Fruit Crops News

Biological Control of Strawberry Sap Beetle

Several types of sap beetles (or picnic beetles) infest strawberry plantings. The small hard black beetles can feed in ripe fruit and are a nuisance to pickers. Some types of sap beetles are most attracted to over-ripe fruit; these are best controlled by sanitation methods to try to keep overripe or injured berries out of the field. Chemical control is often not effective because many types breed in any decaying vegetation and can rapidly move into plantings from outside areas. The specific picnic beetle known as the strawberry sap beetle (Stelidota geminata) is different because it will also attack ripening fruit. Chemical control is difficult because of the proximity to harvest time.

For the past several years researchers at Ohio State have evaluated a tiny parasitic wasp that attacks the larvae of strawberry sap beetle. By attacking the larval stage, the parasite does not prevent injury to individual fruit, but it does keep the larva from maturing into an adult beetle, thereby eliminating reproduction and reducing subsequent sap beetle populations. The parasite, Brachyserphus abruptus, occurs naturally, but is most prevalent in late summer and fall, which is too late for protection during the normal strawberry season. The goal of the Ohio research has been to mass produce the parasites in the lab and release them at the time of strawberry fruit set to get earlier control. Releases resulted in 18% parasitism of sap beetle larvae by the end of the growing season in 1993. The number of strawberry sap beetle larvae decreased from 63 per plot in 1992 to 12 per plot in 1993.

The parasite can be successfully mass-reared under lab conditions and releases can increase parasitism and reduce sap beetle infestations. The next step will be the successful commercial production of Brachyserphus by commercial insectaries so that they become available to growers.


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