No Sex-Related Differences in Mortality in Bed Bugs (Hemiptera: Cimicidae) Exposed to Deltamethrin, and Surviving Bed Bugs Can Recover

Abstract

Exposure of a pyrethroid-susceptible strain of bed bugs, Cimex lectularius L. (Hemiptera: Cimicidae) to varying concentrations of deltamethrin for 24 h indicated no significant difference in mortality between males, females, and nymphs at 24 nor at 168 h postexposure when bed bugs were removed to untreated surfaces at 24 h. In addition, many bed bugs classified as morbid or moribund at 24 h and removed to untreated surfaces at this time, recovered by 336 h (2 wk) and were capable of feeding when given the opportunity. Adult female bed bugs that survived were able to lay eggs and the resulting nymphs blood-fed. By contrast, all bed bugs classified as morbid or moribund at 24 h that remained on deltamethrin-treated surfaces for 336 h either died or were still classified as morbid or moribund at the end of this time. No bed bugs classified as morbid or moribund blood-fed when given the opportunity at 2 wk, regardless of whether they remained on the treated surfaces or were removed to untreated surfaces. A power analysis demonstrated we would have detected even moderate differences in mortality between males and females, had differences existed. Therefore, using males exclusively in efficacy assays is a suitable strategy to preserve females for laboratory colony purposes. Results also indicated there is little reason to assess efficacy beyond 1 wk, even when bed bugs are exposed for only 24 h.

Cuticle Thickening in a Pyrethroid-Resistant Strain of the Common Bed Bug, Cimex lectularius L. (Hemiptera: Cimicidae)

“…at day 1) or starved for up to 9 days [ 56 ]. This aligns with the practices of other laboratories employing bed bugs in insecticide-based bioassays, with most selectively using male bed bugs, aging between 7–10 days after emergence, and not feeding for 5–8 days prior to the experiment(s), if at all [ 6 , 11 , 13 , 57 – 59 ].…”

Effects of Starvation on Deltamethrin Tolerance in Bed Bugs, Cimex lectularius L. (Hemiptera: Cimicidae)

“…We evaluated only adult males, while the previous studies on mosquitoes were forced to evaluate only females because they are the only life stage that consumes a blood meal [ 24 , 25 ]. Feldlaufer et al [ 12 ] reported no difference in the toxicity of insecticides between males and females, however they only measured the effects of continuous exposure. In addition, Choe and Campbell [ 16 ] found a significant difference in the tolerance of 1 d and 9 d starved bed bugs when continually exposed to dried residues of deltamethrin, but no differences at these times when topically applied.…”

“…The World Health Organization has standards for mosquito testing (non-blood fed, 3–5 d post emergence), however no such standard exist for bed bugs [ 32 ]. Numerous studies have tested bed bugs at various times post feeding, ranging from 5 d to >12 d [ 11 , 12 , 13 ]. Difference in feeding status among tests may confound our understanding of the effects of various insecticides, which is critical as we continue to search for the most effective management strategy.…”

“…Most insecticide bioassays involving bed bugs use bugs starved for some period of time, although starvation times vary widely. Insecticides of various types and formulations have been tested against bed bugs starved for 5 d [ 11 ], 8 d [ 12 ], and >12 d [ 13 ]. Starving bed bugs has been reported to contribute to more consistent mortality measurements [ 13 ], however the behavior and physiology of bed bugs make it important to assess tolerance at different times after feeding.…”

“…Blood meals can increase the body mass of bed bugs by 1.5–6.1 times, depending on life stage [ 14 ]. Although many studies have investigated mortality to continuous insecticide exposure, these results generally ignore the mass of the insect being tested [ 11 , 12 , 13 , 15 , 16 ]. The per-bug estimate provides numbers that have practical relevance for studies improving control of this pest, but may result in increased within-stadia variability as mass is affected by nutritional status.…”