A New Parasitoid Wasp from Russia May Help the Fight Against Emerald Ash Borer
By Ed Ricciuti
Scientists working on environmentally friendly ways to combat insect pests continually quest for biological control’s version of a better mousetrap: natural enemies of a harmful species that outperform those already employed against it. In the case of invasive pests, the hunt may take scientists far afield, even to remote corners of the globe. So it was that Dr. Jian J. Duan, an entomologist at the United States Department of Agriculture’s Agricultural Research Service in Delaware, trekked twice into the vast forests of Russia’s Primorsky Krai region, a magnificent wilderness of mixed hardwoods and conifers so wild that it is a last stronghold of the majestic Siberian) tiger.
The search for parasitized eggs drew Dr. Duan, accompanied by Russian forestry scientists, into the deep woods of interior Primorsky during 2009 and 2010. Finding wasp eggs was rather like a game of hide-and-seek because EAB deposits its eggs under loose bark or crevices in bark. Duan went from tree to tree, stripping away bark and looking for eggs. Not just any eggs, but eggs that had turned black, a tip that the wasp had visited them.
Duan was hoping to identify potential new parasitoids of the emerald ash borer (EAB), a glossy beetle from northeastern China, the Russian Far East, Japan, and the Koreas, that has killed tens of millions of ash trees in the United States since it was detected in 2002. A parasitoid is a parasite that spends a significant part of its life cycle attached to or within its host. While he did not encounter a tiger, Duan found a hitherto unknown species of EAB parasitoid that he and colleagues taxonomically separated from a known look-alike after painstaking research in a USDA laboratory back in Delaware. The research was published in the Annals of the Entomological Society of America.
The two parasitoids are tiny stingless wasps of the genus Oobius, morphologically so similar they are distinguishable only by infinitesimal differences in structures, such as certain segments of the antennae and ratio of length to width. Telling one from the other is a tough task that is not always foolproof when conducted on insects the size of a gnat. The real evidence came from analyzing the genome of both, which showed they were distinct at a molecular level. In addition, research showed that the two species differ drastically in their strategy of diapause, dormancy for aestivation, and overwintering.
Researchers named the new species O. primorskyensis after the area in which it was found, a region administered from the Pacific port of Vladavistok (“primorsky” means maritime in Russian). It and its close cousin, O. agrili, are both parthenogenetic and thus easy to breed for release. O. Agrili has been used to control EAB in the United States since 2007.
Parasitism takes place when the wasps insert their eggs into those of EAB, which provide food for the wasp larvae. Ecological differences in life cycles of the two wasps, according to Dr. Duan, suggest that O. primorskyensis provides a weapon with more firepower against EAB than its relative, especially in areas with cool climates. Observations indicate that it has a life cycle that, in cool climates, may synchronize more in step with that of EAB than does O. Agrili. In a nutshell, almost a full generation of O. primorskyensis larvae overwinters and then emerges as adults in July, ready to parasitize the EAB when it is laying the bulk of its eggs, a period of only 10 to 120 days at most. Thus, under cool conditions, it could destroy a significant proportion of the season’s EAB production.
O. agrili, on the other hand, may produce two or three summer generations, but only a fragment of them diapause for overwintering, so they may be more effectively employed in warmer southern areas, where the period in which EAB lays eggs is longer than in the north.
Eventually, pest control managers may be able to tailor the use of each wasp to the geography and climate of the areas threatened by EAB. O. primorskyensis, currently under quarantine, is undergoing evaluation for possible deployment in the field. If approved for use, it may be a great complement to O. agrili, giving pest control managers a double-barreled blast with which to target EAB. Understanding the ramifications of a few tiny details in biology and a smattering of genetic differences between two species that are nearly identical, morphologically, could have a practical payoff of immense importance in the effort to save the ash trees.
Read more at:
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.