In order to survive and to repel herbivores, many plants defend themselves by producing toxic or deterrent substances. In the course of evolution, many insects have succeeded in adapting to the defensive chemistry of their host plants and thereby circumventing plants' defense mechanisms. However, the plants have also adapted their defensive system to further protect themselves against their enemies, which, in turn, generated counter-adaptations in the insects; biologists refer to this phenomenon as an "evolutionary arms race" between plants and insects. Many insects are plant pests that can be categorized as "specialists" and "generalists." Whereas generalists feed on many different plants, specialists have adapted to one or few closely related plant species as their food. The moth species Heliothis subflexa analyzed in this new study is such a host specialist. The researchers measured and compared the effects of withanolides on relative weight gains, survival rates. and the immune status in two moth species: the specialist Heliothis subflexa and the generalist Heliothis virescens. They knew from earlier studies that the specialist moth possesses a weaker immune response compared to the closely related generalist. "We were surprised to find that only Heliothis subflexa benefits from withanolides by increasing larval growth and immune system activity, but not its close relative, Heliothis virescens," says Hanna M. Heidel-Fischer, Ph.D., the leader of the study. The article was published online on August 26, 2016 in Nature Communications.
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