Suppression of Soybean Aphid by Generalist Predators Results in a Trophic Cascade in Soybeans

Abstract

Top-down regulation of herbivores in terrestrial ecosystems is pervasive and can lead to trophic cascades that release plants from herbivory. Due to their relatively simplified food webs, agroecosystems may be particularly prone to trophic cascades, a rationale that underlies biological control. However, theoretical and empirical studies show that, within multiple enemy assemblages, intraguild predation (IGP) may lead to a disruption of top-down control by predators. We conducted a factorial field study to test the separate and combined effects of predators and parasitoids in a system with asymmetric IGP. Specifically we combined ambient levels of generalist predators (mainly Coccinellidae) of the soybean aphid, Aphis glycines Matsumura, with controlled releases of the native parasitoid Lysiphlebus testaceipes (Cresson) and measured their impact on aphid population growth and soybean biomass and yield. We found that generalist predators provided strong, season-long aphid suppression, which resulted in a trophic cascade that doubled soybean biomass and yield. However, contrary to our expectations, L. testaceipes provided minor aphid suppression and only when predators were excluded, which resulted in nonadditive effects when both groups were combined. We found direct and indirect evidence of IGP, but because percentage parasitism did not differ between predator exclusion and ambient predator treatments, we concluded that IGP did not disrupt parasitism during this study. Our results support theoretical predictions that intraguild predators which also provide strong herbivore suppression do not disrupt top-down control of herbivores.

Landscape diversity enhances biological control of an introduced crop pest in the north‐central USA

“…Following the methods of Costamagna et al (2007a), we used cages to exclude natural enemies from selected plants, contrasting the population growth of aphids in the presence or absence of these antagonists. When an average population of 10 aphids per plant was reached in the overall field, cages were erected in the center of each plot (four per site), each enclosing a single plant.…”

“…Feeding by A. glycines on the leaves, stems, and pods of the soybean plant causes reductions in photosynthetic rate (Macedo et al 2003), plant growth, and seed yield of soybean plants (Ragsdale et al 2007). Soybean aphid is consumed by a diversity of natural enemies that can provide strong top-down regulation of its populations (Costamagna and Landis 2007) and result in a trophic cascade of increased crop yields (Costamagna et al 2007a). Although several parasitoids can be found attacking soybean aphid, generalist predators currently dominate the natural enemy community (Costamagna et al 2008).…”

Bats initiate vital agroecological interactions in corn

“…Although agricultural production tends to degrade biodiversity, intact ecological communities also provide valuable ecological services to humans, such as regulation of crop pests (2). These agricultural ecosystems are characterized by simplified food webs with distinct trophic levels (3,4), and thus may be particularly prone to trophic cascades wherein predators release plants from herbivory (5), suppressing crop damage and bolstering yields. In many countries, these services may be important for food security (6); thus, assessment of pest-regulating services provides key knowledge that can benefit human well-being.…”

Thiamethoxam Toxicity and Effects on Consumption Behavior in Orius insidiosus (Hemiptera: Anthocoridae) on Soybean

“…Thus, the A. glycines is considered the most important pest of soybean in the North Central Region of the United States , Tilmon et al 2011. In absence of predation, soybean aphid populations have been reported to grow from 2 to 7 times faster than when predators are present (Costamagna and Landis 2007). Based on the importance of predatory insects in the management of A. glycines, there has been increased interest in the implementation of pest control practices that allow the conservation of these species (Tilmon et al 2011).…”