Aphids that eat Brussels sprouts are smaller than normal and live in undersized populations, which has a negative knock-on effect up the food chain according to new research published today (8 February) in Science.
The study shows for the first time that the nutritional quality of plant food sources for herbivores has a far-reaching impact on an ecosystem as a whole, potentially impeding important functions that the ecosystem performs, such as the natural predation and control of agricultural pests.
The scientists compared aphids living on sprouts to aphids living on wild cabbages in a field experiment which took place on a farm in the Netherlands. They could see that the sprouts were of a lower nutritional value for aphids than the cabbages, because the aphids feeding on them were smaller in size, and the number of aphids living on them was fewer.
They then traced the effects up through the food chain to discover that the implications of poor nutritional quality in plants spread throughout the extended network of feeding relationships in an ecosystem known as a food web. This means that the sprouts affect not only the herbivore aphids that eat them, but also the primary parasitoid wasp predators that mummify and eat the aphids, and the secondary parasitoid wasps that in turn eat the primary parasitoid wasps.
The scientific team made this discovery by analysing the food webs associated with both types of plants. They found that food webs based on sprout-eating aphids are less complex and involve a less diverse network of predators than those food webs based on higher quality plants like wild cabbage.
This is because larger, cabbage-eating aphids produce larger primary
parasitoid predators, which in turn attract more of the opportunistic
generalist feeders among the secondary parasitoids, leading to a greater
diversity of species and complexity in the ecosystem. This shows that
|Contact: Danielle Reeves|
Imperial College London