Assessment of physiological sublethal effects of imidacloprid on the mirid bug Apolygus lucorum (Meyer-Dür)

Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae) is currently one of major mirid pests in the Yangtze River and the Yellow River regions in China. Imidacloprid (neonicotinoid) is widely used against pierce-sucking pest insects, including against A. lucorum. In addition to its direct lethal effect, multiple negative sublethal effects may also occur in exposed insects. We assessed potential sublethal effects of imidacloprid on some biological characteristics of A. lucorum aiming at increasing rational use of imidaclorpid against that cotton pest. The lethal toxicity of imidacloprid on adults of A. lucorum was determined in laboratory conditions by a topical application bioassay, and the LD50 was determined as 6.70 ng a.i. [active ingredient] / A. lucorum adult. We also estimated a sublethal dose, the LD5, as 0.38 ng a.i. / adult, a low lethal dose; LD25, as 1.96 ng a.i. / adult, and an intermediate lethal dose, the LD40, as 3.97 ng a.i. / adult. The sublethal dose of imidacloprid (LD5) shortened the pre-oviposition period duration of females but increased the time required for eggs to develop (longer embryogenesis). The low lethal dose (LD25) also reduced the pre-oviposition duration in females. Females exposed to the LD40 laid eggs that developed faster but overall percentage of eggs hatching was reduced. LD25 and LD40 drastically reduced longevity of males but not of females. In addition, we showed that A. lucorum previously exposed to imidacloprid LD25 did not modify their sensitivity to eight insecticides generally used in Chinese crops. Our results demonstrate sublethal effects of imidacloprid low doses on A. lucorum, which may have an impact on population dynamics, notably by modifying pre-oviposition duration and egg development.