A new study has found that agricultural environments drive insects to reproduce without sex - a trait that is uncommon in most of the animal kingdom - but may provide methods for controlling their damaging effects.

Researchers at the University of Melbourne have found that when insect pests have a stable environment with abundant resources - such as grain crops, orchards, vineyards, pastures and plantations where the same crops are grown every season - they were four times more likely to reproduce without sex compared to insects overall.

 “So increasing the complexity and variability of agricultural environments provides a way of potentially controlling asexual pest species” said Professor Ary Hoffmann from the Centre for Environmental Stress and Adaptation Research at the University of Melbourne.

These pests include species like aphids that suck sap, mites that eat leaves, scale insect pests that feed on plant sap, beetles that eat plants and thrips that puncture plant cells.

“We looked at insects from Italy and North America, comparing databases of agricultural pest species with the insect species that can reproduce asexually - a method that is effectively cloning and so doesn’t require males and sex for reproduction”.

“We discovered that the asexual species comprised 45 per cent (North America) or 48 per cent (Italy) of pest species in genera where asexual reproduction occurred, compared to an overall incidence of 10% or 16% in these genera”.

“The advantage farmers have is that asexual pests will have difficulty overcoming control methods that require the evolution of changes at multiple genes, which is more easily achieved with sexual reproduction where two sets of genes combine to produce a more variable genetic make-up than just cloning,” added Dr Andrew Weeks from the department of Genetics at the University of Melbourne.

This means that asexual pests should be slower at adapting and becoming resistant to chemical controls, and should be susceptible to biological controls such as fungi that can be released like pesticides.

Asexual pests will also find it harder to adapt to new varieties of plants bred to be resistant to pests, as long as the resistance mechanisms involve several genes.

“Asexual reproduction may be favoured in agricultural environments when particular clones are selected in the same stable environment across multiple generations. Asexual reproduction may also be favoured as populations can be initiated by single individuals whereas sexual species require the presence of males and females”.

“Another factor is that in agricultural ecosystems, sexual reproduction cues may be absent”.

Researchers found that the high incidence of asexual reproduction in pest species is spread across different families and several insect orders.

The study was published online in the journal Proceedings of the Royal Society B.