Sublethal Pyrethroid Insecticide Exposure Carries Positive Fitness Effects Over Generations in a Pest Insect

Abstract

Stress tolerance and adaptation to stress are known to facilitate species invasions. Many invasive species are also pests and insecticides are used to control them, which could shape their overall tolerance to stress. It is well-known that heavy insecticide usage leads to selection of resistant genotypes but less is known about potential effects of mild sublethal insecticide usage. We studied whether stressful, sublethal pyrethroid insecticide exposure has within-generational and/or maternal transgenerational effects on fitness-related traits in the Colorado potato beetle (Leptinotarsa decemlineata) and whether maternal insecticide exposure affects insecticide tolerance of offspring. Sublethal insecticide stress exposure had positive within-and transgenerational effects. Insecticide-stressed larvae had higher adult survival and higher adult body mass than those not exposed to stress. Furthermore, offspring whose mothers were exposed to insecticide stress had higher larval and pupal survival and were heavier as adults (only females) than those descending from control mothers. Maternal insecticide stress did not explain differences in lipid content of the offspring. To conclude, stressful insecticide exposure has positive transgenerational fitness effects in the offspring. Therefore, unsuccessful insecticide control of invasive pest species may lead to undesired side effects since survival and higher body mass are known to facilitate population growth and invasion success.

Figure 1

Survival (%) of insecticide stress exposed (solid line) and control (dashed line) of the Colorado potato beetles at different life stages. Insecticide stress exposure increases survival in the adult stage (0–10 days) when compared to control group.

Figure 2

Body mass for (a) female and (b) male Colorado potato beetles in the first generation measured at the age of 10 days. Body mass for (c) female and (d) male beetles in the second generation measured at the age of 7 days. Control: Control- offspring control: maternal control (within-generational treatment: transgenerational treatment).

Figure 3

Within- and transgenerational insecticide stress effects on survival (%) between different life stages in the second generation Colorado potato beetles. Within-generational insecticide stress exposure decreases larval  and pupal survival within the 24 h when compared to control group. Transgenerational insecticide treatment decreases larval mortality when compared to larvae descending from control mothers. Insecticide: Control within-generational treatment: transgenerational treatment means that within generational treatment was insecticide stress and transgenerational treatment was control.

Figure 4

Experimental design to test the within- and transgenerational effects of sublethal insecticide exposure on survival and body mass in the Colorado potato beetle. Here the progress of the study is visualized by the ordering of the nodes. The vertical axis describes the observational time and different generations and the horizontal axis describes the causal order of events. Here the dashed arrows correspond to transgenerational (TG) causal relationships. For example, the treatment of the first generation parents has an effect on body mass of the offspring in the second generation. Open circles denote unobserved variables. Filled circles denote variables that have been measured from the sample. Similarly, diamonds denote variables that have been determined by the researcher, such as the assigned treatments or mating of each generation in this case. Our graphical presentation is a simplified version of.