Host discrimination and impact of superparasitism on biological quality of Diachasmimorpha longicaudata artificially reared on Ceratitis capitata

F. DEVESCOVI; C.A. CONTE; M.M. VISCARRET; S.B. LANZAVECCHIA; J. L. CLADERA; D. F. SEGURA

Panamá

Congreso; Tephritid Workers of the Western Hemisphere, 8th Meeting; 2012

The use of Diachasmimorpha longicaudata as a biological agent against fruit fly pests has been successfully implemented in many countries. In Argentina it is experimentally and massively reared on Ceratitis capitata. We evaluated three hypotheses regarding superparasitism, an interesting phenomenom that can negatively affect the rearing process: 1. Females are able to recognize parasitized and unparasitized hosts, 2. Supernumerary larvae should be eliminated before a certain threshold to allow a normal development of the winner and 3. Crescent levels of superparasitism (LSP) will decrease biological quality parameters on emerged parasitoids. Background: The use of insect parasitoids to control fruit fly pests has been successfully implemented worldwide. In Argentina, the solitary endoparasitoid Diachasmimorpha longicaudata is experimentally and massively reared on Ceratitis capitata. A potential problem in the rearing process is given by ovipositions in a previously parasitized host [phenomenon called superparasitism (SP)], resulting in intraspecific larval competition and wastage of eggs. In a first experiment, we evaluated the ability of D. longicaudata to avoid oviposition in parasitized hosts. Then, we carried out a second experiment to assess the impact of SP on biological parameters associated with reproductive success. Methods: To investigate discrimination ability, four non-parasitized and four parasitized larvae were offered to a single female, arranged in an alternated fashion in a 24-well plate. We recorded the foraging behavior of the female for 30 minutes. In order to evaluate the effects of SP, C. capitata larvae were exposed to female parasitoids so as to obtain increasing levels of SP (LSP): 0 (control), 1 (control), 2, 3, 5 and 10 eggs of D. longicaudata per host. Parasitoids emerged from each LSP were maintained and evaluated individually. For each LSP, we evaluated percentage of emerged parasitoids, male and female survival, female fecundity and sex ratio of females´ offspring. Results: We did not find evidences of discrimination ability against previously parasitized hosts. No parasitoids emerged from LSP 0 and LSP 10, and the percentage of emergence was not statistically different among the remaining LSPs (1 to 5). Neither males nor females survival were affected. Female fecundity and its progeny sex ratio were not affected by the LSP. Conclusions: A negative effect triggered by SP is only reached at extremely high LSP. In preliminary observations, we found that supernumerary larvae are suppressed at first instar, leaving the host in conditions for an appropriate development of only one parasitoid. This early elimination of competitors could explain the lack of effect of SP on parasitoid development. The fact that no detrimental effects in biological parameters were observed for the intermediate LSP evaluated supports the lack of discrimination of parasitized hosts, as there is no apparent selective force enhancing this behavior.