Azadirachtin-Induced Hormesis Mediating Shift in Fecundity-Longevity Trade-Off in the Mexican Bean Weevil (Chrysomelidae: Bruchinae)

Abstract

Insecticides can have lethal or sublethal effects upon targeted pest species, and sublethal effects may even favor pest outbreaks if insecticide-induced hormesis occurs. Hormesis is a biphasic dose-response of a given chemical compound that is stimulatory at low doses and toxic at high doses. The former response may result from the disruption of animal homeostasis leading to trade-off shifts between basic ecophysiological processes. A growing interest in the use of biorational insecticides, such as azadirachtin to control stored-product pests, raises concerns about potential sublethal effects. In this study, we explored the hypothesis that azadirachtin can negatively impact the reproductive capacity of the Mexican bean weevil, Zabrotes subfasciatus (Boheman) (Chrysomelidae: Bruchinae), a key pest of stored beans. In addition, we investigated whether adults of this species could compensate for any sublethal effect that might have affected any of their reproductive parameters by adjusting the allocation of its reproductive efforts. The results showed that females of Z. subfasciatus increased fecundity daily to compensate for azadirachtin-induced decreased longevity. In addition, a stage-structured matrix study revealed that populations of Z. subfasciatus engendered from females exposed to azadirachtin exhibited a higher rate of population increase (r) and a higher net reproductive rate (R(o)). Finally, a projection matrix analysis showed notably higher densities along the generations for azadirachtin-exposed Z. subfasciatus populations. Thus, our study provides empirical evidence for the capacity of Z. subfasciatus to adapt to sublethal effects caused by biorational insecticides; consequently, this study highlights the importance of understanding this phenomenon when devising pest management strategies.

Insecticide‐induced hormesis and arthropod pest management

“…The initial suspicion that hormesis in individual traits may not translate into improved fitness has been challenged of late by reports of enhanced population fitness due to insecticide-induced hormesis in insects and mites. 31,45,47,49,50 These recent findings suggest that insecticideinduced hormesis in arthropods may indeed be adaptive, as suspected and reported with other stress agents for other taxa, 14,51 -54 with potential consequences for arthropod pest management.…”

“…14,31 Cadmium-exposed springtails and azadirachtin-exposed bean beetles (bruchids) both exhibited trade-off shifts, the first favoring longevity at the expense of growth and reproduction, and the latter favoring reproduction at the expense of longevity. 46,47 In both situations, improved performance of one trait impairs the performance of the other. This may have either positive or negative fitness consequences for the individual depending on the traits involved and may exhibit transgenerational effects.…”

Toxic and hormetic-like effects of three components of citrus essential oils on adult Mediterranean fruit flies (Ceratitis capitata)

“…Low amount of sweet orange EO had a stimulatory effect by increasing fecundity and decreasing preoviposition periods while the opposite was observed with high doses of sweet orange EO. Hormetic-like effects of phytochemicals and insecticides have been recorded as increased fecundity in other insect species, as well [5, 30, 34]. Azadirachtin sub-lethal doses increase the fecundity of Zabrotes subfasciatus (Boheman) (Chrysomelidae: Bruchinae) and decrease the survival [34], possibly indicating a trade-off between longevity and reproduction in stressful environments that is induced by either an increase of juvenile hormone levels [35] or a shift in resource allocation [36].…”

Lethal, sublethal and transgenerational effects of the novel chiral neonicotinoid pesticide cycloxaprid on demographic and behavioral traits of Aphis gossypii (Hemiptera: Aphididae)

“…In addition to direct mortality, pesticides can induce various physiological and behavioral sublethal effects in exposed arthropods (Desneux et al, 2007;Biondi et al, 2012) and changes of insect population dynamics (Desneux et al, 2006a, b;Stark et al, 2007;Biondi et al, 2013a). Transgenerational effects and hormesis may also occur owing to exposure to pesticides (Cordeiro et al, 2013;Guo et al, 2013;Vilca Mallqui et al, 2014;Qu et al, 2015). All these effects should be considered for comprehensive assessment of potential effects that pesticides could have on insects (Tan et al, 2012;Zhang et al, 2014;Chen et al, 2015, and see Guedes et al, 2016 for a thorough review).…”