Mutual interference in the mass rearing of Diachasmimorpha longicaudata (Hymenoptera: Braconidae), a fruit fly parasitoid

Abstract

Diachasmimorpha longicaudata (Ahsmead) is a fruit fly solitary endoparasitoid that is mass produced in Mexico for the biological control of Anastrepha spp. We studied the effect of mutual interference among conspecific foraging females during the host parasitization process, to better understand the parasitoid: host dynamics in the mass rearing system of this species. We used a constant host availability, 60 third instar larvae of Anastrepha ludens Loew (per oviposition unit type Petri dish), which were exposed during three hours individually to 1, 2, 4, 8, 10, 14 and 20 D. longicaudata females, 7 day-old and without oviposition experience. The main parameters determined were: total number of attacked hosts (i.e., larvae with at least one oviposition scar), number of attacked hosts / female; percentage of adult emergence, and sexual ratio. The second assay was performed at mass rearing level, contrasting the current proportion (2 larvae / female) with the alternant treatment (5 larvae / female) derived from the previous assay. Results showed that the density of foraging females on a patch presents an inverse relationship to the number of hosts attacked by a single female. The best patch exploitation (94.6% = 56.83 ± 0.8 larvae h-1), occurred in the ratio of 6 larvae / female, the highest percentage of emergence (73.4%) in the ratio of 7.5 larvae / female, but the best sex ratio was obtained in the treatment of 4.3 larvae / female. Under mass rearing conditions we found that a lower density of females per cage (alternant treatment) reduced the levels of superparasitism without affecting the percentages of emergence and sexual ratio compared to the control. This suggests that the number of females in the rearing cages can be diminished thus improving the mass rearing effectiveness of this species.