Mutual interference in Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae) when foraging for patchily-distributed light brown apple moth

• Results are broadly consistent with the predictions of the Ideal Free Distribution.
• Negative relationship between search-efficiency and parasitoid density.
• D. tasmanica might deposit a marking pheromone on a visited patch.
• D. tasmanica chooses those patches which initially offer the highest oviposition rates.
• As the numbers of foragers increased, they stopped searching more often and earlier.

Dolichogenidea tasmanica (Hymenoptera: Braconidae) is a solitary endoparasitoid of light brown apple moth (LBAM) and other tortricids that is native to Australia. The foraging behavior of single and multiple female D. tasmanica in the presence of patchily-distributed hosts was observed in wind tunnels. Results show that D. tasmanica was able to choose those patches which initially offered the highest oviposition rate. Single foragers spent the longest times on patches with higher host densities, but they visited patches with lower host densities sooner in presence of other foragers. The overall rate of parasitism was equalized across patches at the end of the experiment, which indicates that hosts were equally susceptible to attack by D. tasmanica, irrespective of their local density. A decrease in the searching efficiency of individual parasitoids with increasing parasitoid density was evidence of interference among female D. tasmanica. Nonlinear regression indicates that there was a consistent pattern of mutual interference as wasp density increased and the area of discovery and mutual interference coefficients of Hassell and Varley’s (1969) model of parasitoid foraging were estimated as Q = 0.45 and m = 0.526, respectively. Females chose to visit patches that were not previously visited, which suggests that repellent chemicals were produced by attacked hosts or marking pheromones were deposited by searching females on patches they have visited. This is one factor that can reduce searching efficiency and cause mutual interference among competing D. tasmanica.

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