2012 Annual Report
1a.Objectives (from AD-416):
Objective 1: Characterize the basic biology of target weeds, such as hoary cress, swallow-worts, medusahead, and guineagrass, and their natural enemies.
Sub-objective 1.A. Characterize the genetic diversity and basic biology of target weeds and determine their regions of origin.
Sub-objective 1.B. Conduct foreign exploration in Europe, Asia, and Africa for natural enemies of U.S. target weeds.
Objective 2: Elucidate plant-natural enemy interactions and identify potential candidates for U.S. introduction.
Sub-objective 2.A. Conduct preliminary host-specificity and effectiveness testing and facilitate U.S. introduction through prioritization and rearing of agents for target weeds, including, but not limited to giant reed, and swallow-worts.
Sub-objective 2.B. Evaluate plant-insect interactions in evolutionary and ecological contexts – the role of visual ecology in host plant finding, selection and acceptance by candidate agents; evolution of differential host specificity in a biological control agent; efficacy of multiple vs. single weed biological control agents.
1b.Approach (from AD-416):
We have adopted a “weed management pipeline” approach to our research that answers essential questions for successful classical biological control. A significant focus of this research is aimed at understanding the basic biology of target weeds, especially characterization of the genetic diversity of targets in their native and adventive ranges. This work will help identify the target’s region of origin, as well as the region(s) from which populations of the target have been introduced into the U.S. Foreign exploration for natural enemies will be conducted concurrently with these studies on target biology; this exploration will provide candidate biological control agents for the following studies. These investigations address target weed-natural enemy interactions, which will include host-specificity and effectiveness testing to facilitate introduction to the U.S., as well as experiments aimed at developing a mechanistic understanding of the evolutionary, ecological, and physiological factors of plant-insect interactions relevant to weed biological control. Successful control of a target weed usually requires decades of research effort, and the research proposed here will be an important step towards ecologically-rational management of some of the most important invasive weeds in the U.S.
Progress was made on both objectives and their subobjectives. Under subobjective 1a, we developed neutral inter-sample sequence repeats (ISSRs) for silverleaf nightshade and began genetic analyses to compare native populations to Greek populations. We obtained samples of native populations from Mexico and Arizona. Results suggest that Greek populations of silverleaf nightshade are the result of multiple introductions. We continued to analyze sequences of two chloroplast regions in Guinea grass (modern African and Texan samples), as well as historical specimens in the CIRAD collection, some dating back to 1944. Samples of giant reed infested by a leaf mining cecidomyiid fly were collected to inventory fungi present in the fly’s galleries to identify a possible insect-fungal symbiosis. DNA extraction yielded 16 species (51 strains) of fungi from 25 localities in Spain, France, Sicily, and Crete. Under subobjective 1b, we conducted foreign exploration in Ukraine to collect medusahead seeds; these seeds were included in a host specificity study that evaluated the impact of a smut using native and North American medusahead seeds. Our rangeland weed research is supported by Projects 0212-22000-023-10R and 013R (USDI-BLM) and 023-14S (BBCA in Italy). We continued mass collections of two giant reed biological control agents in Spain and France for shipment to our collaborator in Texas. More than 5 million specimens were shipped, and one of the agents is now well-established in the Rio Grande Valley. American Farm School MOU 0212-22000-023-11M gives our Greek substation lab and office space, facilitating exploration and field work in the Balkans. We initiated work at our Greek substation to evaluate epidemiology of plant diseases on Canada thistle, milk thistle, and silverleaf nightshade. Under subobjective 2a, we made significant progress toward understanding plant-herbivore trophic relationships, insect oviposition and feeding behavior, and bionomics. A field experiment was conducted in Turkey to evaluate damage by a chloropid fly on medusahead seed production; this is a newly discovered host association for the fly. Host specificity, life history, and behavioral studies were conducted with two potential biocontrol agents of swallow-worts; one of these insects shows promise for future swallow-wort control. Host specificity and dispersal tests were conducted with a psyllid, a potential biocontrol agent of French broom, under field conditions at EBCL. A petition for release of a candidate agent of hoary cress was submitted. Field studies were conducted to identify and evaluate the factors affecting leafy spurge invasiveness, and develop an integrated control strategy for this weed. Research was planned to study the impact of a chloropid fly on common reed at our Greek substation. Under subobjective 2b, we began characterizing spectral reflectance curves of weeds to be used in future host finding studies. We developed microsatellites for a weevil that is a potential biocontrol agent of hoary cress and shipped weevil samples to our ARS collaborator. We established a field experiment to assess Rhizoctonia-weevil-hoary cress interactions.
Hybrid origin of invasive Guinea grass. Guinea grass is a native of Africa that has been extensively and successfully introduced as a source of animal fodder to tropical areas of both hemispheres. On a global scale, but particularly in the southwestern United States, the Caribbean, and Hawaii, it is becoming a serious threat to biodiversity not only due to its invasiveness but also because it depletes surface water, crowds out native plant species, and produces high fuel loads for wildfires. Moreover, in the Rio Grande corridor of Texas it is an impediment border patrol activities. Using molecular tools, source populations of the Texas invasion were identified in the native range in order to facilitate the search for potential biological control agents. Results indicate that Texas populations are hybrids between two species, one of which occurs only in eastern Africa. These results will be instrumental in guiding future exploration and collection of natural enemies of Guinea grass in Africa.
Herbivorous insect is a candidate for biocontrol of swallow-worts. Swallow-worts are invasive weeds in northeastern North America and pose a significant threat to native biodiversity. Two species of swallow-worts are abundant in this region and are expanding their range at an alarming rate; pastures, right of ways, riparian areas, and forests are being inundated. ARS EBCL researchers in Montpellier, France evaluated the biological characteristics of a European moth, Abrostola asclepiadis, to determine its potential as a biocontrol agent for swallow-worts. Feeding specificity tests using a wide range of possible plant species indicated that this insect feeds only on a very narrow range of swallow-worts – an important attribute for a biocontrol agent. Biological studies with the moth on different plant species confirmed this specificity to swallow-worts. These promising results show that this insect has potential for swallow-wort management in the U.S.
A petition for field release of a biological control agent of hoary cress, an invasive weed. Hoary cresses are perennial noxious weeds accidentally introduced from Europe in the late 19th century that have spread to most of the U.S. and Canada. They are difficult to control using chemical or cultural control practices. To date no biological control agents have been introduced into North America. ARS EBCL-Thessaloniki research identified a plant-parasitic mite as a candidate agent and helped demonstrate its high specificity and potential impact on the target weed. The mite causes abnormal growth of developing shoots and flowers that greatly reduces or prevents seed production. The petition to APHIS proposes initial field releases to be made in Montana with future releases in adjacent states. The intent of the proposed release is to limit further spread of hoary cress infestations and reduce population densities.
Berner, D.K., Smallwood, E.L., Cavin, C.A., Eskandari, F., Tunali, B., Buyuk, O., Yildirim, A., Mukhina, Z., Kolomiets, T., Matveeva, T., Bogomaz, D., Kassanelli, D., Souissi, T., Mejri, D., Latiri, K., Kashefi, J., Lagopodi, A. 2011. Mutual benefits through formalized international collaboration on biological control of weeds with plant pathogens. Tunisia Journal of Plant Protection. 6(1):49-74.
Bon, M., Guermache, F. 2012. First report of black swallow-wort as an alternate host of the two-needle pine stem rust pathogen, Cronartium flaccidum (Alb & Schwein.) G. Winter, in France. Plant Disease. 96 (4),585. http://dx.doi.org/10.1094/PDIS-11-11-0966.
Gaskin, J.F., Schwarzlaender, M., Williams, L., Gerber, E., Hinz, H. 2012. Minimal genetic diversity in the facultatively outcrossing perennial pepperweed (Lepidium latifolium) invasion. Biological Invasions. 14:1797–1807. Available: DOI.10.1007/s10530-012-0190-4.
Guermache, F., Rodier-Gaud, M., Caesar, A.J., Heraud, C., Bon, M. 2012. Bi-fluorescence imaging for estimating accurately the nuclear condition of Rhizoctonia spp.. Letters in Applied Microbiology. 54, 568-571. doi:10.1111/j.1472-765X.2012.03245.x.
Guggisberg, A., Welk, E., Sforza, R., Horvath, D.P., Anderson, J.V., Foley, M.E., Rieseberg, L.H. 2012. Invasion history of North American Canada thistle, Cirsium arvense. Journal of Biogeography. 39/10:1919-1931. doi:10.1111/j.1365-2699.2012.02746.x.
Williams III, L.H., Hagler, J.R., Tonkel, K.C. 2011. Retention of immunolabels by Diorhabda carinulata (Coleoptera: Chrysomelidae), a biological control agent of saltcedar. Entomologia Experimentalis et Applicata. 141:154-162.