STUDIES ON MASS PRODUCTION OF TELENOMUS DENDROLIMUSI CHU AND EFFECTIVENESS OF LIBERATION

The Scelinoid Telenomus dendrolimusi is an effective indigenous egg-parasite of the pine ca-terpillar. It has long been estimated as playing an important role in the control of the pine cater-pillar eggs. The parasite is specific in host selection, having high host-finding ability, and is ableto parasitize a large numbcr of the pine caterpillar eggs under natural conditions. On account ofa considerably high percentage of winter mortality, the population of this parasite increased tooslow1y in the following spring to make it effective in reducing the damage done by its host. Attempts have been made during winter seasons on artificial breeding of the eggparasite and its host,aiming to solve the problem of increasing its effectiveness by early liberation.Under laboratory conditions larvae of the pine caterpillar collected from winter quarters resume their activities When bred under room temperature range of 24--30℃. Under 30℃ andwith 80% relative humidity the life cycle of the caterpillar requires 49 days, whilst at 24℃ ittakes 65 days to complete. Larvae of the 1st and 2nd instars require a fairly high temperature andan abundance of moisture. Humiddity below 80% results in high mortality. However, the larvaeof the later instars are easier to handle, they pupate and emerge successfully. After mating thewings of the adults were cut off, in order to avoid the scattering of the noxious scales and to obtainthe largest proportion of eggs laid in the first and second days. Eggs thus obtained may be keptin icebox for one month, after which they were still effective for parasitization. Egg-parasitesmay be obtained either by exposing the egg masses in the forest or just by collecting the caterpillar'seggs from the field.Temperature and moisture play important role in Telenomus development. The optimum fordevelopment of this egg parasite is at 24--31.3℃. wth 90--95% of relative humidity. Tem-perature far above 37℃. would result in sudden death of the parasite. In order to obtain goodresult, the proportion between the parasite and its host eggs should be maintained at 1:10--15. Acti-vity of parasitization is increased when the Telenomus is exposed to strong light. Both longevityand fecundity are increased when the adult parasites are fed with honey solution.Methods onrearing of both parasites and hosts are discussed in detail.Field experiments were made by fastening bundles of the pine needles with host eggs to pinetrees in different zones. The most favorable time for release of this eggparasite is in the eveningjust before sunset. Since during this time there is little sunshine and no strong air current in thevicinity of the forest, thus permitting even distribution of the parasite.Experiments were carried out by hanging bundles of pine needle with host eggs on the pinetrees and then releasing the egg-parasites from a single point of liberation in the center of theexperimental field. Results indicated that the percentage of parasitization varies with differentzones from the center. In the 0-5-meter area, the maximum parasitiaztion was 85% and theminimum 57.7%. In the 5--10-meter area, the maximum was 66% and the minimum 58%. Inthe 10--15-meter area, the maximum was 84% and the minimum 56%. In the 15--20-meter area,the maximum was 61% and the minimum 35%, In the 20--25-meter area, the maximum andminimum being 47% and 18%.It has also been shown, however, that the liberation of another egg-parasite, Trichogrammaevancescens Westw., togther with Telenomus resulted an increase of percentage of total parasi-tization and therefore increased effectiveness in the pine caterpillar control.