Etude sur le produit commercialisé sous le nom de Mosi-guard

Journal of the American Mosquito Control Association, 12(2):329-33O, 1996 Copyright © 1996 by the American Mosquito Control Association, Inc.

EVALUATION OF A EUCALYPTUS-BASED REPELLENT AGAINST CULICOIDES IMPUNCTATUS (DIPTERA: CERATOPOGONIDAE) IN SCOTLAND

J. K. TR1GG

ABSTRACT. A eucalyptus-based insect repellent (PMD) was evaluated against Culicoides impunctatus in Scotland in comparison with deet. In human landing catches, both repellents still afforded 98% pro­tection from biting 8 h after application of 0.5 ml to the forearm. A second trial looking at protection between 8 and 10 h after repellent application showed 99.5% protection for PMD and 97% for deet as compared with controls.

In a preliminary laboratory evaluation (Trigg and Hill 1996) a new eucalyptus-based insect repellent (PMD) with principal active ingredient /?-menthane-3.8-diol was reported to give com­plete protection from the biting midge. Culicoi­des variipennis Coquillett, for up to 6 h after an application of 0.032 ml to a 90-cm^: area of the forearm. In a laboratory trial with the malaria vector Anopheles gambiae Giles, PMD was found to be almost as effective as a repellent formulation containing deet (diethyl methyl benzamide). In this paper, a field comparison be­tween PMD and deet against the Scottish biting midge. Culicoides impunctatus Goetghebuer is reported.

The trial was undertaken in July 1994 on the Ormsary Estate, Argyllshire. Scotland (56°N, 5°W). The area is dominated by damp, acidic, peat-based soil, rushes (Juncus acutilflorus and /. articulatus), grass (Molinia caerulea), and moss (Sphagnum spp.). providing ideal breeding conditions for several species of Culicoides, though notably C. impunctatus (Blackwell et al. 1994).

A comparison was made between a spray for­mulation of PMD (50% AI. MASTA. London. United Kingdom) and a spray formulation of Autan® (20% deet, Bayer AG, Leverkusen. Ger­many), when applied to the forearms of 3 human subjects. Repellent was applied to one arm only, at a dose of 0.5 ml delivered from a micropipette and spread evenly from elbow to fingertips. The dose was chosen by team members as a realistic amount as used in practice. Earlier laboratory trials (Trigg and Hill 1996) had suggested that the repellent would give at least 5 h of protec­tion from midge biting: therefore, the dose was applied and left untouched on the arm 5 h before the start of the biting catch. On any one day, one subject applied PMD. one applied deet, and one remained an untreated control, with the treat­ments being rotated daily over a 3-day period.

Arms were exposed to midges hourly over a period of 3 h. Due to very high numbers of midges in the area the exposure time was limited to 10 min in each hour as longer periods of ex­posure would have resulted in unnecessary suf­fering by the subjects involved. Subjects stood spaced at least 3 m apart with their test arm ex­posed but all other skin surfaces covered. The test arm was observed closely over the 10-min period and all midges that were biting were col­lected using an aspirator and blown into a tube of alcohol to be counted and identified later. Midge biting behavior is influenced by factors such as light intensity, wind, and temperature. To maintain uniform control biting levels, we found it necessary to use 2 sites throughout the course of each catch. Early evening tests were conducted in a wood; later evening tests were conducted outside the laboratory with a carbon dioxide supply switched on to attract midges, with subjects standing approximately 1.5 m from the supply.

The results of the 3-day trial showed that PMD and deet gave complete protection for 6-7 h. and by the end of 8 h protection remained high, at 98'%-. An additional 3-day trial was con­ducted, this time applying repellents 8 h before the start of collections and continuing until 10 h after repellent application.

Both deet and PMD showed strong repellency for up to 10 h against C. impunctatus (Table 1) with no apparent difference between them. Al­though complete repellency was lost, protection afford for up to 8 h after application was on average 98% for both repellents. In the addition­al trial to assess the repellent 8-10 h after ap­plication protection remained high, at 99.5% for PMD and 97% for deet.

The present study and laboratory investiga­tions (Trigg and Hill 1996) have demonstrated that PMD is an effective midge repellent. The high level of protection is very encouraging, as

The day on which each test was done is shown in parenthèses.

in many parts of the world (including the west of Scotland) Culicoides spp. constitute a major seasonal biting nuisance resulting in severe dis-ruption to outdoor activities (e.g., forestry and tourism). That PMD gave as high a level of pro­tection as deet is also encouraging. The majority of commercially available repellents contain deet. but there are disadvantages associated with its usage, which stem from its activity as a sol-vent of paints, varnishes, and some plastics and synthetic fabrics. Unlike deet, PMD does not possess these undesirable solvent properties. Further trials conducted against anopheline mos-quitoes in Tanzania (Trigg 1996) hâve also dem-onstrated PMD to be comparable to deet in terms of efficacy and longevity. These studies suggest that PMD is an effective alternative to deet and will be important in the armory of per-sonal protection against biting insects.

My thanks to Fiona King and Sheona Drum-mond for their enthusiastic participation in the biting catches. I am also grateful to Alison Blackwell for her support and provision of field equipment.

REFERENCES CITED

Blackwell, A., M. R. Young and W. Mordue. 1994. The microhabitat of Culicoides impunctatus (Dip- tera: Ceratopogonidae) larvae in Scotland. Bull. En- tomol. Res. 84:295-301.

Trigg, J. K. 1996. Evaluation of a eucalyptus-based repellent against Anopheles spp. in Tanzania. J. Am. Mosq. Control Assoc. 12:243-246.

Trigg, J. K. and N. Hill. 1996. Laboratory évaluation of a eucalyptus-based repellent against four biting arthropods. Phytother. Res. (in press).