The Bactrocera dorsalis complex of tropical fruit flies (Diptera: Tephritidae: Dacinae) contains 75 described species, largely endemic to Southeast Asia. Within the complex are a small number of polyphagous pests of international significance, including B. dorsalis sensu stricto, B. papayae, B. carambolae, and B. philippinensis. Most species within the complex were described in 1994 and since then substantial research has been undertaken in developing morphological and molecular diagnostic techniques for their recognition. Such techniques can now resolve most taxa adequately. Genetic evidence suggests that the complex has evolved in only the last few million years, and development of a phylogeny of the group is considered a high priority to provide a framework for future evolutionary and ecological studies. As model systems, mating studies on B. dorsalis s.s. and B. cacuminata have substantially advanced our understanding of insect use of plant-derived chemicals for mating, but such studies have not been applied to help resolve the limits of biological species within the complex. Although they are commonly regarded as major pests, there is little published evidence documenting economic losses caused by flies of the B. dorsalis complex. Quantification of economic losses caused by B. dorsalis complex species is urgently needed to prioritize research for quarantine and management. Although they have been documented as invaders, relatively little work has been done on the invasion biology of the complex and this is an area warranting further work.

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Invasive phytophagous pests arising through a recent tropical evolutionary radiation: the Bactrocera dorsalis complex of fruit flies.

The biology of dacine fruit flies

The distribution, systematics and ecology of Bactrocera tryoni, the Queensland fruit fly, are reviewed. Bactrocera tryoni is a member of the B. tryoni complex of species, which currently includes four named species, viz. B. tryoni ssp., B. neohumeralis, B. melas and B. aquilonis. The species status of B. melas and B. aquilonis is unclear (they may be junior synonyms of B. tryoni) and their validity, or otherwise, needs to be confirmed as a matter of urgency. While Queensland fruit fly is regarded as a tropical species, it cannot be assumed that its distribution will spread further south under climate change scenarios. Increasing aridity and hot dry summers, as well as more complex, indirect interactions resulting from elevated CO2, make predicting the future distribution and abundance of B. tryoni difficult. The ecology of B. tryoni is reviewed with respect to current control approaches (with the exception of sterile insect technique (SIT) which is covered in a companion paper). We conclude that there are major gaps in the knowledge required to implement most noninsecticide-based management approaches. Priority areas for future research include host–plant interactions, protein and cue-lure foraging and use, spatial dynamics, development of new monitoring tools, investigating the use of natural enemies and better integration of fruit flies into general horticultural IPM systems.

The ecology of Bactrocera tryoni (Diptera: Tephritidae): what do we know to assist pest management?

From the guts of new and old colonies (female and male) of Mexican fruit flies, Anastrepha ludens (Diptera: Tephritidae), we identified a total of 18 different bacterial species belonging to the family Enterobacteriaceae, Pseudomonadaceae, Vibrionaceae, Micrococcaceae, Deinococcacea, Bacillaceae, and the genus Listeria. Enterobacter, Providencia, Serratia, and Staphylococcus spp. were the most frequently isolated genera, with Citrobacter, Streptococcus, Aerococcus, and Listeria found less frequently. We found Bacillus cereus, Enterobacter sakazakii, Providencia stuartii, and Pseudomonas aeruginosa only in the new colony, Aeromonas hydrophila and Klebsiella pneumoniae spp. pneumoniae only in the old colony. We also studied resistance/sensitivity to 12 antibiotics for six bacterial isolates such as Enterobacter cloacae, E. sakazakii, K. pneumoniae spp., Providencia rettgeri, P. aeruginosa, and Bacillus cereus. Isolates on the whole were resistant to penicillin and ampicillin (five of six isolates) and sensitive to rifampin and streptomycin (six of six isolates). Antibiotic resistance profiles might be useful characteristics for distinguishing among species and strains of these bacteria, probably having ecological significance with respect to intra- and inter-specific competition within host cadavers, and could have implications for the utility of these organisms for biological control, including the alternative control strategy, paratransgenesis.

Isolation and Identification of Bacteria Associated with Adult Laboratory Mexican Fruit Flies, Anastrepha ludens (Diptera: Tephritidae)

Systematic quantitative observations of locations and diel patterns of activities of adult Mediterranean fruit flies, Ceratitis capitata (Wiedemann), were made in a semiisolated mixed orchard and surroundings in southern Egypt during 4 wk in early autumn 1984. Flies were regularly sighted on all fruiting and nonfruiting hosts, whereas on nonhost vegetation they were observed occasionally. At dawn, both sexes were at rest in upper sunlit parts of tree canopies, where females began primarily feeding and males released pheromone and began calling activities. With increasing temperature and light, flies moved progressively to lower, more shaded positions. Most feeding events occurred on juice oozing from ripe guava and wounds on orange fruit. Bird droppings and leaf surfaces (probably providing bacteria as nitrogen sources) were additional important feeding sites. Male feeding on fruit peaked in the late afternoon; most ovipositions (on orange and guava) also occurred then. The high level of predation on fruit is proposed as an explanation of the origin of lek behavior on foliage. We, as observers, could detect leks by the odor of the male pheromone. Preferred sites for lek formation were the illuminated areas of tree canopies that were on or near fruiting host trees and that were protected by dense foliage from intense predation by Odonata and wasps. The greatest number of calling males, bouts of male-male competition, leks, and mating pairs were found on fruiting citrus trees. Attraction of females to calling males and formation of mating pairs peaked in midmorning and again following hot midday temperatures.

Mediterranean Fruit Fly (Diptera: Tephritidae) in Nature: Location and Diel Pattern of Feeding and Other Activities on Fruiting and Nonfruiting Hosts and Nonhosts

Bacteria isolated from crops and stomachs of adult fruit flies feeding on mulberry fruit and leaf surfaces were cultured on agar and proved highly attractive to adult fruit flies and provided them with virtually a complete breeding diet. Diets of bacteria, sugar and water gave equal longevity and increased fecundity in Dacus tryoni (Froggatt) compared with the conventional diet of autolysed brewer's yeast, sugar and water. The type and abundance of leaf and fruit surface bacteria appears to be an important factor in the life history of tropical fruit flies.

A. C. Courtice

Papers

Bacteria as a natural source of food for adult fruit flies (Diptera: Tephritidae)