Insecticide Control of Vector-Borne Diseases: When Is Insecticide Resistance a Problem?

Abstract

Many of the most dangerous human diseases are transmitted by insect vectors. After decades of repeated insecticide use, all of these vector species have demonstrated the capacity to evolve resistance to insecticides. Insecticide resistance is generally considered to undermine control of vector-transmitted diseases because it increases the number of vectors that survive the insecticide treatment. Disease control failure, however, need not follow from vector control failure. Here, we review evidence that insecticide resistance may have an impact on the quality of vectors and, specifically, on three key determinants of parasite transmission: vector longevity, competence, and behaviour. We argue that, in some instances, insecticide resistance is likely to result in a decrease in vector longevity, a decrease in infectiousness, or in a change in behaviour, all of which will reduce the vectorial capacity of the insect. If this effect is sufficiently large, the impact of insecticide resistance on disease management may not be as detrimental as previously thought. In other instances, however, insecticide resistance may have the opposite effect, increasing the insect's vectorial capacity, which may lead to a dramatic increase in the transmission of the disease and even to a higher prevalence than in the absence of insecticides. Either way—and there may be no simple generality—the consequence of the evolution of insecticide resistance for disease ecology deserves additional attention.

Delayed mortality effects cut the malaria transmission potential of insecticide-resistant mosquitoes

“…Some studies have shown that exposure to insecticides alters the behavior of IR arthropods in a way that could indirectly reduce their fitness [e.g., altered dispersal, reduced neurosensory perception and higher risk of predation (13,28)]. For example, exposure to neonicotinoid insecticides at sublethal concentration decreases the feeding activity of the grain aphid (23).…”

Evolution of adaptive phenotypic traits without positive Darwinian selection

“…Verified cases of positive Darwinian selection in response to human-induced environmental changes have been relatively few, mostly involving drugs, pesticides and other toxins (Mita et al, 2009;Rivero et al, 2010). Rather, the main biotic result of human-induced environmental alteration has been 'a few winners replacing many losers,' in the memorable phrase of McKinney and Lockwood, 1999.…”

Plasmodium infection decreases fecundity and increases survival of mosquitoes

“…In addition, the evolution of these two mechanisms of insecticide resistance in Cx. pipiens has been shown to entail a battery of correlated life-history changes in the insect, which have been widely interpreted as being the result of pleiotropic effects of the insecticide-resistant genes [22]. Yet the role of insecticide resistance in determining the outcome of mosquito-Plasmodium interactions has been largely unexplored ( [22], but see [23]).…”