- Agronomic: canola
- Vegetables: broccoli, cabbages, cauliflower, radishes (culinary), turnips, brussel sprouts
- Crop Production: application rate management, catch crops, double cropping, intercropping, multiple cropping, relay cropping
- Pest Management: biorational pesticides, botanical pesticides, chemical control, cultural control, field monitoring/scouting, integrated pest management, physical control, trap crops
Harlequin bug is a pest of cole crops (Brassica oleracea), such as broccoli, cabbage, collards, cauliflower, Brussels sprouts, etc. There is potential to control this pest by using a trap crop, a preferred host plant planted near a protected cash crop, to draw insect feeding from the cash crop and to concentrate insecticide application to that trap crop rather than the cash crop. The research presented herein identifies plant species that are preferred by the harlequin bug over collards, a B. oleracea cash crop, identifies the role of plant odors in host plant selection, and evaluates a trap crop control strategy using border rows of mustard in the field.
Harlequin bug (HB) (Murgantia histrionica) is a pest of cole crops (Brassicaceae) and, while it has been reported to feed on plants of other families, it does so only in the absence of other brassicals (McPherson and McPherson 2000). Both adults and nymphs are piercing-sucking feeders on leaves and stems. Feeding causes blotching of leaf tissue, which reduces the marketability of crops sold as greens, such as collards and turnips. As feeding continues wilting and browning of leaves may occur eventually leading to the death of the plant (White and Brannon 1933). There are several broadspectrum insecticides (mostly carbamates, pyrethroids, or neonicotinoids) that provide effective control (Kuhar and Doughty 2009). However, there has been a shift toward the use of narrow-spectrum, reduced-risk insecticides in cole crops primarily for control of other pests such as lepidopteran larvae, or aphids. Unfortunatley, the majority of these newer chemicals have little to no toxicity to stink bugs such as HB.
There is potential to implement a trap cropping system as an alternative to broad spectrum foliar insecticide applications to manage HB. Insect feeding is diverted to a preferred host plant or “trap crop” planted near the protected cash crop (Hokkanen 1991). This could result in an elimination of chemical sprays targeted to this pest, or in a dramatic reduction in insecticide, as any necessary sprays would be applied to the trap crop only. In some cases there exists a “dead-end” trap crop, which is more attractive than the cash crop, but that the insect cannot complete development because that host lacks essential nutrition or due to toxicity (Shelton and Nault 2004). Toxicity can be applied to an attractive trap crop through genetic modification or by systemic insecticide. A “dead-end” trap crop also eases the fear of attracting more of the pest to the general area and acting as a source of herbivores rather than a sink.
Ludwig and Kok (1998) found that a perimeter border row of mustard (Brassica juncea) was successful at slowing the movement of HB into broccoli plots in low populations. A perimeter planting ensures that the trap crop is the first thing encountered by invading insects, keeping them in the edge. However, border rows may be a better fit into existing planting schemes over a complete perimeter border around the cash crop. Male HB produce a semiochemical, murgantiol, that attracts both male and female HB (Zahn et al. 2008). Production of this aggregation pheromone indicates that long-distance olfactory cues play a role in attraction of HB to a host plant; however, long-distance attraction of HB may rely on a combination of plant and insect odors.
Trap crops have been used for the control of other brassica specialists (Shelton and Badenes 2006), and long-distance orientation to crucifer compounds has been demonstrated (Pivnick et al. 1992, Bartlett 1996, Smart et al. 1997, Rojas 1999). Glucosinolates, a family of chemical toxins (e.g. sinigrin, glucobrassicin, allyl isothiocynate) produced by brassica plants for herbivore defense, have been shown to stimulate feeding and oviposition in several brassica specialist herbivores (David and Gardiner 1966, Feeny et al. 1970, Nault and Styer 1972, Stadler 1978, Renwick and Radke 1990, Renwick et al. 1992, Huang et al. 1995).
This project seeks to identify host plant species preferred by HB, to better understand the role of plant and insect cues involved in long distance host plant selection, and to evaluate the efficacy of a border row trap crop of mustard at the field level.
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Project objectives:div style="margin-left:1em;">
a. Survey the pest status and incidence of HB on various cole crops in Virginia.
b. Identify HB host plant preference and performance.
b1. Field-cage choice tests using whole plants
b2. Lab-cage choice tests using potted plants
b2. Lab feeding performance tests using potted plants
c. Determine the role of olfactory cues from host plants in long-distance attraction of HB.
d. Evaluate a trap crop strategy using mustard border rows for management of HB on the field level.