So what's the problem?
Field bindweed (Convolvulus arvensis) is a perennial vine of Eurasian origin. It tends to form dense tangled mats and out-compete native forbs and grasses. Furthermore, field bindweed can harbour plant diseases and is toxic to horses. The weed was introduced to North America and Australia and is now considered one of the most noxious weeds of agricultural fields throughout temperate regions of the world. Field bindweed is difficult to control with conventional methods due to its extensive root system and seed longevity.
What is this project doing?
In the 1970's, the United States Department of Agriculture (USDA) initiated a programme to control field bindweed using biological control. Two biological control agents have been released to date: the gall mite Aceria malherbae and the bindweed moth Tyta luctuosa. The gall mite became established but its impact under field conditions varies, whereas establishment of the bindweed moth could not be confirmed. The weed continues to be a problem, thus, additional biological control agents are needed.
Through an initiative of Dr Richard Hansen (USDA-APHIS-CPHST), the project was revisited and CABI’s centre in Switzerland provided with start-up funding to investigate additional potential agents.
Results so far
Three insect species were so far selected as potential additional biological control agents: the stem-mining agromyzid fly Melanagromyza albocilia and the root-feeding flea beetles Longitarsus pellucidus and L. rubiginosus.
In 2010 and 2011, we conducted no-choice larval transfer tests (where newly hatched larvae are physically transferred onto plants) with the root-feeding flea beetle, L. pellucidus, with C. arvensis (the target weed) of various European and North American origins and 20 test plant species (15 native to North America). Adults developed on six test species, including the native North American Convolvulus equitans and several native Calystegia species. However, plants from other genera were not attacked. In a subsequent multiple-choice cage test (exposing multiple test plants and the control, field bindweed), all plant species were attacked.
Longitarsus rubiginosus is a closely related species to L. pellucidus, also associated with field bindweed in the literature and it occurs on the same sites. Preliminary host range tests were conducted with seven test plant species and the control (C. arvensis). Adults emerged from field bindweed, Calystegia sepium and two native North American species.
As results of preliminary no-choice larval transfer tests were similar for L. rubiginosus and L. pellucidus, we included both species in an open-field test and choose a site where both species occur. Unfortunately, only few flea beetles emerged. While L. pellucidus only emerged from C. arvensis control plants, L. rubiginosus also emerged from the native North American Convolvulus equitans and Calystegia macrostegia.
Although L. pellucidus had a high attack rate on most test plants in the multiple-choice test conducted in 2011, results of the open-field test indicate a narrow ecological host range. However, since only few adults emerged, results are not conclusive and the test would need to be repeated. In contrast, L. rubiginosus does clearly not appear specific enough to be further considered as a potential biological control agent for field bindweed.
The stem-mining agromyzid fly Melanagromyza albocilia has 2-3 generations per year. Between 2010 and 2012, plants were collected in the field in Southern Germany and dissected for pupae. The parasitism rate varied between 50 and 75% and only about 10 to 20% of the flies emerged from overwintered pupae. Between 10 July and 4 October 2012, plants were collected in the field in southern Germany. A subsample of the plants was measured and fully dissected (N=540) to assess seasonal variations in attack rate. The attack rate was variable over time and across field sites with peaks at the end of July and the end of August. The roots of the remaining plants (over 3,700) were dissected and 238 live pupae and 39 larvae were extracted and are being overwintered to continue host specificity tests in 2013. The relatively low attack rates in the field, combined with low adult emergence and high parasitism, demand sustained efforts in mass collection.
Attack by this agromyzid fly proved difficult to obtain in captivity. In 2010 attempts to obtain oviposition (egg laying) and development were unsuccessful. To better understand requirements for mating, feeding and oviposition of M. albocilia, several different methods were tried in 2011. We observed greater fly activity in larger containers, and the addition of honey as a food source appeared to trigger mating and oviposition. In longevity and oviposition trials conducted in 2012, females had a variable lifespan with an average of 15.6 ± 3.9 days, and a maximum of 59 days. One female laid an average of 20.9 ± 8.9 eggs during its life; about one egg per day. The maximum observed was 73 eggs over a lifespan of 37 days.
In 2011, two native North American test plant species received eggs in preliminary no-choice tests. Subsequently, sequential no-choice tests were conducted, offering cut shoots of a test or control (C. arvensis) plant for a period of 1-3 days to a mated fly female. Of nine additional test species exposed, eggs were found on four North American natives, usually at a lower level than on C. arvensis. None of the Ipomea species exposed received eggs. Feeding was relatively low on the non-target species compared to C. arvensis, indicating a clear preference for the target. Potted plants exposed in preliminary development tests did not yield sufficient results with only one out of four controls attacked. In 2013, we will focus to improve development tests using potted plants, to investigate, whether plants accepted for egg laying will also support larval development.
An updated test plant list is currently being circulated among our North American partners for submission to USDA, APHIS TAG (Technical Advisory Group).
Hariet L. Hinz
Address: Rue des Grillons 1, CH-2800 Delemont, Switzerland
Tel: +41 (0)32 4214872
Tel: +44 (0) 1491 829053
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by A Bailey, D Chandler, W Grant, J Greaves, G Prince, M Tatchell
28 October 2010
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