By John P. Roche
The bagrada bug, Bagrada hilaris, is a species of stink bug that was introduced into North America in 2008. It feeds on plants of the mustard family and can cause severe feeding damage to cruciferous crops, including cabbage, broccoli, and cauliflower. The bagrada bug could develop into a devastating economic problem if the pest is unchecked. The National Agricultural Statistics Service estimates that the value of the broccoli crop in California in 2013 was over 800 million dollars.
Gaps still exist in our understanding of the ecology and life history of this invasive species. Some studies have been done on the bagrada bug in the Old World, but little information on its life history has been available in North America. Such information is crucial because it could help steer effective control of bagrada bug outbreaks. A recent study of the bagrada bug’s life history in New Mexico by Melise Taylor and colleagues Scott Bundy and Jay McPherson helps fill these gaps.
Taylor and colleagues conducted a field survey of bagrada bugs from January 2012 to August 2014 in Las Cruces, New Mexico. They sampled mostly on London rocket and mesa pepperwort, which are both preferred hosts of the insect. They also sampled broccoli plants. In addition to field sampling, they reared about 100 females and 100 males in the laboratory. In their field sampling, they found adult and nymph bagrada bugs throughout all months of the year. They found mating pairs on mesa pepperwort throughout the year, and eggs were found in soil near host plants from early February to early October. Their data suggest that there are two reproductive generations in New Mexico per year, and that the insects go through five instars — which they describe in detail, with illustrations — before reaching the adult stage.
What significance can life history information have to pest management focused on control of this species? It is significant because control measures could in theory be applied to bagrada bugs when these measures would have the greatest effect on reducing the population and limiting feeding damage. No natural predators of bagrada bugs are known in North America, but parasitoid species from the old world have been observed to attack bagrada bugs in the lab. Bagrada bugs lay eggs singly, which makes it harder for biological-control species to limit their population. Also, because they are stink bugs, they are noxious to many species of potential predators, which complicates biological control. The current primary strategy relies on chemical applications targeted at crops when the bagrada bug density reaches a certain threshold.
Additional chemical and non-chemical control strategies are under development, which is important. Nymphs and adults can begin consuming seedlings as soon as they emerge from the soil, and mortality of cruciferous seedlings studied by John Palumbo and Eric Natwick in 2009 was as high as 60%. The bug’s range has now expanded throughout California and into Arizona, Nevada, Utah, New Mexico, Texas, Mexico, and most recently, Hawaii. It is a particular concern in California and Texas, which produce large crops of broccoli, cauliflower, and cabbage.
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John P. Roche is a science writer and author with a PhD and a postdoctoral fellowship in the biological sciences. He has served as editor-in-chief of university research periodicals at Indiana University and Boston College, has published more than 150 articles, and has written and taught extensively about science and science writing. Dr. Roche also directs Science View Productions™, which provides technical writing and developmental editing for clients in academia and industry.