Economically Beneficial Ground Beetles. The specialized predators Pheropsophus aequinoctialis (L.) and Stenaptinus jessoensis (Morawitz): Their laboratory behavior and descriptions of immature stages (Coleoptera: Carabidae: Brachininae)

Abstract

Adults of Pheropsophus aequinoctialis (L.) (Coleoptera: Carabidae: Brachininae: Brachinini), are largely nocturnal predators and scavengers on animal and plant materials. The daily food consumption of a pair of adults is the equivalent to 1.2 - 2.3 large larvae of Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). Larvae developed under laboratory conditions on a diet restricted to mole cricket eggs (Orthoptera: Gryllotalpidae); none survived under any other diet offered, thus they are specialists. Large numbers of brachinine eggs were laid in the laboratory, even on a paper towel substrate, and in all months of the year albeit with a strong suggestion of an annual peak in oviposition. Many eggs failed to hatch, but those that did so incubated an average 13.5 days. Many neonate larvae failed to feed and died. On average, the larvae that developed took 25.9 days to do so on an average 38.4 mole cricket eggs. The pupal period averaged 20.4 days, so the total developmental period was 59.9 days from oviposition to emergence of adult offspring at 26oC. After initial trials, an improved method of handling adults and rearing immature stages was developed, resulting in initiation of feeding by most neonate larvae and control of contaminating organisms (nematodes, mites, and Laboulbeniales). Most neonate larvae need to be in a cell or pit of sand (or earth) resembling a mole cricket egg chamber before they will feed on mole cricket eggs. The cause of infertility of many eggs was not resolved because it continued under the improved handling method for adults which permitted weekly mating; the presence of Wolbachia spp. (Bacteria: Rickettsiae) in the laboratory culture may be implicated. Sex ratios of emergent adults were not substantially different from 1:1. Larvae of the Asian bombardier beetle Stenaptinus jessoensis (Morawitz) had been claimed in the literature to feed only on Gryllotalpa mole cricket eggs. We found they will feed on Neocurtilla and Scapteriscus mole cricket eggs in the laboratory. The behavior of S. jessoensis as adult and larva is very similar to that of P. aequinoctialis except that adults are mainly diurnal. Many of its eggs likewise are infertile. Many of its neonate larvae likewise were reluctant to feed. It, too, may have an annual peak in oviposition which alters under ambient laboratory conditions. Sex ratios of emergent adults were not substantially different from 1:1. The structure of immature stages (eggs, larvae, and pupae) of P. aequinoctialis is contrasted with those of S. jessoensis and, in part, Brachinus pallidus. Proof of restriction of the larval diet of P. aequinoctialis still is inadequate. Three Scapteriscus spp. are adventive pests in Florida, but N. hexadactyla (Perty) is a non-pest native species. This beetle might be used as a biological control agent in Florida if its larvae can be shown to cause great harm to Scapteriscus yet little or none to Neocurtilla mole crickets or other non-target organisms. It is conceivable this could be the case because of maternal care of eggs by Neocurtilla but not by Scapteriscus. However, the supporting research has not been done, mainly because of lack of a robust method for rearing Neocurtilla, under which maternal care and the fate of the eggs may easily be observed.