| Title |
Investigators | Department | Objectives | Approach Keywords | Progress Reports | Impact Statements | Publications | |
Project * COL00746 | |
| Title | Ecology of Pests and Pest Management Systems |
| Investigator(s) | Norton, AP; |
| Department | Bioagricultural Sciences and Pest Mgmt. |
| Objectives | (1) Experimentally examine the interactions between resource availability and weed biological control performance and impact. (A) Determine how a key limiting resource (water) alters Dalmatian toadflax performance and tolerance to herbivory by the biological control agent Mecinus janthinus. (B) Determine how water availability to Dalmatian toadflax alters Mecinus preference and performance. (C) Determine how water-induced changes in both toadflax performance and tolerance and Mecinus preference and performance interact to determine the efficacy of biological control in: i. Small-plot cage studies gardens where I manipulate the ability of Mecinus to choose between Dalmatian toadflax growing under three water availability treatments. ii. Large plot studies where I manipulate water availability to Dalmatian toadflax and Mecinus presence but allow the weevils to select plants in a more natural setting. (2) Evaluate the establishment and impact of Diorhabda elongata releases against the invasive plant, Tamarix spp. in Colorado . |
| Approach | Objective 1A - I will use single potted plants grown under 3 water availability treatments and exposed to 5 different levels of Mecinus attack to describe the relationship between water availability, tolerance to weevil attack and Mecinus performance. I will establish three different water availability treatments: Low (10% of field capacity) intermediate (50% of field capacity) and high (80% of field capacity). Mecinus will be introduced into cages containing a single plant at densities of 0, 2, 5, 10, or 20 weevils per plant. In fall plants will be harvested to determine plant performance and weevil performance. Objective 1B - I will use a series of paired choice tests to examine if changes in water availability alter Mecinus preference and if these preferences are altered if other Mecinus adults or larvae have previously fed upon the plant. Objective 1C (i) Cage studies - Each of 36 cages will contain 3, 0.5 m patches of toadflax in a linear array with patches 0.75 m apart. Each patch serviced by a separate drip system so that I will be able to manipulate the amount of water each receives. I will establish the following treatments: a) No-choice - all plants within a cage receive the same water addition treatments. b) Choice - Each plot within a cage receives one of the above water addition treatments. c) Mecinus additions of either 160 per cage or no addition. One half of the cages will receive 160 adult Mecinus and one half will serve as no weevil controls. Every two weeks I will measure soil water under each patch of toadflax in each cage, the number of Mecinus adults present in each patch, the number of flowers and ripe fruit present, and the number and height of each stem. In fall I will measure toadflax above ground biomass, weevil densities and survivorship. (ii) Large plot studies - Each of 42 2 x 2 m plots will contain 16 toadflax plants. Using a RCB design I will establish High, Medium, and Low water availability treatments crossed in a full factorial design with Mecinus additions of either 96 weevils per plot or none. Each spring the previous years stems will be harvested and returned to the laboratory for dissection to determine above ground biomass and weevil densities and survivorship. Objective 2 - Diorhabda elongata was released at 4 sites in Colorado in August 2005. Beetles were released in Echo Park, Dinosaur National Monument in May 2006. At these sites, I will measure Diorhabda population densities, spread, and impact on Tamarix and associated vegetation. The presence and status of D. elongata will be determined every two weeks throughout the growing season. The number of eggs and egg masses, 1st, 2nd, and 3rd instar larvae as well as adult beetles will be recorded on 25 permanently marked trees. Every two weeks throughout the growing season tree size and condition will be assessed on the same 25 permanently marked trees. Once each year in June we will assess the species richness and percent cover of associated vegetation in 2 1m x 1m plot located under each tree. |
| Keywords | Biological control, Plant invasions, Mecinus janthinus, Diorhabda elongata, Tamarix, Linaria dalmatica, Impact, Resource availability |
| Progress Reports | |
| 2004 | Progress for Objective A. We examined the impact of several commonly used pesticides on the survivorship of the fungal-feeding beneficial mite, Homeopronematus anconai. Laboratory bioassays of the effects of 24 hour old residues of field rates indicated that ithe fungicides Quadris (azoxystrobin) and Sovran (kresoxim-methyl) and the insecticide Provado (imidacloprid) did not significantly reduce survivorship relative to controls. The fungicides Flint (trifloxystrobin) and Dithane (mancozeb) and the insecticide Sevin (carbaryl) exhibited intermediate effects, resulting in 24 hour survivorship of 77%, 68% and 43% respectively. The acaricides Pyramite (pyridben) and Kelthane (dicofol) and the fungicide sulfur were the most toxic, killing greater than 97% of the beneficial mites exposed to residues of these compounds . Progress for objective D. Animal-mediated pollination is a vital process that occurs throughout angiosperms, and pollinators may mediate the interaction between different species of flowering plants. A majority of flowering plants are limited in seed production by the amount of pollen they receive and the loss or reduction of pollinators has been directly implicated in the population decline of some native plants. We examined the influence of the invasive weed Carduus nutans (musk thistle) on pollinator visits to the native plant, Campanula rotundifolia (common harebell). The study took place in the Arapahoe-Roosevelt National Forest in Larimer County, Colorado at an elevation of 2500 meters. The site of the experiment was dominated by open grass meadows interspersed among Pinus ponderosa, Pseudotsuga menziesii, and Pinus contorta. In these meadows we constructed 20, 4 x 4 meter plots that contained arrays of potted plants. We randomly assigned 10 plots as control plots and 10 as treatment plots. Control plots consisted of six potted C. rotundifolia plants while the treatment plots consisted of four potted C. rotundifolia and four potted C. nutans. Each plot was separated from its nearest neighboring plot, or any naturally occurring C. nutans, by at least 100 meters. We observed a subset of C. rotundifolia plants in both the control and treatment plots on 6 occasions in August and early September, the peak blooming period for both of these species. During each bout, we recorded the number of flowers visited per bout per pollinator. We calculated proportion of flowers visited per minute. We also recorded the total number of pollinators visiting the plot during each bout. In response to the presence of C. nutans, C. rotundifolia plants in treatment plots experienced a 37.5% decrease in the proportion of flowers visited per minute (P < 0.05). In addition, 53% fewer individual pollinators visited C. rotundifolia when C. nutans was present (P < 0.05). Both the proportion of flowers visited and the number of pollinators visiting Campanula rotundifolia decreased in the presence of Carduus nutans. This indicates that C. nutans has the potential to negatively affect C. rotundifolia by decreasing pollinator visitation rates, and thus (potentially) seed set of this native plant. |
| 2005 | Progress on Objective C: Determine the impact of arthropod biological controls on Dalmatian toadflax populations. Dalmatian toadflax (Linaria dalmatica, Scrophulariaceae) is an introduced weed, declared noxious by 11 states. This weed has become a significant problem species in a number of western states. This plant is common in mesic to xeric locations, but larger plants in higher densities are associated with a greater abundance of early spring water deposition. At our study area in southern Wyoming, Dalmatian toadflax is found in greatest abundance in portions of the landscape that experience higher winter snow deposition or higher water accumulation from snow melt (i.e. lower areas adjacent to snow deposition that accumulate spring run off). The stem-boring weevil Mecinus janthinus was introduced into the United States as a biological control agent for this weed in 1997, and has since become established in Washington, Montana, Idaho, Wyoming, Colorado and Oregon. Adults of this species feed on the leaves of the plant, but the majority of plant damage is attributed to larval feeding within plant stems. Dramatic impacts of the weevil on Dalmatian toadflax populations have been seen in some, but not all locations. The purpose of this research was to determine: (1) The impact of water availability on Dalmatian toadflax size and fruit production, (2) The impact of well watered vs. moderately vs. severely drought stressed plants on weevil survivorship and (3) The impact of weevil attack on well watered, moderately , or severely drought stressed plants. I examined the impact of host-plant water stress on plant performance, weevil oviposition rates, and survival. Beetles were caged on potted toadflax plants and given the choice between plants in each of three water treatments. The weevil had greatest impact on toadflax fruit production in high water treatment plants, but had greatest impact on stem production and plant weight in the intermediate water treatment. None of the plant performance variables measured significantly responded to weevil feeding in the low water treatment. Weevils preferred well-watered plants, but there was no significant impact of water treatment on weevil survivorship. These results indicate that the impact of this biological control agent on its host plant is context dependent, and varies with the amount of water available to the plant. Continuing research will allow us to determine where this biological control agent will be most effective in reducing the spread and impact of Dalmatian toadflax. Improved understanding of where and how biological controls can be effective will improve the efficacy and efficiency of weed management systems. |
| 2006 | Dalmatian toadflax (Linaria dalmatica, Scrophulariaceae) is an introduced weed, declared noxious by 11 states. This weed has become a significant problem species in a number of western states. This plant is common in mesic to xeric locations, but larger plants in higher densities are associated with a greater abundance of early spring water deposition. At our study area in southern Wyoming, Dalmatian toadflax is found in greatest abundance in portions of the landscape that experience higher winter snow deposition or higher water accumulation from snow melt (i.e. lower areas adjacent to snow deposition that accumulate spring run off). The stem-boring weevil Mecinus janthinus was introduced into the United States as a biological control agent for this weed in 1997, and has since become established in Washington, Montana, Idaho, Wyoming, Colorado and Oregon. Adults of this species feed on the leaves of the plant, but the majority of plant damage is attributed to larval feeding within plant stems. Dramatic impacts of the weevil on Dalmatian toadflax populations have been seen in some, but not all locations. Previous research has demonstrated that the impact of this biological control agent is context dependant: Plants given more water are more tolerant of weevil feeding than plants that receive only a moderate amount. Thus the highest performing plants appear to be the least susceptible to biological control. Because these high performing plants have a greater impact on the rangeland they infest this increased tolerance in high performing plants is troubling. I examined whether (a) the biological control agent preferred well watered plants over low water plants and (b) whether the biological control agent produced more offspring in well water vs. low water plants. (a) In choice tests performed within cages, Mecinus significantly preferred well-watered plants over low water plants. More than 80% of the weevils were found on the high water treatment plants after 24 and 48 hours. (b) Well-watered plants enabled the weevil to produce more offspring. High water plants generated nearly one hundred adult weevils, while low and moderately water plants produced approximately 50 and 75 weevils, respectively. These results suggest that although well-watered plants may be more tolerant of Mecinus feeding, the weevil's increased preference for and performance on these plants may be able to overcome tolerance. Mecinus may be able to contribute to biological control of toadflax in the portions of the landscape where it is most problematic. |
| Impact | |
| 2004 | An increased understanding of the ecological interactions between pests, pest management tactics and the environment is essential for the development of improved management strategies . These results will A) Allow grape growers to select pesticides that have less of an impact on beneficial mite species, and B) Give resource managers improved information of the impact of noxious weeds on native plants and the environment. |
| 2005 | Biological control has at times provided spectacular control of noxious weeds. Not all biological control agents are effective, and not all effective agents are effective in all locations. This research will improve our understanding of under which conditions biological controls are most effective. In the present study, Mecinus janthinus was most effective under conditions that were most favorable to its host plant. These results will aid land managers in determining which control strategies are most appropriate for their site, and will aid in the selection of the most economically sound and environmentally appropriate management strategies . |
| 2006 | Biological control has at times provided spectacular control of noxious weeds. Not all biological control agents are effective, and not all effective agents are effective in all locations. This research will improve our understanding of under which conditions biological controls are most effective. In this study I found that biological control agent preference and performance differences may be able to overcome differences in host plant tolerance to biological control. These results will aid land managers in determining which control strategies are most appropriate for their site, and will aid in the selection of the most economically sound and environmentally appropriate management strategies. |
| Publications | |
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