Host Fruit Surveying for Quarantine Surveillance 
in The Pacific Islands Countries and Territories

Host fruit surveys involve collecting samples of commercial/edible and wild fruits and incubating them in containers for two to three weeks to determine whether flies emerge from the fruits.  They yield information on the range of hosts attacked by each fly species, levels of infestations (number of larvae per fruit and percentage of fruits infested) in each commodity, the stage of maturity when attacked, and diversity and impact of natural parasitoids.  They complement trapping for quarantine surveillance and help in sampling species that are not attracted to male lures.

Two approaches may be used in fruit surveys.  In general or broad host surveys, commercial/edible and wild fruits are collected and set up in bulk.  In damage assessments, large samples (e.g., 50-100 fruits) of commercially important fruits are collected and fruits are set up and incubated individually in separate containers.  Alternatively, fruits may be held in bulk for 5 days, dissected and examined, and those infested are transferred to individual containers and held for a further 7-9 days. 

Fruits set up in individual containers for damage assessment  (Photo: A. Allwood)	Fruits set up in bulk for general host surveying  (Photo: L. Leblanc)

Mature and ripe fruits are collected from the tree and/or from the ground and stored in paper bags, not plastic bags.  The bag is labeled with the following information: sample number, precise location, date of collection, collector’s name, host plant name (scientific or at least common or local name), state of fruit collected (on tree or fallen; green, mature green, ripe; damaged or undamaged).  In the laboratory, fruits from each sample are weighed and counted and data sheets are filled in with the following information: sample number, location, date collected, plant species and common name, state of fruit, weight in grams and number of fruits.

Fruit samples are incubated in containers over moist, finely sieved sawdust from untreated timber for at least two weeks (see figure below).  Sawdust must be sterilised, before and after use, by placing it in an oven (120°C) for two hours or by freezing overnight.  Small fruits not likely to release juice may be placed directly on top of sawdust in a plastic container whose top is covered with fine gauze fabric for ventilation.  Fruits likely to release lots of juice while breaking down are placed on fine gauze fabric over chicken wire fixed to the top of a plastic container into which juices will drain, as illustrated below.  The plastic container is placed inside a larger plastic box or a cardboard box whose bottom is lined with a newspaper layer tightly taped to the box bottom and covered with sawdust.  The cardboard box top is tightly secured with masking tape to prevent entry of small flies.

Figures: Steps in setting up fruit sample (Photos by S. Wilson)

Fruits from trees and fallen fruits and fruits of different stages of maturity must be set up in separate containers and be assigned separate sample numbers. For damage assessments, each fruit is assigned a separate sample number.

After 10-12 days of incubation, check samples by slicing open fruits to make sure that all larvae have left the fruit and by sieving the sawdust with a strainer to separate puparia from sawdust.  The number of puparia from each sample is noted on the data sheet.  Puparia from each sample are placed in a petri dish on a piece of tissue paper lining the bottom of the dish and covered with sterilized sawdust moistened with a hand spray bottle.  Petri dishes are placed in a small plastic container with top covered with fine gauze fabric for ventilation and labeled with sample number.

Adult flies that emerge from puparia must be kept them alive for at least 5 days by providing them with sugar and a wet sponge that is moistened daily, placed on the fine gauze top covering the plastic emergence container.  Small parasitoids may also emerge, often several days after all flies have emerged.  When all flies and parasitoids have emerged, they are killed by placing the container in a freezer for at least one hour.  Flies and parasitoids are stored in small cardboard boxes labeled with sample number and host fruit name.  A data sheet (available here in PDF format), indicating fly species (if known), number of male and female flies, parasitoid species (if known), number of parasitoids and any extra observations, must be completed. A small amount of thymol is added to prevent mould.

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 Page updated on: 17 October, 2002