INTRODUCTION

There are two methods for verifying the presence and progress of the blueberry fruit fly in a wild blueberry field. The first one is to use Pherocon AM traps to capture the adults (see factsheet C.2.3.0), and the second is to determine the number of maggots in a litre of fruit samples.

The trap method will allow you to detect the insects before they start laying eggs. The fruit sample method will indicate whether or not this is a problem but the control will be feasible only at the next production cycle. This method is explained in this factsheet. There is no scientific information about the number of samples needed for a given area, however the bigger the field, the more samples are needed to ensure that it represents the actual insect distribution in the field. For fields up to 6 ha (15 acres), at least three samples of one litre should be analyzed. For bigger fields you should at least double the number of samples. The sampling should be done at random in the field, just prior to or during the harvest.

There are two methods for detecting the amount of berries infested by the blueberry fruit fly:

1. WATER TEST

• Place 1 litre of berries in a pot.
• Barely cover the berries with water.
• Bring the water and berries to a frothy boil, and boil for 1 minute.
• Pour the mixture into a 4 mm mesh screen over a roasting pan. The puree and the larva will pass through while the pulp will stay on the screen.
• Rinse the berries with cold, running water to make sure that all the larvae have been collected.
• Allow the berries and larvae to settle, then decant the floating solids and most of the water.
• Repeat washing and decanting until the water is clear.
• White maggots will be visible against the black bottom of the pan.

2. BROWN SUGAR TEST

Sugar concentration: 3.5 kg brown sugar per 20 litres of water.

• Place 1 litre of berries in a 4-litre container.
• Gently crush the berries in the container.
• Add sugar concentrate to 3 cm above the crushed berries.
• Agitate the crushed berries in the sugar solution.
• Allow maggots to float to the surface.

INTERPRETATION OF RESULTS

There is no written record of maggots/L in berries at harvest as an action threshold for control, either here or in Maine. The rule of thumb is to initiate action if more than 4 maggots/L are found. Please verify with your processors for their requirements.

Prepared by Gaétan Chiasson, P.Ag., Horticultural Specialist , and John Argall, P.Ag., Blueberry Specialist, N.B. Department of Agriculture & Rural Development

Winter 96