The effect of intraspecific competition on progeny sex ratio in Gonatocerus spp. for Homalodisca coagulata egg masses: Economic implications for mass rearing and biological control

Abstract

The eVect of the number of simultaneously ovipositing females on progeny sex ratio of three Homalodisca coagulata egg parasitoids, Gonatocerus ashmeadi, G. triguttatus, and G. fasciatus was investigated in the laboratory. When one female Gonatocerus parasitoid was present, progeny production was strongly female biased producing »1 male:8 females, 1:14 and 1:9 for G. ashmeadi, G. triguttatus and G. fasciatus, respectively. Increasing the number of simultaneous ovipositing females from 1 to 3, signiWcantly increased percentage of male oVspring by up to 61% for all three Gonatocerus species. Overall percentage male oVspring ranged from 31-34%, and did not signiWcantly diVer among species. Overall mean percentage parasitism by G. ashmeadi was up to 16% higher compared with G. triguttatus and G. fasciatus, whereas, average clutch size and mean progeny production was more than twofold higher for G. fasciatus when compared with G. ashmeadi and G. triguttatus. Additional laboratory trials with only G. ashmeadi demonstrated that when H. coagulata egg masses consisted of 2-13 eggs, 67-100% of females allocated one male oVspring per egg mass. When one egg mass was presented to Wve female G. ashmeadi searching concurrently, male oVspring was up to 22% higher compared with male oVspring from host eggs exposed to one female G. ashmeadi. Experiments indicated that allocation of male eggs was not inXuenced by constant female-to-female contact for 19 h prior to host exposure, and female G. ashmeadi did not alter allocation of male eggs when sibling and non-sibling conspeciWcs were contesting host egg masses. The economic signiWcance for mass rearing is substantial. For G. ashmeadi at 2003 production costs and under optimal conditions, estimated cost per female was $1.42, under suboptimal conditions, cost per female increased to $4.51; a 218% increase in production cost per female parasitoid.

Cold Storage of Adult <I>Gonatocerus ashmeadi</I> (Hymenoptera: Mymaridae) and Effects on Maternal and Progeny Fitness

“…Irvin and Hoddle (2006) observed that laboratory manipulation of the adult diet for G. ashmeadi females resulted in a Ͼ370% increase in progeny production, which also supports our suggestion that egg development occurs during the adult stage of this species.…”

“…ashmeadi is a haplodiploid species (Irvin and Hoddle 2006) in which unfertilized (haploid) eggs normally develop as males and fertilized (diploid) eggs develop as females. Our results showed that the proportion of males in the F 1 generation signiÞcantly increased after their female parents were stored for Ն30 d. This indicates that the female parents were lacking viable sperm or manipulated the fertilization process as the length of storage increased.…”

Host size, superparasitism and sex ratio in mass-reared Diachasmimorpha longicaudata, a fruit fly parasitoid

“…In Anaphes nitens (Hymenoptera: Mymaridae), Santolamazza-Carbone and CorderoRivera (2003) found that at low parasitism levels, sex ratio was clearly female biased. Irvin and Hoddle (2006) reported that when only one female of the mymarid Gonatocerus spp. parasitoid was present, the progeny production was strongly female biased and that increasing the number of simultaneous females ovipositing significantly increased the male offspring.…”

Multi-Generation Effects of Bt Rice on Anagrus nilaparvatae, a Parasitoid of the Nontarget Pest Nilapavarta lugens

“…Many studies indicated that genetic, cytoplasmic, and behavioral factors were linked in various ways with arrhenotokous parthenogenesis (arrhenotoky) in Hymenoptera (van Wilgenburg et al 2006, Heimpel andBoer 2008). Irvin and Hoddle (2006) found that increasing the number of simultaneously ovipositing females from 1 to 3 resulted in signiÞcantly increased percentage of male offspring in three mymarid egg parasitoids of Homaladisca coagulate (Say) (Hemiptera: Cicadellidae). Three or four pairs of A. nilaparvatae adults were used in our study.…”