Risk assessment of cyromazine and methoxyfenozide resistance suggests higher additive genetic but lower environmental variation supporting quick resistance development in non-target Chrysoperla carnea (Stephens).

Abstract

Insecticides are effective against economic pests, but these pose serious threats to the environment and ecosystem components such as natural enemies. Resistance risk assessment forecasts insecticide resistance development in target pests and non-target biological control agents under special conditions. Field-collected Chrysoperla carnea was selected with two Insect Growth Regulators (IGRs) viz. cyromazine and methoxyfenozide for 15 generations to determine the resistance development potential of this natural enemy. Selection to cyromazine and methoxyfenozide induced 759.08-fold and 3531.67-fold resistance with realized heritability of 0.37 and 0.62 in C. carnea, respectively, suggesting higher additive genetic variations in first half of selection (h2 = 0.46 for cyromazine and h2 = 0.75 for methoxyfenozide) than in second half (h2 = 0.18 and 0.25, respectively). Estimates of projected rate of resistance development indicate C. carnea will take only 6 to 2 generations at h2 = 0.37, 8 to 2 at h2 = 0.27, and 5 to 2 at h2 = 0.27, at constant slope = 1.81 for a tenfold increase in cyromazine resistance. At h2 = 0.37, 3-1, and 10-8 generations would be needed for this increase in LC50 if slope = 0.82 and 2.82, respectively. Similarly, it may take 3 to 1 generations at h2 = 0.62 and 0.72, but 4 to 1 at h2 = 0.52, at constant slope = 1.62, for a tenfold increase in methoxyfenozide resistance. On the same h2 = 0.62, 1-0, and 5-1 generations would be required for increase if slope = 0.62 and 2.62, respectively. Selection and resistance to both insecticides induced an insignificant difference in the sex ratio of C. carnea. These results confirm that this natural enemy has tremendous potential for resistance development under selection pressure.