Behavioral and metabolic effects of sublethal doses of two insecticides, chlorpyrifos and methomyl, in the Egyptian cotton leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae)

International audienceInsecticides have long been used as the main method in limiting agricultural pests, but their widespread use has resulted in environmental pollution, development of resistances, and biodiversity reduction. The effects of insecticides at low residual doses on both the targeted crop pest species and beneficial insects have become a major concern. In particular, these low doses can induce unexpected positive (hormetic) effects on pest insects, such as surges in population growth exceeding what would have been observed without pesticide application. Methomyl and chlorpyrifos are two insecticides commonly used to control the population levels of the cotton leafworm Spodoptera littoralis, a major pest moth. The aim of the present study was to examine the effects of sublethal doses of these two pesticides, known to present a residual activity and persistence in the environment, on the moth physiology. Using a metabolomic approach, we showed that sublethal doses of methomyl and chlorpyrifos have a systemic effect on the treated insects. We also demonstrated a behavioral disruption of S. littoralis larvae exposed to sublethal doses of methomyl, whereas no effects were observed for the same doses of chlorpyrifos. Interestingly, we highlighted that sublethal doses of both pesticides did not induce a change in acetylcholinesterase activity in head of exposed larva

Impact de stress thermique sur la survie et l'activité métabolique chez un insecte coléoptère, Alphitobius diaperinus.

25 p.Mémoire de Master 2 Physiologie intégrée et conditions extrème

Critical thermal minima of three sub-Antarctic insects from the French southern Indian Ocean islands

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A model for the time–temperature–mortality relationship in the chill-susceptible beetle, Alphitobius diaperinus, exposed to fluctuating thermal regimes

Exposing insects to a fluctuating thermal regime (FTR) compared with constant low temperature (CLT) significantly reduces cold-induced mortality. The beneficial effects of FTR result from physiological repair during warming intervals. The duration and the temperature experienced during the recovery period are supposed to strongly impact the resulting cold survival; however, disentangling the effects of both recovery variables had not been broadly investigated. In this study, we investigate cold tolerance (lethal time, Lt50) of the polyphagous beetle Alphitobius diaperinus. We examined adult survival under various CLTs (0, 5, 10 and 15 1C), and under 20 different FTR conditions, where the 0 1C exposure alternated with various recovery temperatures (Rt) (5, 10, 15 and 20 1C) combined with various recovery durations (Rds) (0.5, 1, 2, 3 and 4 h). Under CLTs, Lt50 increased with temperature until no mortality occurred above the upper limit of cold injury zone (ULCIZ). Under FTRs, Lt50 increased with both Rt and Rd. The magnitude of the survival gain was clearly boosted when Rt was above the ULCIZ (at 20 1C). Based on a data matrix of lethal times with multiple Rt  Rd combinations, a predictive model showed that cold survival increased exponentially with Rt and Rd. This model was subsequently validated with additional survival tests. We suggest that increasing recovery durations associated with optimal recovery temperatures eventually leads to a progressive chilling compensation

Thermal fluctuations in insects: How much does it improve survival in chill susceptible species

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Insect cold tolerance and repair of chill-injury at fluctuating thermal regimes: Role of 70 kDa heat shock protein expression.

International audienceExpression of heat shock proteins has been proposed as an underlying mechanism of increased cold tolerance in insects exposed to fluctuating thermal regimes (FTRs) in comparison to constant low temperatures (CLTs). We found that the levels of Pahsp70 mRNA increase by up to 3 orders in the linden bugs, Pyrrhocoris apterus exposed to FTR -5 degrees C (22h)/25 degrees C (2h). The 2h-long warm pulses, however, were not sufficient for accumulation of PaHSP70 protein and thus no significant difference in expression of PaHSP70 protein was detected between FTR and CLT regimes. Hence, we conclude that the accumulation of PaHSP70 protein is not the mechanism underlying the increased cold tolerance in P. apterus at the particular FTR used in this study. The relevance of some other possible mechanisms is discussed

Insect cold tolerance and repair of chill-injury at fluctuating thermal regimes: Role of 70 kDa heat shock protein expression.

International audienceExpression of heat shock proteins has been proposed as an underlying mechanism of increased cold tolerance in insects exposed to fluctuating thermal regimes (FTRs) in comparison to constant low temperatures (CLTs). We found that the levels of Pahsp70 mRNA increase by up to 3 orders in the linden bugs, Pyrrhocoris apterus exposed to FTR -5 degrees C (22h)/25 degrees C (2h). The 2h-long warm pulses, however, were not sufficient for accumulation of PaHSP70 protein and thus no significant difference in expression of PaHSP70 protein was detected between FTR and CLT regimes. Hence, we conclude that the accumulation of PaHSP70 protein is not the mechanism underlying the increased cold tolerance in P. apterus at the particular FTR used in this study. The relevance of some other possible mechanisms is discussed

Insect cold-tolerance and repair of chill-injuries in adult tropical beetles exposed to fluctuating thermal regimes.

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Growth potential : effects of temperature on cellular proliferation at molecular levels in Plodia interpunctella (Lepidoptera : Pyralidae).

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Effects of cold-exposure and subsequent recovery on cellular proliferation with influence of 20-hydroxyecdysone in a lepidopteran cell line (IAL-PID2).

International audienceIn developing insects, the peak level of 20-hydroxyecdysone (20E) initiates a decrease in cyclin expression, which subsequently triggers an arrest of cellular proliferation and the start of differentiation, finally culminating in the moult. We investigated the impact of cold-exposure (4 °C) and recovery (26 °C) on the cell cycle activity of the Plodia interpunctella Lepidoptera cell line IAL-PID2 and on the expression of B-type cyclin (PcycB), ecdysone receptor (B1-isoform; PiEcR-B1), and Hsc70 (PiHsc70) mRNA. Cold-exposure significantly reduced expression of these mRNAs, while their levels increased to above control values during subsequent recovery at the normal growth temperature. When cold-exposed cells were returned to 26 °C, cell cycle activity restarted, but apoptosis was strongly increased. The presence of 20E appeared to increase this apoptotic phenomenon. This result is consistent with the described protective role of 20E against a variety of stressors and with the capacity of 20E to induce cell death in different situations. Here, we illustrate for the first time a connection between 20E treatment and Hsc70 expression during cold-exposure and subsequent recovery in insect cells. Combined with the 20E-induced apoptotic response, our results suggest that regulation of Hsc70 expression by 20E could act in synergy with the control of apoptotic cell death in order to optimize the survival of specific cell populations after a period of cold-exposure