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BG-Cage test

In 2005, Biogents modified and improved the conventional Arm-in-Cage test procedure that was based on a guideline published by the American Environmental Protection Agency (EPA). The BG-Cage test is suited for the evaluation of topical repellents (cremes, lotions, and spray formulations) and impregnated textiles.
Compared to conventional cages, the new BG-Cages are smaller, provided with a test window in the floor of the cage, and can be connected to an air ventilation system.

These modifications offer certain advantages

  • The treated forearm is not introduced into the cage through a sleeved opening, but exposed at the test window. Uneven abrasion of test substances and resulting contaminations of the gauze sleeve are therefore avoided. Test mosquitoes are not constantly exposed to the active substances, and thus a rapid exhaustion or increased tolerance can be excluded.
  • The test window creates a well defined and comparable test area.
  • The air ventilation system provides clean and conditioned air to the cages, thereby preventing an accumulation of active substances and host odors. In this way, mosquitoes are more likely to show a high biting activity throughout the test day.
  • BG-Cages work with 30 mosquitoes instead of 200. Density-related stress is avoided, and the test situation is much more comfortable for the volunteers.

Procedure

Test cages with a size of 41 x 41 x 16 cm are filled with 30 host-seeking mosquito females. Test products are applied to a 100 cm² rectangular area on the forearms of the volunteers, and exposed to the caged population every 30 minutes. Tests are performed for up to eight hours post-application or until repellency fails.

A comparison of the BG-Cage test and conventional Arm-in-Cage tests using a standard repellent and including four volunteers showed that protection times obtained in BG-Cages could be better related to field data, whereas repellency failed significantly earlier in the conventional set-up (Obermayr et al., 2010).

Criteria

The efficacy of a repellent formulation is usually compared to a reference substance, and evaluated according to the following criteria:

  • estimation of complete protection time (CPT): time between repellent application and the first confirmed bite (one bite followed by another one within the same test or within the consecutive test after 30 min)
  • the time until two or more bites occur on the treated arm (according to ECHA Transitional Guidance on PT18 + PT19).

Other protocols suggest using the first event (e.g., landing or probing, EPA Product Performance Test Guidelines, OPPTS 810.3700: Insect Repellents to be Applied to Human Skin / WHO Guidelines for Efficacy Testing of Mosquito Repellents for Human Skin).

For product registration, we recommend the use of five to ten volunteers and test mosquitoes from three different genera (Aedes, Culex, Anopheles). During product development, tests with two to three volunteers and one or two species will suffice.