Specific volatile compounds from mango elicit oviposition in gravid Bactrocera dorsalis females

Selecting a suitable oviposition site is crucial to the fitness of female insects because it determines the successful development of their offspring. During the oviposition process, an insect must use cues from the external environment to make an appropriate choice of where to lay eggs. Generalist insects can detect and react to a plethora of cues, but are under selection pressure to adopt the most reliable ones to override noise and increase efficiency in finding hosts. The oriental fruit fly, Bactrocera dorsalis (Hendel), is a generalist that utilizes a multitude of fruits as oviposition sites. However, the identity and nature of oviposition stimulants for B. dorsalis is not well known. Recently, we identified a volatile compound γ-octalactone that elicits an innate oviposition response in B. dorsalis. We screened 21 EAD-active volatiles, identified from mango, for their oviposition stimulant activity. 1-Octen-3-ol, ethyl tiglate, and benzothiazole instigated oviposition in gravid B. dorsalis females. Flies deposited most of their eggs into pulp discs with oviposition-stimulants, and only a small fraction of eggs were laid into control discs. In a binary choice oviposition assay, 95.1, 93.7, and 65.6 % of eggs were laid in discs treated with 1-octen-3-ol, ethyl tiglate, and benzothiazole, respectively. Single plate two-choice assays proved that oviposition-stimulants were crucial in oviposition site selection by gravid female B. dorsalis. In simulated semi-natural assays, gravid B. dorsalis females accurately differentiated between fruits with and without 1-octen-3-ol, ethyl tiglate, and γ-octalactone by laying more eggs on the treated fruit. However, benzothiazole did not elicit an increase in oviposition when presented in this context. Our results suggest that the identified oviposition-stimulants are 'key' compounds, which the flies associate with suitable oviposition sites.