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Abstract
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Chemical pesticides have important role in integrated pest management strategies. However, they can
adversely affect on natural enemies as non-target organisms, even in sublethal concentrations. In this study,
sublethal effects of two insecticides, thiamethoxam and pirimicarb, were examined on demographic parameters
of an important predator, Macrolophus pygmaeus. Bioassay results indicated that LC30 of thiamethoxam and
pirimicarb, applied on the third instar larvae, were 451.6 and 2013.4 mg (ai) L-1, respectively. The two
insecticides extended the pre-adult duration, significantly. Demographic parameters were analyzed by two-sex
life table. The results showed that all of the main demographic traits (r, λ, R0 and T) have been changed
significantly and there are also some changes in other parameters such as age-specific survival rate (lx) and life
expectancy (ex). Intrinsic rate of increase in control was 0.15 but it reduced to 0.10 and 0.99 day-1 in
thiamethoxam and pirimicarb treatments, respectively. Also, finite rate of increase in control, thiamethoxam
and pirimicarb treatments was 1.11, 1.08 and 1.03 day-1 respectively. Reproductive rate in control showed
36.75 offspring/individual but this statistic in thiamethoxam and pirimicarb treatments was 19.62 and 18.24,
respectively. Mean generation time was 22.69 days in control but it extended in both treatments and illustrated
27.79 and 31.24 days in thiamethoxam and pirimicarb treatments, respectively. Thus, obtained results in this
study showed that although pirimicarb and thiamethoxam are selective insecticides, they have potential to
affect on the predator, M. pygmaeus severely, and need to take care in IPM programs.
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