Female-female aggression in Bactrocera tryoni (Diptera: Tephritidae) and the influence of fruit quality on combat intensity

Frugivorous tephritid (Diptera: Tephritidae) females compete over access to fruit for oviposition through aggressive interactions. These aggressive displays are for oviposition site maintenance to reduce the probability of subsequent larval competition. While female aggressive behaviours have been described for several frugivorous tephritid species, studies quantifying behavioural frequencies and sequences and examining how quality of the host fruit might modify the intensity of aggressive behaviours are minimal or absent. We used behavioural analysis software of video playback to describe and quantify antagonistic behaviours between pairs of Bactrocera tryoni females and measured changes in the frequency of behaviours when females were defending three fruit types known to vary in their quality for offspring development. Seven behaviours were identified as part of competitive contests between B. tryoni females, which were not performed in any regular order or with any obvious escalation in the intensity of an aggressive display. Crabbing, [wing] supination and pushing were the most common behaviours, constituting 78% of all observed aggressive behaviours. Increasing fruit quality resulted in aggressive behaviours happening significantly sooner and more often. Our results are similar to previous studies in the types of behaviours exhibited by female frugivorous tephritids but are contrary to other studies in that no sequential pattern or escalation of behaviours was documented. Increased female investment in defence of higher quality hosts aligns with theoretical predictions but has not been previously tested.