The influence of larval temperature and nutrients on dog heartworm ( Dirofilaria immitis (Spirurida: Onchocercidae)) transmission in Aedes albopictus (Dipte

Abstract

The filarial nematode, Dirofilaria immitis (Leidy) (Spirurida: Onchocercidae), is an obligate mosquito-borne pathogen transmitted by at least 26 species of mosquitoes in the United States. Due to its size and migration through mosquito tissues during its first 3 larval stages (L1-L3), it can damage the mosquito to the point of death, thereby hindering transmission to its vertebrate host (eg canids and other carnivores). Mosquito species vary in competency for D. immitis, where some species facilitate the development of more viable, infectious L3 worms (host tolerance), while others produce few to no worms (host resistance). Here, we investigated how resistance and tolerance may be impacted by larval rearing conditions (ie temperature and nutrition), specifically quantifying D. immitis burden and development in 2 mosquito species (Aedes triseriatus (Say) and Aedes albopictus (Skuse)). Post-emergence, we offered either a D. immitis positive or negative blood meal to adult female mosquitoes and tracked their development for 15 days before quantifying worm burdens. For both mosquito species, growth rates increased and adult size decreased under conditions with warmer temperatures and lower nutrition. Larval conditions did not have consistent effects on the burden or development of D. immitis, but a higher proportion of Ae. triseriatus developed L3 worms than Ae. albopictus. Poor survival to the end of the incubation period and low numbers of blood-fed mosquitoes for each treatment combination may have hindered our ability to detect significant effects of larval environment on worm transmission, highlighting important considerations for future studies.