Plant chemistry varies both among and within species. As plant chemistry can affect ecological interactions, it has been constantly questioned how the intraspecific variation is maintained and how it is affecting herbivore animals. A useful approach for answer those questions is working with plant chemotypes which present discrete variation in the presence or abundance of secondary metabolites. The Australian tea tree Melaleuca alternifolia shows variation in the proportion of terpenes produced in the leaf. Six chemotypes have been identified, with differences in the abundance of mainly three terpenes (cineole, terpinen-4-ol and terpinolene). These chemotypes are the product of a simple genetic system which is based on three terpene synthases genes. However, we still lack information about the importance of this variation in ecological interactions. Therefore, we analyzed the influence of the plant chemical variation on the performance of two species of specialist herbivores (Faex sp and Paropsisterna tigrina, both Coleoptera:Chrysomelidae). We measured life history traits on herbivores fed with plants from the six chemotypes in a no-choice feeding test.
Results/Conclusions
Larval mass gain, pupa and adult mass, developmental time and survival were not significantly different among all the diets. There was a trend in which the sex ratio in surviving adults of P. tigrina was related with plant chemistry. Those insects fed with plants containing terpinolene showed a female biased sex ratio, while the opposite was observed in plants without terpinolene. It is suggested that survival on different chemotypes depends on the herbivore sex. This in turn could affect the growth rates of insect populations when only some chemotypes are present. As there is variation in the distribution of chemotypes among natural plant populations, it is possible that in some populations insects can be controlled by a reduction of the female fitness.