The dynamics of laboratory populations of the German cockroach, Blattella germanica (L.), and the influence of juvenoids on their population dynamics
Abstract
Laboratory chambers were developed for demographic studies of the German cockroach, Blattella germanica (L.). Chambers were provided with refugia (harborage units) and sampled by capturing insects in a harborage unit. These were then counted and classified according to nymphal stage and adult sex. Sample data possessed strong bias against adult males, but the use of adult females to estimate adults (assumed 1:1 sex ratio) allowed accurate estimation of age structure. Density and growth rates could be estimated, but growth rates were underestimated (10% to 20%), and the monitoring of growth was limited by harborage unit dimensions (= capacity). Rate of increase and age structure displayed patterns of stability during exponential growth, when populations increased by 35% every two weeks. In exponential growth, reproduction was constant and age distributions became stable; ca. 50% small nymphs (1-3 instar), ca. 25% large nymphs (4-5 instar) and ca. 25% adults. An intrinsic rate of increase was estimated, r = 0.0223, which should be more accurate than previous estimates because it was based on a known stable age distribution. The influence of the juvenoid hydroprene on population dynamics revealed distinct patterns. Reduction in gravid females (= reproduction) preceded reductions in populations size and nymphal abundance by 4 wks; this was also seen during population recovery. Frequencies of male and female adultoids (juvenoid-induced, morphogenetic affected adults) were equivalent, but the morphogenetic effects were more severe in male adultoids. Reductions in reproduction, population size and nymphal abundance were detected as adultoid frequencies reached 80%. Declines in adultoid frequencies below 80% were associated with slight increases in reproduction, and preceded the recovery of nymphal abundance (= population size) by 4 wks. Decreasing adultoid frequency indicated declining juvenoid efficacy, and declines below the 80% frequency predicted population recovery. This limit will be an effective action threshold for timing juvenoid retreatments in long-term management programs for chronic B. germanica infestations.
Degree
Ph.D.
Advisors
Bennett, Purdue University.
Subject Area
Entomology|Ecology
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