Semiochemicals from the African weaver ant, Oecophylla longinoda (Hymenoptera: Formicidae) and their repellency on mango fruit flies

Abstract

Fruit flies (Diptera: Tephritidae) include more than 4300 described species associated with fruits and other plant crops of economic importance. The oriental fruit fly, Bactrocera dorsalis (Hendel), endemic to Southeast Asia and the mango fruit fly, Ceratitis cosyra (Walker), the African native fruit fly species, are the dominant pest species attacking mango fruits in sub-Saharan Africa. Different methods have been used to control and suppress the populations of fruit flies. These methods include the use of synthetic insecticides, Sterile Insect Technique (SIT), Male Annihilation Technique (MAT), baiting technique, cultural and biological control methods. The African weaver ant, Oecophylla longinoda (Hymenoptera: Formicidae) a major predator of pest insects in agriculture has been shown to have a repellent effect on the oviposition behaviour of fruit flies. This study investigated and compared the role of O. longinoda semiochemicals on the oviposition responses of two major fruit fly species of mango: B. dorsalis, and C. cosyra in choice assays with ant-exposed and unexposed mangoes, using extracts of ant whole-body and body parts (head, thorax, and abdomen). The results show that both fruit fly species avoided and laid fewer eggs on weaver ant-exposed than unexposed mango peel discs. In addition, the whole-body extracts reduced oviposition responses in C. cosyra, and discs treated with abdominal extracts affected egg-laying in B. dorsalis and C. cosyra. The results obtained suggest that abdominal glands contain chemicals that the flies avoid. Further investigation was carried out using abdominal gland extracts. The flies avoided components in Dufour’s and poison glands, indicating the repellent chemical compounds in these organs are detected by the flies and caused a change in oviposition behaviour. Using Solid Phase Microextraction (SPME) to collect gland headspace volatiles and solvent extraction for the secretions, gas chromatography-mass spectrometry (GC-MS) was used to analysed secretions of the Dufour’s, poison glands, as well as rectal sternal glands for the first time. A total of 78 components were identified from the four glands, Dufour, poison, sternal and rectal, of which 62 were reported for the first time from these glands. The Dufour’s glands of O. longinoda contained mainly hydrocarbons. The effect of major compounds: undecane (12 ng/ul), tricosane (5.4 ng/ul), heneicosane (4.2 ng/ul), pentadecane (2.6 ng/ul), tridecane (1.9 ng/ul) and their blends in three different concentrations were tested on the oviposition responses of B. dorsalis using dual-choice assays. Neither the compounds nor their blends deter the flies from ovipositing even at higher concentrations (100 gland equivalents). This study demonstrated the repellent effects of O. longinoda semiochemicals on the oviposition behaviour of fruit flies. Chemical extracts from the Dufour’s and poison glands significantly reduced oviposition. This repellence could be attributed to the chemical composition produced by the ants in the respective glands. The study also provided data on the chemical composition of the Dufour’s, poison, sternal and rectal glands located in the ants’ abdomen and their potential use in developing pest control measures for fruit fly in mango orchards.