Understanding the consequences of sub-lethal insecticide concentrations for insecticide resistance management and malaria control
Open Access
- Author:
- Glunt, Katey Diana
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- None
- Committee Members:
- Andrew Fraser Read, Dissertation Advisor/Co-Advisor
James Harold Marden, Committee Chair/Co-Chair
Matthew Brian Thomas, Committee Member
Tracy Lee Langkilde, Committee Member
Christopher Albert Mullin, Committee Member - Keywords:
- Mosquito
Anopheles
insecticide
insecticide resistance
mosquito control
malaria control
Plasmodium - Abstract:
- Malaria threatens the lives of millions of people every year. The most effective tools yet available to reduce disease incidence and interrupt transmission are chemical insecticides directed against the mosquito vectors. However, in the face of insecticide resistance, it is becoming clear that continuing to use insecticides in the current way will not be enough to eradicate malaria. Here, we aimed to establish proof-of-principle for a new approach to insecticide deployment: the dilution solution. Using reduced concentrations of currently-used compounds to selectively eliminate only the mosquitoes that are infected or that have lived long enough to have developed the Plasmodium parasites and be infectious would allow us to achieve effective malaria control, yet reduce the selection pressure for exposed mosquito populations to become insecticide resistant. We showed that reduced concentrations of permethrin or malathion, representatives of two classes of insecticides used in public health, can preferentially kill older, potentially-infectious, Anopheles stephensi females in the laboratory. Parameterizing a model with our data, we also showed that certain reduced concentrations of these chemicals can also delay the spread of insecticide resistance, though being able to use the intervention longer trades off with the initial, maximum level of disease control. This low-dose insecticide strategy also comes with the potential problem that there could be sub-lethal effects of exposure that reduce mosquito fitness, negating the resistance management gains garnered by allowing some young females to reproduce. Indeed, in our experiments, mosquitoes exposed to permethrin immediately after bloodfeeding produced fewer offspring than unexposed members of their cohort, which advanced the spread of resistance alleles through our modeled populations. Due to the decay of insecticide residues from treated walls and bednets, low-dose insecticide exposure might already be common in the field; how it might affect mosquitoes under highly variable field conditions remains a largely open question. We investigated one environmental condition that is highly variable and known to interact with many aspects of mosquito- and malaria parasite- life history: temperature. Temperature significantly affected insecticide susceptibility even at high concentrations. At lower concentrations, under simulated daily temperature fluctuations, insecticide susceptibility differed at different times of day, depending on the chemical to which the mosquitoes were exposed. It is clear that there is still a lot to be discovered about how chemical insecticides work to control mosquitoes and, especially, how they work to control malaria in the field. Overall, our results show that, when assessing the efficacy of chemicals during new compound screening, during field tests of residual persistence, and insecticide resistance monitoring, it is important to take into account variables such as the age of the mosquitoes you wish to control and the environmental temperatures at which you wish to control them.