Rw. Palmer et al., TIMING OF LARVICIDE TREATMENTS FOR THE CONTROL OF PEST BLACK FLIES (DIPTERA, SIMULIIDAE) IN A SEMIARID ENVIRONMENT IN SOUTH-AFRICA, JOURNAL OF VECTOR ECOLOGY, 21(1), 1996, pp. 48-59
Seasonal changes in the abundance of larvae, the rate of larval develo
pment, and the survival adults of the pest black fly Simulium chutteri
Lewis were used to determine the timing of larvicide treatments in th
e middle and lower reaches of the Orange River, South Africa. Larval a
bundance was highest in late winter (July/August), low in late summer
(January/February), and dropped sharply during blue-green algal blooms
in autumn (March/April). The time taken for the first cohort of larva
e to pupate, following larvicide treatment, ranged from seven days in
midsummer (water temperature 25-29 degrees C) to 37 days in midwinter
(10-16 degrees C). Adult abundance was consistently high in spring (Se
ptember and October) and sometimes in autumn (April and May). Abundanc
e dropped sharply in summer when evaporation exceeded 12 mm/day. The e
stimated number of generations per year was 11-13, although adequate c
ontrol during normal (non-flood) years was obtained with six ''spring'
' and three ''autumn'' larvicide applications. It is recommended that
applications to prevent a spring outbreak should start towards the end
of July, when most of the population is in the larval stage, and cont
inue into late October. Applications to prevent an autumn outbreak, wh
en necessary, should start in mid-March and continue to the end of Apr
il. Although water temperatures provided reasonably accurate informati
on for the correct timing of treatments, single-site applications unde
restimated the appropriate timing of subsequent large-scale control tr
eatments. Treatment intervals should be based on water temperature acc
ording to the function y=exp(0.065t-4.13), where y=larval development
rate (in days(-1)), and t=water temperature (in degrees C).