Heterogeneity in the host preference of Japanese encephalitis vectors in Chiang Mai, northern Thailand

Experiments, using the capture-mark-release-recapture technique inside larg e nets, were carried out in Chiang Mai, northern Thailand, to examine heter ogeneity in the host preference of Japanese encephalitis (JE) vectors. A si gnificantly higher proportion of the vector species that were initially att racted to a cow fed when released into a net with a cow than when released into a net containing a pig. However, Culex vishnui individuals that had be en attracted to a pig had a higher feeding rate in a net containing a pig r ather than a cow. When mosquitoes were given a choice by being released int o a net containing both animals, they exhibited a tendency to feed on the h ost to which they had originally been attracted. This feeding preference wa s, however, not shown by the offspring of pig-fed individuals. We have ther efore shown evidence of physiological/behavioural conditioning in the host preference of JE vectors rather than genetic variability. Our results sugge st that effective control of JE might be achieved by increasing the availab ility of cows (the dead-end hosts of JE virus) to deflect the vectors from pigs (the amplifying host). The behavioural imprinting which we have found would tend to re-inforce the initial tendency of the vectors to bite cows.