OSB archive
OSB archive

Insects: 'good mothers' after all

Pete Wilton

Insects aren't necessarily renowned for their maternal instincts but new research suggests that we may be unfairly maligning many of our six-legged friends.

Sofia Gripenberg from Oxford University's Department of Zoology, and colleagues from the Universities of York and Helsinki, have reviewed the evidence for 'bad' insect mothers and report their findings in the March issue of Ecology Letters.

I asked Sofia about genes, evolution and the fine line between selfish and selfless behaviour:

OxSciBlog: Why has it been suggested that insects are 'bad mothers'?
Sofia Gripenberg: In plant-feeding insects, 'good' and 'bad' mothers differ largely in terms of what food they pick for their offspring. Since those larvae will typically have to make do with the particular plants on which they were laid as eggs, their mother’s judgement may literally mean the difference between life and death. In some cases, that judgement has actually been found to be anything but sound, with larvae found on lousy plants.

OSB: How have people tried to explain this 'bad' behaviour?
SG: A 'bad' mother may still be doing the best she can. Sometimes the plants of highest quality may simply not be around when needed, and the female will then have to lay her eggs on what she can find. According to another idea, insects may simply be faced with 'information overload': if two plants differ in terms of too many traits, the insect may not know which trait to go for.

Also, even an insect mother may also have to think of herself. In some cases, mothers have been shown to put their own needs above those of their offspring. For example, by laying her eggs where she can get some food for her own, an insect mother may be prepared to knock off a bit of quality for her offspring.

Paradoxically, a female may sometimes increase the chances of passing on her genes to future generations by ignoring the well-being of individual offspring.

OSB: What does your study tell us about the choices of insect mothers?
SG: We basically revive the myth of the good insect mother. Where previous research has often focused on explaining the cases where mothers tend to err, our study shows good choices to be the rule, not the exception for insect mothers.

Importantly, what we have done is not to add one more study of one specific insect species, but to summarise work published to date. In this context, our results also reveal a little bit about why some mothers may be better than others. In particular, our study seems to support the idea about 'information overload', since insects choosing between a few different plant species actually seem to make more accurate choices than insects choosing between a wide assortment of plants.

OSB: How do these results contribute to our understanding of evolution?
Our results suggests that 'good motherhood' is a result of fine-tuned natural selection. Where many previous studies have focused on factors preventing evolution towards good motherhood, our study shows that when you look at the combined evidence, these are still just blemishes on the bigger picture; that one still shows the picture of a beautiful insect mother!

OSB: What new avenues of research does your study suggest?
SG: When we started this study, we hoped to be able to say more about why insect mothers differ in terms of their judgement - about the factors causing some females to make worse choices than others. After now having read everything we have found on the topic, we have actually discovered that only a small fraction of articles are written in a way which allow straightforward comparisons of key results. This is something that we want to improve upon.

What we hope is that the database that we put together for our paper will continue to grow, and later allow for deeper synthesis of factors affecting optimal motherhood. By establishing this joint depository for all ecologists working in this field, we hope to get everybody to think more about how their own work can contribute as efficiently as possible towards the broader picture.

Dr Sofia Gripenberg is based at Oxford University's Department of Zoology