OECD 183. 5 - Assays for testing efficacy of baits against cockroaches (Series on Testing and Assessment No. 183, Series on Biocides No. 5).
Test not accredited in our laboratory.
This laboratory test is intended to assess the efficacy of test substances and/or the effectiveness of test products used as baits for the control of cockroach species in indoor environments.
The baits contain one or more active insecticidal ingredients combined with a food or non-active attractant compound for cockroaches. The active ingredients are toxic with lethal action on all mobile stages, or growth regulators that are active against nymphal stages, so that according to the active components should choose one or other stages to perform the tests. Baits should be attractive and effective even when there are alternative sources of food, and should maintain their insecticidal activity, their consistency and attraction even in damp locations, such as kitchens, toilets or pipes. The OECD 183.5 guidance document applies to all blatticides that are effective as baits. This includes formulations for use in bait stations as well as those applied in the open (e.g. in cracks and crevices).
The following species are candidates for testing in Europe, North America, Australia and Asia due to its public health importance in these regions: Blatella germanica (German cockroach), Blatta orientalis (oriental cockroach), Periplaneta americana (American cockroach), Supella longipalpa (brown cockroach or of bedrooms), or Periplaneta australasie (Australian cockroach, Hawaiian and Southeastern US).
Due to the specificity of baits, only effects against species that have been tested should be claimed (single species claims). In case a general claim is to be made (such as “for use against cockroaches”), usually the two species most prevalent to the region are the minimum to be tested. In Europe, Blattella germanica and Blatta orientalis are the most prevalent species, whereas Periplaneta americana is sometimes used as an example of large cockroaches. Whereas, in North America, Blattella germanica and Periplaneta americana are the most often tested. In our laboratory, the species available are Blatella germánica, Blatta orientalis and Periplaneta americana.
According to the OECD 183.5, for the scientific evaluation of the efficacy of a bait product and of validity of the test results, a minimum of three repetitions of the assay at different times and with different batches of cockroaches should be conducted. The procedure described below includes only one repetition of the test.
Tests can be designed as no-choice test (no alternative food available) or as choice test (alternative food available). No-choice testing is employed to determine if a bait matrix is palatable to cockroaches and to detect repellency to the bait matrix and/or level of active ingredient in the formulation, for screening the amount of active ingredient required to kill cockroaches consuming the bait and detecting behavioral avoidance of a bait type or bait station. Choice testing, in contrast, will give additional insights that are important, but not necessarily evident from no-choice tests; this relates particularly to an evaluation of the attractiveness of test baits in comparison to alternative food sources.
The cockroaches used in the tests are reared in the laboratory, and adults or nymphs from early, middle, or late stages are used. For testing products against adults, the OECD No.183.5 recommends to perform the test with 50 adult specimens (25 males and 25 females for any of the three species); for testing products against adults and late nymphs a mixture of adults and late nymphal stages (40 nymphs, 20 adult males and 20 adult females for Blatella germanica, with slight variations in number for other species), for testing products against early nymphs only, 50 to 100 nymphs (depending on the species chosen).
The test is carried out in test arenas or test chambers designed to caters for the needs of cockroaches as far as size and hiding space is concerned. Prior to the test, test organisms are allowed to habituate in the arenas for three days. The recommended duration of the test depends on the type of the test bait: 3 weeks for classical insecticides, 6-8 weeks for Chitin synthesis inhibitors, and 8 weeks for Juvenoids. A minimum of three replicate groups are dosed with each test concentration. As the improvement in power wears off substantially as the number of replicates increases beyond five, it is usually sufficient to conduct three, four or five replicate tests at each dose level. The bait position is symmetrically changed in the replicates to minimize effects potentially resulting from the variability of lighting conditions. At least two negative (not treated) controls should be included, that are of the same strain and batch as the test insects. The negative controls can equal the bait as close as possible except for not containing the active ingredient if it is sent by the customer. If not, regular feed would be used as negative control. Two replicates of the positive control should be included in each test. This should preferably be a product registered for the intended use and with the same mode of action of the product to be tested, according to the IRAC scheme (IRAC 2010). The customer must provide a commercialized positive control with the test product.
The tests are carried out at a test temperature that depends on the enviromental conditions in which the product is to be used (19ºC to 35-40ºC), for example around 22 ± 3°C in temperate regions, and a relative humidity of 55 ± 10% but, it can be higher for products that are going to be used in wet areas. The test organisms are usually kept at normal periods of light and dark, with a minimum of 8 hours darkness each day, but testing in complete darkness can be carried out to mimic conditions in sewers and/or underground environments.
During the exposure time, dead and moribund cockroaches should be determined and followed up for at least 7 days after the end of the test, providing them with water and normal feeding, to ensure if moribund cockroaches can recover or not. Mortality is evaluated on days 1 and 2 and every 24 hours (for 21 days for test performed with adults), and recorded separately for gender, developmental stage, and location of bodies. In case of knock- down, the potential for recovery should be assessed.
At the end of the test, the mortality rates in the treated and control groups are used to calculate the efficacy of the bait. To consider a bait as effective, a corrected 95% mortality rate in a "non-choice-test" or a corrected 90% mortality rate in a “choice-test” must be obtained.
Variables to be selected by the applicant:
- Concrete species to be used depending on the claim to be made: one species for single species baits, or most prevalent to the region for a general claim.
- Type of insecticide (classic insecticide, juvenoids or chitin synthesis inhibitors).
- "No choice" or "choice" method.
- Phases of insects that are to be used according to the activity of the insecticidal compounds containing the baits (adults, adults and later nymphal stages, only early nymphal stages).
- Test duration (the recommended time according to the OECD-183 are: 3 weeks for classical insecticides, 6-8 weeks for Chitin synthesis inhibitors, and 8 weeks for Juvenoids)
- Environmental conditions of temperature, humidity and photoperiod: for example, for temperate regions: temperature 22 ± 3ºC, relative humidity 55 ± 10%, and normal photoperiod with a minimum of 8 hours of dark each day. The conditions for testing must be specified.
- If the test product is a photosensitive gel bait, it must be notified.
- The customer must indicate if the bait should be replenished during the test if necessary or if the product claims being efficacious using a single dose.