A Review of Arthropod Repellents

Efficacy of Unregulated Minimum Risk Products to Kill and Repel Ticks

Human-biting ticks threaten public health in the United States. Registration by the Environmental Protection Agency of products to kill host-seeking ticks or repel ticks contacting humans is indicative of their safety and effectiveness. Unregulated minimum risk products, exempt from Environmental Protection Agency registration and often based on botanical oils, are proliferating in the marketplace, but there is concern about their effectiveness to kill and repel ticks. Evaluations of such products are limited in the published literature. A review showed considerable variability among minimum risk products to kill host-seeking blacklegged ticks, with effectiveness similar to chemical pesticide products for some minimum risk products but minimal impact on the ticks for other products. Evaluations of minimum risk tick repellents have typically focused on individual active ingredients rather than formulated products, which often combine multiple active ingredients. Consumers should be aware that effectiveness to kill and repel ticks can differ among unregulated minimum risk products.

Preliminary Evaluation of Human Personal Protective Measures Against the Nymphal Stage of the Asian Longhorned Tick (Acari: Ixodidae)

The invasive, human-biting Asian longhorned tick, Haemaphysalis longicornis Neumann, is establishing in the United States. This tick is a threat to public health in its native range in Asia, serving as a vector of severe fever with thrombocytopenia syndrome virus and Rickettsia japonica, the agent of Japanese spotted fever. However, there is a lack of published information specifically for H. longicornis concerning the efficacy of generally recommended personal tick bite prevention measures. We, therefore, evaluated permethrin-treated clothing and formulated human skin repellent products, representing the six repellent active ingredients generally recommended for tick bite prevention by the Centers for Disease Control and Prevention (CDC), against H. longicornis nymphs from a colony established with adult ticks collected in New York state. Reluctance of H. longicornis nymphs to stay in contact with nontreated human skin precluded the use of a human skin bioassay to optimally evaluate repellency. In a Petri dish choice bioassay, all tested product formulations were highly effective with estimated repellencies ranging from 93 to 97%. In addition, we observed strong contact irritancy of a summer-weight permethrin-treated garment against H. longicornis nymphs, with 96% of introduced ticks dislodging from the vertically oriented textile within 3 min. These preliminary studies indicate that personal tick bite prevention measures currently recommended by the CDC are effective against the invasive H. longicornis. However, additional studies are needed to explore the efficacy of the evaluated products against different life stages of H. longicornis, as well as ticks collected in the field rather than reared in the laboratory.

The Behavioral Response of Blattella germanica (Blattodea: Ectobiidae) Exposed to DEET Varies Throughout Its Life Cycle

The German cockroach, Blattella germanica L., is a hemimetabolous insect pest of economical and medical importance. N,N-diethyl-3-methylbenzamide (DEET) is an insect repellent whose effect on this species has received very little attention. The objective of this work was to determine whether the behavioral response of B. germanica to DEET varies along its life cycle. DEET repellence was assessed in small, medium, and large nymphs, and in adults of both sexes, all originated from the same laboratory colony (CIPEIN). The experimental arena consisted in a piece of filter paper treated with repellent on one half (195 µg/cm2) and solvent alone on the other half. A cockroach was placed on the filter paper, and its behavior was filmed. An image analyzer was used to quantify how long the insect spent on each side of the paper. As a control, a cockroach was exposed to a piece of filter paper treated with solvent (acetone) alone. Each assay was repeated independently six times. Distribution coefficient (DC) values were calculated, a parameter that ranges between 0 (attraction) and 1 (repellence). Small nymphs were more sensitive to DEET (mean DC = 0.93). The mean DC values of the other groups varied between 0.62 (medium nymphs) and 0.71 (male adults). The group of medium nymphs was the only one whose behavior was not significantly altered by exposure to DEET. The results show the importance of assessing insect repellents at different stages of the insect's life cycle in order to obtain a complete panorama of its effect.

Rosemary-Whitefly Interaction: A Continuum of Repellency and Volatile Combinations

The sweet potato whitefly Bemisia tabaci Genn (Hemiptera: Aleyrodidae) has been recorded to differentially prefer rosemary (Rosmarinus officinalis) varieties in commercial fields in Israel. As chemical signaling is a significant component in plant-insect interaction, the present study examined the involvement of rosemary essential oil volatiles in this differential colonization to elucidate the rosemary-whitefly ecological interaction. Thirty-two rosemary varieties with different chemical profiles were used. The average whitefly preference was 25.1% with a significant variation of 51.4%, partitioning the sampled varieties into five preference groups, hence suggesting rosemary as a non-preferred host for the insect. All relations between preference and the major volatiles 1,8-cineole, camphor, linalool, verbenone, bornyl acetate and borneol were significantly (P ≤ 0.05) or notably (0.05 < P ≤ 0.09) negative (r < 1). Therefore, revealing that whitefly preference for rosemary is based on a continuum of repellency rather than attraction. 'Choice' bioassays with a range of the major volatile concentrations and gas chromatography-mass spectrometry (GC-MS) volatile blends (fractions) validated this observation. Principle component analysis of the entire chemical profile of two extreme varieties, representing high and low preferences, identified that approximately 43% of the volatiles in the essential oil were directly associated with repellency. Keeping in mind the remaining 57% of the compounds, this myriad of volatiles exhibit the ecological complexity of the rosemary-whitefly eco-system, explaining that whitefly preference to rosemary is repellency based.

Impact of Wearing and Washing/Drying of Permethrin-Treated Clothing on Their Contact Irritancy and Toxicity for Nymphal Ixodes scapularis (Acari: Ixodidae) Ticks

Permethrin-treated clothing is available as consumer products to prevent bites by tick and insect pests. We used bioassays to examine the impact of wearing and washing/drying of permethrin-treated shirts, pants, and socks, and wearing of treated shoes, on their contact irritancy and toxicity for nymphal Ixodes scapularis Say (Acari: Ixodidae) ticks, the primary vectors in the eastern United States of the causative agents of Lyme disease, human anaplasmosis, and human babesiosis. Pristine permethrin-treated clothing displayed strong contact irritancy and toxicity toward I. scapularis nymphs, with 0-30% of ticks across clothing types and tick sources displaying normal movement 1 h after forced contact for 30-120 s with treated textile. Following 16 d of wear and 16 rounds of machine washing and drying, we recorded reduced concentrations (by 50-90%) of permethrin, compared with pristine treated clothing, from shirts, pants, and socks. This loss of permethrin was associated with reduced contact irritancy and toxicity for ticks after forced contact with worn and washed/dried treated clothing: 31-67% of ticks displayed normal movement 1 h after contact. Nevertheless, the worn and washed/dried treated clothing was still superior to nontreated textile, for which 90-100% of ticks displayed normal movement. Treated shoes, which were worn but not washed, remained as toxic to the ticks as pristine treated shoes. We caution that these laboratory bioassay results should not be interpreted as being directly indicative of the outcome of using washed/worn permethrin-treated clothing in daily life. Although wear and washing/drying did reduce the irritancy and toxicity of permethrin-treated clothing for I. scapularis nymphs more than we had expected, the remaining effect might still reduce the risk of tick bites in a real-life scenario.

Deltamethrin-resistant German Cockroaches Are Less Sensitive to the Insect Repellents DEET and IR3535 than Non-resistant Individuals

The German cockroach, Blattella germanica (L.) (Blattodea: Blattellidae), is a serious worldwide pest with a considerable economical and sanitary impact. It is mainly controlled by the application of synthetic insecticides, but repeated use of these substances has promoted the appearance of resistance in cockroach populations throughout the world. The aim of this study was to compare the behavior of deltamethrin-susceptible (CIPEIN colony) and deltamethrin-resistant (JUBA and VGBA colonies) first instar nymphs exposed to the repellents N,N-diethyl-3-methylbenzamide (DEET) and ethyl 3-[acetyl(butyl)amino]propanoate (IR3535). Firstly, the behavior of the nymphs was assessed in an experimental arena in the absence of repellents. The parameters Distance Traveled, Velocity, Mobility Time, and Time Spent (in each half of the arena) were quantified using an image analyser, and showed that the behavior elicited by the three colonies was similar. After this, the behavior of the nymphs was quantified in an arena, half of which had been treated with repellent. The repellency of DEET increased as a linear function of log concentration for the three colonies. DEET elicited repellency as from a concentration of 97.49 µg/cm2 for the CIPEIN and JUBA colonies and 194.98 µg/cm2 for the VGBA colony. The repellency of IR3535 was weaker and started at a concentration of 389.96 µg/cm2 for the CIPEIN colony, 779.92 μg/cm2 for JUBA, and 1559.84 μg/cm2 for VGBA . Finally, nymphs were exposed to 3:1, 1:1, and 1:3 DEET:IR3535 mixtures, and a synergistic effect was observed only in the CIPEIN colony.

Lyme borreliosis

Lyme borreliosis is a tick-borne disease that predominantly occurs in temperate regions of the northern hemisphere and is primarily caused by the bacterium Borrelia burgdorferi in North America and Borrelia afzelii or Borrelia garinii in Europe and Asia. Infection usually begins with an expanding skin lesion, known as erythema migrans (referred to as stage 1), which, if untreated, can be followed by early disseminated infection, particularly neurological abnormalities (stage 2), and by late infection, especially arthritis in North America or acrodermatitis chronica atrophicans in Europe (stage 3). However, the disease can present with any of these manifestations. During infection, the bacteria migrate through the host tissues, adhere to certain cells and can evade immune clearance. Yet, these organisms are eventually killed by both innate and adaptive immune responses and most inflammatory manifestations of the infection resolve. Except for patients with erythema migrans, Lyme borreliosis is diagnosed based on a characteristic clinical constellation of signs and symptoms with serological confirmation of infection. All manifestations of the infection can usually be treated with appropriate antibiotic regimens, but the disease can be followed by post-infectious sequelae in some patients. Prevention of Lyme borreliosis primarily involves the avoidance of tick bites by personal protective measures.

Evidence for Personal Protective Measures to Reduce Human Contact With Blacklegged Ticks and for Environmentally Based Control Methods to Suppress Host-Seeking Blacklegged Ticks and Reduce Infection with Lyme Disease Spirochetes in Tick Vectors and Rodent Reservoirs

In the 1980s, the blacklegged tick, Ixodes scapularis Say, and rodents were recognized as the principal vector and reservoir hosts of the Lyme disease spirochete Borrelia burgdorferi in the eastern United States, and deer were incriminated as principal hosts for I. scapularis adults. These realizations led to pioneering studies aiming to reduce the risk for transmission of B. burgdorferi to humans by attacking host-seeking ticks with acaricides, interrupting the enzootic transmission cycle by killing immatures infesting rodent reservoirs by means of acaricide-treated nesting material, or reducing deer abundance to suppress tick numbers. We review the progress over the past three decades in the fields of: 1) prevention of human-tick contact with repellents and permethrin-treated clothing, and 2) suppression of I. scapularis and disruption of enzootic B. burgdorferi transmission with environmentally based control methods. Personal protective measures include synthetic and natural product-based repellents that can be applied to skin and clothing, permethrin sprays for clothing and gear, and permethrin-treated clothing. A wide variety of approaches and products to suppress I. scapularis or disrupt enzootic B. burgdorferi transmission have emerged and been evaluated in field trials. Application of synthetic chemical acaricides is a robust method to suppress host-seeking I. scapularis ticks within a treated area for at least 6-8 wk. Natural product-based acaricides or entomopathogenic fungi have emerged as alternatives to kill host-seeking ticks for homeowners who are unwilling to use synthetic chemical acaricides. However, as compared with synthetic chemical acaricides, these approaches appear less robust in terms of both their killing efficacy and persistence. Use of rodent-targeted topical acaricides represents an alternative for homeowners opposed to open distribution of acaricides to the ground and vegetation on their properties. This host-targeted approach also provides the benefit of the intervention impacting the entire rodent home range. Rodent-targeted oral vaccines against B. burgdorferi and a rodent-targeted antibiotic bait have been evaluated in laboratory and field trials but are not yet commercially available. Targeting of deer-via deer reduction or treatment of deer with topical acaricides-can provide area-wide suppression of host-seeking I. scapularis. These two deer-targeted approaches combine great potential for protection that impacts the entire landscape with severe problems relating to public acceptance or implementation logistics. Integrated use of two or more methods has unfortunately been evaluated in very few published studies, but additional field evaluations of integrated tick and pathogen strategies are underway.

Suppression of Amblyomma americanum (Ixodida: Ixodidae) for short-term field operations utilizing cypermethrin and lambda-cyhalothrin

Tick-borne diseases pose significant risks to U.S. military personnel who conduct operations, both domestic and abroad. To determine the feasibility of protecting personnel from tick vectors during short-term field deployments, acaricides cypermethrin (Demon WP, Syngenta, Greensboro, NC) and lambda-cyhalothrin (Surrender Pestabs, CSI, Pasadena, TX) were applied to plots within two separate field sites on Camp Blanding Joint Training Center in Starke, FL, from May to June 2011. We analyzed their effectiveness in reducing tick counts for 6 wk after application. In total, 8,193 ticks were identified and counted, of which > 99% were a mix of nymphs and adult-stage Amblyomma americanum (L.). Our results indicate that both cypermethrin and lambda-cyhalothrin were effective in significantly reducing tick numbers and preventing entry into treated plots for 6 wk after application. Thus, these two acaracides can be used to effectively suppress tick populations and provide residual protection in small geographic areas of recreation or public health significance.