Abstract
Simple SummaryMany studies have shown that ground beetles feed on different agricultural pests, but little is known about their species communities from US cropping systems. We assessed the biological control potential of the most common carabid beetle species in Oregon annual ryegrass grown for seed by investigating spatial and temporal overlap of the most common species with those of the most damaging autumn- and winter-active pests (slugs, caterpillars and cranefly larvae) and determined the number of field-collected specimens that had fed on the respective pests using molecular gut content analysis. Only the non-native Nebria brevicollis was abundant during pest emergence and tested positive for all three pest groups. While the other common carabid beetle species—Agonum muelleri, Calosoma cancellatum and Poecilus laetulus—were also found to have consumed pests, they were active only during spring and summer, when crop damage by pests is less critical. We also show that disk tilling did not affect any of the four common carabid beetle species and that only N. brevicollis was significantly associated with a vegetated field margin. This study contributes to expanding our knowledge on conservation biological control in a system where chemical pesticides are still the mainstay of control against invertebrate pests.While carabid beetles have been shown to feed on a variety of crop pests, little is known about their species assemblages in US annual ryegrass crops, where invertebrate pests, particularly slugs, lepidopteran larvae and craneflies, incur major financial costs. This study assesses the biological control potential of carabid beetles for autumn- and winter-active pests in annual ryegrass grown for seed by: (a) investigating the spatial and temporal overlap of carabids with key pests; and (b) molecular gut content analysis using qPCR. Introduced Nebria brevicollis was the only common carabid that was active during pest emergence in autumn, with 18.6% and 8.3% of N. brevicollis collected between September and October testing positive for lepidopteran and cranefly DNA, respectively, but only 1.7% testing positive for slug DNA. While pest DNA was also detected in the guts of the other common carabid species—Agonum muelleri, Calosoma cancellatum and Poecilus laetulus—these were active only during spring and summer, when crop damage by pests is less critical. None of the four carabid species was affected by disk tilling and only N. brevicollis was significantly associated with a vegetated field margin. However, as its impact on native ecosystems is unknown, we do not recommend managing for this species.
Highlights
Ground beetles (Coleoptera: Carabidae) are one of the most common arthropods in agroecosystems and their ability to aid in biological pest control has been demonstrated for several groups of pests including slugs [1,2,3,4,5,6] and caterpillars [7,8]
A potential problem is that N. brevicollis activity abundance decreases sharply in mid-November (Figure 1A) when N. pronuba and cranefly larvae are increasing in numbers (Figure 1F,G) and none of the larvae of N. brevicollis, which are active throughout the winter and early spring, were found to have consumed caterpillars or cranefly larvae
While feeding incidences were slightly lower and the spatial and temporal overlap with any of the pest taxa was not as distinct, the other common spring-active species P. laetulus and A. muelleri and, to a lesser degree, the summer-active C. cancellatum still have some potential to reduce the populations of the pests at the times critical for crop damage
Summary
Ground beetles (Coleoptera: Carabidae) are one of the most common arthropods in agroecosystems and their ability to aid in biological pest control has been demonstrated for several groups of pests including slugs [1,2,3,4,5,6] and caterpillars [7,8]. A more accurate way to assess actual pest predation is molecular gut content analysis of field-collected carabids using either standard polymerase chain reaction (PCR) or quantitative PCR (qPCR), which has been shown to be even more effective in detecting DNA traces of prey items in predator guts [10]. This approach has been used successfully in many studies investigating predation by carabids [11,12,13] and has the added benefit of being able to determine the timing of feeding incidences. Despite evidence of the opportunistic feeding behavior of certain species of carabids [20,21,22], it has been shown that some pests are consumed even if their numbers are low [23,24,25,26]
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