Temperature thresholds and statistical modelling of larval Wuchereria bancrofti (Filariidea:Onchocercidae) developmental rates.

Developmental rates for Wuchereria bancrofti larvae maturing in the vector Aedes polynesiensis were estimated by analysing stage-frequency data consisting of counts of larval stages in mosquitoes reared at 20, 22.5, 25, 27.5, 30 and 32 degrees C. Base temperatures (i.e. low temperature thresholds) for W. bancrofti development were estimated by the x-intercept method and the model of Lactin et al. (1995). Resulting values were similar with both methods and were approximately 12.5 degrees C for microfilariae (mf) in thorax, approximately 17 degrees C for L1, 15.5 degrees C for L2 and 16.5 degrees C for L3. Upper thresholds estimated by the Lactin et al. model were 29.3 degrees C for mf, 29.1 degrees C for L1, 32.2 degrees C for L2 and 31.5 degrees C for L3. In addition, an original method was devised for computing the L3 upper threshold, by modelling L3 length shrinkage with temperature. It gave a value of 31.4 degrees C. At 32 degrees C, L2 and L3 stages exhibited altered morphology, larvae being shorter and wider than expected. The model of Lactin et al. described adequately the non-linear relationship between developmental rate and temperature, but a linear degree-day approach may be applied for temperatures below 27-28 degrees C.