Behavioral and physiological responses of the aphelinid parasitoid, Encarsia formosa, to interspecific competitors.

The inter- and intra- specific competition is a key factor influencing population dynamics, ecosystem stability, and adaptive evolution in invertebrates, especially within parasitoid communities. Numerous parasitoid species can detect cues left by other parasitoid species, yet it remains unclear whether these cues influence parasitism behavior and competitive outcomes. Here, we show that the endo-parasitoid Encarsia formosa adjusts reproductive, behavioral and physiological strategies when detecting competition cues from Eretmocerus hayati, which shares the same whitefly host. The results indicate that En. formosa produces an increased number of mature eggs and exhibits more frequent parasitic behavior, changes that likely enhance its competitive ability. Transcriptomic analyses indicate that visual perception of competition alters neurotransmitter and hormone expression, promoting vitellogenin production and egg formation. However, probably due to energy and resource constraints, these additional eggs are smaller and exhibit higher developmental mortality, ultimately leading to a reduction in number of viable offspring. This reproductive adjustment may ultimately increase lifetime fitness under actual competition in the field. Our findings clarify how parasitoids integrate sensory cues into physiological responses, offering a framework for understanding competition-driven reproductive strategies and informing future ecological and evolutionary research.