Paederus, sensu lato (Coleoptera: Staphylinidae): natural history and medical importance.

Abstract

Staphylinids (Coleoptera) are known as predators of Diptera and other arthropods of medical and veterinary importance, but the genus Paederus has achieved greater notoriety. Paederus includes over 600 described species distributed in all temperate and tropical continents. Many species exist in moist habitats, and some have their life cycles attuned to seasonal fluctuations in water level. Temperate-zone species may have a single annual breeding season in the warmer months, but in tropical species timing of the breeding season appears to depend upon rainfall seasonality. Widely distributed species with a broad latitudinal range seem to be multivoltine, with more generations at lower latitudes. Adults of some species are capable of running on water, navigating in response to light. Unlike most staphylinid adults, which avoid daylight, Paederus adults are active in the open in daylight. However, flight seems largely restricted to nights of high temperature. Adults of some species are wingless, and in other species adults show individual variation in wing length. Adults of at least some species are attracted at night to incandescent and fluorescent lights. Eggs are laid singly on a moist substrate and are susceptible to desiccation. There are 2 larval instars. Larvae remain in concealed, moist habitats and are largely predatory. Pupation occurs in earthen cells. Adults, too, are largely predatory but will feed on certain plant materials. Enormous populations of adults have been recorded in some agricultural habitats; in these cases the beetles are beneficial to agriculture owing to their predation on insect pests. However, they are highly susceptible to insecticides. Adults inadvertently come into contact with humans, especially in the tropics and by attraction to light at night. Hemolymph is released when the insects are crushed on human skin (deliberately or by accident) and can be introduced into the eyes. This hemolymph contains a potent contact toxin that causes dermatitis linearis and conjunctivitis in humans. Epidemics of dermatitis linearis are recorded for many tropical and some temperate countries. The epidemics can be mitigated by simple precautions. The dermatitis can be severe, painful, and unsightly, with erythema persisting for months. Conjunctivitis can result in temporary blindness. The toxic effects of Paederus were unknown to Western medicine until this century, but they were known to Chinese medicine 1,200 years earlier. The principal toxin is pederin, the most complex nonproteinaceous insect secretion known. Pederin occurs in all developmental stages of Paederus fuscipes , the Old World species on which most research has been performed. It has been synthesized and, in pure form, is a crystalline amide soluble in alcohol and water. It is a DNA inhibitor and acts at the cellular level by blocking mitosis. Experimentally, it has suppressed cancerous tumors in mice, rats, and plants, has stimulated regeneration of damaged tissues, has healed chronic, necrotic lesions in geriatric patients, and has induced cell fusion in human skin fibroblasts. It is more toxic externally and internally to rabbits, rats, mice, and guinea pigs than to hedgehogs, chickens, frogs, and toads. It is not known to be toxic to insects, is not attractive to insects, and has little effect against bacteria. Its function as a defensive secretion has not been demonstrated.