembles a sponge or chamois. The number of eggs in one of these masses varies from fewer than 100 to more than 1,000 eggs, with an average of 700 eggs for females feeding on unlimited quantities of preferred foliage. The egg masses are placed in sheltered positions on trees, behind rocks or fallen logs on the ground.



These two figures below show female gypsy moth laying eggs (ovipositing) on the bark of hardwood trees in eastern Canada. Note adult females, pupal cases and egg masses on the top photo.

Hatching depends on warming weather and commonly occurs from mid to late April, occasionally extending to late May even at the same location. This photo shows the newly hatched caterpillars.

This is a close-up photograph of a second stage (known as an instar) larva. Note the hairy body and the coloured spots on its back. The newly hatched, small and hairy larvae move up host plants to newly emerged foliage where they begin feeding. Some may be blown by the wind to new locations, assisted by their light, hairy bodies and long silk threads produced by special glands in their heads. This spring "ballooning" is a major means of natural dispersal for both races (Asian and European), and is the primary natural means of dispersal for the European race. Although ballooning has been recorded over 50 km, it usually adds about five km per year to new infestations.
This is a close-up photograph of a fifth stage (known as an instar) larva. Note that the coloured spots on its back are more obvious. Also, note the distinctive markings on the head.
	Feeding usually continues for six to eight weeks, varying with weather, host conditions and location. There are normally five male and six female larval stages or instars. Larvae in the first three stages feed mainly at night; those in later stages feed day and night and consume the largest quantity of foliage. The large, final-stage caterpillar is voracious. Each may consume as much as 1,000 square centimetres of foliage in their lifetime. This represents about 10 to 15 entire leaves of a red oak. When larvae are numerous and food becomes insufficient they may disperse along the ground in search of more foliage, becoming a greater nuisance in urban areas. Contact with the histamine-containing hairs of the caterpillars induces allergic reactions, such as a skin rash or respiratory problems, in many people. Known host list
Close up of the head of a gypsy moth larva	Feeding is usually completed by late June or early July and most larvae move to protected locations, such as bark crevices, to pupate. The pupal stage lasts an average of 10 days for individual females and 13 days for males, and occurs over a month (July) or more for a local population.


	Pupal case following adult emergence. Note cast larval skin.
Moths start emerging in July, peaking about mid-month and extending into August in eastern north America.	Adult Male Gypsy Moth - note the feathered antenna
Adult Female Gypsy Moth	Despite having full-size wings, the female cannot fly but will emit a pheromone to attract the highly mobile and responsive males. Adults mate, do not feed, and live for about one week. After mating, indiscriminate laying of a single egg mass per female occurs from late July to September.

Should you locate gypsy moth eggs or require further information, please contact the nearest Ministry of Forests and Range office or the Canadian Food Inspection Agency (CFIA) at (250) 363-3618 (Vancouver Island) or (604) 666-2408 (Mainland/Interior). Photograph of pupa by R.S. Hodgkinson, BC Ministry of Forests. Remaining photographs and images are courtesy of the Canadian Forest Service.

Contact Tim Ebata if you have comments on the presentation of this information. BC Ministry of Forests and Range Forest Practices Branch P.O. Box 9513 Stn. Prov. Gov. Victoria, BC V8W 9C2 Section phone: (250) 387-8739 Section fax: (250) 387-2136