BIOLOGICAL CONTROL AGAINST FRUIT FLIES IN 
PACIFIC ISLAND COUNTRIES AND TERRITORIES

Despite large amounts of effort devoted to the use of biological control agents (predators and parasitoids) to control fruit flies, there have been relatively few instances that may be regarded as sustainable successes.

Generally, predators have little effect on fruit fly populations in an orchard or vegetable production situation.  Invertebrate predators may include spiders, ants, carabid beetles, assassin bugs, staphylinid beetles and probably others.  In Crete, olive flies (B. oleae) are reduced by birds that eat 81% of infested fruits.  In consuming the fruits, predators, unfortunately, also consume parasitoids so there is an indirect adverse effect.  In the endemic forest habitat, however, predation by fruit-eating vertebrates, such as birds and primates, results in marked reductions in fruit fly numbers.

The use of parasitoids to control fruit flies biologically has always had wide appeal, but tropical fruit flies have not, in general, proved to be good targets for biological control.  The most documented research on using parasitoids to reduce fruit fly populations has been in Hawaii, where a large number of species have been introduced and released to control oriental fruit fly (Bactrocera dorsalis), Mediterranean fruit fly (Ceratitis capitata), and melon fly (Bactrocera cucurbitae).  The parasitoids belong to the families Braconidae (see picture below), Chalcididae and Eulophidae.  Releases of a range of parasitoids resulted in up to 95% reductions in populations of Mediterranean and oriental fruit flies.  Also, in normally heavily infested commercial fruits, levels of damage caused by fruit flies were reduced to a point where fruits were virtually free from infestation.  These results were due mainly to the establishment of the wasp Fopius arisanus and, to a lesser extent, the establishment of Fopius vandenboschii and Diachasmimorpha longicaudata.  By 1968, it was claimed that oriental fruit fly was no longer a major pest of many kinds of fruits, except guava.  This level of control, however, has not been sustained. Oriental fruit fly and Mediterranean fruit fly are still very serious pests of a wide range of fruits and vegetables.  Inundative releases of laboratory-reared parasitoids may be an appropriate option and is being researched in Hawaii.

Fruit fly parasitoid wasp Diachasmimorpha kraussi (Photo: M.W.Johnson, University of California)

In Australia, there are several native parasitoids of Queensland fruit fly (B. tryoni), but they exert very little control on populations of fruit flies.  CSIRO introduced several species of parasitoids into Australia in the 1950s.  F. arisanus apparently bred in seven dacine and trypetine hosts, but by 1966, neither F. arisanus nor D. longicaudata affected the incidence of Queensland fruit fly.  Now, only F. arisanus is established.

In PICTs, there are only a few native parasitoids of fruit flies.  For example, Diachasmimorpha hageni and Psyttalia fijiensis were recorded in Fiji as early as 1916.  Parasitism levels of 5-10% were recorded in 1935.  These promising results, together with results from Hawaii, saw a major effort to introduce parasitoids to Fiji and Cook Islands between 1927 and 1935 and in the 1950s.  Parasitoids such as F. arisanus, D. longicaudata, Aceratoneuromyia indica, Tetrastichus giffardianus and Psyttalia concolor were introduced into Fiji.

At least sixteen species of parasitoid wasps have been introduced or naturally occur in Cook Islands, Fiji islands, Guam, New Caledonia, Commonwealth of Northern Mariana Islands, Samoa, Papua New Guinea, Solomon Islands, Tonga, Vanuatu, Federated States of Micronesia and Palau.  Two of the most common and widespread are Fopius arisanus and Diachasmimorpha longicaudata.  F. arisanus is native to Asia.  The adult wasp inserts its ovipositor into the fruit through the fruit fly’s egg-laying puncture and lays a tiny egg inside the fruit fly’s egg.  The parasitoid larva lives inside the host (fruit fly larva) until the host has pupated in the ground.  At that point, the parasitoid larva kills its host and completes its development, feeding on the host flesh.  Consequently, a parasitoid emerges from the pupa instead of an adult fly.  Female F. arisanus search for their hosts mostly on fruits in trees, and rarely forage on the ground.  Because it attacks at the early stages of host maturity, this species generally outcompetes other parasitoid species.  D. longicaudata, is native to the Indo-Pacific region, including Papua New Guinea, and is also present in Guam, Commonwealth of the Northern Mariana Islands, Fiji Islands and New Caledonia.  Parasitoids infest third instar larvae of fruit flies, puncturing through the fruit’s skin with its very long ovipositor.  By preference, it attacks ripe and fallen fruits and spends lots of time foraging on the ground.

Table: Fruit fly parasitoids recorded in Pacific Island countries and territories. N = Native; I = introduced at an unknown date; 1951 = introduced at a known date.

	Cook Islands	Fiji Islands	Guam	Micro- nesia (FSM)	New Cale- donia	Northern Marianas	Palau	Papua New Guinea	Samoa	Solomon Islands	Tonga	Vanuatu
Braconidae: Biosteres sp	-	-	-	-	-	-	-	-	-	-	-	N
Braconidae: Diachasmimorpha hageni	-	N	-	-	-	-	-	-	-	-	-	-
Braconidae: Diachasmimorpha kraussi	-	-	-	-	-	-	-	N	-	N	-	-
Braconidae: Diachasmimorpha longicaudata	-	1951	N	1997	N	N	-	N	-	-	-	-
Braconidae: Fopius arisanus	I	1951	-	1997	-	-	N	-	I	-	I	-
Braconidae: Fopius deeralensis	-	-	-	-	-	-	-	N	-	-	-	-
Braconidae: Opius froggatti	-	-	-	-	N	-	-	-	-	-	-	-
Braconidae: Opius sp	-	-	-	-	-	-	-	N	-	-	-	-
Braconidae: Psyttalia fijiensis	-	N	-	-	N	-	-	N	-	-	N ?	-
Braconidae: Psyttalia fletcheri	-	-	1950	-	-	-	-	-	-	1997	-	-
Eulophidae: Aceratoneuromyia indica	-	1938	1952	-	-	-	-	-	1935	-	-	-
Eulophidae: Tetrastichus giffardianus	-	1935	-	-	-	-	-	-	-	-	-	-
Pteromalidae: Pachycrepoideus vindemiae	-	N	-	-	-	-	-	-	-	-	-	-
Pteromalidae: Spalangia cameroni	-	1927	-	-	-	-	-	-	-	-	-	-
Pteromalidae: Spalangia endius	-	N	-	-	N	-	-	-	-	-	-	-
Pteromalidae: Spalangia sp	-	-	-	-	-	-	-	-	-	-	?	-

Recent surveys in PICTs during the Regional Fruit Fly Project, which began in 1991, show that parasitism levels are still relatively low, generally at less than 10%.  This level of parasitism is consistent with parasitism levels throughout northern Australia and Southeast Asia.  There are occasions when levels of parasitism exceed 60%, but this is usually towards the end of a major fruiting season, e.g. guava.  From these results, no special effort has been made in PICTs to encourage augmentative releases of existing parasitoids.  However, field control systems based on protein bait sprays take cognizance of the need to conserve parasitism levels that now occur naturally.

With respect to melon fly in Solomon Islands, the parasitoid Psyttalia fletcheri was introduced from Hawaii in 1997, with the aim of reducing its populations to a level that may reduce the pressure on the efficacy of protein bait sprays.  As the populations of mango fly (B. frauenfeldi) are extremely high throughout the year on Pohnpei and Kosrae Islands in the Federated States of Micronesia, F. arisanus and D. longicaudata were introduced in 1997 on Pohnpei and Kosrae Islands, respectively.  F. arisanus has become quickly established on Pohnpei, but it is too early to assess its long term impact on mango fly populations.  The establishment of D. longicaudata on Kosrae is being been confirmed at present.

 

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Page updated on: 28 December, 2004