Foraging Drosophila suzukii larvae exhibit chemotaxis and invade intact, uninfested fruit.

Spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a destructive pest of ripening berries and stone fruits, where larval feeding rapidly renders fruit unmarketable. Larvae are widely assumed to remain inside their natal fruit until pupation, limiting exposure to external management tactics. Here, we challenge this paradigm by demonstrating that D. suzukii larvae exhibit complex chemotactic capabilities and dynamic interactions with host fruit throughout development. Third-instar larvae responded in a dose-dependent manner to fermentation-associated volatiles and discriminated between conspecific and heterospecific larval developmental cues, indicating the capacity for substrate assessment. Complementary to these chemotaxis assays, direct observations across multiple hosts revealed frequent larval emergence from fruit, including posterior spiracle, head, and whole-body exposure, as well as a previously undocumented behavior: secondary infestation of neighboring, uninfested fruit. Secondary infestation occurred across all hosts tested and throughout larval development, with cumulative movement into fresh berries exceeding 60% in some fruit types. Host species and larval density modulated the frequency and timing of emergence, and inter-fruit dispersal, highlighting the influence of natal environment on larval behavior. Together, these findings suggest that D. suzukii larvae are not confined to a single fruit but can interact repeatedly with fruit surfaces and move into neighboring hosts. This revised understanding of D. suzukii larval ecology exposes new vulnerabilities in the life cycle and has possible implications for the development of management strategies targeting immature stages.