Chemically mediated asymmetric competition and semiochemical-based management of Bactrocera cucurbitae and B. tau in melon fields

Bactrocera cucurbitae and B. tau are two economically important tephritid pests with closed ecological niches and host ranges in tropical and subtropical regions. Their co-occurrence in cucurbit fields raises questions about interspecific competition and chemically mediated mechanisms. This study investigated whether their competition was driven by chemical cues and whether these cues could be used in tephritid pest control. Field surveys were conducted in three melon fields to examine co-occurrence patterns. Laboratory experiments assessed oviposition behavior and competition outcomes under varying adult introduction ratios. Gas chromatography–mass spectrometry (GC–MS) and behavioral assays were used to identify species-specific compounds from infested melons. Finally, field trials were conducted to evaluate the efficacy of these compounds in reducing melon damage. Field surveys across three melon fields revealed a strong negative association: B. cucurbitae significantly suppressed B. tau occurrence. Laboratory assays confirmed that both species avoided melons previously infested by the other. In competitive rearing, B. cucurbitae produced more F1 offspring than B. tau, even when introduced at lower ratios. GC–MS and behavioral tests identified phenylacetaldehyde and nicotine as key volatile compounds: phenylacetaldehyde repelled both species, while nicotine selectively repelled <i>B. tau</i>. Field application of a repellent blend (phenylacetaldehyde: nicotine = 1:1) at 10 μL/mL significantly reduced B. cucurbitae trap captures and melon damage. These results reveal asymmetric, chemically mediated competition favoring B. cucurbitae, and demonstrate the potential of semiochemicals to manage tephritid pests through behavioral interference.