Electrophysiological Responses to Cuelure of Raspberry Ketone-Fed Queensland Fruit Flies

1-Octanol emitted by Oecophylla smaragdina weaver ants repels and deters oviposition in Queensland fruit fly

Humans have used weaver ants, Oecophylla smaragdina, as biological control agents to control insect pests in orchards for many centuries. Over recent decades, the effectiveness of weaver ants as biological control agents has been attributed in part to deterrent and oviposition inhibiting effects of kairomones produced by the ants, but the chemical identity of these kairomones has remained unknown. We have identified the kairomone responsible for deterrence and oviposition inhibition by O. smaragdina, providing a significant advance in understanding the chemical basis of their predator/prey interactions. Olfactometer assays with extracts from weaver ants demonstrated headspace volatiles to be highly repellent to Queensland fruit fly, Bactrocera tryoni. Using electrophysiology and bioassays, we demonstrate that this repellence is induced by a single compound, 1-octanol. Of 16 compounds identified in O. smaragdina headspace, only 1-octanol evoked an electrophysiological response from B. tryoni antennae. Flies had greatly reduced oviposition and spent significantly less time in an olfactometer arm in the presence of 1-octanol or a synthetic blend of headspace volatiles containing 1-octanol than in the presence of a synthetic blend of headspace volatiles without 1-octanol, or clean air. Taken together, our results demonstrate that 1-octanol is the functional kairomone component of O. smaragdina headspace that explains repellence and oviposition deterrence, and is hence an important contributor to the effectiveness of these ants as biological control agents.

Pre-release dietary supplements of methoprene and raspberry ketone increase field abundance of sterile Queensland fruit flies (Diptera: Tephritidae)

The sterile insect technique (SIT) is a sustainable pest management tool based on the release of millions of sterile insects that suppress reproduction in targeted populations. Success of SIT depends on survival, maturation, dispersal, and mating of released sterile insects. Laboratory and field cage studies have demonstrated that dietary supplements of methoprene and raspberry ketone (RK) promote sexual maturation of adult Queensland fruit fly, Bactrocera tryoni (Froggatt), and may hence shorten the delay between release and maturity in the field. We investigated the effects of methoprene and RK dietary supplements on field abundance of sexually mature sterile Q-flies relative to untreated flies fed only sugar and yeast hydrolysate before release at 2 d of age. Compared with untreated flies, more methoprene- and RK-treated flies were recaptured in cuelure traps to which only sexually mature males are attracted. At distances of 100 and 200 m from the release point, recapture rates were higher for methoprene- and RK-treated flies than for untreated flies, but at 300 m recapture rates were low and were similar for treated and untreated flies. Rainfall, relative humidity, wind speed, and wind direction did not affect recapture rates, but temperature was positively correlated with recapture rates for all treatments. There was a strong correlation between the number of sterile and wild flies caught in traps, indicating co-location in the field. Dietary supplements of methoprene and RK can substantially increase abundance of sexually mature sterile male Q-flies in the field following release as 2-d-old immature adults.

Electrophysiological Responses of Bactrocera kraussi (Hardy) (Tephritidae) to Rectal Gland Secretions and Headspace Volatiles Emitted by Conspecific Males and Females

Pheromones are biologically important in fruit fly mating systems, and also have potential applications as attractants or mating disrupters for pest management. Bactrocera kraussi (Hardy) (Diptera: Tephritidae) is a polyphagous pest fruit fly for which the chemical profile of rectal glands is available for males but not for females. There have been no studies of the volatile emissions of either sex or of electrophysiological responses to these compounds. The present study (i) establishes the chemical profiles of rectal gland contents and volatiles emitted by both sexes of B. kraussi by gas chromatography–mass spectrometry (GC–MS) and (ii) evaluates the detection of the identified compounds by gas chromatography–electroantennogram detection (GC–EAD) and –electropalpogram detection (GC–EPD). Sixteen compounds are identified in the rectal glands of male B. kraussi and 29 compounds are identified in the rectal glands of females. Of these compounds, 5 were detected in the headspace of males and 13 were detected in the headspace of females. GC–EPD assays recorded strong signals in both sexes against (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-ethyl-7-mehtyl-1,6-dioxaspiro[4.5]decane isomer 2, (E,Z)/(Z,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, and (Z,Z)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. Male antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-methyl-6-pentyl-3,4-dihydro-2H-pyran, 6-hexyl-2-methyl-3,4-dihydro-2H-pyran, 6-oxononan-1-ol, ethyl dodecanoate, ethyl tetradecanoate and ethyl (Z)-hexadec-9-enoate, whereas female antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and 2-methyl-6-pentyl-3,4-dihydro-2H-pyran only. These compounds are candidates as pheromones mediating sexual interactions in B. kraussi.