Aedes albopictus (Diptera: Culicidae): an experimental and natural host of Dirofilaria immitis (Filarioidea: Onchocercidae) in Florida, U.S.A

Females of an Aedes albopictus (Skuse) colony from southeastern Florida, U.S.A., ingested low (22.9 +/- 3.2 mg/female) and high (243.2 +/- 37.6 mf/female) numbers of microfilariae from a dog infected with Dirofilaria immitis (Leidy). High mortality of females occurred during the first 4 d after infection regardless of the number of microfilariae ingested; daily mortality was almost negligible during 5-15 d after infection. Percentage of survival 15 d after infection was higher (63%) in females that ingested low numbers of microfilariae than those (15%) that ingested high numbers of microfilariae. The development of most of the D. immitis larvae was arrested in late L(1) stage with some of the L(1) stage larvae becoming melanized intracellularly in the Malpighian tubule cells of Ae. albopictus. Fifteen days after infection, development of D. immitis to the infective L(3) stage occurred in only 10.9% of the surviving F(1) and F(2) Ae. albopictus that ingested low numbers of microfilariae, but in 94% of Anopheles quadrimaculatus Say ingesting similar numbers of microfilariae, as a control. Females of Ae. albopictus ingesting high numbers of microfilariae had more surviving females with L(3) than those ingesting low numbers of microfilariae. The number of L(3) larvae in the Malpighian tubules, hemocoel, head capsule and proboscis ranged from 1 to 37 per female, indicating the potential of Ae. albopictus to transmit D. immitis. Development of D. immitis larvae was not affected by co-infection with Ascogregarina taiwanensis (Lien & Levine), although both parasites infect the Malpighian tubules, the first intracellularly and the second extracellularly. After one generation of selection, a strain of Ae. albopictus susceptible to D. immitis developed 2.5 times more L(3) than the parent strain. These results show that a small portion of the natural population of Ae. albopictus is susceptible to infection with D. immitis and that susceptibility may be increased rapidly by selection. The presence of developing Dirofilaria sp. larvae in the Malpighian tubules of field-caught females indicated that Ae. albopictus may be infected naturally with D. immitis in Florida.