Dense populations of caterpillars likely correlate with increased risk of sperm competition when adult moths emerge. Previous results have shown that increased sperm counts correlate with a greater likelihood for sperm precedence in H. veriscens. Here, we test the hypothesis that moths from dense rearing conditions develop larger testes relative to body size as compared with moths reared in isolation. In the laboratory, we reared Heliothis verscens from egg to adult in two densities; isolated larvae and grouped (15-30) larvae. The testis was extracted from each male, and testis diameter and weight, was compared to pupa weight between the isolated and grouped moths. On average, isolated males had the largest testes, yet, compared to body mass, grouped males had larger testes. These data show that caterpillars are sensitive to their social settings and devote more resources to testicular development when sperm competition risk is greatest.
Species 1: Lepidoptera Noctuidae Heliothis virescens (tobacco budworm)
Keywords: sperm competition, testis size
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