LONGEVITY AND MIGRATION OF WUCHERERIA-BANCROFTI INFECTIVE LARVAE AND THEIR DISTRIBUTION PATTERN IN RELATION TO THE RESTING AND FEEDING-BEHAVIOR OF THE VECTOR MOSQUITO, CULEX-QUINQUEFASCIATUS

The longevity, migration and distribution of infective larvae (L3) of Wuchereria bancrofti within the host mosquito were studied by feeding Culex quinquefasciatus on microfilaraemic human blood and allowing the microfilariae to develop to L3. The L3 were found to remain alive and active for 46-50 days, i.e. as long as the host mosquitoes survived. The larvae started their migration to the head of the mosquito soon af ter their development to L3, on day 13 after the initial, infective bl oodmeal. Although more L3 were usually found in the head region of the mosquitoes than in the thorax or abdomen, the larvae showed an oscill atory pattern of movement between all three regions. This movement was significant in the mosquitoes fed only on microfilaraemic blood, but not in those that took a second bloodmeal on normal human blood on day 8 after the infective bloodmeal. The distribution of the L3 in the th ree regions of the mosquitoes was independent of parasite density. Obs ervations on L3 movement over a 24-h period indicated that there were always more L3 in the head than in the thorax and abdomen and that the number of L3 in the head was maximal at 18.00 hours and minimal at 06 .00 hours. When infective mosquitoes were fed on human blood through a Parafilm membrane, 45.2% of the L3 present in the mosquitoes were she d into the blood or on the membrane. All the L3 present in each mosqui to migrated to its head during feeding.