Alvaro Romero

Insecticide resistance in the bed bug: a factor in the pest's sudden resurgence?

Abstract Infestations of the bed bug, Cimex lectularius L. (Heteroptera: Cimicidae), are increasing around the world at an alarming rate and have become a major public health concern. The evolution of insecticide resistance could be a primary factor in explaining this resurgence. Extremely high levels of resistance to two pyrethroid insecticides, deltamethrin and &lgr;-cyhalothrin, relative to a susceptible colony, were detected in populations collected from human dwellings in Kentucky and Ohio. Offspring of a cross between a resistant and susceptible colony had intermediate susceptibility. Evaluations of populations from across the United States indicate that resistance to pyrethroid insecticides is already widespread. Without the development of new tactics for bed bug management, further escalation of this public health problem should be expected.

Widespread distribution of knockdown resistance mutations in the bed bug, Cimex lectularius (Hemiptera: Cimicidae), populations in the United States

We previously reported high deltamethrin resistance in bed bugs, Cimex lectularius, collected from multiple areas of the United States (Romero et al., 2007). Recently, two mutations, the Valine to Leucine mutation (V419L) and the Leucine to Isoleucine mutation (L925I) in voltage-gated sodium channel alpha-subunit gene, had been identified to be responsible for knockdown resistance (kdr) to deltamethrin in bed bugs collected from New York (Yoon et al., 2008). The current study was undertaken to investigate the distribution of these two kdr mutations in 110 bed bug populations collected in the United States. Out of the 17 bed bug populations that were assayed for deltamethrin susceptibility, two resistant populations collected in the Cincinnati area and three deltamethrin-susceptible lab colonies showed neither of the two reported mutations (haplotype A). The remaining 12 populations contained L925I or both V419L and L925I mutations in voltage-gated sodium channel alpha-subunit gene (haplotypes B&C). In 93 populations that were not assayed for deltamethrin susceptibility, 12 contained neither of the two mutations (haplotype A) and 81 contained L925I or V419L or both mutations (haplotypes B-D). Thus, 88% of the bed bug populations collected showed target-site mutations. These data suggest that deltamethrin resistance conferred by target-site insensitivity of sodium channel is widely spread in bed bug populations across the United States.

Behavioral Responses of the Bed Bug to Insecticide Residues

ABSTRACT The recent resurgence of bed bugs, Cimex lectularius L. (Heteroptera: Cimicidae), has increased the demand for information about effective control tactics. Several studies have focused on determining the susceptibility of bed bug populations to insecticides. However, behavioral responses of bed bugs to insecticide residues could influence their efficacy. The behavioral responses of bed bugs to deltamethrin and chlorfenapyr, two commonly used insecticides for bed bug control in the United States, were evaluated. In two-choice tests, grouped insects and individual insects avoided resting on filter paper treated with deltamethrin. Insects did not avoid surfaces treated with chlorfenapyr. Harborages, containing feces and eggs and treated with a deltamethrin-based product, remained attractive to individuals from a strain resistant to pyrethroids. Video recordings of bed bugs indicated that insects increased activity when they contacted sublethal doses of deltamethrin. Insecticide barriers of chlorfenapyr or deltamethrin did not prevent bed bugs from reaching a warmed blood source and acquiring blood meals. We discuss the impact of these responses on bed bug control practices.

Evaluation of piperonyl butoxide as a deltamethrin synergist for pyrethroid-resistant bed bugs.

ABSTRACT An understanding of the mechanisms of insecticide resistance in the bed bug, Cimex lectularius L., has the potential to lead to new approaches for the control of resistant populations. We used the cytochrome P450 monooxygenase (P450) inhibitor piperonyl butoxide (PBO) to assess the role of P450s in deltamethrin resistance in three field-collected bed bug strains, LA-1, CIN-1 and WOR-1. In addition, we exposed two highly resistant strains, CIN-1 and WOR-1 (resistance ratio [RR] >2,500-fold), to dry residues of piperonyl butoxide-synergized pyrethroid formulations to determine the utility of synergism by PBO. Piperonyl butoxide synergized deltamethrin in all three strains, but its impact was variable. The synergistic ratio varied from 40 in CIN-1 to 176 in WOR-1. Because the resistance ratio for each strain after piperonyl butoxide treatment was 174 and 39, respectively, our results suggest that P450s have some involvement in deltamethrin resistance, but other resistance mechanisms must be involved as well. No significant synergistic effect of formulated deltamethrin was observed with the addition of synergized Pyrethrins or formulated piperonyl butoxide in the CIN-1 strain, but synergism occurred in the WOR-1 strain. Addition of PBO to pyrethroids is not a comprehensive solution to pyrethroid resistance because strains vary in both overall resistance level and the proportion of that resistance attributable to P450s.

Circadian rhythm of spontaneous locomotor activity in the bed bug, Cimex lectularius L.

Bed bugs must avoid detection when finding hosts and returning to hidden harborages. Their stealthy habits include foraging when hosts are asleep. Characteristics of spontaneous locomotor activity rhythm of bed bugs with different feeding histories were studied. In the absence of host stimuli, adults and nymphs were much more active in the dark than in the light. The onset of activity in the scotophase commenced soon after lights-off. The free-running period (tau) for all stages was longer in continuous darkness (DD) than in continuous light (LL). The lengthening of tau in DD is an exception for the circadian rule that predicts the opposite in nocturnal animals. Activity in all stages was entrained to reverse L:D regimes within four cycles. Short-term starved adults moved more frequently than recently fed adults. While bed bugs can survive for a year or more without a blood meal, we observed a reduction in activity in insects held for five weeks without food. We suggest that bed bugs make a transition to host-stimulus dependent searching when host presence is not predictable. Such a strategy would enable bed bugs to maximize reproduction when resources are abundant and save energy when resources are scarce.

Evaluation of chlorfenapyr for control of the bed bug, Cimex lectularius L.

BACKGROUND The presence of bed bug populations resistant to pyrethroids demands the development of new control tactics, including the use of insecticides with new modes of action. Insecticides that disrupt oxidative phosphorylation in insect mitochondria can be an option. Laboratory assays were used to measure the toxicity of chlorfenapyr to susceptible strains and two strains highly resistant to pyrethroids. The effectiveness of two chlorfenapyr-based formulations was compared, and behavioral responses of bed bugs to dry residues of aerosol sprays were evaluated. RESULTS Chlorfenapyr was effective against all bed bug strains, killing them at a similar rate, regardless of their susceptibility status to pyrethroids. Dry residues aged for 4 months were as toxic as fresh dry residues. The aerosol formulation had contact activity and caused faster mortality than a water-based formulation. Bed bugs did not avoid resting on surfaces treated with aerosol. CONCLUSION Chlorfenapyr is an option for controlling pyrethroid-resistant bed bugs. While it does not cause quick knockdown, its long residual activity and no avoidance behavior of bed bugs to dry residues appear to make this insecticide suitable for bed bug control. A faster insecticidal effect is obtained with the aerosol formulation, suggesting greater bioavailability of the toxicant.

High Levels of Resistance in the Common Bed Bug, Cimex lectularius (Hemiptera: Cimicidae), to Neonicotinoid Insecticides

Abstract The rapid increase of bed bug populations resistant to pyrethroids demands the development of novel control tactics. Products combining pyrethroids and neonicotinoids have become very popular for bed bug control in the United States, but there are concerns about evolution of resistance to these compounds. Laboratory assays were used to measure the toxicity of topical applications of four neonicotinoids to a susceptible population and three pyrethroid-resistant populations. Activity of esterases, glutathione S-transferases, and cytochrome P450s of all strains was also evaluated. High levels of resistance to four neonicotinoids, acetamiprid, imidacloprid, dinotefuran, and thiamethoxam, relative to the susceptible Fort Dix population, were detected in populations collected from human dwellings in Cincinnati and Michigan. Because activity of detoxifying enzymes was increased in these two populations, our results suggest that these enzymes have some involvement in neonicotinoid resistance, but other resistance mechanisms might be involved as well. Detection of high levels of resistance to neonicotinoids further limits the options for chemical control of bed bugs.

Isolation and Partial Characterization of the Montecitos Strain of Boophilus microplus (Canestrini, 1877) Multiresistant to Different Acaricides

A primary problem for livestock production in tropical and subtropical regions of the world is the infestation with ticks, in particular Boophilus microplus. In Colombia, this tick is one the major constraints on the improvement of livestock productivity, mainly because of the difficulty of introducing improved breeds to lowlands with the problems of tick infestation and hemoparasitic diseases. 1 The most currently used method for tick control in the country is treatment with acaricides; however this practice has started to become ineffective as a result of development of tick resistance. 2 Day by day, multiresistant ticks are emerging. 3 The understanding of the multiresistance phenomenon in B. microplus and the design of control strategies requires that different tick strains be maintained in the laboratory in order to characterize the spectrum and the mechanisms of resistance involved. In Colombia the presence of multiresistant ticks has not yet been reported for B. microplus. 4

Blood constituents as phagostimulants for the bed bug Cimex lectularius L.

Many hematophagous arthropods are stimulated by blood constituents to initiate feeding. We used a membrane-based feeding system to identify chemicals that stimulate acceptance and engorgement responses in various life stages of bed bugs. Water was fortified with a variety of compounds (e.g. salts, amino acids, vitamins, nucleotides, cholesterol and fatty acids) in these bioassays. ATP was the most effective phagostimulant in adults and nymphs, resulting in >70% of bed bugs fully engorging. Addition of NaCl to low ATP solutions that alone elicited <50% engorgement significantly enhanced feeding responses of bed bugs. A comparison of feeding responses with solutions of various adenine nucleotides showed that ATP was more stimulatory than ADP, which was more effective than AMP. Feeding assays with physiological levels of other blood constituents such as d-glucose, albumin, globulin, cholesterol and mixtures of vitamins and amino acids did not stimulate engorgement, suggesting that adenine nucleotides are the most important feeding stimulants in bed bugs. Identification of phagostimulants for bed bugs will contribute towards the development of artificial diets for rearing purposes, as well as for the development of alternative methods to eliminate bed bug infestations.

Attenuated Trivalent Vaccine against Babesiosis and Anaplasmosis in Colombia

In Colombia, where altitude regulates climate, Boophilus microplus ticks breed in areas under 2,000 m.a.s.l. and are considered a major constraint on improved animal production. They transmit to cattle Babesia bigemina, B. bovis, and Anaplasma marginale . 1,2 Protection against tick borne diseases is required in situations of endemic instability and when cattle require to be moved from highlands to endemic areas. Previous experience in Colombia of the use of vaccines for hemoparasites dates to the seventies, using locally attenuated Babesial organisms and the Illinois attenuated Anaplasma isolate. 3,4 However, a commercial alternative has not been widely available to farmers. In 1995, CORPOICA and LIMOR started cooperative efforts to produce a commercial live trivalent vaccine using, as far as possible, previously characterized and/or attenuated strains.