Biological Control of Mole Crickets by Bombardier Beetles
Larvae of Old-World bombardier beetles of the genus Stenaptinus have been known for some decades as specialized predators of eggs of Gryllotalpa mole crickets. Studies in Japan and China showed that the adult beetles feed as predators on various insects, but larvae make their way into mole cricket egg chambers, and there feed on the eggs. A very closely related genus Pheropsophus (ferr-OPS-off-us), with several species, occurs in South America. One of the species, Pheropsophus aequinoctialis, has a wide distribution in various countries, and inhabits river banks and other wet places in particular.
The diet of P. aequinoctialis was unknown until living specimens were imported from Uruguay, Brazil and Bolivia, into a quarantine facilty in Gainesville. There, adults were found to be generalist feeders (like those of Stenaptinus), but larvae developed only when provided with a diet of mole cricket eggs. Improvements in methods for rearing the beetles are necessary before tests can be completed. New stocks of the beetles are needed from South America to do this.
An adult Pheropsophus aequinoctialis
If, after further trials, P. aequinoctialis larvae continue to develop only on mole cricket eggs, then permission may be obtained for releasing some in nature in Florida. If a population can be established and thrives, then specimens could be moved to additional sites. If the beetle can be demonstrated to reduce mole cricket populations substantially at two or more sites, then effort could be made to distribute it more widely. The species has three advantages over other classical biological control agents. First, it is the only known agent to target mole cricket eggs (as contrasted with nymphs and adults). Second, its preference for riverbanks and other wet sites has the advantage that mole crickets may be controlled there without use of chemicals, whose use in such sites poses risks to aquatic organisms. Third, the adult beetles are predators and scavengers and do not require a nectar or honeydew source (as do Ormia depleta and Larra bicolor) so are impervious to damage to plants caused by cold weather.
A large larva of Pheropsophus aequinoctialis next to mole cricket eggs, on which it feeds.
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