Laboratory-Rearing
Techniques for Tephritid fruit flies
in
Pacific Islands Countries and Territories
Egging
CONTENTS OF ON-LINE REARING GUIDELINES:
Introduction
Fruit collecting and colony establishment
Rearing
facilities
Requirements
for adult flies
Egging
Rearing
larvae
Pupae
Quality
control and recording procedures
Eggs are collected after the pre-oviposition period by placing artificial egging devices or fruit domes in cages where flies are about 3-7 weeks old.
Fruit domes
Fruit domes are produced by cutting the fruit in half and piercing the skin with a 1 mm diameter needle 30-100 times, depending on the size of the fruit and the number of females in the cage. The flesh is scooped out leaving as little flesh as possible on the skin. Domes are washed and sealed onto a petri dish or equivalent with moistened filter paper to prevent flies from entering the dome. Wet filter paper should be placed inside to keep the domes and eggs as moist as possible.
Artificial domes
Various artificial egging devices have been developed locally, but most consist of a thin plastic receptacle perforated with oviposition holes and smeared on the inside with a natural oviposition stimulant. Small (1 mm) holes should be punctured in the sides of the receptacle. Host fruit pulp or larval diet should then be smeared onto the inside of the container. Juice is pushed through the holes and then excess material inside the container wiped away. The container should be scaled onto a petri dish with moist tissue. Wet tissue or sponge should be placed inside the artificial dome to maintain humidity. The eggs must never become dry.
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| Egging dome preparation from papaya fruit hollowed out with spoon (left and centre) and natural pawpaw and artificial (made of plastic cup) egging domes domes (right) (Photos: A. Allwood and L. Leblanc) | ||
Collecting and counting eggs
Eggs are collected by washing out the dome with water using a hand sprayer, or if using fruit domes, washing and then teasing egg bundles out of flesh with a scalpel or probe, or squeezing flesh gently with soft forceps. Egg numbers are estimated volumetrically by counting a measured sub-sample of eggs (e.g. one drop or a marked volume on a pipette) on moistened black filter paper.
Egg hatch test
An egg hatch test should be set up whenever egging is undertaken. At least 100 eggs are pipetted onto moistened black filter paper and held in a petri dish sealed in an air-tight container. Eggs must remain moist at all times. Percentage egg hatch is recorded after about three days.
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| Egg extraction (left) and egg plating on moist filter paper to determine percent egg hatch (Photos: L. Leblanc) | |
Egg / diet ratio and seeding diet
Eggs should be dispensed onto diet at a known ratio of numbers of eggs to weight of diet to ensure an excess of food for the larvae. This ratio should be 2 viable eggs per gram of diet when establishing colonies, but the ratio may be adjusted after adequate studies to determine the optimum ratio. An optimum rate is one that does not affect the quality of flies while minimizing underutilized (wasted) diet. If the diet is underutilized, there is a risk of excessive yeast growth and a resultant mortality of young larvae. Eggs are pipetted directly onto the diet surface. The eggs must remain moist and they should be evenly distributed over the diet. Eggs with fruit residues from the domes placed on diet may lead to mould growth on the diet surface so eggs should be rinsed several times to remove contaminants (e.g. bits of fruit pulp). Eggs can be surface-sterilized in 0.025% NaCl0 for about 5 minutes, after which they must be immediately rinsed three times in fresh water.
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Rearing
larvae
Page updated on: 17 October, 2002