A research team from the Nanjing Agricultural University in Nanjing, China, and the Max Planck Institute for Chemical Ecology in Jena, Germany, showed that isothiocyanates produced by cruciferous plants to fend off pests serve as oviposition cues. The plant defense substances serve as odor signals for females of the diamondback moth to lay their eggs on these plants. The scientists identified two olfactory receptors whose sole function is to detect these defense substances and to guide the moths to the ideal oviposition sites. They uncovered the molecular mechanism that explains why some insects that specialize in feeding on certain host plants are attracted by substances that are supposed to keep pests away.
From repellent to attractant
Cruciferous plants, such as cabbage, rape (canola), mustard and horseradish, produce glucosinolates. Upon mechanical damage of the plant tissues, e.g. caused by a chewing insect, glucosinolates are hydrolyzed by the endogenous plant enzyme myrosinase. This leads to the formation of a variety of toxic breakdown products, mainly isothiocyanates, to defend themselves against voracious insects. This defense mechanism is very effective against most herbivores. The diamondback moth Plutella xylostella, however, has evolved mechanisms of its own to outwit this defense: It is able to feed successfully on plants of the cabbage family and make use of the plants for its own reproductive purposes.
"We wanted to know whether the moths use isothiocyanates as odor cues to locate their host plants. In fact, behavioral experiments showed that three isothiocyanates are key signals for female moths to locate and lay eggs on cruciferous plants," says study leader Shuang-Lin Dong from Nanjing Agricultural University.
Two olfactory receptors specialized on isothiocyanates control egg-laying
Read on: https://www.sciencedaily.com/releases/2020/09/200910120123.htm