When laying eggs, tobacco hawks accept beetles that compete for food in order to be safe from parasitic wasps.
A research team at the Max Planck Institute for the Chemical Ecology has found that tobacco-enthusiastic females, when laying eggs, show an unusual preference for the prickly apple plant that is actually spread by leaf beetles. The beetles and their larvae actually compete with the larvae of the tobacco hawk for food. Plants infected with beetles give off a different aroma containing alpha-copaen and make them more attractive to tobacco lovers. Despite food competition, caterpillars seem to benefit from choosing such host plants because they are better protected from parasitic wasps, which avoid plants that smell like beetles. The researchers were also able to identify the scent receptor in tobacco lovers that controls this behavior.
Tobacco aficionados lay their eggs. The moth bends its stomach to the underside of the leaf to lay an egg. At the top of the sheet you can already see an egg laid on the left edge.
By choosing the best possible site for laying eggs, many insects determine the path for the best possible development of their offspring: there must be enough food, and the larvae that hatch from the eggs must be as safe as possible from pathogens and predators.
In a previous study, a research team led by Marcus Kenadin and Bill Hanson from Department of Developmental Neuroanatomy It can already be proven that tobacco lovers avoid laying their eggs on plants where they can smell the droppings of other species. “So they obviously want to avoid food competition. So we asked ourselves whether the moths also avoid plants that other herbivorous insects are infested with,” says first author Jin Zhang, summarizing the research question in the current study.
beetle infested mites
Behavioral experiments with thorn apple plants Datura my bookColorado beetle family daturaphila . logo They were infested, but with completely unexpected results: it is clear that the female tobacco hawks even preferred to lay their eggs there, compared to plants where the beetles did not infess them. “To be honest, we were a little frustrated at first because we expected that the experiments would confirm our initial hypothesis, which is that egg-laying tobacco hawks avoid competitors for food. But in our case, the unexpected result suddenly made sense. We found that plants infested with beetles smell completely different and that Parasitic wasps, which often use plant odors to find their host insects, are less efficient at tracking tobacco hawk larvae on beetle-infested plants, study leader Marcus Kenadin explains.
In nature, it is not always possible to avoid all threats and at the same time choose a place with a lot of food. Studies assume that up to 90 percent of tobacco hawk larvae come from wasps Cotesia conigligata be intrusive. These types of parasitic wasps lay their eggs in larvae and also transmit pathogens. Parasitic larvae eventually die and the wasp offspring hatch.
The smell of infected plants is different
The researchers used this knowledge to investigate the behavior of tobacco lovers, which seemed strange at first. They analyzed the scent of prickly apple plants infested by Colorado beetles and compared it to control plants without the infestation. Above all, there was an unusual increase in alpha-copaen in the aromatic bouquet of plants.
The team’s next question was how moths perceive and process this smell. Since tobacco aficionados have about 70 olfactory receptors that could be candidates for the alpha copaen trace, it can take a very long time to test all candidates individually. Instead, a combination of complex molecular biological approaches enabled them to reduce the number of potential olfactory receptors from about 70 to 6 and eventually identify Or35 as likely to be involved in egg-laying options and to be activated by alpha copaen.
The researchers also examined the behavior of parasitic wasps that control odor. Experiments in which wasps chose between two scents, on the one hand, showed a preference for Cotesia conigligata To smell the plants on which the larvae feed. On the other hand, they also showed that wasps avoid the smell of plants also infected with Colorado beetles. These findings can also be confirmed by behavioral experiments in a test tent where only prickly apple plants or tobacco hawks or Colorado beetles were infested with tobacco hawks.
Cost-benefit analysis
Although tobacco hawk larvae do not grow as well on beetle-infested plants as well as they do on uninfected plants, female moths are receptive to this defect when laying eggs, as the advantage of protection against parasitic wasps clearly prevails. This cost-benefit analysis, also known as ‘trade-off’, plays an important role in environmental interrelationships. Our results show that simple explanations are often inadequate in nature. Tobacco lovers not only have to think about whether the plant is suitable as food for their offspring, but also whether there are indeed potential competitors and whether their presence helps avoid the dangers of predators, summarizes Bill Hanson.
Other studies will show why prickly apple plants emit different odors, depending on the insects that eat them. Both the larvae of tobacco hawks and the larvae of the Colorado beetle species daturaphila . logo They are insects that chew and cause similar damage to plant tissues. It is assumed that microorganisms play a role in the animals’ oral secretions. Interdisciplinary approaches, which also focus, for example, on the role of microorganisms in these complex interactions, help to reveal other exciting aspects of the diverse interactions between organisms.
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