Answer: Based on your description I suspect the problem is the gooseberry maggot, which is the larval stage of the currant fruit fly. The adult flies emerge in mid spring and are yellow or orange, about 1/5" long, and have dark bands across the wings. The female flies lay eggs just under the skin of the gooseberries. When the maggots hatch, they burrow in and feed on the berries. This causes the berries to turn reddish and sometimes drop; a severe infestation can cause significant fruit drop. The maggots move from the fruit to the soil and overwinter there to emerge the following spring as adult flies.
To control them, you can place tarps under the bushes to prevent the larvae from entering the soil to pupate, or you can remove and destroy all of the infested fruit each day. There is no chemical control for this.
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