Laboratory studies on the biology ofOrgilus jenniae(Hymenoptera: Braconidae), a parasitoid of the potato tuberworm,Phthotimaea operculetta(Lepidoptera: Gelechiidae)

Abstract

Studies were conducted on behavior, host relationships, immature morphology and population growth potential of Orgilus jenniae Marsh, an exotic parasitoid of the potato tuberworm (PTW), Phthorimae operculella (Zeller). Results were compared with similar studies on the exotic species, O. lepidus Muesebeck and O. parcus Turner, previously colonized but not established in southern California. Stalked eggs of O. jenniae are deposited in the abdominal hemocoel of host larvae. A solitary parasitoid larva develops internally, emerges before host pupation, and constructs a translucent-white cocoon within that of its host. The first of three larval instars is initially caudate- and and finally vesiculate-mandibulate; the last two are hymenopteriform. Immature dimensions and descriptions are presented. Parasitoids preferentially oviposit in first or second instar PTW in potato foliage, but there is an interaction between host age and density in tubers arising from actual parasitoid preference and characteristics of host mines. Developmental time from oviposition to adult parasitoid emergence depends on the host’s age at the time of oviposition, as the first parasitoid molt is synchronized to occurrence of the fourth host instar. Parasitism significantly reduces host larval growth. If O. jenniae has a preoviposition period, it is less than 3-hrs, but female progeny are not produced during the first 6-hrs after adult emergence or mating. A diurnal oviposition rhythm does occur, with progeny production peaking during the last half of the photophase. Courtship, mating, searching and oviposition behaviors are described. The mean fecundity was 375.2 and 436.8 eggs/female, the mean sex ratio, 23.6% and 28.4% females, and the mean adult female longevity, 25.5 and 16.9 days, when hosts were in potato tubers and foliage, respectively, at 25 ± 1 °C, 45 ± 5% RH and 12-hr photoperiod. Parasitoid life tables and statistics for hosts in potato tubers and