Overige insecten

An international science body tasked with tracking the ecological health of the planet has announced the findings of its first report. The review warns that the ongoing decline in the number of pollinating insects and animals threatens global crop production. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) was established in 2012, and is roughly modelled on the Intergovernmental Panel on Climate Change (IPCC). The reponse to the pollinator report, announced on 26 February at a meeting in Kuala Lumpur, may be an early sign of whether the body's influence will one day match the IPCC's political and scientific clout. Robert Watson, an environmental scientist at the Tyndall Centre for Climate Change at the University of East Anglia in Norwich, UK, who is vice-chairman of the IPBES, says that he is confident that the assessment will have an impact. The IPBES has 124 member governments, and its pollinator assessment went through two rounds of external peer review. And just as with the IPCC’s climate reports, the assessment was debated word for word, Watson says. “The fact that all governments requested this document really bodes well that they will use the results,” he says. But Dave Goulson, a bee researcher at the University of Sussex in Brighton, UK, says: “I would question whether any practical on-the-ground action to help pollinators will happen as a result of this document. We are in the midst of the sixth global mass-extinction event, and we sit around spending thousands of hours writing documents about biodiversity, but we do not take action to address the fundamental issues that are causing this ecological catastrophe.”

Der Fasan (Phasianus colchicus) ist auf Norddeutschlands Feldern immer seltener zu beobachten. Besonders gravierend sei der Rückgang in den eigentlich fasanenreichen Gebieten wie dem Emsland, sagte Egbert Strauß, der an der Tierärztlichen Hochschule Hannover für die Wildtiererfassung zuständig ist. Dort untersuchen Forscher seit 2011 die Ursachen für den Rückgang von Fasan und Rebhuhn in Niedersachsen, Nordrhein-Westfalen sowie Schleswig-Holstein. Sowohl der Mangel an Insekten als auch die gestiegene Zahl an Raubwild könnten nach Erkenntnissen der Wissenschaftler die Populationen verringert haben. Im Gegensatz zum stark gefährdeten Rebhuhn wird der Fasan noch gejagt.

Consideration of insect-related ecosystem services has largely focussed on terrestrial taxa while those inhabiting freshwater have been neglected. However, freshwater insects are fundamental to processes such as decomposition and nutrient cycling. In Scotland, freshwater ecosystems cover around 2% of the land area with our lochs and rivers containing 90% of the UK’s surface freshwater. Freshwater insects can be extremely abundant and species rich. However, around 25% of freshwater invertebrate species are under threat of extinction worldwide including several Scottish species such as the Northern summer mayfly (Siphlonurus alternatus). A decline or loss of specific species and overall species richness is likely to lead to adverse effects on the delivery of services. The breakdown and decomposition of organic matter in freshwater systems is strongly dependent on specific insect groups and their abundance. Their feeding activities therefore contribute to nutrient flows and cycling. Filter-feeders such as blackflies (Diptera) improve water quality by removing microscopic particles, such as cellular algae. Net-spinning caddisfly larvae contribute to the stability of fine-gravel due to the binding of grains by silk strands. Burrowing species aerate and rework sediments further influencing biogeochemical processes. Contribution to the diets of fish is arguably the most economically important ecosystem service provided by freshwater insects and around two-thirds of their predators are fish species. However, they are important prey for a wide range of other invertebrates, reptiles, amphibians, mammals (e.g. bats) and birds. Freshwater insects also contribute to the survival of species higher up the food chain. For example, to fish-eating otters. The adult stages of many freshwater insects, particularly damselflies and dragonflies, consume vast quantities of midges and mosquitoes that are otherwise a nuisance to humans. Hoverflies with aquatic larvae (e.g. Eristalis species) are important pollinators. In the absence of freshwater insects, few other service providers could replicate the same level and degree of service. The most serious consequences for freshwater habitats would be a build-up of organic matter or a decline in fish size or populations with repercussions further up the food chain.

The Dwingelderveld national park is an area of nature of about 3766 ha in size. It consists of a large area of wet heath land (about 1600 ha), dry heath land and drift sands, pine, mixed and deciduous forest and some small parcels of grass- and farmland. In 1991, Sjouke van Essen completed an area covering inventory on ground beetles in the Dwingelderveld National Park. Seventeen year later, in 2008, this research was repeated in exactly the same way. Throughout the entire Dwingelderveld, especially at the areas with heather, 38 series of 5 pitfall traps were dug in, using 4% formalin-solution as a conservative. At two new locations, in an abandoned arable field, two series of pitfall traps were placed as well. These traps operated from March till October 2008. Also data collected from 3 permanent catching sites at the Dwingelderveld were incorporated. These permanent sites are already in use since the early sixties. The catching effort at the permanent sites consisted of two normal 25x25 cm can traps and one funnel trap of the same size but with a tube of formalin at the end of the funnel. Window traps were used to capture any flying ground beetles and other insects. During the above mentioned period, all ground beetles caught were determined to the level of species. For other many groups of invertebrates volunteers were found to do the same: these groups were spiders, ants, bees, bumblebees, ichneumon wasps, centipedes, millipedes, woodlice, earwigs, pseudo scorpions, different beetle species other than ground beetles, heteroptera and grasshoppers. The main research question was whether or not there had been any change in species composition and/or changes in numbers of individuals per species since 1991, 17 years ago. In 2008, 15.000 specimens distributed over 78 ground beetle species were collected. In 1991 these numbers were much higher, mounting up to almost 45.000 individuals covering 94 species.

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.

The results show that, in the same two areas, sampled in the years 1989 and 2013, there was a dramatic fall in the number of flying insects. Using the same traps, in the same areas, significant reductions of insect populations, of more than 75%, were found. Our data confirms, that in the areas studied, less than 25% of the original number of flying insects collected in 1989, were still present in 2013.

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.