Bactrocera tau

The following is the typical life-cycle of a Bactrocera sp. Eggs are laid below the skin of the host fruit. These hatch within a day or 2 days and the larvae feed for another week or more. Pupariation is in the soil under the host plant for a week or more but may be delayed for several weeks under cool conditions. Adults occur throughout the year and begin mating after about 2 weeks; data from Christenson and Foote (1960). Adult flight and the transport of infected fruit are the major means of movement and dispersal to previously uninfected areas. Males are attracted to cue lure.

Some specific details are available for B. tau which suggest variation in parameters between hosts (Borah and Dutta, 1996), for example, 10 larvae in Momodica charantia to 40 in Lagenaria siceraria. In Trichosanthes cucumerina development was completed 11 days (up to 16 days in other hosts). Further details were given by Kabir et al. (1997), who noted that mating took place throughout the night and that adult longevity was up to 121 days for males and 191 for females; in Bangladesh populations peaked in September and to a lesser extend April.

[Erratum: In previous versions of this datasheet, it was stated that “many Bactrocera spp. can fly 50-100 km (Fletcher, 1989)” but a review of Fletcher (1989a) and Fletcher (1989b) by Hicks et al. (2019) found no evidence to support this statement and it has been removed. Fletcher (1989b) provides dispersal data for only 11 of 651 species of Bactrocera, many of the case studies lack the necessary numerical data, and the study did not discern between active flight and passive wind-assisted dispersal. There are differences among fruit fly species and further studies are required to determine dispersal distances for individual species. For further information on trapping Bactrocera species to monitor movement, see Weldon et al. (2014).]

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Regulatory Control

Many countries, such as the mainland USA, forbid the import of susceptible fruit without strict post-harvest treatment having been applied by the exporter. This may involve fumigation, heat treatment (hot vapour or hot water), cold treatments, insecticidal dipping, or irradiation (Armstrong and Couey, 1989). Irradiation is not accepted in most countries and fumigation is a hazardous operation. Heat treatment tends to reduce the shelf life of most fruits and so the most effective method of regulatory control is to preferentially restrict imports of a given fruit to areas free of fruit fly attack.

Cultural Control and Sanitary Methods

One of the most effective control techniques against fruit flies in general is to wrap fruit, either in newspaper, a paper bag, or in the case of long/thin fruits, a polythene sleeve. This is a simple physical barrier to oviposition but it has to be applied well before the fruit is attacked. Little data is available on the attack time for most fruits but few Bactrocera spp. attack prior to ripening.

Chemical Control

Although cover sprays of entire crops are sometimes used, the use of bait sprays is both more economical and more environmentally acceptable. A bait spray consists of a suitable insecticide (e.g. malathion) mixed with a protein bait. Both males and females of fruit flies are attracted to protein sources emanating ammonia and so insecticides can be applied to just a few spots in an orchard and the flies will be attracted to these spots. The protein most widely used is hydrolysed protein, but some supplies of this are acid hydrolysed and so highly phytotoxic. Smith and Nannan (1988) have developed a system using autolysed protein. In Malaysia this has been developed into a very effective commercial product derived from brewery waste.

Male Suppression

The males of most pest species of Bactrocera are attracted to either cue lure (4-(p-acetoxyphenyl)-2-butanone) or to methyl eugenol (4-allyl-1,2-dimethoxybenzene). Males of B. tau are attracted to cue lure. On a small scale many farmers use male suppression as a control technique; however, with flies attracted over a few hundred metres the traps may be responsible for increasing the fly level (at least of males) on a crop as much as for reducing it. However, the technique has been used as an eradication technique (male annihilation), in combination with bait (Bateman, 1982).

Early Warning Systems

Many coutries that are free of Bactrocera spp., e.g. USA (California and Florida) and New Zealand maintain a grid of methyl eugenol and cue lure traps, at least in high risk areas (ports and airports) if not around the entire climatically suitable area. The trap used will usually be modelled on the Steiner trap (White and Elson-Harris, 1994).

Field Monitoring

Monitoring is largely carried out by traps (as above) set in areas of infestation. However, there is evidence that some fruit flies have different host preferences in different parts of their range and host fruit surveys should also be considered as part of the monitoring process.