HOST INSTAR PREFERENCES AND DEVELOPMENTAL TIMES OF 2 ICHNEUMONID PARASITES OF THE GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE)

Laboratory observations were made on oviposition behavior, host suitability, rates of parasitization, sex ratio, and developmental times of two exotic ichneumonids, Casinaria arjuna Gupta & Maheshwary and Hyposoter lymantriae Cushman, using the gypsy moth, Lymantria dispar (L.), as a host. C. arjuna ovipositional preferences were second > third = fourth > first instars. No significant preferences were noted in H. lymantriae. Older instars were not tested. Second instars were optimal for development of C. arjuna, whereas both second and third instars were optimal for H. lymantriae. In large cages, net parasitization was highest in second instars for C. arjuna, and second and third instars for H. lymantriae. The sex ratio (percentage females) of C. arjuna averaged 29% with no significant differences between host instars in which oviposition occurred; that for H. lymantriae averaged 27%; the highest mean (35%) was for second instars and the lowest (19%) for first instars. Developmental times for females of both species were similar, about 18 d from egg to adult at 25-degrees-C when oviposition occurred in second instars. Males of C. arjuna developed more rapidly than females. Both sexes of H. lymantriae had similar developmental times.