Growth and development of Colorado potato beetle larvae, Leptinotarsa decemlineata, on potato plants expressing the oryzacystatin II proteinase inhibitor.

Plant proteinase inhibitors (PIs) are attractive tools for crop improvement and their heterologous expression can enhance insect resistance in transgenic plants. PI oryzacystatin II (OCII), isolated from rice, showed potential in controlling pests that utilize cysteine proteinases for protein digestion. To evaluate the applicability of the OCII gene in enhancing plant defence, OCII-transformed potatoes were bioassayed for resistance to Colorado potato beetle (Leptinotarsa decemlineata Say). Feeding on transformed leaves of potato cultivars Desiree and Jelica significantly affected larval growth and development, but did not change mortality rates. During the L2 and L3 developmental stages larvae consumed the OCII-transformed foliage faster as compared to the nontransformed control. Also these larvae reached the prepupal stage (end of L4 stage) 2 days earlier than those fed on control leaves. However, the total amounts of consumed OCII-transformed leaves were up to 23% lower than of control, and the maximal weights of prepupal larvae were reduced by up to 18% as compared to larvae fed on nontransformed leaves. The reduction in insect fitness reported in this study in combination with other control measures, could lead to improved CPB resistance management in potato.

The effect of mitochondrial complex I inhibitor on longevity of short-lived and long-lived seed beetles and its mitonuclear hybrids.

Mitochondria are suggested to play a central role in ageing and evolution of longevity. Gradual decline in mitochondrial function during ageing and concomitant increase in production of reactive oxygen species (ROS) leads to oxidative damage of macromolecules and impairment of ATP synthesis. To assess relationship between ageing and oxidative stress resistance we exposed different longevity lines of the seed beetle (Acanthoscelides obtectus) to four concentrations of tebufenpyrad, mitochondrial complex I inhibitor. Complex I is one of main sites of ROS production during normal respiration and its inhibition elevates oxidative stress. Our results showed that 24 h of exposure to tebufenpyrad decreased survival and post-stress longevity due to increased baseline mortality. Higher resistance was recorded in beetles from lines selected for late reproduction and extended longevity (L) than in early reproducing beetles (E). Also, females were more resistant than males. Since complex I is under dual genetic control, our second aim was to disentangle relative contribution of nuclear and mitochondrial genes to the variation in longevity. We used crossed combinations of distinct mitochondrial and nuclear genotypes (E × L, L × E) and compared them to control hybrids where mitochondrial genome was "transplanted" onto the original background (E × E, L × L). Our study revealed significant effect of nucleus, i.e. higher survival and post-stress longevity in beetles harbouring L nucleus. Mitochondrion effect was significant only within L nuclear background where E mitochondrion gave advantage.