Resistance to a chemical pesticide increases vulnerability to a biopesticide: Effects on direct mortality and mortality by predation

Abstract

Pesticide mixtures are increasingly used to fight pest species that developed resistance to pesticides. To assess the pesticide control efficiency and to reduce ecological damage to nontarget species, it is important to quantify the effect of these mixtures and compare them with the effect of their single pesticides on pest species, non-target species and their predator-prey interactions. We studied the effects of the chemical pesticide chlorpyrifos (CPF), the biopesticide Bacillus thuringiensis israelensis (Bti) and their mixture both on the direct mortality and on the mortality by predation. We focused on larvae of a CPF-resistant and a non-resistant strain of the vector mosquito Culex quinquefasciatus and its predator, the pygmy backswimmer Plea minutissima. In the CPF-Bti mixture, both pesticides interacted antagonistically for direct mortality. Exposure to the mixture caused equal direct mortality and equal mortality by predation in both strains. As expected, exposure to CPF resulted in less direct mortality and less mortality by predation in the CPF-resistant mosquito strain compared to the non-resistant strain. Notably, Bti caused a higher mortality in the mosquito larvae of the CPF-resistant strain compared to the non-resistant strain. Furthermore, the predator killed more mosquito larvae of the resistant strain compared to the non-resistant strain when exposed before to Bti alone. These observations identify a novel cost of resistance to a chemical pesticide in terms of increased vulnerability to a biopesticide.

The Exposure Order Strongly Modifies How a Heat Spike Increases Pesticide Toxicity

“…This organophosphate pesticide is used worldwide (although has recently been banned or restricted to use in some countries), and has a higher lethal effect on aquatic animals at higher temperatures. − We expected the heat spike to magnify the toxicity of the pesticide (CITS, ,, ), and the pesticide to reduce the heat tolerance (TICS, ,, ). Recent studies showed strong delayed mortality in mosquito larvae after exposure to heat extremes, but much less after exposure to the pesticide chlorpyrifos, suggesting a more rapid action of chlorpyrifos, and/or a longer toxicodynamic recovery after a heat spike. We therefore expected the toxicity of the pesticide to be more magnified when preceded than when followed by the heat spike.…”

Rethinking biorational insecticides for pest management: unintended effects and consequences

“…Indeed, there is growing evidence of high activity of botanicals against mosquitos with no effects or even stimulatory effects on aquatic predators of mosquito larvae . In contrast, other categories of biorational insecticides can cause adverse effects on non‐target aquatic organisms . Curiously, recent studies indicate that aquatic predators exposed to sublethal doses of Bacillus thuringiensis var israelensis (Bt i ) are more successful predators after exposure …”

Pollution impacts on water bugs (Nepomorpha, Gerromorpha): state of the art and their biomonitoring potential

“…For example, significantly more resistant C. pipiens larvae were consumed by Plea minutissima and Hyrdometra stagnorum but not Sigara lateralis than susceptible ones (Berticat et al, 2004 ). Furthermore, P. minutissima consumed more resistant than susceptible Bti-exposed Culex quinquefasciatus larvae (Delnat et al, 2019 ). These data show that the general cost of the resistance mechanism reduces the energy available for other life processes, making resistant individuals more accessible to predators.…”