Even beetles plump for a balanced diet, study shows

JANUARY is the time of year when many people take a close look at how healthy their diet is — but humans are not the only ones making sure they eat a balanced selection of food.

Predators in the natural world choose their prey based on their needs for a balanced diet, rather than consuming as many calories as possible for survival, research suggests.

An international team of scientists studying a type of beetle found that females chose the right balance of prey foods like slugs, moths and ants to produce the healthiest and largest number of eggs, passing up food if it is not what they need.

Previous research on insects has shown that herbivores such as butterfly larvae and grasshoppers and omnivores like fruit flies and crickets select food that will give them a balanced diet.

This is the first research to show that predators also select food on the basis of its nutritional value.

Lead researcher Dr Kim Jensen, of the University of Exeter, said: “Biologists have previously assumed that predators cannot afford to be fussy and that they are simply focused on getting the right quantity of food, rather than quality.

“We show for the first time that they do actually select the foods that will give them the right balance of nutrients.

“Our findings could help further our understanding of food webs and how communities of animals interact in the wild.”

Writing in the Proceedings of the Royal Society B journal, scientists from Exeter and Oxford University, along with staff from the universities of Sydney, Aarhus in Denmark and Massey in New Zealand, based the study on the ground beetle, Anchomenus dorsalis, a garden insect that feasts on slugs, aphids, moths, beetle larvae and ants.

The team collected female beetles from the wild and split them into two groups in the laboratory. Half were offered a choice of foods, some high in protein and some high in fat. The others were not given a choice of what to eat: Some were given food that was higher in protein and others had higher-fat foods, none of which provided the right nutritional balance.

The beetles provided with a range of foods selected the balance of protein and fat that was optimal for producing healthy eggs. These beetles produced more eggs than the beetles that did not have the right nutritional balance.