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20 January 2018 Spinosad- and Deltamethrin-Induced Impact on Mating and Reproductive Output of the Maize Weevil Sitophilus zeamais
Mayra Vélez, Lorena L. Botina, Leonardo M. Turchen, Wagner F. Barbosa, Raul Narciso C. Guedes
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Abstract

Assessments of acute insecticide toxicity frequently focus on the lethal effects on individual arthropod pest species and populations neglecting the impacts and consequences of sublethal exposure. However, the sublethal effects of insecticides may lead to harmful, neutral, or even beneficial responses that may affect (or not) the behavior and sexual fitness of the exposed insects. Intriguingly, little is known about such effects on stored product insect pests in general and the maize weevil in particular.Thus, we assessed the sublethal effects of spinosad and deltamethrin on female mate-searching, mating behavior, progeny emergence, and grain consumption by maize weevils. Insecticide exposure did not affect the resting time, number of stops, and duration of mate-searching by female weevils, but their walking velocity was compromised. Maize weevil couples sublethally exposed to deltamethrin and spinosad exhibited altered reproductive behavior (walking, interacting, mounting, and copulating), but deltamethrin caused greater impairment. Curiously, higher grain consumption and increased progeny emergence were observed in deltamethrin-exposed insects, suggesting that this pyrethroid insecticide elicits hormesis in maize weevils that may compromise control efficacy by this compound. Although spinosad has less of an impact on weevil reproductive behavior than deltamethrin, this bioinsecticide also benefited weevil progeny emergence, but did not affect grain consumption.Therefore, our findings suggest caution using either compound, and particularly deltamethrin, for controlling the maize weevil, as they may actually favor this species population growth when in sublethal exposure requiring further assessments.The same concern may be valid for other insecticides as well, what deserves future attention.

© The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
Mayra Vélez, Lorena L. Botina, Leonardo M. Turchen, Wagner F. Barbosa, and Raul Narciso C. Guedes "Spinosad- and Deltamethrin-Induced Impact on Mating and Reproductive Output of the Maize Weevil Sitophilus zeamais," Journal of Economic Entomology 111(2), 950-958, (20 January 2018). https://doi.org/10.1093/jee/tox381
Received: 11 November 2017; Accepted: 15 December 2017; Published: 20 January 2018
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KEYWORDS
biopesticide
grain consumption
hormesis
insecticides
progeny production
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