- Vegetables: broccoli, brussel sprouts, cabbages, cauliflower
- Pest Management: trap crops, traps
Harlequin bug, Murgantia histrionica (Hahn), is an important pest of Brassica crops like collards, kale, mustard greens, and broccoli in the southern United States (Wallingford et al. 2011). Unlike the major lepidopteran pests and aphids that attack brassica crops, there are relatively few natural enemies of harlequin bug (HB) and, in general, only broadspectrum insecticides are effective for control. Use of these insecticides are not compatible with IPM programs. Thus, alternative management strategies for HB are needed for maintaining the sustainable balance of IPM in these important vegetable crop systems in the southern U.S. Pest populations of HB are highly variable and unpredictable from farm-to-farm, and therefore accurate monitoring of activity would greatly improve IPM decision-making and the timing of control tactics. To our knowledge, there is no monitoring device or proven trapping system for this pest. The recent identification and synthesis of the HB aggregation pheromone, mugantiol has led to the commercial availability of a potent attractant for this important pest. We are now exploring ways to utilize this new tool for pest management.
In a series of lab choice tests we determined a color preference of harlequin bug for darker colors (black and green) over lighter colors. After reconfirming harlequin bug color preference in the field, we looked at trap shape and circumference to construct a trap-prototype. Since our goal is to build a trap-and-kill device, we assayed whether a commercially-available long-lasting deltamethrin insecticide treated mesh would provide adequate contact mortality of harlequin bug and how quickly it would do so (LT50 bioassay). In conjuncture with our field studies we also investigated the additive and/or synergistic effects of combining the aggregation pheromone murgantiol with benzyl isothiocyanate (a mustard plant host volatile). Isothiocyanate is the chemical group –N=C=S, formed by substituting the oxygen in the isocyanate group with a sulfur. Many natural isothiocyanates from plants are produced by enzymatic conversion of glucosinolates.
Our field and lab behavioral studies determined that visual stimuli are synergistic to volatile attractants. Visual cues—such as color, surface area, and shape—are additive in attracting harlequin bug. Dark colors attracted more bugs than lighter colors. When comparing green and yellow traps baited with murgantiol we found that yellow traps were hazardous to beneficial predatory coccinellids, whereas dark green was not.
Harlequin bug response to the aggregation pheromone, murgantiol, was low during the summer growing season, even when combined with various visual stimuli. It was not until we combined trap-like devices with murgantiol and benzyl isothiocyanate that we saw significant response within dispersing on-farm populations. These are interesting findings as they suggest that murgantiol & benzyl isothiocyanate act synergistically to attract HB. The results of these studies should provide some important information for the development of an effective trap for HB that growers can use on their farms to detect invading populations and possibly to attract and kill them.
Project objectives:div style="margin-left:1em;">
Objective 1. To determine visual cues such as color and trap-architecture that attract more harlequin bugs.
Obj. 1A. Assess HB preference for colors
Obj. 1B. Determine the efficacy of deltamethrin-treated mesh (long-lasting insecticidal mosquito nets) at killing HB – for use on traps
Obj. 1C: To evaluate the field response of HB and natural enemies to dark green versus yellow color in the presence of murgantiol pheromone
Obj. 2: To evaluate the efficacy of the HB aggregation pheromone, murgantiol with and without the addition of mustard oil volatiles