Density‐dependent emergence success of a tephritid fruit fly eclosed in soil as a factor contributing to density‐dependent pupation depth

Abstract

AbstractThe oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), pupates in the soil, and the average pupation depth increases with the number of concurrently pupating individuals at the same location. This study aimed to explain the density‐dependent pupation depth in B. dorsalis. Previous studies demonstrated that increasing pupation depth has the benefit of reduced parasitism and predation risk and the cost of reduced emergence success (i.e., eclosed adults in the soil fail to reach above ground). It was hypothesized that density‐dependent pupation depth is governed by density‐dependent cost. That is, emergence success of eclosed adults increases with density because the soil is more easily loosened as the number of individuals increases. Pupating larvae can reduce parasitism and predation risk by increasing pupation depth, but only those in high density can afford to pupate at deep depths due to the associated cost. To test the hypothesis, density‐dependent emergence success in B. dorsalis was examined in the laboratory. Newly pupated individuals were buried in peat moss approximately 5 cm below the surface, and the relationship between the number of buried pupae (four levels: 1, 25, 50, and 100 pupae) and their emergence success was recorded. To manipulate the difficulty of emergence, the level of peat moss compaction was also varied. Emergence success was uniformly high when peat moss was not heavily compacted regardless of the number of pupae, but the number of pupae had a positive effect on emergence success when the peat moss was heavily compacted. In addition, the timing of emergence was more synchronized in the highest density than in the lower densities. The results of this study, in combination with the previous findings, support the hypothesis.