How insects cope with adverse conditions

Updated Monday 3rd September 2012

2012 has seen unusual and adverse weather conditions for insects—how will that effect their population?

The year 2012 has seen some very unusual weather and we have yet to find out what the effects on insect populations have been. 

Copyrighted image Icon Copyright: David Robinson Metrioptera, a UK bush cricket Saving Species, a series on BBC Radio 4, will be looking at the effects of the adverse weather on a range of species. One group of insects has some interesting adaptations that help populations to survive unpredictable conditions—bush crickets.

So how different has 2012 been? Here are some statistics from the UK Met Office.

Month Rainfall Temperature
March driest since 1953 2.5 °C above average temperature for the month
April wettest April on record 0.6 °C below average and coldest April since 1989
May average rain fall 0.5 °C above average, but first three weeks cool and last week warm
June equal wettest with 1860 since 1766 0.3 °C above average but dullest June since 1929
July twice average rainfall 1.0 °C below average and coolest July since 2000

There are only 14 species of bush cricket that occur naturally in the UK and they are generally seen only in the summer months, overwintering in the egg stage.

Nymph of a cone-head, Conocephalus Copyrighted image Icon Copyright: David Robinson A recently hatched nymph of a cone-head, taken on 23rd July Normally we find the first eggs hatching around the second week of May, although in certain areas they have been observed in late April.

This year our first observations at our field sites were in June, almost 5 weeks later than normal and newly hatched bush crickets were still being spotted in late July, when we photographed this recently hatched nymph of a cone-head (Conocephalus).

Female bush crickets lay their eggs between August and early November and the eggs overwinter, to hatch the following year. Development within the egg is dependant on temperature and, as the temperature drops with the onset of winter, development is suspended until the temperature warms again.

The point in the year at which an egg is laid influences development. Eggs laid early in the year almost complete their development, but then go into suspended development—called diapause—until the spring. A short period of development occurs before hatching.

Eggs laid late in the year have only a short period for development of the embryo before cold temperatures produce diapause. When spring comes, development is resumed, but it may not be completed in that year and a second diapause occurs over the next winter, with final hatching in the second year after laying.

So, eggs laid by a female early in her life may hatch in one year and eggs laid late in her life may hatch in two years. As a result, the population as a whole is more resilient and the female has spread her reproductive output across more than one season, giving her a better chance of at least some of her offspring surviving should conditions be especially bad in one particular year.

Not all species are the same and they are broadly divided into those that have an annual cycle, those that have an annual cycle but some eggs hatch after two or even three years and a third group which have a two-year cycle with the possibility of up to eight years delay in hatching.

Day length is known to influence development, with a higher proportion of eggs hatching after a second winter if they were laid when the day length is short in late summer, in one UK species. However, temperature seems to be critical in most species.

Copyrighted image Icon Copyright: David Robinson A closer look at the Leptophyes hatchlings Copyrighted image Icon Copyright: David Robinson Leptophyes hatchlings High temperatures can also trigger a diapause, which makes sense as the hatchlings are very small and vulnerable to dessication.

Drought conditions can also slow down development and prevent it reaching the final stage.

So, the weather conditions of 2012 will have had some effects on the bush cricket populations in the UK, but many of them have development strategies that help to mitigate the effect of a single year of adverse conditions.

What we shall be doing now is monitoring the populations at our field sites for the rest of this year so that when we get to spring next year we can compare 2012 and 2013. We may then be able to see if the most unusual conditions in 2012 have had any lasting effect.

This article is part of our Saving Species: academic insights section, where we bring you more stories about biodiversity and conservation from our expert academics.


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