Larval secretions and food odors affect orientation in femalePlodia interpunctella

Substrates contaminated by wandering fifth instar larvae ofPlodia interpunctella (Hübner) (Lepidoptera: Pyralidae) elicit oviposition by conspecific female moths, and larval rearing diet enhances oviposition and also induces upwind flight. Two-choice oviposition assays determined that four-day-old gravid femaleP. interpunctella preferred to lay eggs on dishes containing cornmeal-based rearing diet compared to empty dishes. Pieces of cheesecloth contaminated by fifth instar larvae elicited more oviposition than untreated cheesecloth or dishes with food. The combination of larval contamination and food was preferred over food only or larval contamination only in both two- and four-choice experiments. The factor(s) in larval contamination responsible for eliciting oviposition in female moths was extracted in hexane, confirming that organic semiochemicals are responsible for the effect. The oviposition-eliciting activity of larval contamination was retained on cheesecloth for up to 30 days following treatment with larvae, suggesting the active component(s) is stable and of low relative volatility. In two-choice windtunnel bioassays female moths initiated flight only when rearing food was present in one of the treatments, and they displayed the highest landing responses to a combination of larval contamination and food. Earlier work onP. interpunctella and related pyralid species found that larval contamination due to secretions from the mandibular glands acted as both a spacing pheromone for wandering larvae and as a kairomone for host-seeking parasitoid wasps. The present study suggests that the same or a similar secretion acts as an oviposition-eliciting pheromone for conspecific females.