The role of floral structure and biotic factors in determining the occurrence of florivorous thrips in a dystilous shrub

Abstract

Elucidating the factors determining the occurrence of florivorous organisms is an essential step for comprehending arthropod-plant interactions, especially when considering florivores that use flowers/inflorescences as microhabitats. In this study, we characterize the interaction between florivorous thrips (Thysanoptera) and Palicourea rigida (Rubiaceae), a distylous hummingbirdpollinated shrub. We investigated the relative role of different factors in determining thrips occurrence in the flower and inflorescence microhabitats. Furthermore, we experimentally examined the protective role of corolla influencing thrips exploration of floral buds. Frankliniella musaeperda (Thripidae) was the only species recorded on P. rigida, feeding on floral tissue, pollen and nectar. Thrips occurrence was not related to distyly, but rather to floral stage. Open flowers presented the highest abundance of thrips, followed by senescent flowers and then buds. The experimental opening of buds translated in increased thrips occurrence, indicating that F. musaeperda manage to explore the microhabitat offered by the floral chamber, as long as there is an opening in the corolla. In inflorescences, thrips abundance was negatively related to the number of ants visiting extrafloral nectaries. We found that the marked difference between floral morphs of distylous plants is not necessarily reflected in the abundance of florivores. Thrips seek for floral cavities, preferentially those with fresh tissue, which may confer nutrient-rich food and protection. Buds also provide this; however, the enclosed petals are an effective barrier against F. musaeperda entrance. At inflorescence scale, presence of mutualistic ants in high numbers can drive away these flowerfeeding insects. Despite the abundance of thrips in the flowers, there was no evidence of any functional relationship, either of pollination for flowers or of breeding for insects. We demonstrate here that in the flower/inflorescence microhabitat, structural and biotic factors play a key role in the exploitation and occupation by insect florivores.

A signal-like role for floral humidity in a nocturnal pollination system

“…One possibility is that floral humidity serves as an inviting stimulus prompting pollinators to enter a flower. This "microhabitat" hypothesis may also be relevant for the many smaller arthropods that utilize flowers for mating, breeding, and protection without necessarily benefiting the plant 87 . Another possibility is that floral humidity indicates either the presence or the location of nectar.…”

Floral humidity as a signal – not a cue – in a nocturnal pollination system

“…One possibility is that floral humidity serves as an inviting stimulus prompting hovering moths to enter the flower. This “microhabitat” hypothesis may be most relevant for the many smaller arthropods that utilize Datura flowers for mating, breeding, and protection 75 . Another possibility is that floral humidity indicates either the presence or the location of nectar, influencing the rate of discovery.…”