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Title: Contrasting brood-sex ratio flexibility in two opiine (Hymenoptera: Braconidae) parasitoids of tephritid (Diptera) fruit files

item ALVARENGA, CLARICE - Universidade Estadual De Santa Cruz
item DIAZ, VANESSA - University Of Florida
item Stuhl, Charles
item Sivinski, John

Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2015
Publication Date: 12/9/2015
Citation: Alvarenga, C.D., Diaz, V., Stuhl, C.J., Sivinski, J.M. 2015. Contrasting brood-sex ratio flexibility in two opiine (Hymenoptera: Braconidae) parasitoids of tephritid (Diptera) fruit files. Journal of Insect Behavior. 29(1):25-36.

Interpretive Summary: Fruit flies attack hundreds of fruits and vegetables and are responsible for trade restrictions wherever they occur. Augmentative biological control is used for their area-wide control but could be made more economical if the female proportion of mass-reared parasitoids was increased. There are many instances of sex ratio distortions in parasitic wasps and these are usually due to females producing only enough sons to fertilize her daughters or when one sex is better able to win conflicts with other larvae inside hosts. Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida in cooperation with Brazilian colleagues at the Universidade Estadual de Montes Claros examined two parasitic wasps with very different habits and found that both would produced more daughters when appropriate and that in both female larvae outcompeted males. This information shows that high densities in mass-rearing facilities may actually increase female production.

Technical Abstract: Mass-rearing of fruit fly parasitoids for augmentative release would be more economical if production could be biased towards females. If sex ratios are ever to be manipulated under rearing conditions it is important to determine if, then understand why, sex ratio flexibility exists. Unequal brood-sex ratios are common in bisexual parasitic Hymenoptera and one of two reasons are generally advanced for such cases: 1) avoidance of Local Mate Competition (LMC) predicts that the number of females exploiting a host-patch can influence the optimal sex ratio of their offspring; and 2) one sex is more likely to develop under a particular set of physical/ competitive conditions. We hypothesized that LMC is more often encountered in relatively uncommon species with coarse-grained distributions. As a result, isolated females of such species would be more likely to expect future LMC to be high and to bias offspring sex ratios towards females. We proposed that the opiine braconid Utetes anastrephae is such a coarse-grained species and compared its responses to differences to LMC (isolated females and those paired with a conspecific competitor) with those of another opine, Diachasmimorpha longicaudata believed to have a finer-grained distribution. Adult sex ratios were mutable in D. longicaudata and U. anastrephae and, as predicted by avoidance of LMC, males were relatively more abundant among the paired females in both species. However, superparasitized hosts yielded relatively more daughters, perhaps because female larvae are superior intrinsic competitors. Contrary to prediction, there was no suggestion that U. anastrephae was more likely to than D. longicaudata to avoid LMC. While these results did not reveal any species differences in sex-allocation patterns or suggest any modifications to the present practice of fruit fly mass-rearing for augmentative release they did provide new information regarding U. anastrephae, a widespread natural enemy of Anastrepha spp. about which relatively little is known.