Insecticiden

Imidacloprid was shown to act as both a larvicide and an adulticide in studies on cat fleas. Due to its probable main uptake by the flea through the nonsclerotized intersegmental membranes it rapidly reaches the site of action: the postsynaptic membrane. There, the irreversible blocking of the nACh receptors leads to a lethal hyperactivity of the nerves and muscles of the insect. Both stages are sensitive to the drug, and after contact they react in a similar fashion: they stop their jumping or (respectively) crawling movements and display the onset of rhythmic trembling of the legs and the body. This nonreversible phenomenon finally leads to the death of both flea stages. These easily visible effects correspond to the finding that imidacloprid blocks the postsynaptical nicotinic acetylcholine receptors (Abbink 1991). The latter are normally stimulated by acetylcholine that is excreted into the synaptic gap. These receptors initiate the opening of channels in the membrane to let Na+ flow into the cell. This leads to a depolarization of the terminal plate and induces the activation of an action potential. The latter causes the release of Ca2+ from vesicles and thus results in contraction of the myosin/actin complex of the sarcomeres. In normal cases the acetylcholine has a brief connection to the receptor, is subsequently released, and is rapidly hydrolyzed by a membrane-bound cholinesterase. In the case of imidacloprid the binding of the compound and the receptors is stronger; hence, a constant depolarization of the membrane occurs, inducing a tetanus of the activated muscle cell. This mode of action corresponds to the structural findings described herein, since the observed degeneration mainly involved an overall destruction of the mitochondria, damage to the nerve cells, and disintegration of the muscle, Imidacloprid initiates a constant depolarization of the nerves, which is followed by a constant activation of the muscles until the cellular energy systems (mitochondria, glycogen) are depleted and the motile proteins are destroyed.

Cereal fields are central to balancing food production and environmental health in the face of climate change. Within them, invertebrates provide key ecosystem services. Using 42 years of monitoring data collected in southern England, we investigated the sensitivity and resilience of invertebrates in cereal fields to extreme weather events and examined the effect of long-term changes in temperature, rainfall and pesticide use on invertebrate abundance. Of the 26 invertebrate groups examined, eleven proved sensitive to extreme weather events. Average abundance increased in hot/dry years and decreased in cold/wet years for Araneae, Cicadellidae, adult Heteroptera, Thysanoptera, Braconidae, Enicmus and Lathridiidae. The average abundance of Delphacidae, Cryptophagidae and Mycetophilidae increased in both hot/dry and cold/wet years relative to other years. The abundance of all 10 groups usually returned to their long-term trend within a year after the extreme event. For five of them, sensitivity to cold/wet events was lowest (translating into higher abundances) at locations with a westerly aspect. Some long-term trends in invertebrate abundance correlated with temperature and rainfall, indicating that climate change may affect them. However, pesticide use was more important in explaining the trends, suggesting that reduced pesticide use would mitigate the effects of climate change.

During the growing season, neonicotinoid insecticides are frequently transported to surface water systems after rainfall events. However, detectable levels of neonicotinoids have also been found in wetlands during early spring, after ice-off but before crop seeding, representing an unexpected long-term exposure risk for aquatic organisms. This suggests long-term persistence, though origins and transport mechanisms remain unknown. We sampled 16 agricultural fields in the Canadian Prairies to investigate whether snow meltwater, particulate matter, top- (15 cm) or bottom-layer (15 cm) snow were potential sources of spring neonicotinoid contamination to receiving wetlands. Agricultural fields were selected based on the previous year’s crop: eight canola fields (clothianidin-treated seed) and eight oat fields (un-treated). We further sampled the wetlands draining those same oat and canola fields from ice-off to seeding to assess changes in neonicotinoid concentrations over time. Top-layer snow was below the limit of quantification for both canola and oat fields. Neonicotinoid concentrations (sum of clothianidin and thiamethoxam) were highest in meltwater (canola, mean: 267 ± 72.2 ng L−1; max: 633), but also detected in bottom-layer snow (oat, mean: 36.1 ± 9.18 ng L−1; max: 92.9), and soil particulate matter (canola, mean: 10.2 ± 1.82 μg/kg; max: 17.2). Concentrations in meltwater showed a stronger relationship (R2 = 0.35) with initial concentrations in wetland water than any other source type. Temporary wetland hydrology is largely fed by meltwater thus spring total neonicotinoid concentrations were higher in temporary wetlands than seasonal/semi-permanent wetlands (P = 0.003). Only clothianidin was detected in soil particulate matter samples, including from oat fields not treated the year before, confirming this compound can persist over multiple years under local field conditions. The results of this study suggest that under normal agricultural practices, wetlands in colder climates are likely to be contaminated even before seeding occurs through persistence of neonicotinoids in soil and transport by snowmelt and particulate to surface water during spring runoff.

Like many other area farmers, the Bredeson family in Harvey Township, between Grove City and Litchfield, buys corn and soybeans seeds treated with pesticides. Pesticides are designed to improve crop yields, but they have side effects, and the family has been learning more about these effects from an expert — Mark and Julie Bredeson’s own son, Michael. “He’s kind of on the cutting edge of finding that these pesticides that farmers have been using for many years have become a detrimental thing to not only agriculture but mother nature,” Julie said about Michael’s work. Michael, a 2008 Litchfield High School graduate, is pursuing his Ph.D. at South Dakota State University, where he studies the effects of pesticides on organisms, particularly linked to sunflowers, a common cash crop in South Dakota. In commentary in the Independent Review (see below), Michael writes about pesticides’ effects and the long-term implications for birds, reptiles, mammals, fish and plants. Julie and Michael said they’ve both noticed a reduction in wildlife at and near the family’s Meeker County farm over the years. As he grew older, Michael noticed a decline in good fishing holes, which he attributes to runoff from crop fields. “My life revolved around fishing on all the little lakes. A few of my great fishing spots died off, and that kind of irritated me, of course,” he said. Julie said she’s also witnessed a decline in wildlife since she was a child. “The landscape as far as our wildlife, butterflies and bees, has dramatically changed,” she said. “It’s something we need to think about.”

The first ever Britain-wide assessment of the value of wild flowers as food for pollinators, led by the University of Bristol, shows that decreasing resources mirror the decline of pollinating insects, providing new evidence to support the link between plant and pollinator decline. In recent years, there have been considerable concerns over threats to wild bees and other insect pollinators which are vital to the success of important food crops and wild flowers. Amongst the many pressures facing pollinators, a key factor is likely to be decreasing floral resources in Britain. The study, published today in Nature combines vegetation survey data recorded over the last 80 years with modern day measurements of nectar to provide the most comprehensive assessment ever published. In the study, researchers from the University of Bristol and University of Leeds worked with scientists from the Centre for Ecology and Hydrology and Fera Science Ltd, to find substantial losses to nectar resources in England and Wales between the 1930s and 1970s – a period closely linked with agricultural intensification.

Paul Nothers ist diplomierter Landwirt, passionierter Jäger – und liebt die Natur. Als er vor mehr als 50 Jahren auf den Hof seiner Familie in Orbroich zog, war die Welt noch in Ordnung. „Insekten überall, Wild, Hasen, Rebhühner und Fasane im Überfluss“, erinnert er sich. Singvögel hörte und sah er ständig. Und wenn er eine längere Fahrt im Auto unternahm, musste er danach seine Windschutzscheibe von Insekten säubern. Das ist lange her. Heutzutage gibt es eine Fülle von heimischen Tierarten, die laut Bericht des Bundesumweltministeriums kurz vor dem Aussterben stehen. Für den 82-Jährigen ein triftiger Grund, in seiner Dankesrede zur Verleihung des Bundesverdienstkreuzes (WZ berichtete) an die Gäste aus Verwaltung, Politik, Natur- und Umweltschutz in Krefeld einen dringenden Appell zu richten. Deutschland stehe vor einer ähnlichen Öko-Katastrophe wie die USA in den 60er Jahren, als neue Pestizide auf DDT-Basis und Herbizide wie Agent Orange auf den Markt kamen. Viele dieser tödlichen Gifte sind in den vergangenen Jahrzehnten verboten worden. Neue dafür nachgerückt. Beispielsweise die Neonikotinoide, eine neue Generation von Insektiziden.

Entomologists from Krefeld, Germany performing an inventory of insects have made an alarming discovery: since 1989 the amount of insects in two places in the nature reserve Orbroicher Bruch have fallen by more than three-quarters. The researchers have performed the measurements in exactly the same way as performed in 1989; in the same place, according to the same method and by the same people (reports in German and English attached). "So the data can be reliably compared", the entomologists emphasize. Two Malaise insect traps were placed in a pasture about 50 meters from each other over a period of many months to catch and weigh insects. Whereas in 1989 1.4 kg of insects were captured in this way, now less than 300 grams were recovered. According to the entomologists, this dramatic decline has serious consequences for the ecosystem: all insect-eating animals are threatened with extinction and eco-system services, including pollination, decomposition processes or soil fertility, will come under serious threat. The data from Krefeld are consistent with the Henk Tennekes thesis of 2010 that the widespread use of neonicotinoid insecticides in agriculture will wipe out insects. Tennekes pointed out in his book that two-thirds of ground beetles had disappeared in less than two decades from the Dutch heathland reserve Dwingelderveld.

Der NABU warnt vor einem neuartigen Insektensterben mit bislang unbekannten Folgen in Deutschland. Allein in Nordrhein-Westfalen sei in den vergangenen 15 Jahren die Biomasse der Fluginsekten um bis zu 80 Prozent zurückgegangen (siehe beiliegende Veröffentlichung). Ähnlich alarmierende Entwicklungen befürchten die Naturschützer in weiteren Regionen Deutschlands und fordern, die Ursachen und das Ausmaß des Insektenschwunds bundesweit schnell aufzuklären. „Unsere Beobachtungen in Nordrhein-Westfalen sind beängstigend. Wenn uns die Fluginsekten fehlen, gerät die gesamte Nahrungskette in Gefahr: Blumen und Bäume werden nicht mehr bestäubt und Mauerseglern und Schwalben fehlt die Nahrungsgrundlage“, warnte Josef Tumbrinck, Landesvorsitzender des NABU Nordrhein-Westfalen. Er stellte am heutigen Mittwoch im Umweltausschuss des Bundestages die Untersuchungsergebnisse des Entomologischen Vereins Krefeld vor, mit dem der NABU zusammenarbeitet. Ehrenamtliche hatten zwischen 1989 und 2014 an insgesamt 88 Standorten in Nordrhein-Westfalen fliegende Insekten gesammelt, ihre Arten bestimmt und sie gewogen. „Während wir 1995 noch 1,6 Kilogramm aus den Untersuchungsfallen sammelten, sind wir heute froh, wenn es 300 Gramm sind“, so Tumbrinck. Der Rückgang von bis zu 80 Prozent beträfe unter anderem Schmetterlinge, Bienen und Schwebfliegen.