Donald R. Barnard

Laboratory Evaluation of Mosquito Repellents Against Aedes albopictus, Culex nigripalpus, and Ochlerotatus triseriatus (Diptera: Culicidae)

Abstract Four synthetic mosquito repellents (Autan [10% KBR3023], IR3535 [7.5%], Off! [15% deet], Skinsations [7% deet]) and eight natural (primarily plant extracts and/or essential oils) product-based repellents (Bite Blocker [2% soybean oil], ByGone, GonE!, Natrapel [10% citronella], Neem Aura, Sunswat, MosquitoSafe [25% geraniol], and Repel [26% p-menthane-3,8-diol]) were tested in the laboratory against Aedes albopictus Skuse, Culex nigripalpus Theobald, and Ochlerotatus triseriatus (Say). When estimated mean protection time (eMPT) responses for each repellent were averaged for all three mosquito species, Autan, Bite Blocker, Off!, and Repel prevented biting for ≥7.2 h; IR3535, MosquitoSafe, and Skinsations for 3.2–4.8 h; and ByGone, Natrapel, GonE, NeemAura, and SunSwat for 0.9–2.3 h. Against Ae. albopictus, the eMPT for Off! and Repel exceeded 7.0 h and ranged from 5.0 to 5.7 h for Autan, Bite Blocker, and Skinsations. Bygone, GonE, NeemAura, and SunSwat provided 0.2 h protection against Ae. albopictus and Oc. triseriatus, whereas Autan, Bite Blocker, Off!, and Repel prevented bites by Oc. triseriatus for ≥7.3 h. All 12 repellents provided an eMPT ≥2.8 h against Cx. nigripalpus (maximum: 8.5 h for Bite Blocker). When the average eMPT for each repellent (for all species) was divided by the eMPT for 7% deet (Skinsations), the order of repellent effectiveness and the corresponding repellency index (Ri) was Repel (1.7) > Bite Blocker (1.5) = Autan (1.5) = Off! (1.5) > Skinsations (1.0) > IR3535 (0.8) > MosquitoSafe (0.6) > Natrapel (0.5) > Neem Aura (0.3) = SunSwat (0.3) = Bygone (0.3) > GonE (0.2).

Synergistic Attraction of Aedes aegypti (L.) to Binary Blends of L-Lactic Acid and Acetone, Dichloromethane, or Dimethyl Disulfide

Abstract Kairomones produced by humans provide female anthropophilic mosquitoes with vital cues used in host-seeking for a blood meal. These chemicals are emanated primarily by the skin and provide the mosquitoes a means to orient themselves to humans at a relatively close range. Chemical studies of these emanations have provided new ideas for the formulation of attractant blends. We report mosquito attraction responses for three binary blends and their separate components. The blends are comprised of L-lactic acid plus either acetone, dichloromethane, or dimethyl disulfide. At the emission rates used in our bioassays, these blends synergistically attract laboratory-reared female Aedes aegypti. Carbon dioxide is not a necessary component to yield high levels of attraction with these blends. It is postulated that at least one of these synergistic blends (L-lactic acid and acetone) produces mosquito attraction behavior similar to L-lactic acid and CO2.

Mosquito density, biting rate and cage size effects on repellent tests.

Mosquito biting rates and the mean duration of protection (in hours) from bites (MDPB) of Aedes aegypti and Anopheles quadrimaculatus, using the repellent ‘deet’ (N,N‐diethyl‐3‐methylbenzamide) on a 50 cm2 area of healthy human skin, were observed in small (27 l), medium (≈65 l) and large (125 l) cages containing low, medium or high densities of mosquitoes: respectively, 640, 128 or 49 cm3 of cage volume per female. At the initial treatment rate of ≈ 0.4 μl/cm2 (1 ml of 25% deet in ethanol on 650 cm2 of skin), the MDPB for deet against Ae.aegypti ranged from 4.5 to 6.5 h and was significantly less (5.0 ± 0.8 h) in large cages compared with medium (6.2 ± 0.9 h) and small (6.2 ± 0.8 h) cages, regardless of the density. Against An.quadrimaculatus the MDPB for deet 0.4 μl/cm2 was 1.5–8.0 h, less in small (3.7 ± 2.3 h) and large (2.2 ± 1.1 h) cages at medium (3.7 ± 2.3 h) and high (2.5 ± 1.7 h) mosquito densities, and was longest in medium cages (6.2 ± 2.6 h) at low mosquito densities (5.8 ± 2.8 h). With equinoxial photoperiodicity (light on 06.00–18.00 hours) the biting rate was influenced by the time of observation (08.00, 12.00, 16.00 hours) for Ae.aegypti but not for An.quadrimaculatus. For both species, the biting rate was inversely proportional to mosquito density and the MDPB. The shortest MDPBs were obtained in large cages with high densities of mosquitoes and longest protection times occurred in medium sized cages with low mosquito densities.

APPLICATION OF BORIC ACID BAITS TO PLANT FOLIAGE FOR ADULT MOSQUITO CONTROL

ABSTRACT Boric acid (1%) in 5% sugar water bait solution was applied as a spray to the foliage, stems, and other surfaces of plants for control of adult Aedes albopictus, Culex nigripalpus, and Ochlerotatus taeniorhynchus. Initial studies outdoors in small (1.42-m3) screened cages showed that exposure of male and female mosquitoes to 1% boric acid bait for 48 h resulted in 80 to 100% mortality in Ae. albopictus and ≥98% mortality in Cx. nigripalpus and Oc. taeniorhynchus. At 48 h posttreatment, in large (1,178-m3) outdoor screened cages, 1% boric acid bait applied as a spray to plant surfaces significantly reduced the landing rates of Ae. albopictus and Cx. nigripalpus on a human subject as well as the numbers of these two species captured in mechanical traps, compared with responses for adults exposed to 5% sugar water solution only (control). Boric acid bait treatments in large screened cages did not significantly reduce landing rates or trap captures of Oc. taeniorhynchus. The application of boric acid baits to plant surfaces may be an effective adulticidal method for selected species of pest and disease vector mosquitoes.

BIOLOGICAL ASSAY METHODS FOR MOSQUITO REPELLENTS

ABSTRACT Three biological assay procedures for repellents are currently documented in the literature: 1) ASTM E951-94, Laboratory testing of non-commercial repellent formulations on the skin. 2) ASTM E939-94, Field testing topical applications of compounds as repellents for medically important and pest arthropods. 1. Mosquitoes. 3) WHO/CTD/WHOPES/IC/96.1, Report of WHOPES informal consultation on the evaluation and testing of insecticides. One public draft set of repellent-testing guidelines is available on the internet: 4) USEPA OPPTS 810.3700, Product performance test guidelines. Insect repellents for human skin and outdoor premises. In practice, the outcome of a repellent bioassay using any of these procedures is affected by the absorption, penetration, and chemical modification of repellent on skin and by evaporation, abrasion, and perspiration. Other abiotic factors that influence mosquito responses to repellent stimuli are light, temperature, humidity, repellent dose, exposure time, and test-cage shape and size. Biotic variables in repellent bioassays are larval nutrition, carbohydrate availability for adult mosquitoes, age and parity of females, and differences in the innate attraction/repellency of test subjects. Geographic location and seasonal and diel activity cycles in mosquitoes determine when and where repellents can be tested in the field. Critical knowledge of these sources of variation can be converted to improved precision and accuracy in repellent bioassays and the resulting information used to efficiently select new repellent compounds for toxicological evaluation and field testing.

Effects of Body Size and Nutritional Regimen on Survival in Adult Aedes albopictus (Diptera: Culicidae)

ABSTRACT The effects of adult body size and nutritional regimen on the mean lethal time (LT) to death for the 50th (LT50) and 90th centiles (LT90) of large and small male and female Aedes albopictus (Skuse) were determined in the laboratory. The estimated LT50 and the LT90 for large/small females were significantly shorter for test populations receiving water (5.1/3.8 d) or water + blood (6.7/5.0 d) than for those receiving sucrose (44.4/31.7 d) or sucrose + blood (41.4/29.2 d). The estimated LT50 and LT90 for large/small males receiving water (respectively: 3.2/2.5 d and 4.8/3.8 d) were significantly shorter than for those receiving sucrose (respectively: 18.8/15.9 d and 34.9/32.6 d). The availability of sucrose to adult mosquitoes extended the maximum life span of large and small male and female Ae. albopictus by 6–8× when compared with the availability of water or water + blood. Results indicate that sugar availability is more important than blood as a nutritional parameter for survival and longevity of Ae. albopictus in the laboratory.

LABORATORY COMPARISON OF AEDES AEGYPTI ATTRACTION TO HUMAN ODORS AND TO SYNTHETIC HUMAN ODOR COMPOUNDS AND BLENDS1

ABSTRACT Chemical lures can enhance the ability of traps to collect mosquitoes, selectively target species for capture, and provide a realistic assessment of the species and host-equivalent numbers of mosquitoes present in the local area. One approach to the development of chemical lures is to manufacture blends that comprise odors released in human emanations. These blends need to be safe for use in the environment, desirable from an economic standpoint, and transportable to the field for use in traps. In this report, we compared the attraction of mosquitoes to various chemicals, blends, and odors from humans. Noncompetitive (single-treatment) bioassays established that some blends are equivalent or more attractive to Aedes aegypti than human odors. Competitive bioassays were conducted; these involved simultaneous comparison of 2 treatments: single compounds to binary blends; binary blends to a trinary blend of L-lactic acid, acetone, and dimethyl disulfide; and the trinary blend to human odors from 3 volunteers. The overall trend was that the trinary blend was more attractive than binary blends, and binary blends were more attractive than single compounds. However, human odors were still significantly more attractive than the trinary blend. Therefore, further modifications and refinements to blends will be needed to better compete against human odors.

Field Evaluation of Boric Acid- and Fipronil-Based Bait Stations Against Adult Mosquitoes

ABSTRACT The effectiveness of boric acid (1%) and fipronil (0.1%) bait stations in reducing the number of laboratory-reared female Aedes aegypti and Ochlerotatus taeniorhynchus mosquitoes released in outdoor screened cages was evaluated. Both toxicants significantly reduced landing rates of the 2 mosquito species on a human subject. However, no significant reduction in the number of adult mosquitoes caught by counterflow geometry (CFG) traps baited with CO2 was observed in the boric acid– and fipronil-treated cages compared with control cage. The 2 bait stations were further evaluated against natural populations of adult mosquitoes in 3 residential yards (each ca. 0.8 ha) in St. Johns County, FL. Both bait stations failed to significantly reduce counts of female mosquitoes landing on a human subject; and the capture rates of adult mosquitoes by CFG traps baited with dry ice in bait-treated and control experimental yards were not significantly different. Further field research is needed on the density and placement of bait stations in order to determine their utility in adult mosquito control programs.

Effect of Application Rate and Persistence of Boric Acid Sugar Baits Applied to Plants for Control of Aedes albopictus

Abstract The use of toxic bait to kill adult Aedes albopictus is a safe and potentially effective alternative to the use of synthetic chemical insecticides. This study was carried out to determine effective concentrations of boric acid needed in sugar bait solutions applied to plant surfaces, and to determine its residual effect in reducing adult mosquito densities. In outdoor tests in 1,100-m3 screened enclosures, landing rates of Ae. albopictus on a human subject and the number of female mosquitoes in mechanical traps were significantly reduced by a 1% boric acid bait compared with the other tested concentrations (0.25%, 0.50%, and 0.75%) and untreated control. Studies of the duration of boric acid activity on plant surfaces were made in 1.4-m3 cages in the laboratory and outdoors in 78-m3 screened enclosures. In the laboratory tests, 1% boric acid bait resulted in >96% mortality in male and female Ae. albopictus for 14 days, whereas in outdoor tests, mosquito landing rates in the treated enclosures were significantly lower than in the control enclosures for 7 days. Also, mosquito mortality responses to boric acid baits between plants with flowers and nonflowers (1.4-m3 cages in the laboratory) were not significantly different. The results of this study suggest that boric acid baits applied to plant surfaces may provide specific data related to the development of an effective point-source–based adjunct/alternative to the use of conventional adulticides for mosquito control.

Volatile compounds from the integument of White Leghorn Chickens (Gallus gallus domesticus L.): Candidate attractants of ornithophilic mosquito species*

Candidate kairomones of ornithophilic mosquito species are reported from GC/MS analysis of compounds from the skin on the back, the feet, and feathers from the back of White Leghorn chickens (Gallus gallus domesticus). Hexane and ether extracts of chicken feathers differ significantly in attractiveness of Culex spp. mosquitoes. The active (hexane) extracts contained an abundance of alcohols, ketones, and diones. The inactive (ether) extracts contained aldehydes, which also were in the hexane extracts. Analysis of hexane extracts from chicken feet, skin, and feathers demonstrated the qualitative similarity in the compounds collected with subtle differences observed in the quantitative amounts of these compounds. Aldehydes and carboxylic acids were detected in a concentrated ether extract of feathers in quantitatively similar ratios within each compound class for the corresponding series of C(6)-C(9 )aldehydes and acids.