Ixodes dammini and Borrelia burgdorferi in northern New England and upstate New York.

64% in the F4 generation. The percentage of the mosquitoes with 100% filaria encapsulation rate increased during this selection. The offspring of the F4 generation were then reared together and maintained as a separate colony. The filaria encapsulation rate was checked at the F7 and Fi3 generations and it was found that the filaria encapsulation rate was maintained at about 2.5 times that in the parent generation. However, the percentage of mosquitoes with 100% filaria encapsulation rate decreased after the F4 generation when selection was stopped, although only a small number of mosquitoes were available for dissection for comparison between generations and the differences between generations are not significant. The results of the selection study showed that the filaria encapsulation rate could be enhanced by selecting the offspring of female mosquitoes that show d a higher incidence of encapsulation ofmicrofilariae and developing filarial larvae following ingestion of the microfilariae with the blood meal. Mosquitoes with 100% filaria encapsulation rate also can be obtained by selective breeding i An. quadrimaculatus. However, the attempt to pro uce a completely refractory strain of this species to Brugia pahangi infection was not successful. The encapsulation of microfilariae in the haemocoel has been shown to combine