Researchers have found that a specialist species of moth, Heliothis subflexa, is able to take advantage of its host plant’s defensive chemicals. The moth utilizes compounds called withanolides to boost its own immune system and protect its body from bacteria. The findings are in a paper just published in the journal Nature Communications.
Generalist species feed on a variety of food sources while specialists have a more limited diet. One such specialist is Heliothis subflexa, a type of moth from the Noctuidae family. The moth exclusively feeds on fruits of Physalis plants, the genus that includes groundcherries and Cape gooseberries. Physalis plants contain compounds called withanolides, chemicals that normally protect the plants from insects. Withanolides taste bad to most insects and act as both immune suppressants and toxins. H. subflexa has evolved an immunity to these chemicals, allowing it to feed on the plants without much competition.
Researchers from the Max Planck Institute for Chemical Ecology compared H. subflexa moths to a close relative, H. virescens. H. virescens is a generalist and doesn’t feed on Physalis plant species. The team fed purified withanolides to moth larvae and recorded data such as growth speed, immune system response, and survival rates. The team found that the withanolides negatively affected developing H. virescens moths and suppressed their immune systems. Interestingly, H. subflexa wasn’t simply immune to the chemicals. H. subflexa actually benefited from the withanolides; the larvae were healthier and had better immune responses than larvae that hadn’t been fed the compounds.
To further test the effect of withanolides on the moths’ immune systems, the team exposed larvae to Bacillus thuringiensis bacteria. H. subflexa that had been fed the compounds were more resistant to the bacteria; their bodies were somehow taking advantage of the natural antimicrobial properties of withanolides. H. virescens larvae didn’t gain the same benefit.
H. subflexa moths are not only immune to withanolides, they benefit from them. Withanolides boost their immune systems and make them more resistant to bacterial infections. This allows the moths to take full advantage of their specialized diet. The study provides insights into evolution and the advantages of specialist diets.
Andrea Barthel et al. Immune modulation enables a specialist insect to benefit from antibacterial withanolides in its host plant. Nature Communications (2016).