Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/3/2003
Publication Date: 7/20/2003
Citation: Fuester, R.W., Swan, K.S., Taylor, P.B., Dunning, K., Ramaseshiah, G. 2003. Male-biased sex ratios in Glyptapanteles flavicoxis (Marsh) [Hymenoptera: Braconidae], a larval parasite of the gypsy moth, Lymantria dispar (L.)[Lepidoptera: Lymantriidae]. Annals of the Entomological Society of America. 96(4):553-559. 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 control 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 American strain of gypsy moth, but that male-biased sex ratios in laboratory rearings hindered its use as a biological control agent (only females can attack and lay eggs on the caterpillar). Sex determination in this wasp is arrhenotokous, a condition in which fertilized (diploid) eggs give rise to female progeny and unfertilized (haploid) eggs male. We ran three experiments to study the effects of temperature, time from mating to host exposure, and number of matings on the sex ratio (% females) in the progeny of this parasitic wasp. In the first experiment, we found that sex ratios did not differ among progenies of parents stored at 55- or 60-degrees F. and allowed to mate at 68- or 77-degrees F., but that many females produced all male progeny, indicating that they had not mated. In the remaining experiments, only mated females were used. In the second experiment, we found that sex ratios averaged only 12% vs. 30% in progenies of females that were offered hosts soon (1-60 min) or the next day (23-25 h) after mating, respectively. In the last experiment, we found that sex ratios in progeny of females that had mated once or twice were higher (median = 36%) than in those that had mated three or four times (median = 1%). Further research is needed to increase sex ratios to levels (50% or higher) observed in the field in India.
Technical Abstract: Male-biased sex ratios in populations of parasitic wasps used in biological control are undesirable, because they can prevent the establishment of introduced species or hinder commercial production of species used for augmentative control. Studies were conducted on potential factors contributing to male-biased sex ratios in laboratory rearings of the braconid endoparasitoid Glyptapanteles flavicoxis (Marsh) on the gypsy moth, Lymantria dispar (L.). Sex determination in this wasp is arrhenotokous, a condition in which fertilized (diploid) eggs give rise to female progeny and unfertilized (haploid) eggs male. In the first experiment, we found that sex ratios did not differ among progenies of parents stored at 55- or 60-degrees F. and allowed to mate at 68- or 77-degrees F., but that many females produced all male progeny, indicating they had not mated. In the second experiment, females were exposed to hosts soon (0-60 min) after mating or 23-25 h later. Sex ratios were higher in progenies of females provided with a rest period, than in those which were not. In a third experiment, females were allowed to mate from 1 to four times with a given male. Although differences between these groupings were not statistically significant, the data suggested that more than two matings might depress sex ratios of progeny. An alternative analysis with only two groupings (1-2 matings and 3-4 matings) suggested that more than two matings might be detrimental. Therefore, it is concluded that matings of this species should be controlled (limited to 1 or 2) and that females should be provided with a period of repose after mating before they are offered hosts for parasitization.