Posted 04/01/11

Impact of neo-nicotinoid pesticides on all flying insects and water-invertebrate life in the Netherlands. (new report)

This confirms and extends the work carried out by Henk Tennekes last year which describes the collapse of insectivorous bird populations in the Netherlands in large areas where nicotnoid pesticides have poisoned much of the bird's insect-food, both above the water and in the water.

For the full text and diagrams can be downloaded here

Between 1994 and 1996, beekeepers in France noticed greatly increased mortality in honeybees that foraged sunflowers, and discovered that a new pesticide had been introduced as a sunflower seed treatment in 1994. Seed dressing makes spraying crops with pesticides unnecessary because the active substances are spread to all plant tissues when the plant grows. However, the beekeepers suspected this new pesticide, Gaucho®, the active substance of which is imidacloprid, was toxic for honeybees (Bonmatin et al., 2005; Maxim & Van der Sluijs, 2007, 2010), and several studies have provided supporting evidence for this link (e.g. CST, 2003; Yang et al., 2008; Maini, 2010).

Pesticides have to be authorised prior to being brought onto the market, and this authorisation includes testing to guarantee that the chemicals are not harmful to pollinators, especially honeybees. But the effects and doses used for spraying and seed dressing differ greatly, and the tests do not represent this: most sprayed pesticides work for a few hours to days only, while pesticides applied via seed dressing remain in all parts of the plant throughout its lifetime (Rortais et al., 2005). The result of seed treatment with imidacloprid should be the protection of crops from harmful insects, with imidacloprid disappearing from the plants before pollinator activity starts, but instead, relatively high levels have been observed in flowering heads and pollen, and additionally, residues remain in the soil and surface water (Bonmatin et al., 2005).

The effects of neonicotinoid pesticides on several other non‐target species have also been examined.

Imidacloprid and two other neonicotinoid pesticides, thiamethoxam and thiacloprid, in doses that may be considered safe, can negatively influence foraging behaviour in the bumblebee Bombus terrestris (Mommaerts et al., 2010). Imidacloprid was found to be “generally highly toxic” to the one bumblebee species and two wild bee species tested by Scott‐Dupree et al. (2009). The three species of stingless bees tested by Valdovinos‐Núñez et al. (2009) were also highly vulnerable to nicotinoid pesticides. Spraying with imidacloprid, thiacloprid and methomyl at the recommended doses caused mortality of up to 100% in larvae and adults of three predacious coccinellid species (Katsarou et al., 2009). Using imidacloprid against wood‐boring insects in trees by applying it to the soil can also harm litter‐dwelling earthworms if the concentration in litter and upper soil is about 3 mg/kg or higher, which is well within expected concentrations (Kreutzweiser et al., 2008). All these species are of great importance for nature and for humanity: bumblebees, wild bees and stingless bees are pollinators of wildflowers and economic crops, coccinellids help avert aphid pests, and earthworms are decomposers.

As may be clear from the above, many studies examining the effects of neonicotinoid pesticides on non‐target species have been carried out since their application began in 1994. What has not yet been performed, however, is an assessment of the distribution and abundance of these species in the Netherlands, and a comparison with the doses of pesticides applied, as well as the residues in the surface waters. Such an assessment would give more information on the possible relationship between neonicotinoid pesticide application and species mortality.

There is a correlation between the use of neonicotinoid pesticides, and their residues in soil and surface water, and the distribution of and number of individuals per non‐target species, in the Netherlands: where neonicotinoid pesticides are used, and/or there are significant amounts of residues in the soil and surface water, several non‐target species are less abundant.

Priority list
The ordered priority list (see Appendix II) contains 44 species, of which 18 are also found in the Netherlands (Nederlands Soortenregister, 2010). The list consistently shows that flying insects are the most vulnerable to neonicotinoid pesticides. They appear to be more vulnerable than mirid bugs, mites, spiders, aquatic crustaceans, fish and birds, the categories most other species in the list belong to.

Also, in 23 cases data about lethal doses or concentrations over different time spans are available, and in 21 of these cases, the lethal dose or concentration decreases with time. Generally this decrease amounts to about 50% over 24 hours, but in some cases, the factor is 10 or more. This indicates that as species are exposed to neonicotinoids longer, even very low concentrations will affect them. This phenomenon is toxicologically explained by Tennekes (2010) who showed that neonicotinoids in arthropods follow Haber’s rule, which is characterised by a linear relationship (on logarithmic coordinates) between exposure concentration and median time to effect, i.e. mortality. Biochemically this can be understood from the mode of action of neonicotinoids, which derives from almost complete and virtually irreversible blockage of postsynaptic acetylcholine receptors in the central nervous system of insects (Tennekes, 2010).

The flying insect categories selected for further research, based on the priority list, were: flies, mayflies, caddisflies, parasitoid wasps, wild bees, mosquitoes.