Pheromones in Small Rodents and Their Potential Use in Pest Control

The paper reviews social interactions in small rodents in which pheromones have been reported to play a part. Some of the chemical messengers involved may have a potential use in control of rodent pests. Research in this field should be encouraged, because alternatives to the current control methods are highly desirable. In 1959, the German chemist Butenandt and his co-workers suggested the term "pheromones" to denote chemical messengers, which when emitted by an animal, release certain reactions in conspecifics (Karlson and Butenandt, 1959; Karlson and Luscher, 1959). By that time Butenandt had finished his 20-year long research that led to the isolation and identification of the sex attractant pheromone in the female s i l k moth, Bombyx mori. Since then more than a hundred insect pheromones have been identified, and several are now being used on a practical scale for forecasting population levels and in control programs. Pheromonal effects are l i k e l y to occur in any animal phylum and are known to operate in such different groups as e.g. worms, snails, crabs, fish, and snakes, as well as in mammals such as rodents, deer, monkeys, and presumably humans. Only in very few rodents are the chemical composition of pheromones known. These include a house mouse preputial gland pheromone (Spener et_ al., 1969) the ventral gland pheromone in the male Mongolian gerbil (Thiessen et_ al_., 1974), and a sex attractant in hamster vaginal secretion (Singer et_ al_., 1976). The success insect pheromones have had in practical control work should stimulate an extensive exploration into the field of rodent pheromones and their potential use in regulating pest populations. However, the far more complex behavior of rodents as compared to insects constitutes an obstacle to the study of pheromonal effects and the practical use of pheromones in rodent control. A male moth after perceiving a female sex attractant has adequately been described as "a guided missile," homing in on the odor source. Mammalian behavior is much more complex, and rodents w i l l not react that automatically to any pheromone, no matter how strong the lure may be. But there is no doubt that pheromones play an important part with rodents. This can be illustrated by the fact that house mice w i l l eat their own offspring if deprived of the olfactory bulb (Gandelman et_ al_., 1971). These animals are no longer capable of identifying their young in absence of the olfactory cues. The use of chemical signals in communication offers at least two major advantages: the "message" can linger on long after the "sender" has left the stage, and communication works as well in total darkness as in broad daylight. In the restricted space of subterranean tunnels or runways in the bottom vegetation an odor is "trapped" for a much longer period than in the free. In many rodent species the bulk of the activity is restricted to such confined spaces. This is particularly true with populations l i v i n g and multiplying under snow-cover. In rodents, pheromones can be divided into two groups: (1) signal pheromones or releasers, i.e. substances that trigger immediate behavioral responses, and (2) primers, i.e. substances that produce effects that become manifest only after some time has passed, by working through some neuroendocrine pathway. Mammals possess a great number of skin glands (Schaffer, 1940; Quay, 1968), and produce numerous odors (Lederer, 1950). Several scent sources are known or suspected to be involved in chemical communication in mammals: foot-sole glands, preputial glands, coagulation glands, anal glands, unspecialized sebaceous glands, salivary glands, urine, and feces. In this paper I w i l l give an outline of some pheromonal effects that have been shown to operate in small rodents, and speculate on the possible app licab ili ty of some of these pheromones in rodent pest control. Several reviews have been written on chemical communication of mammals in general (e.g. Rails, 1971; Eisenberg and Kleiman, 1972; Mykytowycz, 1972) and that of rodents in particular (e.g. Bronson, 1971; Schultz and Tapp, 1973). Several