By Dr. Rob Morrison
Research recently appearing in the journal Biological Control may change how we view native predators of the brown marmorated stink bug (BMSB). BMSB is an invasive species that was accidentally introduced to the United States from Asia in Pennsylvania, and has since been detected in more than 40 U.S. states. It feeds on more than 150 plant species, making it a large threat to many agricultural systems in the country.
Dr. Tracy Leskey from the USDA-ARS Appalachian Fruit Research Station, Dr. Clarissa Mathews from Shepherd University, and I evaluated 25 native generalist natural enemy species collected from the field as potential predators of BMSB egg masses in the laboratory. More than 450 individual predators were tested, including immature and adult life stages, and they were given the opportunity to feed on BMSB egg masses. The eggs were photographed before and after predator exposure in order to evaluate and characterize damage inflicted by specific predator species. The aim was to link egg damage to specific groups or guilds of predators.
In the past several years, there have been large sentinel egg mass deployments in the U.S. A sentinel egg mass is one where researchers place the eggs on a notecard, and put it in a tree to understand predation and parasitism in the field. These are usually left out for 48 hours, and researchers then retrieve them at the end of the period. However, as researchers have been retrieving them, they have noticed that a great many notecards have egg masses that are missing. In the past, this has been assumed to be from wind, abrasion by leaves rustling against each other, or from rainfall.
However, the current study sheds some light on what may be a more common reason for the missing egg masses, namely biological control by native predators. We were able to categorize the damage caused by the predators to eggs into four feeding syndromes. Both the handling behavior of the predator as well as their type of mouthparts were important for determining which feeding syndrome a species caused on an egg mass.
One of the feeding syndromes was “complete chewing,” where the egg mass was either partially or fully consumed so that there was no trace of it, which could make researchers assume that the egg mass was missing, thereby deflating estimates of biological control. However, the most common and frequent predation was by katydids, and these are complete chewers, which strongly suggests that an alternative explanation for these missing egg masses may be from the good work our native predators are doing.
In addition to katydids, the most frequent and voracious predators of BMSB stink bug eggs included crickets, ground beetles, jumping spiders, and earwigs. While orthopterans such as katydids and crickets are typically thought to primarily eat plants, many are omnivorous and will take advantage of protein-rich resources such as stink bug eggs in crops. We found that these same native predators were also present in vegetable and fruit agroecosystems in the mid-Atlantic. Importantly, we found that lady beetles are not an important source of mortality for BMSB eggs. In total, seven lady beetle species were tested and neither adults nor larvae appreciably consumed any eggs.
Predators were also observed using videography, and some interesting behaviors emerged that further suggest native predators may not be getting as much credit as they deserve in the biological control of BMSB. For example, jumping spiders would often pick up an egg mass, roam around a petri dish with it, and then finally sink their chelicerae into the eggs to feed. This may indicate that other predators may actually be physically removing eggs and taking them elsewhere before feeding on them.
Ultimately, knowing the identity of the main predators of BMSB will provide a basis for designing landscapes to benefit the natural enemy community, which may contribute to the long-term suppression of BMSB.
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Dr. Rob Morrison is a postdoctoral researcher at the USDA-ARS Appalachian Fruit Research Station in Kearneysville, WV and has been studying methods for increasing the sustainability of agriculture for the past decade. He received his PhD from Michigan State University in the Department of Entomology, and has more recently been working on the development of an attract-and-kill approach for managing BMSB in apple orchards. You can find out more about him and his ongoing work with the brown marmorated stink bug at his website: https://williamrobertmorrisoniii.wordpress.com/.