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<p>The control of pests causing postharvest loss of stored grain has become increasingly difficult due to the emergence of insecticide resistance. Therefore, this study aimed to investigate the insecticide resistance levels and underlying resistance mechanisms of two predominant stored product pests, <i>Sitophilus oryzae</i> (Rice weevil), and <i>Callosobruchus maculatus</i> (Cowpea weevil) in Sri Lanka. The insecticide-impregnated paper method, was employed to assess the resistance status of these pests against organophosphate malathion and pyrethroid deltamethrin. Log-probit curves constructed to determine the lethal concentrations revealed resistance in <i>S. oryzae</i> and <i>C. maculatus</i> to both insecticides. Both species were highly resistant to malathion where <i>S. oryzae</i> demonstrated greater resistance having an LC<sub>50</sub> of 3,020 ppm compared to <i>C. maculatus</i> (LC<sub>50</sub> =2,512 ppm). Along with the presence of malathion-specific carboxylesterases, altered AChE target-sites, may have contributed to greater levels of resistance to malathion. Additionally, 75% of <i>S. oryzae</i> exhibited elevated carboxylesterases, further enhancing resistance to organophosphates. <i>Callosobrachus maculatus</i> showed ⁓15 times lower level of resistance for deltamethrin (LC<sub>50</sub> = 151 ppm) than <i>S. oryzae</i> (LC<sub>50</sub>=2,399 ppm). Higher levels of glutathione S-transferases and monooxygenases in more than 60% of the <i>S. oryzae</i> population explain the greater resistance to deltamethrin, unlike in <i>C. maculatus</i>, which had significantly lower levels of these insecticide detoxifying enzymes (<i>p</i> &lt; 0.05). The identified insecticide resistance mechanisms in both <i>S. oryzae</i> and <i>C. maculatus</i> could lead to cross-resistance against various insecticide groups, posing a significant challenge to effective pest control strategies due to their potential to develop resistance to a broad range of synthetic insecticides.</p>

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Insecticide resistance and underlying mechanisms in Sitophilus oryzae and Callosobruchus maculatus in Sri Lanka: challenges for stored grain pest management

  • 期刊论文

  • 发表日期：

    2026年8月3日

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  • G. N. P. V. Anuradha,
  • W. R. G. W. N. Rajapaksha,
  • W. A. P. P. de Silva,
  • S. H. P. P. Karunaratne,
  • T. C. Weeraratne

摘要

The control of pests causing postharvest loss of stored grain has become increasingly difficult due to the emergence of insecticide resistance. Therefore, this study aimed to investigate the insecticide resistance levels and underlying resistance mechanisms of two predominant stored product pests, Sitophilus oryzae (Rice weevil), and Callosobruchus maculatus (Cowpea weevil) in Sri Lanka. The insecticide-impregnated paper method, was employed to assess the resistance status of these pests against organophosphate malathion and pyrethroid deltamethrin. Log-probit curves constructed to determine the lethal concentrations revealed resistance in S. oryzae and C. maculatus to both insecticides. Both species were highly resistant to malathion where S. oryzae demonstrated greater resistance having an LC50 of 3,020 ppm compared to C. maculatus (LC50 =2,512 ppm). Along with the presence of malathion-specific carboxylesterases, altered AChE target-sites, may have contributed to greater levels of resistance to malathion. Additionally, 75% of S. oryzae exhibited elevated carboxylesterases, further enhancing resistance to organophosphates. Callosobrachus maculatus showed ⁓15 times lower level of resistance for deltamethrin (LC50 = 151 ppm) than S. oryzae (LC50=2,399 ppm). Higher levels of glutathione S-transferases and monooxygenases in more than 60% of the S. oryzae population explain the greater resistance to deltamethrin, unlike in C. maculatus, which had significantly lower levels of these insecticide detoxifying enzymes (p < 0.05). The identified insecticide resistance mechanisms in both S. oryzae and C. maculatus could lead to cross-resistance against various insecticide groups, posing a significant challenge to effective pest control strategies due to their potential to develop resistance to a broad range of synthetic insecticides.