Laboratory and field studies of the southern house mosquito, Culex pipiens quinquefasciatus Say, infected with the dog heartworm, Dirofilaria immitis (Leidy), in Louisiana.

Abstract

Tests were conducted in East Baton Rouge Parish, Louisiana, to determine the species and seasonal abundance of mosquitoes feeding on dogs and to identify the primary vectors of the dog heartworm, DIROFILARIA IMMITIS (Leidy). The southern house mosquito, CULEX PIPIENS QUINQUEFASCIATUS Say, accounted 91% of 11,248 mosquitoes captured in dog-baited traps during the 2-year test period. An average of 63.3 C. p. quinquefasciatus was captured per night with 1.45% containing D. immitis larvae. Mosquitoes which were naturally infected seemed to harbor smaller larval burdens than mosquitoes that were reared and infected under laboratory conditions. Naturally infected C. p. quinquefasciatus were found to harbor moderate to low D. immitis larval burdens. High natural infection rates of C. p. quinquefasciatus with D. immitis were correlated with high numbers of dogs being present in the immediate area of the trap locations. The population density of C. p. quinquefasciatus was proportional to high daily temperatures as long as the temperature did not remain excessively high or become too low. Constant high temperatures seemed to cause high mortality of adult C. p. quinquefasciatus and did not allow mosquitoes infected with D. immitis to survive long enough to reinfect dog hosts. CULEX PIPIENS QUINQUEFASCIATUS is an excellent intermediate host of D. immitis in the laboratory and survival of infected mosquitoes under natural conditions was seen to be sufficient to allow infection of dog hosts. The combined laboratory and field results indicate that those mosquitoes which are potentially infective in nature are those which carry medium to low larval burdens of D. immitis . Where polluted sites existed for C. p. quinquefasciatus breeding and dogs were available for blood meals, the incidence of dog heartworm was high. No other mosquito species captured during the course of this study seemed to be present in large enough numbers or to exhibit sufficient vector potential in nature to be important vectors of D. immitis .