thiamethoxam (ISO); 3-(2-chloro-thiazol-5-ylmethyl)-5-methyl[1,3,5]oxadiazinan-4-ylidene-N-nitroamine

Toxicity to terrestrial arthropods

Description of key information

All studies are included as supporting information and are not considered for the CSA.

Additional information

Additional studies on other terrestrial arthropods (not soil dwelling)

Information on toxicity to bees

In acute exposure experiments under laboratory conditions, the substance was highly toxic to adult honey bees (Apis mellifera L.) following oral or topical application. The observed 48-hour LD50 values were 5 ng/bee for oral and 25 ng/bee for topical application, respectively (Kleiner 1995). These laboratory studies represent the worst-case with regards to bee toxicity of the substance.

Bee larvae (Apis mellifera L.) were exposed via artificial diet to dose levels of the substance ranging from 0.12 to 10.0 µg/larva/day from two to five days after grafting of larvae. Statistically significant effects on the mortality of larvae were observed at all dose levels. The calculated LD50 on day 7 of the study was 0.23 µg/larva/day (Eckert 2015). Thus, larvae were less susceptible to exposure to the substance in this acute toxicity study than adult honey bees.

A range of colony feeding, semi-field and field studies representing a variety of exposure conditions were conducted with the substance to determine the effects to honey bees and their colonies under more realistic conditions, reflecting the use of the substance as an active substance in plant protection products by different application techniques. The results obtained in the studies are consistent with the information presented above. Because the substance is no longer approved as an active substance in plant protection products in the EU, the conditions of use and exposures applied in the colony feeding, semi-field and field studies are not representative of the conditions of use that occur during the industrial manufacture of the substance and its use in the formulation of plant protection products at industrial sites supported in the REACH registration. Consequently, no details on these additional studies are presented in the Lead Dossier.

Information on other terrestrial arthropods

The results obtained from (extended) laboratory tests show that the test item is toxic to a range of arthropods under laboratory conditions; therefore, a large number of additional toxicity studies were performed on terrestrial arthropods under specific conditions to determine the practical significance. This information was considered outside the scope of REACH, hence the studies are not summarized as individual endpoint study entries, but briefly discussed here:

Laboratory tests using species such as predatory bug (Orius laevigatus), predatory beetle (Poecilus cupreus), and predatory Staphylinid beetle (Aleochara bilineata) on substrates such as glass plates, summer wheat seeds, cotton seeds or wheat seeds, predicted a range of 66.7% to 100% mortality and reduced food consumption (Kleiner, 1998a,b; Grimm, 1998a,b; Reber, 1997; Candolfi, 1997; Hargreaves & Stacey, 2005).

Extended laboratory tests using green lacewing (Chrysoperla carnea), predatory bug (Orius laevigatus), predatory staphylinid beetle (Aleochara bilineata), predatory coccinelid beetle (Coccinella septempunctata), parasitoid wasp (Leptomastix dactylopii), lycosid spider (Pardosa spp.), and predatory beetle (Poecilus cupreus) on substrates such as apple leaves, soil, bean leaves, pea seeds and barley seeds predicted LR50 values ranging from 0.014 g a.s./ha to >200 g a.s./ha based on mortality (Schuld, 2000; Kuehner, 1999; Kemmeter, 2000; Eyre, 2000; Brown, 2000; Reber, 2000a,b).

Semi-field tests using predatory beetle (Poecilus cupreus), predatory bug (Orius laevigatus), predatory bug (Macrolophus caliginosus), parasitic wasp (Aphidius rhopalosiphi) and predatory staphylinid beetle (Aleochara bilineata) predicted mortality ranging from 3% to 100% (Moll, 1997; Kuehner, 1998; Balluff, 2000; Aldershof, 1997; Schuld, 2002a,b; Engelhard, 1997; Kuehner, 1999; Candolfi, 1998a,b).

Field tests using predatory mite (Typhlodro-mus pyri), full fauna within a pear orchard (Southern France), full foliar fauna within an orange orchard or full fauna on vines, pear, citrus or grassland meadow predicted decreased population density ranging from 12.5% to 29.6% and mortality ranging from 34% to 94% (Reber, 1998; Brown, 1999; Grimm, 2001; Grimm, 2003; Bakker & Aldershof, 2014a,b).

Furthermore, there are two additional scientific publications, scored as Klimisch 3 due to methodological deficiencies. The published studies investigated the effects of the test material on non-target arthropods: In the first study (Duso, 2014), field and laboratory experiments were conducted to evaluate the effects of the test substance on mites (K. aberrans). Single or multiple applications of the test substance caused no detrimental effects on predatory mites. In laboratory studies, the test item did not affect female survival, but it was associated with a significant reduction in fecundity.

In the second study (Beers, 2005), a series of 20 field trials (54 treatments) was conducted, designed primarily to look at efficacy against the codling moth (Cydia pomonella). Nearly half of the treatments using four or more applications of the test material had peak mite densities exceeding the economic threshold of 5 mites per leaf. The predatory mite populations in the test item treatments were not different from the control.