Changes in leaf chlorophyll content associated with flowering and its role in the diversity of phytophagous insects in a tree species from a semiarid Caatinga.

Leandro Sousa-Souto,Adriana Bocchiglieri,Douglas De M Dias,José P De L Filho,Anthony S Ferreira

doi:10.7717/peerj.5059

Abstract

Phytophagous insects choose their feeding resources according to their own requirements, but their feeding preferences in the semiarid Caatinga have rarely been studied. Flowering trees leads to a greater diversity of flower visitors and their predators in the host plant, but little is known about why the diversity of phytophagous insects not associated with flowers is also increased. The purpose of this study was to evaluate the diversity of sap-sucking, wood-boring and leaf-chewing insects associated with leaf chlorophyll content in flowering and non-flowering plants of Poincianella pyramidalis, an endemic tree of Caatinga. We used a leaf chlorophyll index (LCI) as a surrogate for resource quality, and an entomological umbrella to collect phytophagous insects. We show that trees which bloomed demonstrated higher chlorophyll content, greater abundance and a significant difference in the composition of phytophagous insect species when compared to non-flowering trees (p < 0.05). The results suggest that not only the presence of flowers themselves, but also the higher nutritional quality of leaf tissue, can explain the differences in species diversity and abundance of phytophagous insects. Exceptional flowering trees in the Caatinga area studied may thus act as spots of high quality resources, favouring changes in the diversity of insects in this environment.

Highlights

In the semiarid Brazilian Caatinga, the availability of high-quality resources for insects is concentrated in a short period of time, generally three to four months in the year
The present study investigates the role of plant nutritional status in the diversity of phytophagous insects in individuals of Poincianella pyramidalis (Fabaceae), during the dry season
It is clear that inflorescences attract a large number of herbivorous insects and pollinators, providing the complexity of the microhabitats and the supply of nectar, pollen and other food resources (Bairstow et al, 2010; Pearse & Karban, 2013); this study demonstrated that flowering plants were able to attract a higher abundance of insects not directly associated with flower consumption, probably due to the nitrogen content in leaves and branches

Summary

Introduction

In the semiarid Brazilian Caatinga, the availability of high-quality resources for insects is concentrated in a short period of time, generally three to four months in the year (the rainy season). This seasonality results in less phytophagous insect diversity, even when compared to other dry forest ecosystems (Leal et al, 2016). Nitrogen is usually the most limiting nutrient for plant growth in tropical forests (Sinclair & Horie, 1989), and changes in its availability have a strong effect on the photosynthetic capacity of canopy leaves (Kull, 2002)

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