Submitted to: USDA Interagency Research Forum on Gypsy Moth and Other Invasive Species
Publication Type: Proceedings
Publication Acceptance Date: 6/20/2004
Publication Date: 8/20/2005
Citation: Fuester, R.W., Swan, K.S., Taylor, P.B., Wingard, S.C., Ramaseshiah, G. 2005. Effects of parental age at mating on sex ratios of the gypsy moth parasitoid Glyptapanteles flavicoxis (Hymenoptera: Braconidae), p. 32. In K.W. Gottschalk (Ed.), Proceeedings XV USDA Interagency Research Forum on Gypsy Moth and Other Invasive Species 2004; 2004 January 13-16; Annapolis, MD Gen. Tech. Rep. NE-332 Newtown Square, PA. US Department of Agriculture, Forest Service, Northeastern Research Station 98p. Interpretive Summary: The gypsy moth is the most important forest and shade tree pest in the northeastern U.S. One of the natural enemies imported for study as a potential agent for its biological is GLYPTAPANTELES FLAVICOXIS, a parasitic wasp that attacks the caterpillar stage of the Indian gypsy moth. Earlier studies by ARS scientists indicated that it readily attacked and successfully developed within caterpillars of the European gypsy moth, the strain present in North America, but that male-biased sex ratios (% females) in laboratory rearings hindered its use as a biological control agent (only females can attack and lay eggs in the caterpillar). Sex determination in this wasp is conditional, whereby fertilized(diploid) eggs give rise to female progeny and unfertilized (haploid) eggs, male progeny. In this study, we studied the effects of parental age on sex ratios in the wasp's offspring by crossing males and females 0-, 1-, 4-, 9- and 16-days-old for each of the 25 possible age combinations (5 paternal age classes times 5 maternal age classes), then tracking the sex ratios among the offspring produced by each pair over the mother's lifetime. Females laid most of their eggs in the hosts offered to them the first day after mating, so it was concluded that only the first day's production need be used in mass rearing of this species. The highest sex ratios (about 50% females) were produced when 1-day-old males were mated with newly-emerged females.
Technical Abstract: GLYPTAPANTELES FLAVICOXIS (Marsh) is an oligophagous, gregarious larval parasitoid of the Indian gypsy moth, LYMANTRIA OBFUSCATA (Walker), that readily attacks the European gypsy moth, LYMANTRIA DISPAR (L.). Though attempts to establish G. FLAVICOXIS in the U.S. were unsuccessful due to its stringent alternate host requirements, it is believed to have potential for inundative releases against gypsy moth populations, because it can be reared in large numbers with relatively few hosts. Unfortunately, sex ratios in laboratory reared G. FLAVICOXIS are usually male-biased. Male-biased sex ratios hinder efforts to mass release parasitic Hymenoptera for biological control by making the production of females costly. Because parental age at time of mating is known to affect the sex ratio in some Braconidae, we crossed haploid males and virgin females 0-, 1-, 4-, 9-, and 16-days-old with at least 10 trials for each of the 25 combinations. Numbers and sex ratios of progeny produced by females each day were recorded and subjected to two-way analysis of variance. We used Tukey's test to detect differences in sex ratios among progeny of differently aged parents and G-tests to test for treatment differences in proportions of females producing mixed and all male progeny. Both progeny and sex ratios (% females) among progeny produced by ovipositing females of G. FLAVICOXIS decreased markedly over time, so only the first days production need be used in mass rearing. The reduction in the proportion and numbers of females among progeny as ovipositing females aged is consistent with depletion of sperm in the spermatheca. Therefore, we focused our analyses on sex ratios in progeny produced on the first day hosts were provided to females. Females in all age classes mated to newly emerged males (day 0) were more likely to produce all male progeny (30%) than those mated to older males (10-15%). When crosses with only male progeny were excluded from the analysis, females mated to males one day old had higher sex ratios than those mated to males in other age classes. In addition, females mated the day that they emerged tended to have the highest sex ratios. Therefore, one should not use newly emerged males in rearing this species, but newly emerged females appear to be good candidates for a rearing program.