BIOLOGICAL INVESTIGATIONS ON HYMENOPTEROUS EGG-PARASITES OF THE PINE CATERPILLAR AND THEIR UTILIZATION IN BIOLOGICAL CONTROL

In this paper the writer reports on the result of his investigation on threehymenopterous egg-parasites of Dendrolimus spectabilis Butler on Pinus masso-niana Lamb and Dendrolimus sibiricus Tschtun on Larix gmelini Pilg., togetherwith suggestions for practical application of Telenomus dendrolimusi Chu inbiological control. 1. Telenomus dendrolimusi is the most important hymenopterous parasites ofDendrolimus eggs and is widely distributed in China. This species has 10 gene-rations a year, and the mated females over winter becoming active about themiddle of March the following year The eggs of the first brood of the pinecaterpillar, however, are produced and subjected to parasitization in the middlepart of May.A large number of the overwintered adults of Telenomus dendro-limusi perished from low temperture in cold winter,and from shortage of foodor hosts in spring. The duration of each generation varies with temperature, the shortest periodis 11 days; from oviposition to pupation 6 days are required and the pupalstage takes 5 days under average temberature of 30℃. The longest period of ageneration is 53 days, taking 32 days from oviposition to pupation and 21 days inthe pupal stage under average temperature of 14.8℃. Base on a study of 12 females, a maximum of 48 eggs, a minimum of 21and an average of 39 eggs were oviposited by each individual. The number ofthe host-eggs parasitized by a female Telenomus varied from 6 to 14, with anaverage of 11 eggs. Parasites found in an egg varied from 1 to 7. 48.18% of theeggs studied contained 3 parasites per egg, and 20.91% contained 4 parasites,averaging 3.25 parasites per egg. Of the population in the field the females usually number over 70%, some-times amounting to 90.48%. Usually less than 10% of the first brood of thepine caterpillar eggs are parasitized, while in the second brood, the number ofparasitized eggs reaches as high as 77.77$. This species cah reproduce parthenogenically. Adults from the unfertilizedeggs being all males. Only one other undetermined species of Arctiidae, besidethe pine caterpillar, is found to be successful as a host of Telenomus dendroli- musi under laboratory conditions. 2. Trichogramma evanescens Westwood, widely distributed in China, is a well-khown eggs-marasite of various insect pests. This species has 18-19 generationsa year and hibernates in the papal stage in some snitable host eggs. The duration from the egg to the adult stage generally requires 6-26 days.The overwintering generation lasts about 5 months. Over 20 days are requiredby a generation developing under temperature conditions below 20℃. 9-14 daysare required at 21-27℃, and only 6-8 days above 27℃. A female of Trichogramma evanescens can produce a maximum of 121 adults,a minimum of 5 and an average of 66.86 adults. A female can parasitize 2-16host eggs, 8.09 being the average. The number of individuals developing fromone host eggs usually varies with the size of the eggs parasitized. The largestnumber is 33 from one pine caterpillar eggs. The females in a population usually occupy more than 84%,and sometimesreaeh 96.89%. The proportion of females is correlated with the size of the hosteggs, i. e. the larger the host egg, the higher the percentage of females will be. In the laboratory the parasites were reared with success with any suchhost eggs as from newly deposited to the day before hatching, or with infertileeggs before desiccating, or with dead eggs kept in cold storage. 3. Anastalus gastropachae Ashmead is also a common egg-parasite of Dendro-limus spectabilis Butler. This species has 8 generations a year and overwintersin the papal stage in the eggs of the pine caterpillar or in eggs of other hostinsects. The adults emerge from the last part of April to the middle of Mayand parasitize the first-brood eggs of the pine caterpillar. The duration of ageneration varies with temperature. The shortest period for a generation is 14days under an average temperature of 29℃.; the longest period is 57 days withtemperature averaging at 14℃. The overwintering generation requires 5.5-