Research published on 11th February by Sánchez-BayoaKris & Wyckhuys (2019) in the scientific journal Biological Conservation have shown a devastating decline in the numbers of insects worldwide with up to 40% of insect species threatened with extinction. The highest rates of decline are in Lepidoptera (butterflies and moths), Hymenoptera (ants, bees and wasps) and Coleptera (beetles, especially dung beetles). In addition, a number of aquatic species groups are also threatened including mayflies, damselflies and dragonflies. The main causes of these species declines appear to be due to habitat loss and conversion to intensive agriculture; urbanisation; pollution (mainly agricultural pesticides and fertilizers) and climate change. The exact implications of these declines are not fully understood, but are likely to have repercussions through the food chain and affect species which rely on these species as a food source.
The majority of amphibian species rely on insects and other invertebrates as their main food source. A decline in the number of insect species available may have devastating impacts on amphibian species worldwide. With 43% of amphibian species experiencing population declines and 32% globally threatened with extinction (AmbhibiaWeb, 2019; Stuart et al., 2004), additional stresses could trigger further declines. Although the effects on amphibian species may vary by location and habitat, species which are specialists on the insects that are in highest decline are most likely to be worst affected. For example, Brachycephalus is a genus comprising 36 species of frog which inhabit the forest floor in the Atlantic Forest, Brazil. They are specialist feeders on ants and mites, a group identified as fastest in decline (Figure 1). Many of these species are threatened as they occupy small patches of habitat in isolated mountain regions that are under threat from habitat loss and deforestation for agriculture (e.g. Bornschein et al., 2016). These species would be highly vulnerable to a loss in insect diversity and abundance which may trigger population declines.
The loss of aquatic invertebrates is likely to affect amphibians which rely on these species whilst as larvae. Salamanders, including newts such as Triturus cristatus (great crested newt), Ichthyosaura alpestris (alpine newt) and Lissotriton species (e.g. smooth newt) all rely on small aquatic invertebrates such as mayfly and damselfly nymphs. A loss in diversity and abundance of these species in aquatic habitats may have detrimental impacts on developing larvae and adult newts. In addition, species of frog which are highly aquatic such as Oriental skittering frogs (Euphlyctis cyanophlyctis) of India rely completely on aquatic insects through their whole lifecycle.
The loss insect biodiversity worldwide is worrying and may have far-reaching impacts on a multitude of species groups from birds to reptiles and amphibians. The implications on food webs and eco-system function is not fully understood but highlights that we need to take action to halt habitat loss, intensification of agriculture and pollutants if we are to reverse declines in these species.
AmphibiaWeb. 2019. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 11 Feb 2019.
Bornschein, M. R., Ribeiro, L. F., Blackburn, D. C., Stanley, E. L. & Pie, M. R. (2016) A new species of Brachycephalus (Anura: Brachycephalidae) from Santa Catarina, southern Brazil. PeerJ, 4: e2629; DOI 10.7717/peerj.2629.
Sánchez-Bayo, K. & Wyckhuys, K. A. G. (2019) Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232: 8-27.
Stuart, S., Chanson, J. S., Cox, N. A., Young, B. E., Rodrigues, A. S. L., Fishman, D. L. and Waller, R. W. (2004) Status and trends of amphibian declines and extinctions worldwide. Science, 306: 1783-1786.