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Biological Responses in Context
Published in Arthur T. Johnson, Biology for Engineers, 2019
Antagonistic hormone control pervades living systems. Blood calcium level in mammals is regulated by the action of two hormones with opposing effects: calcitonin produced in the thyroid gland that reduces calcium and parathyroid hormone (PTH) that raises its level (Figure 6.20.9). Insect development is controlled by the hormones ecdysone and juvenile hormone (JH); ecdysone stimulates molting of the exoskeleton and growth, but the presence of JH hinders development of pupa and adult stages; only when JH levels wane does the insect progress to the next life-form stage.
Properties, toxicity and current applications of the biolarvicide spinosad
Published in Journal of Toxicology and Environmental Health, Part B, 2020
Vanessa Santana Vieira Santos, Boscolli Barbosa Pereira
Despite the efficacy of spinosad against specific target organisms, several investigators examined the performance of mixtures containing the compound (Darriet and Corbel 2006; Darriet et al. 2010). Various researchers investigating the efficacy of a mixture of spinosad and pyriproxyfen, a juvenile hormone analogue that blocks larval development, thus compromising adult insect characteristics and emergence (Caixeta et al. 2016; Santos et al. 2017). Darriet and Corbel (2006) found a significant synergism between both pesticides, whose mixture combined both the juvenoid activity of pyriproxyfen and the larvicidal effects of spinosad. Darriet and Corbel (2006) suggested a reduction by fiveand ninefold of pyriproxyfen and spinosad, respectively, to kill almost 100% mosquitoes. In agreement Darriet et al. (2010) reported that the activity of the mixture spinosad + pyriproxyfen lasted twofold longer in comparison to the use of the isolated compound. Accordingly, the use of insecticides initiated a powerful selection pressure on the target organisms, and prolonged use led to a resistance to the compound. However, the association of two pesticides with different MOA acting on different targets reduced the risk of evolution to resistance. In fact, the mixture of spinosad and pyriproxyfen combined the efficacy of the first against larvae and the second more specifically against the pupal stage, indicating a strong synergistic effect between the insecticides, hence leading to rapid mortality frequency of both larvae and pupae.