O dilema das plantas entre crescer, defender-se, reproduzir e gerar descendentes mais resistentes a insetos

Abstract

Herbivorous insects feed on vegetative and reproductive structures, compromising energy resources for plant growth and reproduction. Herbivory also causes indirect costs when herbivory-induced phenotype changes reduce flower attractiveness to visitors with consequences to plant fitness. In general, these herbivory-induced phenotype changes are adaptive plant defense mechanisms that are activated only in the presence of herbivores. Thus, this plasticity in the energetic balance among growth, reproduction and defense is an adaptation to varying herbivore pressure in space and time. Some of the herbivory-induced traits can be transmitted to subsequent generations, phenomenon known as transgenerational resistance. This study aimed to evaluate if herbivory by beetleDiabroticaspeciosa(Germar) (Coleoptera: Chrysomelidae) in sweet pepper plants Capsicum annuum L. (Solanaceae) alters the attractiveness to floral visitors and plant reproduction of the maternal generation; and affects progeny resistance to conspecific and non-conspecific herbivores. It was also investigated if maternal herbivory by a sucking insect, the aphid Myzuspersicae(Sulzer) (Hemiptera: Aphididae), enhances plant resistance of the next generation with consequences for energy allocation to growth and reproduction. In the field, it was verified that herbivory by D. speciosa in sweet pepper plants decreased abundance, richness and diversity, and altered the composition of the floral visiting insect community, changes that were associated with the reduction in size and number of fruits and seeds. Herbivory by D. speciosa progenies decreased progeny resistance to conspecifics. However, progeny were more resistant to the non-conspecific aphid, suggesting that the signaling pathways that regulate defenses against chewing and sucking are distinct. At the same time, progeny plants of herbivore-infested plants invested more energy to growth and reproduction, because they exhibited higher germination rates, greater dry weight and produced more flowers, fruits and seeds compared to progeny plants of uninfested plants. When mother plants were infested with M. persicae, the progeny became more resistant to the subsequent M. persicae herbivory, while germination rate and vegetative dry weight were reduced relative to progeny of uninfested plants. The higher herbivory resistance of the progeny of infested plants coincided with an increase of approximately 60% in the level of total phenols in relation to the progeny of uninfested plants. In addition, the concentration of this phytochemical was even higher in the progeny of infested plants when exposed to subsequent M. persicae herbivory. Maternal herbivory by M. persicae also caused an increase in indirect defenses in the progeny, because the parasitoid, Aphidius platensis (Brethes) (Hymenoptera: Braconidae) preferred herbivory-induced volatiles emitted by progeny of infested plants against those emitted by progeny plants of uninfested plants. In conclusion, the results showed that herbivory by D. speciosacauses direct and indirect costs for sweet pepper plant and, depending on the herbivore's identity, the plant transfers different information to the offspring, implying different strategies in the energy partition between growth, defense and reproduction.