Combined influences of transgenerational effects, temperature and insecticide on the moth Spodoptera littoralis.

Climate warming is expected to impact the response of species to insecticides. Recent studies show that this interaction between insecticides and temperature can depend on other factors. Here, we tested for the influence of transgenerational effects on the Insecticide × Temperature interaction in the crop pest moth Spodoptera littoralis. Specifically, we analysed reaction norms among experimental clutches based on a split-plot design crossing the factors temperature, insecticide and clutch. The study was performed on 2280 larvae reared at four temperatures (23, 25, 27 and 29 °C), and their response to the insecticide deltamethrin (three concentrations and a control group) was tested. Temperature had a global influence with effects on larval survival, duration of development, pupal body mass, and significant reaction norms of the clutches for temperature variations of only 2 °C. In addition to the expected effect of deltamethrin on mortality, the insecticide slightly delayed the development of S. littoralis, and the effects on mortality and development differed among the clutches. Projection models integrating all the observed responses illustrated the additive effects of deltamethrin and temperature on the population multiplication rate. Variation in the response of the clutches showed that transgenerational effects influenced the impact of insecticide and temperature. Although no evidence indicated that the Insecticide × Temperature interaction depended on transgenerational effects, the studies on the dependence of the Insecticide × Temperature interaction on other factors continue to be crucial to confidently predict the combined effects of insecticides and climate warming.

Effects of low concentrations of deltamethrin are dependent on developmental stages and sexes in the pest moth Spodoptera littoralis.

Effects of low concentrations of pesticides, with no or moderate mortality of targeted species, are poorly studied even though these low concentrations are common under natural conditions. Studying their effects is critical because they can induce positive hormetic responses, possibly leading to greater pest multiplication and promoting the evolution of pest resistance. Here, we investigated the responses of the pest moth Spodoptera littoralis to low concentrations of deltamethrin, and tested for variation in effects of the pesticide between developmental stages and sexes. Indeed, we show that a given concentration of deltamethrin has different effects between stages, and even between sexes. Two experimental concentrations led to very high mortality early in S. littoralis development (4th larval instar), but only to low mortality rates in adults. Moreover, our highest experimental concentration had only detrimental effects in adult females, but improved the reproductive success of adult males. Model projections showed that the lethality from treatments at the 4th larval instar was the predominant effect. Because of the high multiplication rate of S. littoralis, it was also found that treatments with very similar effects on larval mortality can lead to either population extinction or rapid pest resurgence.

Effects of bisphenol A on post-embryonic development of the cotton pest Spodoptera littoralis.

Endocrine-disrupting chemicals encompass a variety of chemicals that may interfere with the endocrine system and produce negative effects on organisms. Among them, bisphenol A is considered a major pollutant in numerous countries. The harmful effects of BPA on environmental and human health are intensely studied. However, the effects of BPA on terrestrial insects are still poorly investigated, despite that several plants can accumulate BPA in their tissues, leading to potential contamination of herbivorous insects. Here, we used the leafworm Spodoptera littoralis, a polyphagous species, to study BPA effects on post-embryonic development. We studied the effects of BPA ingestion at environmental doses (e.g., 0.01, 0.1, and 1 µg/g of BPA) and high doses (e.g., 25 µg/g) on larval weight and stage duration, pupal length and sex ratio. BPA effects were investigated in more detail during the last larval instar, a crucial period for preparing pupation and metamorphosis, which are under endocrine control. We monitored the haemolymph concentration of ecdysteroids, hormones controlling moult and metamorphosis, as well as the expression levels of several nuclear receptors involved in the ecdysteroid signalling pathway. Our integrative study showed that, upon exposure doses, BPA can induce various effects on the viability, developmental time, growth and sex ratio. These effects were correlated with a delay of the ecdysteroid peak during the last larval instar and a modification of expression of EcR, USP, E75AB, E75D and Br-c. We provide new evidence about the events that occur after BPA exposure in insect contaminated by food ingestion.

Adult male mice exposure to nonylphenol alters courtship vocalizations and mating.

The neural circuitry processing male sexual behavior is tightly regulated by testosterone and its neural metabolite estradiol. The present study evaluated the effects of adult exposure to low doses of nonylphenol (NP), a widespread environmental contaminant, on the neuroendocrine regulation of testosterone and expression of sexual behavior. Oral exposure of C57BL/6J males to NP (0.5, 5 or 50 µg/kg/day) for 4 weeks did not affect circulating levels of testosterone or the kisspeptin system, a key regulator of the gonadotropic axis. In contrast, mice exposed to NP at 5 µg/kg/day emitted an increased number and duration of ultrasonic vocalizations, took longer to reach ejaculation and showed increased number of mounts, intromissions and thrusts. This was associated with normal olfactory preference and locomotor activity, and increased anxiety level. Analysis of the neural circuitry that underlies sexual behavior showed changes in the number of cells expressing androgen and estrogen receptors in males exposed to NP at 5 µg/kg/day. The neural circuitry underlying sexual behavior is thus highly sensitive to adult exposure to NP. Furthermore, almost all the observed effects were induced at 5 µg/kg/day of NP, indicating that this endocrine disrupter triggers a non-monotonic response in the adult male mouse brain.