Diapause and Reproduction in Nebria brevicollis (F.) (Coleoptera:Carabidae)

Abstract

The failure to catch any adults of Nebria brevicollis in pitfall traps during the summer months has been noted in many studies on carabid activity in Britain (Gilbert 1958; Williams 1959; Tipton 1960; Greenslade 1964). The teneral adults are active for only 2-3 weeks after their emergence in early summer; during this time they feed rapidly and build up vast food reserves (Penney 1965) prior to a period of diapause which lasts until the beginning of the breeding season, in early autumn. During diapause there is a complete cessation of locomotor activity and the animals do not feed, energy for body maintenance being supplied by oxidation of their fat reserves. Various theories have been advanced concerning diapause in N. brevicollis but no experimental work has been done. Gilbert (1958) thought diapause might give the animals time to develop their gonads; Tipton (1960) regarded diapause as a means of avoiding low humidities associated with high temperatures during the summer months. Greenslade (1965) suggests a number of possible reasons for diapause, to synchronize the breeding cycle or to ensure that breeding is delayed and the larvae are not present under conditions of, for example, low humidity during the summer months. He suggests that summer diapause may be triggered off by increasing temperatures while the termination of diapause and the onset of breeding may be stimulated by short day length in the autumn. The present paper describes experiments in which these suggestions are examined; both the adaptive significance of diapause and the part played by various environmental factors in controlling the onset and extent of diapause are studied. Factors involved in the control of reproduction are also considered.