The recent discovery of a sesquiterpene, β-caryophyllene (CP) as a male attractant of the guava fruit fly, Bactrocera correcta (Bezzi) (Diptera: Tephritidae) prompted investigations into the attractancy of CP to the Oriental fruit fly, B. dorsalis (Hendel). This is because males of both species of fruit flies are attracted to, and feed on a phenylpropanoid compound, methyl eugenol (ME). Although CP was a more potent attractant than ME for B. correcta, it is not known if males of B. dorsalis are also attracted to CP. The possible attraction of B. dorsalis to CP as a sesquiterpene may indicate its wide host range through its attraction to different groups of plant volatiles i.e., phenylpropanoids and sesquiterpenes. In this paper, we report that males of B. dorsalis were also attracted to, and feed on CP. Subsequently, we conducted a probit regression analysis to determine the quantal response of sexually mature male flies that were attracted to CP in cage bioassays. Therefore, as a measure of male B. dorsalis' sensitivity of CP, the median dose of CP required to elicit a positive response in 50% of the tested B. dorsalis population (ED50) was calculated as 3.7 mg. This value was over 10,000x higher than known ED50 of B. dorsalis' male attraction ME (between 171 and 268 ng). We propose that the attraction of male B. dorsalis flies to CP was much weaker than to ME. Further, we suggest that in any fruit fly surveillance and monitoring programme, application of lures must consider the specificity and potency of each compound to target fruit fly species. The probit regression analysis of male fly quantal response to lure offers such information.
The Artocarpus fruit fly, Bactrocera umbrosa (Fabricius) (Diptera: Tephritidae), is an oligophagous fruit pest infesting Moraceae fruits, including jackfruit (Artocarpus heterophyllus Lamarck), a fruit commodity of high value in Malaysia. The scarcity of fundamental biological, physiological and ecological information on this pest, particularly in relation to behavioural response to phytochemical lures, which are instrumental to the success of many area-wide fruit fly control and management programmes, underpins the need for studies on this much-underrated pest. The positive response of B. umbrosa males to methyl eugenol (ME), a highly potent phytochemical lure, which attracts mainly males of many Bactrocera species, was shown to increase with increasing age. As early as 7 days after emergence (DAE), ca. 22% of males had responded to ME and over 50% by 10 DAE, despite no occurrence of matings (i.e. the males were still sexually immature). Male attraction to ME peaked from 10 to 27 DAE, which corresponded with the flies' attainment of sexual maturity. In wind-tunnel assays during the dusk courtship period, ME-fed males exhibited earlier calling activity and attracted a significantly higher percentage of virgin females compared with ME-deprived males. ME-fed males enjoyed a higher mating success than ME-deprived males at 1-day post ME feeding in semi-field assays. ME consumption also promotes aggregation behaviour in B. umbrosa males, as demonstrated in wind-tunnel and semi-field assays. We suggest that ME plays a prominent role in promoting sexual communication and enhancing mating performance of the Artocarpus fruit fly, a finding that is congruent with previous reports on the consequences of ME acquisition by other economically important Bactrocera species.
Bactrocera dorsalis, the Oriental fruit fly, is one of the world's most destructive agricultural insect pests and a major impediment to international fresh commodity trade. The genetic structuring of the species across its entire geographic range has never been undertaken, because under a former taxonomy B. dorsalis was divided into four distinct taxonomic entities, each with their own, largely non-overlapping, distributions. Based on the extensive sampling of six a priori groups from 63 locations, genetic and geometric morphometric datasets were generated to detect macrogeographic population structure, and to determine prior and current invasion pathways of this species. Weak population structure and high genetic diversity were detected among Asian populations. Invasive populations in Africa and Hawaii are inferred to be the result of separate, single invasions from South Asia, while South Asia is also the likely source of other Asian populations. The current northward invasion of B. dorsalis into Central China is the result of multiple, repeated dispersal events, most likely related to fruit trade. Results are discussed in the context of global quarantine, trade, and management of this pest. The recent expansion of the fly into temperate China, with very few associated genetic changes, clearly demonstrates the threat posed by this pest to ecologically similar areas in Europe and North America.