Bactrocera tryoni
(Queensland fruit fly)

B. tryoni, the Queensland fruit fly, is the most costly horticultural pest in Australia and has invaded several countries in the surrounding region (White and Elson-Harris, 1994). It has the potential to spread to many places around the world because of its wide climatic and host range (Meats 1989b; Sutherst et al., 2000) and a tendency to be carried by human travellers at the larval stage inside infested fruit. B. tryoni is a very serious pest of a wide variety of fruits throughout its range. Damage levels can be anything up to 100% of unprotected fruit.

B. tryoni is found throughout the eastern half of Queensland, eastern New South Wales, and the extreme east of Victoria. In 1989 it became established in the Perth area of Western Australia and it was declared eradicated by 1991. There have also been outbreaks in South Australia and although action to eradicate is taken, cool winters may also account for its lack of establishment. The record for Tasmania in CABI/EPPO (1998) is an error. B. tryoni has never been found in Tasmania.

A few males have been trapped in Papua New Guinea but it is unlikely to be established there (Drew, 1989). It is also adventive in French Polynesia (Austral and Society Islands) and New Caledonia and has twice been adventive in Easter Island, but eradicated (Bateman, 1982). The distribution of this species was mapped by Drew (1982) and IIE (1991).

B. tryoni has a distribution almost entirely sympatric with B. neohumeralis, and both species attack a similar range of hosts, although B. tryoni is by far the more damaging. These two species mate at different times of day (B. tryoni at dusk; B. neohumeralis at midday). There is genetic evidence that the two species hybridize (Morrow et al., 2000). Reports of hybridization between B. tryoni and B. aquilonis (EPPO, 2002) (a similar species in the Northern Territory) are almost certainly erroneous as those two species lack sympatry.

See also CABI/EPPO (1998, No. 31).

The major risk is from the importation of fruit containing larvae, either as part of cargo, or through the smuggling of fruit in airline passenger baggage or mail. For example, in New Zealand Baker and Cowley (1991) recorded 7-33 interceptions of fruit flies per year in cargo and 10-28 per year in passenger baggage. Private individuals who successfully smuggle fruit are likely to discard it when they discover that it is rotten. An isolated catch of B. tryoni in a cue lure baited trap in California (Foote et al., 1993) probably had an origin of this sort.

B. tryoni is the most serious insect pest of fruit and vegetable crops in Australia, and it infests all commercial fruit crops, other than pineapple (Drew, 1982). Most of the data given here are from the host catalogue of Hancock et al. (2000), much of which derives from host data gathered in a major survey in the Cairns area. That revised list recorded B. tryoni from 49 families of plants, represented by 234 species.

In addition to the hosts listed, Garcinia dulcis, Diplocyclos palmatus, Flaacourtia inermis, Sandoricum indicum, Artocarpus odoratissima, Casimiroa tetrameria, Murraya exotica and Solanum muricatum are economically important hosts of B. tryoni. Other major wild hosts are Annona atemoya, Terminalia aridicola, T. muelleri, T. platyphylla, T. sericocarpa, T. subacroptera, Syzgium suborbiculare, S. tierneyanum and Nauclea orientalis.

Eggs are laid below the skin of the host fruit. These hatch within 2-3 days and the larvae feed for another 10-31 days. Pupariation is in the soil under the host plant for about 7 days but may be delayed under cool conditions. Adults occur throughout the year in 4-5 overlapping generations and overwinter as adults; up to 70 individuals have been recorded as developing from a single infested fruit (Christenson and Foote, 1960). Adult flight and the transport of infected fruit are the major means of movement and dispersal to previously uninfected areas. Male B. tryoni are collected in very large numbers in cue lure traps, which will also trap B. neohumeralis in slightly lower numbers in most of its range (Osborne et al., 1997).

[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).]

Bactrocera spp. in general can be attacked as larvae either by parasitoids or by vertebrates eating fruit (either on the tree or as fallen fruit). Mortality due to vertebrate fruit consumption can be very high, as can puparial mortality in the soil, either due to predation or environmental mortality (see White and Elson-Harris, 1994, for brief review). Parasitoids appear to have little effect on the populations of most fruit flies and Fletcher (1987) noted that 0-30% levels of parasitism are typical. To date, complete biological control in the classical sense, has never been achieved for any Bactrocera or Dacus spp. (Wharton, 1989). Three opiine parastoids (Hymenoptera: Braconidae), Fopius arisanus (Sonan), Diachasmimorpha tryoni (Cameron) and D. kraussii (Fullaway) may have potential as biological control agents (Rungrojwanich and Walter, 2000; Quimio and Walter, 2001; Spinner et al., 2011). These species have established following introduction in Australia. Their ecology throughout their ranges requires study and no augmentative releases have been made. In some places frugivorous birds and rodents can destroy a large percentage of wild fruit that would be otherwise available to fruit flies or may have fruit fly larvae already in them (Drew, 1987).

Due to difficulties in verifying the identifications of both parasitoids and (in some cases) the fruit fly hosts, no attempt has been made to catalogue all natural enemy records; see White and Elson-Harris (1994) for major sources. Consequently, no comprehensive list of parasitoid records is given here; those listed were extracted from Waterhouse (1993) and Wharton and Gilstrap (1983).

Fruits (locally grown or samples of fruit imports) should be inspected for puncture marks and any associated necrosis. Suspect fruits should be cut open and checked for larvae. Larval identification is difficult, so if time allows, mature larvae should be transferred to sawdust (or similar dry medium) to allow pupariation. Upon emergence, adult flies must be fed with sugar and water for several days to allow hardening and full colour to develop, before they can be identified. Detection is described under "Control: Early Warning System".

B. tryoni is separated from most of the other pest species by the coloured cells bc and c (i.e. the costal band extends from the wing base, not just from cell sc [the stigma]). However, it occurs sympatrically with B. neohumeralis, which also has that feature but from which it differs in having yellow postpronotal (=humeral) lobes. In Australia both species attack a similar range of hosts and can even be reared from the same individual specimens of field-collected fruit (Gibbs, 1967). These two species mate at different times of day (B. tryoni at dusk; B. neohumeralis ~ 10 AM–4 PM. There is no genetic evidence that the two species hybridize (Gilchrist and Ling, 2006).

B. tryoni is allopatric from B. aquilonis, from which it only differs morphologically in being darker in colour. Previous arguments about distinguishing B. tryoni from B. aquilonis in northern Australia are well discussed in Morrow et al. (2000; see also CABI/EPPO, 1998, No. 31) but the evidence and analysis provided by Cameron et al. (2010) favours the conclusion that B. tryoni is found in allopatric populations across northern Australia from north Queensland to the northwest coast of Western Australia.

The minimum characters which differentiate B. tryoni from all other Bactrocera and Dacus spp. (White and Hancock, 1997) are as follows: postpronotal lobe entirely yellow. Scutum predominantly red-brown; with lateral vittae (yellow stripes) not extended anterior of suture, posteriorly reaching to the posterior supra-alar setae; with prescutellar acrostichal setae. Anepisternal stripe not reaching as far as anterior notopleural seta. Wing cell c covered in microtrichia; cell bc devoid of microtrichia. Tergite 3 dark laterally and basally.

B. tryoni is larger than a house fly (wing length 4.8-6.3 mm).

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.

Biological Control

Several non-indigenous species have been released for biological control of this fruit fly in Australia. Of these, only Fopius arisanus became established, and although it reduced the number of flies per fruit it had little effect on the percentage of fruits damaged (Waterhouse, 1993).

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). Recent work on hot water dipping was reported by Waddell et al. (2000). Irradiation is not accepted in most countries and many have now banned methyl bromide fumigation. 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 information 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 proteinaceous bait (usually termed ‘protein’). Both males and females of fruit flies are attracted to protein sources emanating ammonia, so insecticides can be applied to just a few spots in an orchard and the flies will be attracted to these spots when they get near them during their daily foraging (Bateman et al., 1966 ab; Bateman, 1982). The protein most widely used in Australia was acid-hydrolysed yeast. This was neutralised by sodium hydroxide yielding a concentrate with a salt content of up to 50%. In South Australia an effective concentration was found to be strongly phytotoxic due to its high salt content. Thus from 1983 yeast autolysate was used instead (Madge et al., 1997). This product can be made cheaply from brewery waste (Umeh and Garcia, 2008). Horticultural mineral oil (HMO) is strongly repellent to female B. tryoni and can be used successfully to protect fruit in small crops, including home gardens (Nguyen et al., 2007; Meats et al., 2012).

Male Suppression/Annihilation Techniques and SIT.

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. tryoni are attracted to cue lure, sometimes in very large numbers. Combined with an insecticide it can be impregnated into small caneite blocks or other absorbent material. If these are distributed at sufficient density (~ 30m spacing) most males can be annihilated (Bateman, 1982). This has been termed the ‘male annihilation technique’ (MAT). Bateman et al. (1966a,b) pioneered combined MAT and bait spray in Australian coastal and inland towns and on Easter Island (Bateman et al.,1973; Bateman, 1982). This tactic is now used in are-wide management programmes.

The sterile insect technique (SIT) has been used for localised outbreaks in quarantined areas (Jessup et al., 2007).

Early Warning Systems

Many countries that are free of Bactrocera spp., such as the 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) or Lynfield (pot) trap (Cowley et al., 1990).

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.

IPM

The control of tephritid fruit flies is practised in two ways. The first is area-wide control that requires quarantine regulations and expensive technology such as SIT in a restricted and defendable area, but may require grower and community participation (Jessup et al., 2007). Features include trap arrays for early warning and prompt responses, border inspections, community awareness programmes as well as bait-spraying and the male annihilation technique (MAT) (Jessup et al., 2007). A good example and case study is given by Lloyd et al. (2010).

The second is farmer-operated local or ‘crop by crop’ control and is generally suited to local economies with local (non-export) distribution and is particularly relevant to areas with naturally high endemic pest populations and to village horticulture in tropical Asia and the South Pacific islands (Allwood & Leblanc 1997; Vijaysegaran 1997), where high infestation rates would damage local economies and cause migration to towns.

31/03/14 Updated by:

Alan Meats, University of Sydney, Australia