Effects of starvation on deltamethrin tolerance in bed bugs, Cimex lectularius L. (Hemiptera: Cimicidae)

Bed bugs, Cimex lectularius L., are a major pest in the urban environment. Their presence often results in physical, psychological, and financial distress of homeowners and apartment dwellers. Although many insecticide bioassays have been performed on this pest, little attention has been paid to bed bug feeding status, which is closely linked to metabolism, molting, and mass. Therefore, we evaluated the toxicity of topically applied deltamethrin on insecticide susceptible adult male bed bugs fed 2 d, 9 d, and 21 d prior to testing. When toxicity was evaluated on a “per-bug” basis, there was no difference between 2 d [LD50 = 0.498 (0.316 0.692) ng·bug 1] and 9 d [LD50 = 0.572 (0.436 0.724) ng·bug 1] starved bugs, while 21 d starved bugs had a significantly lower LD50 [0.221 (0.075 0.386) ng·bug 1].When toxicity was evaluated in terms of body mass, 9 d starved bugs had the highest LD50 values [0.138 (0.102 0.176) ng·mg 1], followed by 2 d starved bugs [0.095 (0.060 0.134) ng·mg 1],and then 21 d starved bugs [0.058 (0.019-0.102) ng·mg 1]; the LD50 values of 2 d and 9 d starved bugs were significantly different from 21 d starved bugs. These results indicate that feeding status plays an important role in the toxicity of deltamethrin. In addition, the lack of differences between 2 d and 9 d starved bugs indicate that the blood meal itself has little impact on tolerance, but rather it is some physiological change following feeding that confers increased tolerance to bed bugs.