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 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 facility in Gainesville. There, adult beetles were found to be generalist feeders like those of Stenaptinus, but beetle larvae developed only when provided with a diet of mole cricket eggs. Not even Gryllidae cricket eggs proved a suitable diet. However, in the quarantine facility under artificial conditions, the beetle larvae fed not only on eggs of the three pest Neoscapteriscus mole cricket species, but also on eggs of the nonpest, nontarget, native mole cricket Neocurtilla hexadactyla.
Female Neoscapteriscus mole crickets block the entrance to their underground egg chamber when they have finished ovipositing. In contrast, the female native mole cricket does not block the entrance, but constructs a second chamber where she remains until some time after hatchlings have appeared. From time to time she enters the egg chamber as if to guard her offspring. We do not really know what she is guarding against, but suspect that it is fungal pathogens and/or predators. Entry of a beetle larva might trigger her to kill it to protect her offspring.
We wanted to watch the actions of the female native mole cricket underground. This proved very difficult because when she is disturbed, she moves her eggs just as a mother cat moves her small kittens when she is disturbed. Our attempts to build a strong colony of native mole crickets in which we could watch the female’s behavior were thwarted when we did not really understand the diet of the adults. Two graduate students were accepted to study these behaviors, but they avoided the difficult issue by studying other aspects of the behavior, and thus ensured their successful theses without solving the important questions.
The UF/IFAS Mole Cricket Research Program ended in 2004, and the Pheropsophus culture in quarantine was terminated, so Pheropsophus aequinoctialis never has been released into the Florida environment. If it could be proved that larvae of this beetle are consistently killed by female native mole crickets under natural conditions, but they impose substantial mortality on eggs of pest Neoscapteriscus mole crickets, there would be a case for release of stock of the beetle in Florida.
Pheropsophus aequinoctialis 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, which pose risks to aquatic organisms in such sites. 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 they are impervious to damage to plants caused by cold weather.