Teflubenzuron

Toxicity to terrestrial arthropods

Description of key information

Toxicity of the test item was tested in both, an acute oral and contact toxicity test on honey bees according to OECD 213/214. The LD50 (48 h) of the oral toxicity study was > 72 µg a.s./bee (solvent sugar solution). The LD50 (48 h) was > 100 µg a.s./bee in the contact toxicity test.

Additional information

One valid acute oral and contact toxicity test with the test item according to OECD 213 and 214 on honey bees is available.

The presented study was peer-reviewed during the assessment of teflubenzuron according to Council Directive 91/414/EEC.

 

Key information

GAB (2003): BAS 309 I (Technical Teflubenzuron): Acute Toxicity to the Honey Bee, Apis mellifera L. under Laboratory conditions. Unpublished report, report No. 20031160/01 BLEU, according to Draft Assessment Report (2007) according to Council Directive 91/414/EEC, crossreference:  MCA 8.3.1/01

The objective of the study was to determine the effect of the test item on the honey bee (Apis mellifera carnica) from oral and contact exposure according to OECD 213 and 214. The test was carried out for 48 h with one dose (limit test) of the test item, four concentrations of the reference item (dimethoate) and control(s). Bees were exposed to the test item by feeding and topical applica­tion. The tested concentration was 100 µg a.s. per bee in the oral toxicity test and in the contact toxicity test. In the oral toxicity test the bees of one control group received a 50% (w/v) aqueous sucrose solution, the second control group received aqueous sucrose solution mixed with dimethylsulfoxide (DMSO) and the third control group was fed with pure honey mixed with DMSO. In the con­tact toxicity test the bees of the control group were treated with DMSO.

The test was carried out with healthy, young adult worker bees. One day before the start of the test, the bees were collected randomly from the combs of the colony, for both test procedures. In both test procedures (oral and contact) the bees were kept in steel cages (width: 10 cm, depth: 5.5 cm, height: 8.5 cm). The front sides were equipped with a transparent pane and the bottom consisted of a perforated board for air supply. The test cages were lined with filter paper. At each concentration and treatment respectively, five replicate groups containing 10 bees were tested.

For the oral toxicity test, a stock solution was prepared by dissolving the test item in DMSO. For one test item group the final dose was prepared by mixing a definite amount of the stock solution with 50% aqueous sucrose solution such that the intended nominal dose which was calculated for one bee was found in 0.02 mL. For the second test item group the final dose was prepared by mixing a definite amount of stock solution with 10 g pure honey. Per cage a quantity of ~ 225 mg honey-test item mixture was offered. Before the feeding started, the bees starved for 2 hours. A quantity of 0.25 mL (stock solution mixed with aque­ous sugar solution) or 0.12 mL (stock solution with honey) of test item solution was offered for 4-5 hours. The amount of test item solution consumed (mean value of 10 bees) was determined by weighing the feeders before and after feeding. Afterwards, the bees in the test cages were supplied ad libitum with a 50% aqueous sucrose solution without test item

For the contact toxicity test, the test item was dissolved in DMSO and after the bees had been anaesthetised with carbon dioxide they were treated individually by topical application with a micro-applicator. After application the bees were returned to the test cages and fed with a 50% aque­ous sucrose solution ad libitum.

During the experimental phase, the animals were kept under constant darkness except during the assessment. Observations were made under neon light after 4, 24 and 48 h. The average mortality of the five replicates per concentration was calculated after correction for control mortality according to the formula of Schneider-Orelli. The LD₅₀ values within 95% confidence intervals were calculated by means of a probit analysis using the statistic program SAS V8.

The temperature was 23.0 – 25.0°C and the relative humidity was between 56.0 and 65.0%. In the oral toxicity test, the highest nominal test concentration of 100 µg a.s./bee corresponded to an actual intake of 72 µg a.s./bee (dissolved in sugar solu­tion) or 80 µg a.s./bee (dissolved in 10 g honey). At this concentration no mortality was observed after 48 hours. In the contact toxicity test no mortality was observed at the concentration of 100 µg a.s./bee after 48 hours. No mortal­ity was observed in the control groups (oral, contact) until test termination. Regarding the behaviour, no differences could be observed in both test proce­dures between the test item treatment group, compared to the control group. The results are considered to be valid as the mean mortality of the control in the oral and contact toxicity test was ≤ 10% (actual: 0%), the LD₅₀ of the reference item in the oral toxicity test was within the range of 0.1 to 0.35 µg a.s./bee and the LD₅₀ of the reference item in the contact toxicity test was within the range of 0.1 to 0.3 µg a.s./bee.

In the Draft Assessment Report for teflubezuron according to  Council Directive 91/414/EEC (2007) the 48-h LD50 of > 72 µg a.s./bee is indicated as key value for the oral and >100 µg a.s./bee for the contact toxicity of teflubenzuron to honey bees. 

Conclusion

Toxicity of the test item was tested in both, an acute oral and contact toxicity test on honey bees according to OECD 213/214. The LD50 (48 h) was > 72 µg a.s./bee (solvent sugar solution) and > 80 µg a.s./bee (solvent honey) in the oral toxicity test. The LD50 (48 h) was > 100 µg a.s./bee in the contact toxicity test. The 48-h LD50 of is > 72 µg a.s./bee is indicated as key value for the oral toxicity to honey bees and the 48-h LD50 > 100 µg a.s./bee is indicated as key value for the contact toxicity of honey bees. These values are fully in line with the conclusion drawn in the Draft Assessment Report for teflubenzuron prepared according to the Council Directive 91/414/EEC, Volume 3 – B.9 (AS), 2007.