Seasonal dynamics and ecological strategies of the pitcher plant chironomid, Metriocnemus knabi Coq. (Diptera: Chironomidae), in southeast New Brunswick

In southeast New Brunswick the chironomid, Metriocnemus knabi, an inhabitant of the aquatic system contained within the leaves of the pitcher plant, Sarracenia purpurea, show seasonal fluctuations in numbers related to emergence and colonization, but density is usually correlated with the potential volume of the leaves. Females from a May emergence oviposit into overwintered leaves and produce a generation which emerges in August prior to the deterioration of the leaves. The progeny of the August emergence develop in leaves of the current summer growth and do not emerge until the following July. Ovipositing by this generation can be into overwintered or newly opened leaves. Larvae that begin development in overwintered leaves, which show progressive deterioration during the later summer and autumn, migrate to younger leaves that have not achieved complete colonization. The July emergence produces the generation which emerges the following May. Thus, there appears to be two cohorts in the population, each of which produces three generations every 2 years. This unusual life cycle tends towards maximizing use of the living habitat which also has a seasonal pattern of growth and senescence.