Abstract
Males of certain species belonging to the Bactrocera dorsalis complex are strongly attracted to, and readily feed on methyl eugenol (ME), a plant secondary compound that is found in over 480 plant species worldwide. Amongst those species is one of the world’s most severe fruit pests the Oriental fruit fly, Bactrocera dorsalis s.s., and the former taxonomic species Bactrocera invadens, Bactrocera papayae and Bactrocera philippinensis. The latter species have been recently synonymised with Bactrocera dorsalis based on their very similar morphology, mating compatibility, molecular genetics and identical sex pheromones following consumption of ME. Previous studies have shown that male fruit fly responsiveness to lures is a unique phenomenon that is dose species-specific, besides showing a close correlation to sexual maturity attainment. This led us to use ME sensitivity as a behavioural parameter to test if Bactrocera dorsalis and the three former taxonomic species had similar sensitivity towards odours of ME. Using Probit analysis, we estimated the median dose of ME required to elicit species’ positive response in 50% of each population tested (ED50). ED50 values were compared between Bactrocera dorsalis and the former species. Our results showed no significant differences between Bactrocera dorsalis s.s., and the former Bactrocera invadens, Bactrocera papayae and Bactrocera philippinensis in their response to ME. We consider that the Bactrocera males’ sensitivity to ME may be a useful behavioural parameter for species delimitation and, in addition to other integrative taxonomic tools used, provides further supportive evidence that the four taxa belong to one and the same biological species, Bactrocera dorsalis.
Highlights
A number of fruit fly species in the Bactrocera dorsalis complex are pests of economic importance
B. papayae and B. dorsalis demonstrate similar ranges of sensitivity to ME at nanogramme levels, while B. carambolae has been shown to be at least 10 times less sensitive to ME compared to the former two species (Wee et al 2002). This led us to hypothesize that if B. dorsalis, B. invadens, B. philippinensis and B. papayae are different names for the one biological species, their sensitivity to ME could be used as a behavioural parameter to confirm, or refute that assumption, Comparative sensitivity to methyl eugenol of four putative Bactrocera dorsalis complex... 315 i.e. we evaluated if the sensitivity of those putative species to ME were significantly different, or were the same
The validity of the ED50 values was confirmed with heterogeneity factors of each species’ response to ME showing values < 1 (B. dorsalis, 0.484; B. invadens, 0.714; B. philippinensis, 0.502 and B. papayae, 0.859), indicating the data fits well with the model of standardized residuals when plotted against the predicted values
Summary
A number of fruit fly species in the Bactrocera dorsalis complex are pests of economic importance. The most notorious is the Oriental fruit fly, B. dorsalis (Hendel), a widely distributed and invasive species which includes the recently synonymised B. invadens Drew, Tsuruta & White, B. papayae Drew & Hancock and B. philippinensis Drew & Hancock. The presence of this species in the tropics and subtropics has caused significant damage by rendering infested fruits inedible and prohibiting fruit exports due to strict quarantine restrictions. ‘Alphonso’ from India to the EU countries (European Commission 2014) due to detection of Oriental fruit fly, made headlines globally and created an uproar in India, which is the largest mango producer in the world. The ban was lifted in January 2015 (European Commission 2015), the duration of the ban had adversely affected the lucrative mango export and livelihood of growers
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