Circadian rhythms in insecticide susceptibility, metabolic enzyme activity, and gene expression in Cimex lectularius (Hemiptera: Cimicidae)

Abstract

Many insect species display daily variation of sensitivity to insecticides when they are exposed to the same concentration at different times during the day. To date, this has not been investigated in bed bugs. To address this, we explored circadian rhythms in insecticide susceptibility, xenobiotic metabolizing (XM) gene expressions, and metabolic detoxification in the common bed bug, Cimex lectularius . An insecticide susceptible Monheim strain of C . lectularius was most tolerant of deltamethrin during the late photophase at ZT9 (i.e. nine hours after light is present in the light-dark cycle (LD) cycle) and similarly repeated at CT9 (i.e. nine hours into the subjective day in constant darkness (DD)) suggesting endogenous circadian involvement in susceptibility to deltamethrin. No diel rhythm was observed against imidacloprid insecticide despite significant daily susceptibility in both LD and DD conditions. Rhythmic expressions of metabolic detoxification genes, GSTs1 and CYP397A1 displayed similar expression patterns with total GST and P450 enzyme activities in LD and DD conditions, respectively. The oscillation of mRNA levels of GSTs1 and CYP397A1 was found consistent with peak phases of deltamethrin susceptibility in C . lectularius . This study demonstrates that circadian patterns of metabolic detoxification gene expression occur within C . lectularius . As a consequence, insecticide efficacy can vary dramatically throughout a 24 hour period.

Diel and Circadian Patterns of Locomotor Activity in the Adults of Diamondback Moth (Plutella xylostella)

“…The circadian rhythms of certain insects make them more susceptible to insecticides at certain times of the day than at other times [35], because the susceptibility to insecticide can be influenced by the rhythmic activity of xenobiotic metabolizing (XM) enzymes. For example, the enzymatic assay of glutathione S-transferase (GST), esterase and P450 in Cimex lectularius reveal significant time-of-day specific changes that have similar peak phases with the highest activity consistently recorded during the late photophase at ZT9 in LD [36]. The XM gene expression assays also reveal significant time-of-day differences in mRNA expression patterns in both LD and DD.…”

Circadian regulation of night feeding and daytime detoxification in a formidable Asian pest Spodoptera litura

“…In a study of Anopheles gambiae , the GST activity of Pimperena strain mosquito lysates had peak phases at late-night to dawn, whereas in insecticide assays using the Mali strain, the mosquitoes showed rhythmic susceptibility to DDT with a peak at late afternoon 18 . In exploring the daily rhythms of insecticide susceptibility in the bedbug, Cimex lectularius , Khalid et al reported that the nocturnally active larvae repeatedly showed highest tolerance for deltamethrin during the late photophase at ZT9 48 . Other insects such as spotted wing Drosophila , cotton aphid, and brown plant hopper 49 – 51 are also reported to show circadian fluctuations in their detoxification metabolism and insecticide susceptibility.…”

Cuticle thickening associated with fenitrothion and imidacloprid resistance and influence of voltage‐gated sodium channel mutations on pyrethroid resistance in the tropical bed bug, Cimex hemipterus

“…Bed bug samples were subjected to esterase, glutathione S‐transferase (GST) and P450 activity assays following methods described by Khalid et al ., 37 with modifications. The bed bug sample was homogenized completely in 600 μl of ice‐cold 0.1 m phosphate buffer (pH 7.0) containing 0.3% Triton X‐100 (v/v) using a micro‐pestle.…”

“…Blank samples without homogenate were also included in every run as a negative control. Determination of general esterase activity and the GST assay were done according to procedures described in Khalid et al ., 37 whereas P450s assay was determined according to Son‐un et al 39 . with modifications.…”