Insects that deter predators produce fewer offspring

January 25, 2011

Scientists studied the defences used by caterpillars that transform into large white butterflies, called Pieris brassicae. The insects regurgitate semi-digested cabbage leaves to make them smell and taste unpleasant to predators. The team found, however, that frequent use of this defence reduces the caterpillars' growth rate and the number of eggs they produce. It remains unclear why their defences affect them in this way, but the loss of nutrition from frequent regurgitation is thought to play a part.

Caterpillars are a target of pest control, as they destroy food crop by eating the leaves of cabbages and other vegetable crop. This new study, however, suggests that natural , such as farmland birds, do not necessarily have to consume large numbers of insects, to have a significant effect on the size of the population. Researchers found that 40% of that defended themselves from predators by regurgitating food, died before transforming into a butterfly, despite successfully surviving the initial attack.

The study also showed that on average large caterpillars have 60 eggs, but those that used their defences against daily predator attacks produced approximately 30 eggs. It is thought that this effect could be widespread amongst herbivorous insects, suggesting that predators may have a larger impact on reducing the population of agricultural pests than previously thought.

Dr Mike Speed, from the University of Liverpool's Institute of Integrative Biology, explains: "Research has shown that large insects produce more eggs than smaller ones. This is commonly assumed to always be the case, but we have found that those that regurgitate food as a defence against predators, have fewer eggs, similar to the numbers of offspring smaller insects have. We also found that these insects grow at a slower rate and even those that successfully change into a butterfly, are smaller than normal."

Dr Andrew Higginson, from the University of Glasgow, said: "Interestingly, the caterpillars that grew at a slower rate were not forced, as a result of the attack, to metamorphose prematurely. They could have fed for longer, grown larger and produced more offspring, despite the daily use of their defences, but they appear to 'choose' to change into a smaller butterfly. More study is required to understand why they do this, but it could be that the threat of a fatal attack is too large for them to remain at the larval stage for too long and prompts them to transform into a butterfly early."

Dr Speed added: "This work demonstrates that it is important to maintain the diversity of predators such as wild birds, particularly in areas where large numbers of insects can destroy food crop. We now need to look at the defence mechanisms of a variety of to understand if other species react in similar ways."

Explore further: Fat, thin caterpillars are studied

More information: The study, funded by the Natural Environment Research Council (NERC), is published in the Journal of Animal Ecology.

Related Stories

Fat, thin caterpillars are studied

September 21, 2006

A U.S.-led international team of scientists says there's no obesity epidemic among insects and the researchers believe they now know why.

Insects use plant like a telephone

April 23, 2008

Dutch ecologist Roxina Soler and her colleagues have discovered that subterranean and aboveground herbivorous insects can communicate with each other by using plants as telephones. Subterranean insects issue chemical warning ...

Eating like a bird helps forests grow

April 5, 2010

Lions, tigers and bears top the ecological pyramid -- the diagram of the food chain that every school child knows. They eat smaller animals, feeding on energy that flows up from the base where plants convert sunlight into ...

Oak has secret weapon against caterpillar

May 31, 2010

A plague of caterpillars is munching its way through the leaves on our trees. Oak forests are suffering the most, reports the Nature Calendar. Cause for concern? Not according to entomologist and expert on insect pests, Leen ...

Scientists reveal cracks in egg theory

June 8, 2010

(PhysOrg.com) -- Scientists in Cambridge have found cracks in the long-standing theory that the number of eggs animals have -- and the size of those eggs -- is related to how much parental care they invest in their offspring.

Recommended for you

Which insects are the best pollinators?

September 3, 2015

Bees top the charts for pollination success according to one of the first studies of insect functionality within pollination networks, published today by researchers at the University of Bristol and the University of St Andrews.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Moebius
5 / 5 (1) Jan 25, 2011
Maybe because they have a good defense they don't need to reproduce as much. Less reproduction means less competition for its resources, like food. Wow, even a caterpillar might be smarter as a species than we are.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.