Effects of Parasitoid Age, Host Egg Age, and Host Egg Freezing on Reproductive Success of Ooencyrtus mirus (Hymenoptera: Encyrtidae) on Bagrada hilaris (Hemiptera: Pentatomidae) Eggs

Bagrada hilaris (Burmeister) is a serious pest on brassica crops in many regions throughout the world. As part of our efforts to enhance biological control, we have been studying an egg parasitoid that was collected from B. hilaris eggs found on brassica plant debris in Pakistan. This species has recently been described as Ooencyrtus mirus Triapitsyn & Power. A major component of rearing biological control agents is understanding the relationship among host egg age, parasitoid age, and reproductive success. To this end, we used a factorial design to evaluate all combinations of host egg ages 0–5 d and parasitoid ages 0–11 d. The results showed that the best combinations are 0- to 1-d-old host eggs with 3- to 10-d-old parasitoids. A further study using frozen host eggs showed that O. mirus can reproduce as successfully on frozen B. hilaris eggs as on fresh ones.

Effects of biological and environmental factors on sex ratio in Ascogaster quadridentata Wesmael (Hymenoptera: Braconidae), a parasitoid of Cydia pomonella L. (Torticidae)

The sex ratio in the natural population of most Hymenopteran parasitoids is 1 : 1. Females of these parasitoids, however, can regulate the sex of their offspring in response to environmental and biological factors. Under certain circumstances, this may lead to an overproduction of males, which can result in a very negative impact on any control program using these parasitoids. For these reasons, understanding the effect of these factors is very important. In this study, five biological and environmental factors known to affect sex ratio in parasitic Hymenoptera were investigated for Ascogaster quadridentata Wesmael, a parasitoid of Cydia pomonella L. Results showed that food, ambient temperature, and parasitoid age had significant effects on the sex ratio of the offspring of Hymenopteran parasitoids. The percentage of females decreased with lack of food, parasitoid age (when it became 10-days-old or older), and at low (15°C) and high (35°C) temperatures. The effect of host age and density, however, was not significant.

Production of the Parasitoid Cotesia marginiventris (Hymenoptera: Braconidae) in Unicellular Rearing Trays Using the Host Spodoptera exigua (Lepidoptera: Noctuidae)1

Factors that might affect parasitism rate and progeny production of Cotesia marginiventris (Cresson), a solitary endoparasitoid of lepidopteran larvae, were considered in this study. Hosts were Spodoptera exigua (Hübner) larvae, which were feeding gregariously on artificial diet within 270-mL unicellular rearing trays. The following hypotheses were tested: (1) parasitism and superparasitism rates increased as exposure time and parasitoid density increased, and (2) progeny production decreased as parasitoid age increased. Parasitism rate increased significantly as exposure to S. exigua larvae increased from 2 to 6 h, but not from 6 to 18 h. Superparasitism rate was not affected significantly by exposure time. Both parasitism and superparasitism rates were greatest at a density of 3 rather than 1 parental parasitoid per tray; no differences were evident between densities of 3 vs 2 or 2 vs 1 parasitoid per tray. Significantly more offspring were produced (with normal sex ratios) when parental females were inserted into rearing trays as adults rather than as pupae (in cocoons). Also, 1- to 2-d-old and 8- to 9-d-old females produced more progeny (with normal sex ratios) than 15- to 16-d-old females. This study suggests that inserting a single, mated 1- to 9-d-old C. marginiventris female into a unicellular rearing tray containing an abundance of putative hosts could limit superparasitism without seriously reducing progeny production. Partial automated rearing of C. marginiventris is possible.

Effect of Parasitoid and Host Age on Oviposition and Emergence of Microplitis croceipes (Hymenoptera: Braconidae) an endoparasitoid of Helvicoverpa zea (Lepidoptera: Noctuidae)

The effect of parasitoid age and two instars of the host Helicoverpa zea (Boddie) were investigated for the endoparasitoid, Microplitis croceipes (Cresson). Third and fourth instars of H. zea were exposed to three different age ranges (3 to 5, 6 to 8, and 12 to 15-d-old) of mated adult female M. croceipes. No significant differences were shown in rate of parasitism regardless of parasitoid age or host instar. Significant differences (P < 0.05) were found between parental age and adult wasp emergence, sex ratio, and number in pupal stage entering diapause. Six to 8-day-old parasitoids parasitizing third instar hosts yielded the highest percentage of adult emergence (47.5 ± 14%; X̄ ± SD), the highest percentage of females (79%), and the lowest percentage (4.5 ± 6%; X̄ ± SD) entering diapause during the test.