Sublethal insecticide exposure affects reproduction, chemical phenotype as well as offspring development and antennae symmetry of a leaf beetle

Abstract

The area of agriculturally used land and following to that the use of pesticides are steadily increasing. Insecticides do not only reduce pest organisms on crops but can also affect non-target organisms when present in sublethal concentrations in the environment. We investigated the effects of an exposure to sublethal pyrethroid (lambda-cyhalothrin) concentrations, at doses 20 and 60 times lower than the LC50, respectively, on reproductive traits and adult cuticular hydrocarbon (CHC) profiles of a leaf beetle (Phaedon cochleariae Fabricius). Furthermore, we tested for effects on growth and antennae symmetry of the offspring generation that was not exposed to the insecticide. Sublethal insecticide concentrations decreased the egg number produced by the adults and the hatching rate. Moreover, the chemical phenotype (CHC profile) of adults was altered in dependence of the insecticide treatment, with sex-specific effects. In the unexposed offspring of insecticide-exposed parents, a prolonged development time and a fluctuating asymmetry of the females' antennae were detected, revealing transgenerational effects. The insecticide effects on the CHC profiles of the parental generation might have been caused by changes in CHC precursors, which were potentially induced by the insecticide treatment of the insect diet. Such altered CHC pattern may have implications for intraspecific communication, e.g., in mate choice, as well as in an interspecific way, e.g., in interactions with other arthropod species. The observed detrimental transgenerational effects might be explainable by a reduced investment in the offspring, maternal transfer or epigenetic processes. An asymmetry of the antennae may lead to defects in the reception of chemical signals. In conclusion, the results disclose that, besides detrimental (transgenerational) effects on reproduction and development, an exposure to sublethal insecticide concentrations can impair the chemical communication between individuals, with impacts on the sender (i.e., the CHC profile) and the receiver (i.e., caused by asymmetry of the antennae).