Abstract
Habitat manipulation through the incorporation of non-crop plants such as trap crops (to lure pests away from the cash crop) and insectary plants (to provide resources for natural enemies) into agro-ecosystems is an ecological approach to pest management. In a field-scale study, we quantified the effects of integrating the use of trap crops with insectary plants as a novel method to control pest herbivores in an organic cabbage agro-ecosystem. We hypothesized that pests would be concentrated in the trap crop habitat and suppressed by insectary-subsidized natural enemies in situ. We documented arthropod abundance (both adults and immature stages) associated with (1) two insectary plant species (sweet alyssum, Lobularia maritima, and buckwheat, Fagopyrum esculentum) either alone or in combination; (2) a trap crop mixture of mighty mustard (Brassica juncea), red Russian kale (Brassica oleracea var. acephala), and glossy collards (Brassica oleracea var. italica), and (3) cabbage cash crop (Brassica oleracea var. capitata). Trap crops were more attractive to pests than the cash crop. On a per-plant basis, densities of the herbivores Evergestis rimosalis, Trichoplusia ni, and Plutella xylostella were 154, 37, and 161× greater on the kale trap crop than on the cabbage cash crop, and 54, 18, and 89× greater on the collards trap crop than on the cash crop. Insectary plants contributed to the consumption of pests that aggregated on the trap crop. Parasitism of E. rimosalis by the braconid wasp Cotesia orobenae was significantly increased, and the abundance of eggs and larvae of the predatory coccinellid beetle Coleomegilla maculata was greater on the trap crop in the presence of insectary plants compared to trap crops that lacked insectary plants. The ‘Botanical Triad’ of cash crop, trap crop, and insectary plants represents a new type of agro-ecosystem manipulation that integrates ecosystem service providers (e.g., predators and parasitoids) within the cropping system.
Highlights
Modern agriculture practices such as monoculture production, intensive land use, tillage, and chemically-based pest control have contributed to the loss of biodiversity in many agricultural production areas, negatively affecting functional biodiversity and ecosystem services such as pollination and biological pest control [1,2,3,4]
Within an organic cabbage agro-ecosystem, the main goal of this study is to assess the effects of integrating the use of trap crops with insectary plants on the abundance of functionally important arthropod taxa represented by herbivores and their natural enemies
The most abundant herbivore on trap crop plants was E. rimosalis, with mean densities of 18.2 ± 5.4 larvae per kale plant and 6.4 ± 2.5 larvae per collards plant, followed by T. ni
Summary
Modern agriculture practices such as monoculture production, intensive land use, tillage, and chemically-based pest control have contributed to the loss of biodiversity in many agricultural production areas, negatively affecting functional biodiversity and ecosystem services such as pollination and biological pest control [1,2,3,4]. Insects 2019, 10, 181 of landscape simplification, increased pest pressure, and greater pesticide use have contributed to the rapid loss of biodiversity in agroecosystems, which greatly affects the functioning of natural pest control [7,8,9]. Several studies have demonstrated that the establishment of non-crop habitats around field margins can provide ecosystem services, including enhanced biological pest control [17,18,19,20]
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