Butterflies

Populations have fallen by 48 per cent overall with the worst affected species – the white-letter hairstreak – down by 96 per cent. Conservationists say the decline is down to intensive farming practices and fewer wild flowers in the countryside. The survey, carried out for the Department for Environment, Food and Rural Affairs (Defra), examined two classes of butterfly – those that are specific to a particular terrain and those that dwell in the wider countryside, farmland or gardens. Habitat specialists were down 61 per cent, while the latter group fell 41 per cent – an overall drop of almost 50 per cent. The figures do not include migrant species. The survey also found that since 1990, numbers of woodland species have fallen by 51 per cent, reaching a historical low in 2012. Species in severe decline include the brown argus, common blue, gatekeeper, holly blue, and the marbled white.

With most of their prairie habitat sliced and diced by agricultural development, the Dakota skipper (Hesperia dacotae) and Poweshiek skipperling (Oarisma poweshiek) have long been in trouble. The butterflies were put on the Endangered Species List in 2014, and this week, the U.S. Fish and Wildlife Service designated about 46,000 acres of critical habitat for the two species. “That these butterflies have survived at all is because of the good stewardship of some of the region’s landowners,” said USFWS Midwest regional director Tom Melius. “We will continue to work with these and other landowners to ensure the conservation of remnant prairie habitat and these prairie butterflies.” Specifically, the USFWS has designated about 19,900 acres of critical habitat in Minnesota, North Dakota and South Dakota for the threatened Dakota skipper, and about 25,900 acres in 56 units in Iowa, Michigan, Minnesota, North Dakota, South Dakota and Wisconsin for the endangered Poweshiek skipperling. Of the total 33,742 acres of critical habitat, about 12,050 acres is common to both species.

There is growing concern about increased population, regional, and global extinctions of species. A key question is whether extinction rates for one group of organisms are representative of other taxa. We present a comparison at the national scale of population and regional extinctions of birds, butterflies, and vascular plants from Britain in recent decades. Butterflies experienced the greatest net losses, disappearing on average from 13% of their previously occupied 10-kilometer squares. If insects elsewhere in the world are similarly sensitive, the known global extinction rates of vertebrate and plant species have an unrecorded parallel among the invertebrates, strengthening the hypothesis that the natural world is experiencing the sixth major extinction event in its history.

Due to their high numbers of species and their wide range of ecological requirements, butterflies, like birds and vascular plants, are good expressions of the level of biodiversity (that is, the variety of life forms) in our landscapes. Their generally low dispersal capacity, their short life cycle and a high sensitivity and responsiveness to climate conditions also make butterflies good bioindicators of environmental change. In addition, butterflies are emblematic, well known and easy to identify in the field. The European Grassland Butterfly Indicator represents one of the EU biodiversity indicators of the European Environment Agency (EEA). Data for seventeen grassland butterfly species have been used to assess abundance trends between 1990 and 2013. Of those seventeen species, "ten have declined in the EU, three have remained stable and three increased. For one species the trend is uncertain". At the European scale, grassland butterfly abundance has declined by 30% since 1990.

Butterflies including gatekeepers, large skippers, small coppers and small tortoiseshells are in severe decline on agricultural land, while breeding farmland bird populations hit their lowest recorded level in England in 2013, having more than halved since 1970. Breeding farmland birds and butterflies are declining in both the long and short term, while woodland birds and butterflies have also seen numbers fall in past decades. In 2013, breeding woodland birds in England reached their lowest recorded level, more than a quarter (28%) below 1970 levels. Butterfly populations have tumbled by almost a half (48%) since 1990.

The world’s population of creepy crawlies has fallen by nearly half – but that is bad news for us, experts warn. A study published in the journal Science, reveals that the number of slugs, spiders, worms and other invertebrates has fallen by 45 per cent over the past 35 years as the human population has doubled. Experts fear this will harm the planet as creepy crawlies play an important role in pollinating crops, pest control, decomposition and ensuring soil remains packed with nutrients, as well as water filtration. In the UK the number of beetles, butterflies, bees and wasps has fallen by up to 60 per cent. Experts warn that fewer insects would have a huge effect on crop production as up to 75 per are pollinated by insects, amounting to around 10 per cent of the world's food supply. And the cost of pest control without natural predators could be more than £2.6 billion pounds in the United States alone. Scientists fear a drop in the insect population could also spark a decline in birds, which prey on pests that damage crops, and amphibians, which help keep water supplies free from algae. Decreasing invertebrate numbers are also known to compromise food production due to reduced pollination, seed dispersal and insect predation.

Integrated Pest Management (IPM) is a decision making process used to manage pests that relies on many tactics, including cultural and biological control, which are practices that conserve beneficial insects and mites, and when needed, the use of conventional insecticides. However, systemic, soil-applied neonicotinoid insecticides are translocated to pollen and nectar of flowers, often for months, and may reduce survival of flower-feeding beneficial insects. Imidacloprid seed-treated crops (0.05 mg AI (active ingredient) /canola seed and 1.2 mg AI/corn seed) translocate less than 10 ppb to pollen and nectar. However, higher rates of soil-applied imidacloprid are used in nurseries and urban landscapes, such as 300 mg AI/10 L (3 gallon) pot and 69 g AI applied to the soil under a 61 (24 in) cm diam. tree. Translocation of imidacloprid from soil (300 mg AI) to flowers of Asclepias curassavica resulted in 6,030 ppb in 1X and 10,400 ppb in 2X treatments, which are similar to imidacloprid residues found in another plant species we studied. A second imidacloprid soil application 7 months later resulted in 21,000 ppb in 1X and 45,000 ppb in 2X treatments. Consequently, greenhouse/nursery use of imidacloprid applied to flowering plants can result in 793 to 1,368 times higher concentration compared to an imidacloprid seed treatment (7.6 ppb pollen in seed- treated canola), where most research has focused. These higher imidacloprid levels caused significant mortality in both 1X and 2X treatments in 3 lady beetle species, Coleomegilla maculata, Harmonia axyridis, and Hippodamia convergens, but not a fourth species, Coccinella septempunctata. Adult survival were not reduced for monarch, Danaus plexippus and painted lady, Vanessa cardui, butterflies, but larval survival was significantly reduced. The use of the neonicotinoid imidacloprid at greenhouse/nursery rates reduced survival of beneficial insects feeding on pollen and nectar and is incompatible with the principles of IPM.