Do fruit traits of the Senna occidentalis weed influence seed predation by Bruchinae?

Abstract

Pre-dispersal seed predation by specialist insects can affect the performance of plants, and the morphological, morphometrical and physiological traits of fruits/seeds influence the degree of predation. Senna occidentalis is a weed found in degraded pastures and plantations, which is poisonous to cattle and other domestic animals. This study tested the hypothesis that larger and mature S. occidentalis fruits have a higher probability of predation, and larger fruits have more bruchids. It also estimated the predation level and identified the bruchid species associated with this weed. Fruits were randomly selected from 42 plants from pastureland in Mato Grosso do Sul, Brazil. The probability of predation was not influenced by fruit length. Although the fruit length has been positively associated with the seed number, bruchids were not associated with fruit length. The most frequently predated fruits were those measuring between 10 to 13 cm. A possible explanation is that bruchids do not select a specific fruit length because they are not host-specific for this weed. Seed predation of about 7% was recorded for three bruchids: Sennius bondari, Amblycerus submaculatus and Amblycerus sp. This low level of seed predation may be insufficient to have a negative impact on the weed. Acquiring knowledge about predation rates and mechanisms that regulate a plant population can help scientists estimate the efficiency of seed-feeding insects used to biologically control weeds.