The Olfactory World of Silk Moths

A team of researchers from Max-Planck-Institute in Germany, together with scientists from University of Halle-Wittenberg, studied the sense of smell of the domestic silk moth. They found out that males and females of this moth species are sensitive to very different smells. 

What Females Smell

Female moths especially use their sense of smell to find suitable host plants to lay their eggs on. After pairing with the male moth, the female is very sensitive to the smell of the caterpillars’ food plant. But not just the food plant: the females also smell the excrement of other caterpillars very well. This might come a surprise, especially when the researchers found out that the females stay away from this smell. But, if you think about it, it makes perfect sense; just like most things in nature. The females then avoid host plants where other caterpillars are already living on to avoid competition for their own offspring.
So, the two smells that the female domestic silk moth is specialised on are the excrement of other caterpillars – also of its own species – and the smell of host plants. Moreover, a big difference was seen in the behaviour of virgin moths compared to those who had already been fertilised: Virgin moths did not react at all to the smell of caterpillar excrement, whereas already paired moths were repelled by that smell.

What Males Smell

In contrast, male domestic silk moths use their smell especially to find a suitable partner. The females, once they are ready to pair, produce and emit sexual pheromones which attract the males. Interestingly, the female itself is not able to smell her own pheromones.

How Do Moths Smell?

Moths, like butterflies and other insects, have antennae with thousands of so-called sensilla; these are hairs, but unlike human hair, they are a sensory organ, in this case the organ for smell. Inside the sensilla, the moths have nerve cells. For the study, the research team measured especially the activity in single sensilla of female and male moths. Until now, it was believed that female moths are especially triggered by the smell of their host plants; however, this study surprisingly showed that the smell of caterpillars’ excrement has much more impact on the moths and is perceived in a much more sensitive way.
The team of researchers hopes to continue the studies with moths and insects and their sense of smell as some things are still left to discover.