Libellen

Little is really known about the total numbers of insect species our planet holds and it is estimated that only between 10 and 20 per cent of insect and invertebrate species have been classified and named. We may well ask ourselves as to why the world’s insect population is declining with some species facing extinction?

Our mechanistic understanding of the toxicity of chemicals that target biochemical and/or physiological pathways, such as pesticides and medical drugs is that they do so by binding to specific molecules. The nature of the latter molecules (e.g., enzymes, receptors, DNA, proteins, etc.) and the strength of the binding to such chemicals elicit a toxic effect in organisms, which magnitude depends on the doses exposed in a given timeframe.

The May 2019 newsletter of the Saitama Ecosystem Conservation Society describes how, before the introduction of neonicotinoids in the 1990s, numberless brilliant red akiakane or autumn darter dragonflies could be seen around rice fields in the fall. Experiments by Japanese dragonfly expert Tetsuyuki Ueda of Ishikawa Prefectural University showed how the pesticides reduced the number of surviving dragonfly nymphs to a small fraction, and that the chemicals persist for years in the soil of rice paddy fields.

Several reports suggested that rice seedling nursery-box application of some systemic insecticides (neonicotinoids and fipronil) is the cause of the decline in dragonfly species noted since the 1990s in Japan. We conducted paddy mesocosm experiments to investigate the effect of the systemic insecticides clothianidin, fipronil and chlorantraniliprole on rice paddy field biological communities.

Damselfly populations are being harmed by insecticides as researchers find the wildlife scourge of neonicotinoids continues to grow. Some chemicals in this group have already been banned by the EU but thiacloprid is still in widespread use. Similar chemicals in the neonicotinoid family have already been tied to severe decline in bee populations and now it appears the damage is more widespread.

Experts from Suffolk Wildlife Trust, Buglife and the RSPB have all pointed to species in danger of disappearing from East Anglia. They include stone curlew - only 202 pairs nested in the East of England last year; the shrill carder bee - common in the region 25 years ago but now found only in the Thames Gateway area; and the crested cow-wheat - a plant limited to a small number of roadside verges because grassland has disappeared to farming or construction. Indeed, habitat destruction and human disturbance are cited as the two most common reasons these species are on the brink.