Research Indicates that Caterpillar Tracks Can Repel Spider Mites and Offer Benefits to Agriculture

Competition for resources is everywhere in nature. It is a much more dangerous life for an animal whose rival is hundreds of times greater than itself. Small herbivorous pests like spider mites are no strangers to this fate.

The caterpillars consume the same vegetation as the moths, which may suppress the activity of these common pests in their shared ecosystem. In previous studies, moths have been found to avoid trails left by carnivorous ants, but what could be behind the avoidance of herbivorous caterpillars?

Now, a team of researchers at Kyoto University has discovered that spider mites avoid chemicals extracted from the tracks of the larvae. The repellent effect lasts for several days.

“Spider mites, which are less than 0.5 mm long, lose not only their lives, but also their offspring and everything else when they encounter voracious leaf-eating larvae,” says lead author Shiori Kinto of Kyoto Graduate School of Agriculture.

Both species of mites Tetranychus kanzawai and Tetranychus urticae build protective webs on the leaf surfaces of the host plant and usually live beneath them. The butterfly and moth caterpillars then feed indiscriminately on the healthy and spider mite-infested leaves along with the sleeping individuals or their eggs.

“As presumably, adults of T kanzawai and Turticae avoid leaves of food plants that contain traces of silkworms,” ​​adds Kinto.

Of course, spider mites are not hunted by other herbivores, but small herbivores are sometimes consumed along with food plants by larger herbivores using similar resources. This accidental consumption is known as internal predation, or IGP. Little research has been reported on episodic IGP caused by herbivores and their defense strategies against it, in contrast to the many studies on IGP among predators.

While performing double-selection experiments, the Kinto team observed that T kanzawai avoided acetone extracts from the effects of the Bombyx mori silkworm applied to a T-shaped filter paper track. This finding demonstrated a repelling effect of herbivorous trace chemicals on various herbivorous species.

adds team leader Shuichi Yano, referring to a potential application in agriculture.

The results have been published in the journal Scientific reports.