Effects of plant morphological complexity on the efficacy and efficiency of Coccinella septempunctata L. as a predator of the pea aphid Acyrthosiphon pisum Harris

• Main Author: Legrand Pardo, Ana Isabel
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1999
• Subjects: Entomology
• ISBN: 9780599265141; 0599265140

Plant physical traits can influence the effectiveness of insect natural enemies, either directly or indirectly through their prey or host. Physical traits of the plant that have been shown to have effects on natural enemies are plant pubescence, shape of plant organs and architecture in the broad sense. The objectives of this laboratory study were to investigate the direct and indirect effects of plant morphological complexity on Coccinella septempunctata L. as a predator of the pea aphid Acyrthosiphon pisum Harris. Specifically, this study tested the hypothesis that increased morphological complexity reduces the efficacy and search efficiency of the predator. To test the effect of plant morphological complexity, near-isogenic lines of the garden pea, Pisum sativum L., were employed. These plants differed only in the morphology of their leaves. Plants were chosen to represent a scale from low to high complexity. The definition of complexity was based on plant characteristics that seemed relevant for a coccinellid predator. Efficacy of the predators was evaluated at the whole plant scale, while efficiency of area searched was evaluated at the leaf scale. First, the results showed that plant morphology did not have a significant effect on the fecundity, intrinsic rate of increase and within plant settling location of the pea aphid. Thus the plant morphological traits tested are not likely to have indirect effects on the predator through changes in prey abundance or prey location within the plant. Instead, these traits are more likely to alter the aphid's susceptibility to potential predation due to the aphid's location within the leaf. Second, predation experiments showed that at the whole plant scale, plant morphological complexity did not have a significant detrimental effect on the efficacy of the coccinellid. And finally, the morphological complexity of the leaf had a significant direct effect on the residence time and the efficiency of area searched by C. septempunctata. This study's findings support the notion that plant factors should be integrated in the evaluation of natural enemies for biological control, in particular when the biological control agent must operate at low prey densities.