Laboratory-Rearing Techniques for Tephritid fruit flies
in Pacific Islands Countries and Territories

Requirements for adult flies

Colonies should consist of 5-6 cages each containing 5000-10000 adults of known age and quality. Eggs are laid after an initial pre-oviposition period of 2-4 weeks, depending on the species. After this period, eggs may be collected by allowing females to oviposit into fruit domes or artificial egging devices. At the peak of production (weeks 4-8) good cages should produce 50000 eggs in a 1-2 hour period and support egging three times weekly. These eggs must be produced without affecting normal colony maintenance requirements. Cages are discarded when there is significant adult mortality or poor egg hatch, usually after about 10-12 weeks.

Cages

Large colony cages (approx. 50 x 50 x 50 cm) can be made using frames of 10-12mm diameter PVC water piping. These materials are relatively cheap, easy to clean and are also easy to dismantle and transport if required. Synthetic gauze used as a cage cover should have mesh holes small enough to keep ants and Drosophila out. The cage cover is sewn with an extended open sleeve on one side to allow easy access.

Adult food

Adult fruit flies can survive on sugar and water alone and this should be supplied in cages as the adults emerge. Water is supplied using a sealed container with a sponge wick. Sugar is made available in granulated form on tissue, which absorbs any excess moisture. At least two water and sugar sources should be continuously available in each cage. Water sources should be cleaned and replaced weekly.

Protein for adults

A few days after emergence, the females require a source of protein for egg maturation, and this is supplied in the form of enzymatic yeast hydrolysate. Hydrolysed yeast and sugar is normally mixed in a ratio of 1:3 with a minimum of water to make a thick paste which is plastered onto cards. A number of these cards are hung from the top of the cage, ensuring that the adults do not get trapped in the sticky mixture. Adults may perform better with extra nutrients and these can be supplied in the form of mineral (e.g. Wessons salts) and vitamin mixes (e.g. Vanderzant general insect vitamin mix) or added protein (e.g. dried egg yolk).

Fruit fly rearing cage and adult food containers. (Photo: L. Leblanc)

Bacteria for adults

Fruit flies feed on a specific group of bacteria (family Enterobacteriaceae), which are important for both adult and larval development and are supplied to adult cages. A number of bacteria species are used in fruit fly rearing in the region, but the most commonly used in fruit fly rearing include Klebsiella oxytoca, K. pneumonia, and Citrobacter cloacae. The bacteria are isolated by dissecting the crop of wild female flies. Crop contents are smeared onto sterilized peptone yeast extract (PYE) agar plates and the bacteria sub-cultured until a pure culture is obtained (details on preparing agar plates and smearing techniques will later be available on a separate web page). This culture must be checked for purity and identified by a rnicrobiologist before being sub-cultured again onto PYE agar plates for feeding to adult flies. The agar plates, with at least two days of bacterial growth, are supplied twice weekly to new cages by inverting the plates on top of the cages and loosening the agar so that it drops onto the cage cover. Adult dissections and bacterial smears should be undertaken in sterile conditions and utensils sterilised with ethyl alcohol or by flaming.

Bacterial cultures are provided weekly to adult flies on top of cages as essential food (Photo: L. Leblanc)

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 Page updated on: 18 October, 2002