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Harlequin Bug Update

Posted: May 27, 2014

Do you have this pesky type of stink bug on your farm? Here are some notes about this pest and an update on some new research on its biology and control.
Harlequin bug. Russ Ottens, University of Georgia.

Harlequin bug. Russ Ottens, University of Georgia.

The harlequin bug is an important insect pest of crucifers such as cabbage, cauliflower, collards, mustard, brussel sprouts, turnips, kohlrabi and radishes in the southern half of the United States [1]. Its northern limit is often around the Mason Dixon line, but this depends on severity of winter temperatures, and “changing winter climates may allow it to establish further north if extreme winter climates become less frequent,” explains Anthony Dimeglio, USDA ARS researcher.

harlequin fig 1
Figure 1: Harlequin Bug Distribution

Recently harlequins have been reported more frequently in Pennsylvania. The majority of organic vegetable farms in Southeast Pennsylvania reported significant pressure in 2013. Sixty-four percent of 39 growers surveyed rated harlequin pest damage as significant. Figure 1 shows harlequin bug distribution including two sites in Emmaus and Cochranville PA where farmers and scientists worked together to track populations in 2013.

Harlequin bugs can destroy the entire crop when they are not controlled. [Figure 2] They inject salivary secretions into plants, liquefying plant tissue so they can ingest it, and causing crops to wilt, brown and die [1].

harlequin fig 2
Figure 2: Harlequin Bug Damage

Know your pests. Know their biology. Outsmart them.

Early in the season populations and damage are often low and you may be tempted to ignore them. But, with two to three generations in a season, by the time fall crops begin to mature their numbers may be one hundred times as high, causing serious damage. Harlequin bugs reproduce quickly, developing from an egg to an adult in about 48 days. Adult males may live up to 25 days and females up to 41 days. During their adulthood they can mate repeatedly laying multiple egg masses of 12 eggs every 3 days. That means a single female can produce 164 eggs [2]. My advice – don’t ignore harlequins bugs; put together a plan to keep their numbers low.

You may wonder why you find harlequins clustered in certain parts of the field. This is because male harlequin bugs produce an aggregation pheromone [3]. Some growers have noted that this clustering allows them to identify which areas of the field to scout. They do spot management in these areas to keep them from spreading across the farm. Scientists are currently researching how to use the aggregation pheromone against them [4]. Weber, DiMeglio, and coworkers at ARS combined a newly discovered, synthesized version of the aggregation pheromone with mustard-family potted plants to monitor and trap harlequin bugs on farms this year, successfully attracting many harlequin bugs. An important next step is to figure the best spatial arrangement for traps or trap plants relative to the growers’ crops, so as to divert the bugs away from, not attract them to, valuable plantings [4]. Dimeglio and Dr. Weber of USDA-ARS Beltsville hope to have a trap available soon to help lower populations on the farm.

One of the questions researchers worked to answer this season was, “Where do harlequins come from?” Are they migrating north from Southern states every season or overwintering in the Mid-Atlantic? They found that adults overwinter here, burying themselves in dry plant residue, which acts like insulation. “They (harlequin bugs) continue to feed late into the fall and even in the winter, when it’s sufficiently warm, on mustard family plants including forage radish, and rapeseed cover crops. In our region only the adults overwinter. But they are vulnerable to severe winter temperatures,” says Dr. Don Weber, Research Entomologist at USDA-ARS Beltsville, MD.

Did harlequins survive the polar vortex?

Like many invasive species harlequin bugs originate in a warmer climate and are not adapted for extreme cold or large fluctuations in temperature. DiMeglio and Weber found that, in Maryland, the polar vortex took its toll on harlequin pest populations on January 6 and 8, 2014. Sub-freezing temperatures (6.8 F air, 24.8 F soil) killed 88% of harlequin bug adults in the field compared to inside the protected space of a greenhouse [5]. Hopefully the repeated cold temperatures this season will reduce the pest pressure on farms in 2015.

Controls

To control harlequin bug start with cultural controls. Host free periods without brassicas can help limit the population. Remember brassica cover crops like forage radish are known hosts [5]. Harlequin can also feed and reproduce on wild weedy mustards (Sheppards purse, wild mustard, pepperweed). Keeping these weeds under control in fields and on field edges will limit habitat. Left-over crop residue in the field provides a protected host area for over-wintering adult harlequins. Remove or disk in residue to destroy overwintering sites.

Trap crops have been recommended, but they may only work at low populations and should be combined with other strategies if tried. Trap cropping works by planting a preferred crop earlier before the main crop, in strips or surrounding the main crop. Pests moving into the area are likely to be attracted to the trap crop plants they prefer and leave your main crop alone. By concentrating the pest species in an area away from the main crop, you can destroy the pest by plowing it under, flaming or treated with insecticides.

In one study researchers found that a border row of mustards reduced the harlequin in the main crop significantly. Without a trap crop 80% of the main crop plants had harlequin and with it only 30% in one site. In the other site 55% had harlequin with no trap crop and 15% when protected by a border of mustard. It made no difference if the trap rows were sprayed or not [6].

In another study in Virginia trap cropping with mustard was only effective when harlequin bug densities were low. When densities were high harlequin moved from the main crop into the primary broccoli crop [7]. Although the harlequin stayed on the trap plants for six weeks they eventually moved into the main broccoli crop. The researchers suggest that if a trap crop is used it should be monitored frequently and if the harlequin population is increasing and the trap crop is senescing, the trap crop and associated harlequin bugs should be destroyed.One grower has successfully controlled harlequin by frequent vacuuming. At this farm they have a designated person to scout for harlequin frequently in hot spots where the harlequin congregate. Then they use a back pack insect vac to remove adults and nymphs and keep populations low. Another farmer suggested a leaf vacuum which has worked well for Colorado potato beetle.

Insecticide controls include pyrethroids and/or neonicotinoids. See The Pennsylvania Commercial Vegetable Guide here for insecticide options. Pyrethrins are allowable in organic production. According to Dr. Shelby Fleischer, Penn State Extension, starting early in the season with up to three applications within a two week window at the highest labeled rate and continuing until the problem is gone is likely to control harlequin. However, he notes this option would be expensive and labor intensive.

Backpack vacuum example.

Footnotes:

  1. Harlequin Bug. Florida Institute of Food and Agricultural Sciences.
  2. Zahn, D.K., et al., Biology and Reproductive Behavior of <I>Murgantia histrionica</I> (Heteroptera: Pentatomidae). Annals of the Entomological Society of America, 2008. 101(1): p. 215-228.
  3. Zahn, D.K., J.A. Moreira, and J.G. Millar, Identification, synthesis, and bioassay of a male-specific aggregation pheromone from the harlequin bug, Murgantia histrionica. Journal of chemical ecology, 2008. 34(2): p. 238-251.
  4. Weber, Donald C., Guillermo Cabrera Walsh, Tracy Leskey, Anthony S. DiMeglio, Michael Athanas, Kamlesh Chauhan, Megan Herlihy, and Ashot Khrimian. “Attraction of harlequin bug (Hemiptera: Pentatomidae) to male-produced pheromone and host plants in the field.” Presentation at Eastern Branch Entomological Society of America meeting, Williamsburg, Virginia, March 2014.
  5. DiMeglio, Anthony S. , Brennan Bathauer, and Donald C. Weber. “Lethal low temperature in harlequin bug (Hemiptera: Pentatomidae): the Polar Vortex takes its toll.” Presentation at Eastern Branch Entomological Society of America meeting, Williamsburg, Virginia, March 2014.
  6. Wallingford, A.K., et al., Host plant preference of harlequin bug (Hemiptera: Pentatomidae), and evaluation of a trap cropping strategy for its control in collard. Journal of economic entomology, 2013. 106(1): p. 283-288.
  7. Ludwig, S.W. and L.T. Kok, Evaluation of trap crops to manage harlequin bugs, Murgantia histrionica (Hahn) (Hemiptera: Pentatomidae) on broccoli. Crop Protection, 1998. 17(2): p. 123-128.