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Abstract: The main effects and interactions between temperature and host instar on development and survival of Hyposoter didymator (Thunberg) (Hymenoptera: Ichneumonidae), as well as the effects of parasitism on the growth rate of the various host instars of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were studied under laboratory conditions. The duration of development of immature stages of H. didymator in first, second, third, fourth and fifth instar of H. armigera larvae at five constant temperatures (15, 20, 25, 30, and 33°C) was recorded. Developmental time decreased significantly with increasing temperature within the range of 15–30°C. When parasitism took place on first and fifth host instars, the parasitoid development from egg stage up to adult emergence took significantly longer compared to other instars. Parasitoid survival did not vary linearly either with host stage or with temperature, and was generally lower in very young and older hosts in all temperatures tested: it decreased very quickly above 25°C, and fell to zero at 33°C. Between 15 and 25°C the survival of immature stages ranged from 54 to 76% when parasitized in the second and third host instars, respectively. Larval stages of H. didymator exhibited a flexible growth model (Regulator-conformer) that depended on host instar at parasitism. Parasitism by H. didymator reduced the weight gain of parasitized host larvae at an early stage of development (e.g. 1 day after parasitism) when the host larvae were parasitized in larger instars while this effect was delayed up to 4 days when smaller instars were parasitized. [Copyright &y& Elsevier]

Abstract: An improved rearing method for the larval endoparasitoid Hyposoter didymator was developed in the laboratory considering the single locus complementary sex determination (sl-CSD) theory as well as other factors affecting sex ratio: (1) use of the preferred host of the parasitoid in nature; (2) appropriate host size (large enough to favor female development); (3) appropriate parasitoid age (experienced in parasitization); (4) implication of all genotypes on offspring production (unselected parasitizing couples); and (5) genetic variability (regular infusion of wild stock). Firstly, to corroborate the sl-CSD theory, a small rearing was sib-mated in seven generations until males accounted for more than 90%. Secondly, a new parasitoid rearing method was developed using a single large population and two inbred lines (as reservoirs of alleles) to maintain allelic diversity according to the Cook’s Model. The quality of insects obtained with this method was evaluated by measuring the percentages of parasitized hosts and adult emergence and the sex ratio of the progeny during 42 generations. Parasitized host percentages were >80% and an average of 40% of females were obtained in practically all generations. Low percentages (<2%) of dead immature stages were recorded, and life span of adults was 32±1.3 and 18±2.2d for females and males, respectively. The advantages of this rearing method compared to others previously developed for this parasitoid and its application to others hymenopteran parasitoid are discussed. [Copyright &y& Elsevier]

Hyposoter didymator (Thunberg) (Hymenoptera: Ichneumonidae) is an important larval parasitoid of several lepidopteran pests. Under laboratory conditions, the topical toxicity of selected insect growth regulator insecticides, azadirachtin (AZA), diflubenzuron (DFB), methoxyfenozide (MET), pyriproxyfen (PYR), and tebufenozide (TEB), and the naturalyte spinosad (SPIN) was tested against last (third)-instar larvae of this parasitoid up to the maximum field recommended concentration (MFRC). At MFRC, no abnormalities or mortality were scored for MET and TEB (IOBC toxicity classes 1). In contrast, AZA was slightly, PYR moderately, and DFB and SPIN harmful to the parasitoid (IOBC toxicity classes 2, 3, and 4, respectively). These ratings are the result of a reduction in rate of: (i) pupae formation, (ii) pupal mortality, (iii) adult longevity, (iv) parasitism, and (v) adult emergence. In addition, PYR and SPIN caused a direct mortality in the treated larvae. At sublethal concentrations, every insecticide but MET and TEB also affected these life history parameters of the parasitoid. The second part of the study focused on pharmacokinetic parameters important for the toxicological properties of these insecticides. We determined the recovery pattern of 14C-labeled DFB, MET, PYR, and TEB from parasitoid body, larval exuvia, and silken pupal cocoon after topical application to third-instar larvae. For MET, TEF, and PYR, >60% was recovered from the parasitoid body after 24 h, whereas this was only 12% for DFB, which was mostly detected in the silken cocoon (>60%). More than 25% PYR was also detected in the larval exuvia after three days. Data suggest that the silken pupal cocoon and the larval exuvia might play a role in eliminating insecticides. In conclusion, the current results indicated that MET and TEB are harmless to third larvae of H. didymator. In contrast, AZA, DFB, PYR, and SPIN are harmful and their use in IPM should be considered with caution until they are evaluated under field conditions. [Copyright &y& Elsevier]