Philip S. Corbet

Diel periodicities of landing of nulliparous and parous Aedes aegypti (L.) at Dar es Salaam, Tanzania (Díptera, Culicidae).

The results derive from three 24-h catches of Aedes aegypti (L.) (1190 females, 504 males) using human bait at Buguruni, Dar es Salaam, Tanzania, in April 1971. The diel periodicity of all females is predominantly diurnal (at least 99·83% arrive during daylight or twilight) and bimodal, with consistent peaks at 06.00–07.00 h (post-sunrise) and 17.00–18.00 h (pre-sunset). The diel periodicities of nullipars and pars, and of uninseminated and inseminated females are virtually identical. The diel periodicity of males is also bimodal but differs from that of females in that at least two-thirds (instead of about half) of the individuals arrive between noon and sunset, more activity occurs between 09.00 and 15.00 h, and the post-sunrise peak falls at 08.00–09.00 h. A large influx of nullipars one afternoon did little to modify the close correspondence between the diel periodicities of nullipars and pars on subsequent days. Females land on bait in all ovarian stages (I–V), but in these catches more than 80% of nullipars and pars were almost equally divided between stages I and II. Among nullipars relatively more uninseminated females, and among pars relatively more with relict eggs, land in stage I than do so in stage II. It is inferred that pars with relict eggs usually expel them between stages I and II. This work reveals the likelihood that (at least at Buguruni) the frequency of potentially infective bites on a given day could be monitored with acceptable precision by limiting the catch to seven hours and the part that was age-graded to two hours.

Pest Management in Ecological Perspective

Pest management is concerned with the suppression of pests and with the alleviation of pest problems. The concept of a “pest” has meaning only in a human context: a pest is an organism that man regards as harmful to his person, property, or environment. As Rudd (1971) has observed, the word “pest” (like the word “weed”) is defined only according to its impact, direct or indirect, upon man, often in environments that man himself has modified considerably. Man makes an organism a pest as soon as he requires something it needs and which he is not prepared to share with it; and he frequently makes it a “worse” pest by manufacturing an environment that favors its increase and survival. Since pests, by definition, are competitors for resources that man wishes to preempt for his own use, the more resources he tries to preempt, the more pests he will encounter. Thus a study of pest management in ecological perspective must take account of the activities of man—the species that creates and aggravates pest problems and that devises treatment designed to alleviate them.