So, what's the problem
Field bindweed (Convolvulus arvensis) is a perennial vine of Eurasian origin. The plant was introduced to other continents including North America and is now considered one of the most noxious weeds of agricultural fields throughout temperate regions. Forming dense tangled mats of vegetation, it outcompetes native forbs and grasses, and can severely reduce crop yields. It can harbour plant diseases and contains alkaloids that may be toxic to some grazing animals, in particular to horses. Its extensive root system and long-lived seeds make it difficult to control by conventional means. Biological control offers an alternative approach: one reason for the plant’s impact may be the absence of natural enemies that attack it in its area of origin.
The weediness of field bindweed is largely attributable to its extensive root system and North American insects attacking the leaves are having little impact. So the United States Department of Agriculture (USDA) initiated a programme to manage field bindweed using biological control in the 1970s. Two biological control agents were introduced from Europe: the gall mite Aceria malherbae and the bindweed moth Tyta luctuosa. The impact of the gall mite varies, while local establishment of the bindweed moth has only recently been reported from the western USA and its impact is not yet clear. The weed continues to be a problem and additional biological control agents are being sought.
What is this project doing?
The project is being revisited through an initiative set-up by the late Dr Richard Hansen (USDA-APHIS-CPHST). CABI’s centre in Switzerland is investigating additional potential agents. So far, we have studied five insect species that showed potential for biological control, and are planning work on two more species.
A guiding principle for biological control is that any released agent should not impact plants other than the target weed. Risk of potential non-target damage is assessed by testing whether a candidate agent feeds or develops on other plant species that it might encounter if introduced. Assessing the impact an agent might have on the target weed is also important so the most-damaging ones can be prioritised.
We have rejected two root-feeding flea beetles, Longitarsus pellucidus and L. rubiginosus, which proved insufficiently specific. We also rejected two leaf-feeding species: the moth, Emmelia trabealis, and the tortoise beetle, Hypocassida subferruginea. Laboratory tests left questions about the host-specificity of the stem-mining agromyzid fly, Melanagromyza albocilia. In no-choice tests (offering one plant species at a time), it laid eggs on six species, including four native to North America, and larvae were found on three of these, all in the genus Calystegia. Moreover, M. albocilia completed its development to adult on the North American native C. macrostegia. To assess its specificity under more natural conditions; in 2017, we started to expose native North American, or economically important plants, at natural field sites in southern Germany. So far, we have tested eight species, six that were attacked under no-choice conditions (four North American natives) and Ipomea batatas (sweet potato). Beside C. arvensis, some feeding occurred on the European Calystegia sepium and some larvae were found on the native North American Cal. longipes. This method proved to be reliable and we plan to continue these open-field tests with additional critical plants.
We started investigating the root-mining clear-wing moth, Tinthia brosiformis, which is only recorded from C. arvensis. Larval feeding can cause the plant to dieback. Methods for rearing and host-specificity testing are being developed with this moth at the Institute for Plant Protection and Environment in Serbia.
Research Scientist, Weed Biological Control
Country Director and Head Weed Biological Control