Specialist insects undergoing silent mass extinction

The highly threatened Portuguese dappled white (Euchloe tagis). Image credit, Eduardo Marabuto.Carlos Roberto Fonseca has published an ominous forecast for the fate of specialist insect herbivores (i.e. monophages or those that feed on only one species of plant). According to his calculations, somewhere between 213,830 and 547,500 monophagous insect species are trending towards extinction in biodiversity hotspots. This is obviously a much higher figure than the 70 insect species known to have become extinct globally in modern times.  He has published his findings in the journal Conservation Biology.

Monophage insects are particularly sensitive to extinction risk. As specialist herbivores, they rely on a single plant species for food. If their host plant goes extinct, they have to make a long shot evolutionary leap of adapting to another plant species in order to continue with their own survival.

Fonseca estimated the total number of monophagous insect species in 34 biodiversity hotspots at between 795,971 and 1,602,423 based on previously published calculations on the total number of endemic plant species - 150,371. He estimated likely extinction numbers based on the total geographic area of endemic plants compared to calculations of the total habitat area that has been lost in the hotspots. Based on this model, he found that on average one specialist insect herbivore goes extinct for every 37-94 square kilometers of habitat lost.

Certain hotspots are faring much worse than others. The five regions facing the greatest number of monohpage extinctions are:

1) Sundaland (a biogeographic acrea containing much of Indonesia)

2) The Mediterranean Basin

3) Madagascar and the Indian Islands

4) The Tropical Andes

5) Indo-Burma

One unanswered question is whether this habitat loss is leading to quick extinction or whether it will play out over decades or centuries. According to Fonseca, this will largely depend on the pattern of insect diversity in a given region. In areas in which species are narrowly distributed, extinction will likely proceed much faster. From a conservation perspective the message seems to be that we need to work harder to protect to areas with high levels of endemic plants.

Fonseca concludes:

"The effective protection of monophagous species will only be possible if protected areas provide extensive coverage of the geographic distribution of their endemic plants. Protected areas can provide this only if the conservation value of small, protected areas located between large biological reserves is recognized. The success of insect conservation also lies in the quality of the anthropogenic matrix that dominates most landscapes. There is an opportunity for environmentally conscious citizens to engage in biodiversity conservation by improving habitat quality for insects on private lands."

--Reviewed by Rob Goldstein

  FONSECA, C. (2009). The Silent Mass Extinction of Insect Herbivores in Biodiversity Hotspots Conservation Biology DOI: 10.1111/j.1523-1739.2009.01327.x