Bactrocera dorsalis

Mated female B. dorsalis puncture the skin of mature fruit and deposit eggs in a few batches of 3-30 eggs underneath a fruit's skin via ovipositor, depending on the quality and ripeness of the fruit. Eggs usually hatch within a day, although the hatching process can be delayed in cool conditions. Females are capable of laying over 3,000 eggs during their lifetime under optimal conditions, but in field conditions, reports a typical range from about 1,200 to 1,500 eggs laid per female.[9]

Eggs hatch to larvae and moult twice (there are three larval instars) while feeding on the flesh of the fruit for about 6–35 days. Larvae are creamy white in color with a maggot-like appearance and are about 10 mm in length.[14]

The third instar larvae exit the fruit and burrow into the soil under the host plant to pupate. Larvae generally pupate in the upper 4 cm of the soil.[13] Pupation can take approximately 10–12 days, but depending on the season, this process can be delayed in cooler conditions.[14]

B. dorsalis adult

In 1-2 weeks, the adult emerges from the pupae and matures. Most adults emerge from the soil between 7:00 AM and 10:00 AM. Once sexual maturity is reached (which takes approximately 9 days), adults engage in the mating process and the life cycle repeats. The adult lifespan for B. dorsalis is about 90 days, and the flies have been reported to travel up to 30 miles in search of new egg laying sites and food, such as decaying fruit and plant nectar. Adult females prefer to lay eggs in old egg deposit sites on fruits.[9][11][14][15]

Polyandry has been observed in B. dorsalis.[17] For females, there is typically a re-mating refractory period. The length of this period does not vary based on whether the female is mating with a virgin or non-virgin male. However, when there was a refractory period, females lay more eggs.[17] Females who were exposed to two males continuously without a refractory period in between lay fewer eggs, but still lay more eggs than females with only one male. Therefore, there appears to be a reproductive benefit for females with polyandry.[17]

Reproductive senescence does appear to be present in this species, as male and female age correlates negatively with the rate of fertilization.[17]

The flight capacity of B. dorsalis adult females at various life stages has been observed in order to better understand and prevent their spread. Past research has shown that the species can spread extensively following fruit harvests, with a dispersal radius up to 37 km observed in Hawaii.[18] Transmission electron microscopy was employed to view changes in flight muscle ultrastructures. Researchers observed that flight speed and distance changed with the age of the fruit fly, reaching its maximum capacity at 15 days of age.[18]

B. dorsalis has been observed to be capable of long-distance flight. One study investigated the relationship between flight muscle structure and the flies' flight capacity: as the number of mitochondria increased, myofibril diameter increased, and sarcomere length decreased, the researchers found the fly's flight capacity to be maximized. This particular muscle structure was evident in 15-day-old female adult B. dorsalis flies.[18]

B. dorsalis has symbiotic relationships with many bacteria. Different bacteria dominate at different developmental stages of the fruit fly.[19] Proteobacteria are most often present in immature stages, whereas Firmicutes are most often present in the adult stages.[19] Overall, the most abundant families are Enterococcaceae and Comamondaceae. Meanwhile, Comamonas are extremely abundant in pupae, but disappear entirely by adulthood.[19]

Researchers have also tested the relationship between certain gut symbiotic bacteria and fly foraging behavior and nutrient ingestion. Suppression of the fly's microbiome resulted in changes in the foraging behavior in both male and female flies.[20] Aposymbiotic flies responded faster to diets in experimental conditions and fed more, for longer periods of time.[20]

B. dorsalis is not only a highly invasive species, accidentally introduced to Hawaii from Taiwan during the 1940s in World War II, but also very destructive to crop yield for farmers of various fruits, vegetables, and nuts across the world. The larval stage of the life cycle is the most damaging to fruits because of larval feeding on the soft flesh of fruits. After ovipositing occurs by a female fly, the larvae develop under the skin of the fruit or soft tissues of the plant and begin to feed on the fruit or plant's flesh. Once feeding occurs, other microorganisms can invade the site of larval feeding and cause the fruit to decay faster. Although ripe fruits are believed to be preferred for ovipositing, unripe fruits have served as hosts for eggs as well.[16]

B. dorsalis has created many agricultural issues for humans, especially in the areas where it is endemic. In the Pacific Islands, the fly has restricted the development of a diverse tropical fruit and vegetable industry, necessitated that commercial fruits go through quarantine treatment before shipment, and provided an avenue for their introduction to countries not previously exposed to the fly species.[21] The Miami-Dade County in Florida had to perform the quarantine technique when the insect was detected in fruits there in August 2015; they were eliminated from the area in February 2016.[22]

To resolve these concerns, several techniques have been implemented, including sterile insect technique, protein bait sprays, and male annihilation.[21] Male annihilation technique is effective because methyl eugenol attracts male flies prior to the beginning of their sexual maturation, to an extent of 40 to 50 percent of the flies.[4]

One of the most experimentally effective control techniques has been the wrapping of fruit, often in a paper or polythene sleeve. This physical barrier prevents oviposition from occurring.[11] The caveat with this method is that it must be implemented far in advance of the fruit fly's presence. Alternatively, fruits can be harvested earlier in the season than the flies anticipate; this has proven effective with the mango fruit.[11]

Parasitoid wasp

In addition to these, Hawaii has developed methods to suppress Bactrocera species using parasitoid wasps, including Fopius arisanus. The parasitic wasp oviposits its own eggs into B. dorsalis eggs, the parasitoids are reared in the host, and the developed parasitoids emerge in the pupal stage. F. arisanus has been observed to be the most successful example of parasitoid control of B. dorsalis, and researchers are looking to introduce its model of suppression from Hawaii to other areas of the world that the fly affects.[21]

One simple, but effective technique called field sanitation, through which all unmarketable fruits get removed from the fields and disposed as soon as they are observed, so that re-infestation does not occur.[16]

Many organophosphorus insecticides target the enzyme acetylcholinesterase (AChE); mutations in the acetylcholinesterase gene of B. dorsalis have been found to be associated to resistance to such insecticides. Researchers have identified three point mutations in B. dorsalis' gene encoding AChE that generate nonsynonymous changes in the produced amino acid sequence. Two of the point mutations are identical in site to mutations identified in other Bactrocera species, but one of the mutations is specific to B. dorsalis. Widespread use of such insecticides could result in rapid resistance acquisition in populations of B. dorsalis.[23]

• Allwood, A.J., Chinajariyawong, A., Drew, R.A.I., et al. (1999) Host plant records for fruit flies (Diptera: Tephritidae) in south east Asia. Raffles Bulletin of Zoology Supplement 7:1-92.