| dc.description.abstract | Mosquitoes encounter pathogens throughout their holometabolous life cycle, be it in the microbe-rich pools of the aquatic larva stage or the infected blood meals of the terrestrial adult stage. Pathogens that invade the mosquito hemocoel (body cavity) are met with rigorous immune responses, which in the adult life stage are coordinated with the circulatory system. Although many pest control strategies target larvae, and larval stressors impact adult fitness, most of what we know about mosquito immunity derives from studies of adult females, as these transmit pathogens during blood feeding. Because larvae and adults differ both morphologically and ecologically, and the pathogens they encounter and the selection forces they experience vary, I tested whether larval and adult immune responses differ in their interactions with the circulatory system, as well as in their relative strength and composition. I found that, unlike adults, pathogens and hemocytes (immune cells) in the larval hemocoel do not aggregate at the ostia (valves) of the heart (the periostial regions), but rather at the tracheal tufts, respiratory structures that are unique to the larval stage. Comparisons of the larval and adult circulatory systems revealed that, although their hearts are structurally similar, hemolymph (insect blood) in larvae does not flow into the heart via the abdominal ostia, as in adults, but instead via a pair of incurrent openings at the posterior terminus of the heart, where the tracheal tufts are located. Furthermore, I found that larvae display higher bacteria killing efficiency, hemocyte numbers, hemolymph lytic and melanization properties, and immunity gene transcriptional induction compared to newly-emerged adults, and that these differences are even more pronounced when comparing larvae to older adults. Together, these results show that mosquitoes display stage-specific functional coordination between their circulatory and immune systems, and that immunity declines shortly after metamorphosis and with adult age. These developmental differences demonstrate that a holistic approach to the study of mosquito immunity that incorporates findings in both larvae and adults may prove profitable to the creation of novel pest and disease control strategies. | |
