Assessing the Potential for Biological Control of Field Bindweed, Convolvulus arvensi, with the Gall Mite Aceria malherbe, and the Moth Tyta luctuosa

Final Report for ANC93-018

Project Type: Research and Education
Funds awarded in 1993: $0.00
Projected End Date: 12/31/1996
ACE Funds: $75,185.00
Region: North Central
State: Kansas
Project Coordinator:
James Nechols
Kansas State University
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Project Information

Summary:

[Note to online version: The report for this project includes graphs that could not be included here. Please see attachments below for a scan of the complete report and inclusion of graphs.]

The bindweed moth, Tyta luctuosa, was shown to successfully overwinter in Kansas for two consecutive years. However, survival varied considerably among and within locations in Kansas. In 1994-95, the average rate of survival, from the overwintering cocoon stage to fully emerged adult moths capable of flight, ranged from 0 to 23 percent. These findings were similar to those obtained in 1993-94 (range of survival: 0 to 20 percent). The highest survival in a single cage was 64%. Moth survival was no higher at southern sites than at northern ones suggesting that this bindweed enemy may be adapted to cold climates. Very few moths were recovered in a largescale field experiment designed to assess dispersal. Therefore, we began studies to identify the volatile chemicals produced by female moths that are used as sex attractants. Our rationale was that a species-specific sex attractant would be a useful tool for monitoring dispersal. Two major compounds were identified which elicit a response from males. A field experiment revealed that moderately high densities (about 75/m2) of large T. luctuosa caterpillars are necessary for complete defoliation of bindweed in the field. A greenhouse experiment showed that younger (smaller) bindweed plants not only are defoliated by fewer caterpillars, but that the rate of root growth and refoliation is slower when younger plants are damaged. Also, the greater the defoliation of any aged plant, the slower the recovery. Through presentations, publications, tours, radio shows, press releases, and individual on-farm training sessions, we educated large numbers of farmers, county weed personnel, and the general public about our biological control research efforts for field bindweed. These activities have increased awareness of nonpesticide alternatives for managing weeds, and the potential of using natural enemies to control field bindweed, an extremely serious pest in the Midwest and throughout the United States. Dissemination of our project goals and research findings also has led to cooperation from local farmers.

Project Objectives:

Insect biology:

1. To evaluate the overwintering potential of the gall mite, A. malherbe, and the moth T. luctuosa, in different climatic zones within the North Central Region.

2. To determine the dispersal ability of the moth (T. luctuosa) at several release sites.

Plant-insect interactions:

3. To determine the effects of moth (caterpillar) introductions on field bindweed growth, and determine the infestation levels necessary to ensure detrimental effects to field bindweed.

4. To investigate and quantify field bindweed population reduction by the moth (caterpillar).

Grower training and dissemination of knowledge:

5. To train and involve farmers with on-farm releases, surveying, and monitoring of the biological control agent, and in the evaluation of success.

6. To disseminate knowledge of the symptomology, ecology, and biology of moth to farmers and farmer organizations, extension personnel, other researchers, and those concerned with noxious weed control.

Research

Research results and discussion:

1. Overwintering survival.

Bindweed moth. Experiments with an Italian population of Tyta luctuosa in 1993-94 and 1994-95 revealed that this field bindweed natural enemy is able to survive the winter and emerge as adult moths in two different climatic zones in Kansas. In 1993-94, two thirds and three quarters of the pupae survived the winter in the soil in northern (Geary County) and southern (Butler County) Kansas, respectively. However, only 20% of the pupae produced adult bindweed moths at the northern site, and none emerged from the southern site. In 1994-95, the study was expanded to include six counties covering an area from northeastern to southwestern Kansas. Adult moths emerged at 4 of the 6 locations representing both climatic zones. The percentage survival varied greatly among sites and among cages at the same site. Mean survival ranged from 1% in Butler County to 23% in Kingman County. Sixty-four percent of the moths emerged from one of the three cages in Kingman. We released overwintered moths of T. luctuosa at three sites in Kansas as follows: Abilene (Dickinson Co.) 6; Manhattan (Riley Co.) 14; Kingman (Kingman Co.) 26.

Gall mite. In contrast to the positive results for the bindweed moths, there was no evidence of overwintering success of a Greek population of the gall mite Aceria malherbe in northern or southern Kansas. Two sites were tested in 1993-94, and four in 1994-95. It is unclear whether gall mites failed to overwinter, or if they did not successfully infest field plants in autumn prior to overwintering. In 1993, a pre-overwintering check about a month after we had transplanted lab-infested plants to the field sites (where they had been joined to outdoor bindweed) did not reveal galling on the field plants. In 1994, we observed only limited galling of field plants adjacent to potted plants infested with gall mites. Therefore, poor summer survival of gall mites may contribute to the problem of colonizing this natural enemy in Kansas.

2. Dispersal ability of T. luctuosa.

In July 1994, fifty-two mated, female bindweed moths were released at the center of a large (100 meter radius) circular field plot that was heavily infested with field bindweed. This plot had been previously marked off into 3 x 3 meter grids. About 3 weeks after moths were released, an intensive search for bindweed caterpillars was made in thirty-two of the grids surrounding the plot center. Only one larva was recovered in two days of searches. This low recovery may be related to low reproduction, low adult, egg and/or larval survival, or moth dispersal beyond the area of search.

In 1995, we adopted a new approach for studying moth dispersal. Working with Dr. Ralph Charlton, an insect behaviorist/chemical ecologist in the Department of Entomology, Kansas State University, we began to study the chemistry of odors produced by female moths, which they use as species-specific sex attractants to lure male moths. We found that extracts from female moth glands that are attractive to males are composed predominantly of two volatile components — (Z)-9-tetradecenal and (Z)-11-hexadecenal. Flight behavior tests in the laboratory showed that the synthetic chemical compound was not as attractive to male moths (75-80% responded) as the sex attractant emitted by live females (95% response). Three minor components — 16-aldehyde, (Z)-9-14:alcohol, (Z)-11-16:alcohol — also have been extracted from glands of female moths. However, male moths do not appear to be responsive to these trace extracts. Studies are underway to attempt to collect and analyze the volatile chemicals emitted as the active sex attractant by female moths. We expect that this alternative approach will lead to the discovery and synthesis of the specific blend of sex attractants used by moths. Sex attractant traps not only could be used to monitor moth dispersal and distribution, but they also will allow us to determine whether bindweed moths become permanently established at sites where we have released them.

3. To determine the effects of moth (caterpillar) introductions on field bindweed growth, and determine the infestation levels necessary to ensure detrimental effects to field bindweed.

Caterpillar food preference. Laboratory experiments showed that caterpillars of the bindweed moth consumed equal amounts of foliage when given a choice of four field bindweed biotypes plus hedge bindweed (Appendix 1). In no-choice tests, caterpillar growth and development (as measured by weight gain) and foliage consumption rates also were similar among bindweed biotypes, but caterpillars developed the slowest on hedge bindweed. Final caterpillar weights and rates of survival did not differ when fed on the field bindweed biotypes or on hedge bindweed (Appendices 2 & 3).

Feeding impact of Tyta on different aged bindweed plants. Greenhouse experiments were conducted to determine the effect of caterpillar density on field bindweed of different ages. Third instar caterpillars were introduced to 17-, 25-, and 34-day old field bindweed. Caterpillars were allowed to feed until they entered the soil to form cocoons. Feeding damage by the caterpillars and regrowth of the bindweed was evaluated and compared to non-treated (non-infested) plants. Plants 17, 24 and 34 days old were completely defoliated by 2, 8 and 16 caterpillars, respectively. Leaf area regrowth was related to plant age and the amount of defoliation by the caterpillars. Leaf areas of those plants that were younger or were more severely defoliated were not able to recover to the size of the non-infested upon plants of the same age during the course of the experiment. Root growth after cessation of feeding was also slower for those plants with more defoliation, i.e., the plants that were more severely defoliated were not able to recover to the size of the non-infested plants during the course of the experiment. This data supports the hypothesis that continued leaf feeding over time would reduce plant vigor and competitiveness and aid in weed suppression.

4. To investigate and quantify field bindweed population reduction by the moth (caterpillar).

During the summers of 1994 and 1995 field experiments were initiated to determine the impact of Tyta on field bindweed. Ring cages (0.7m2), divided into two equal sections were placed over field bindweed plants such that an equal amount of bindweed was in each ½ of the ring. Newly molted, third instar caterpillars (0, 5, 10, 15, 25 caterpillars) were introduced to ½ of each ring. Each day the cages were evaluated by placing a grid over the cage and noting consumption at 25 points within both sides of the ring. Plant consumption was noted daily until the caterpillars entered the soil to form cocoons and pupate. When the caterpillars entered the soil each ring was rated visually to determine the feeding impact of the caterpillars on the side where they were released compared to the non-infested material in the other ½ of the ring. After evaluation, the remaining bindweed was harvested from the rings and brought back to the lab. Leaf area was determined and compared among treatments. Individual plot ratings varied.

Average control, based on visual estimation, increased with greater caterpillar numbers. An average of 67 percent control was obtained at the highest densities with some plots completely defoliated. Leaf area change was positive at low caterpillar densities indicating that plant growth was exceeding damage caused by caterpillars. At the highest caterpillar density, leaf area reduction averaged 67 percent.

The large ranges in visual and leaf area change indicate the impacts that environmental and plant factors will have on foliage reduction. High plant growth rates will compensate and overcome caterpillar damage at low caterpillar density. If the caterpillar to leaf area ratio is high, better defoliation is obtained.

5. To train and involve farmers with on-farm releases, surveying, and monitoring of the biological control agent, and in the evaluation of success. Several activities have taken place to train farmers about the biological control organisms and to enlist their help in on-farm trials.

In mid-August 1994, farmers and other interested persons were notified of a training session on the potential for biological control of field bindweed. On September 2, 1994, we held this training session at Kansas State University (see attached agenda). Twenty four people attended. The presentations covered the background and rationale for biological control, the advantages and disadvantages of biological control approaches, background on the two bindweed natural enemies that we are evaluating, tours of the rearing facilities, and training of the cooperators in the release and care of some biological control organisms. All participants were provided with T. luctuosa caterpillars to rear, overwinter, and release on their farms. All participants agreed to report on the overwintering success of the moth. Several of the participants also volunteered to provide overwintering sites for our larger-scale experiments. Other activities relating to training are listed under Objective 6, below.

In 1995, we enlisted the help of interested farmers and provided them with on-farm training in support of a portion of our field research. For our overwintering survival experiment with T. luctuosa, we worked with farmers at two of our six study sites. At a third site (Kingman), we met with a grower on whose land we conducted the study and explained the purpose of our research. At Abilene and Coldwater, Kansas, we put our overwintering cages in with the help of the farmer cooperators. These individuals were contacted at different times throughout winter and early spring and helped check for moth emergence. The individuals we worked with had attended our August, 1994, training session, and had expressed an interest in helping with our overwintering research.

6. To disseminate knowledge of the symptomology, ecology, and biology of the moth to farmers and farmer organizations, extension personnel, other researchers, and those concerned with noxious weed control.

To increase interest in and awareness of biological control of field bindweed, and to disseminate the knowledge gained from the experiments, several activities were scheduled including press releases, radio shows, and presentations at weed control meetings. We also worked individually with selected farmers (see Objective 5, above).

Presentations

March 1, 1994. Annual Winter Meeting of the Kansas Association of County Weed Supervisors. Approximately 250 people attended from over 80 of the 105 counties in Kansas. At this meeting we presented an overview of biological control of weeds, information on the organisms that we were working with, and our planned research approach. We also received several inquiries from people wanting to help with the project.

April 20, 1994. Sustainable Agriculture Symposium at Kansas State University. Attendance 250. We presented information on our project in the form of a poster at the meeting. We spent time informally discussing our research with people who viewed our poster. Some of these people became cooperators for our overwintering research.

February 10, 1995. Annual Winter Meeting of the Kansas Association of County Weed Supervisors. Approximately 100 people attended representing the 105 counties in Kansas. At this meeting, we presented a slide program to update noxious weed directors on our biological control of field bindweed research, including results of our first-year overwintering survival and feeding preference experiments. We received several questions from directors who were interested in cooperating on the project.

July 18, 1995. Annual Summer Meeting of the Kansas Association of County Weed Supervisors. We provided a walking tour of our greenhouses and insect rearing facilities for approximately 80 county weed directors. We provided demonstration materials, including life stages of bindweed natural enemies under the microscope and explained the field and laboratory research we are doing.

February 6, 1996. Annual National Meeting of the Weed Science Society of America (Norfolk, Virginia). Three presentations made as follows:

M.J. Horak, J.R. Nechols & D.J. Chessman. The biological control of field bindweed (Convolvulus arvensis L.) with the moth Tyta luctuosa and the gall mite Aceria malherbe.

D.J. Chessman, M.J. Horak & J.R. Nechols. Feeding preference, consumption, and growth of the biological control agent Tyta luctuosa on biotypes of field bindweed (Convolvulus arvensis L.) and hedge bindweed (Calstegia sepium (L.) R. Br.)

J.R. Nechols, M.J. Horak & D.J. Chessman. Environmental factors controlling seasonal development of the field bindweed (Convolvulus arvensis L.) biological control agent, Tyta luctuosa.

Press Releases & Reports

Two press releases were prepared and distributed through the Kansas State University News Service. These releases described the project, expected benefits, and some preliminary results. In addition, two newspapers ("The Salina Journal" and "The Marysville Advocate") ran articles on different aspects of biological control of field bindweed relating to our project. Also, a short popular article describing our bindweed biological control research was included in a semiannual report published for the agricultural community by the Kansas Agricultural Experiment Station ("Noxious weed strangles Kansas crops", pg. 9, KSU Ag Report, Fall 1994).

Publications

Abstracts

Chessman, D. J., M. J. Horak and J. R. Nechols. 1995. Assessing the impact of the biological control agent, Tyta luctuosa, on field bindweed. Proc. North Central Weed Science Society 49: 17.

Horak, M.J., J.R. Nechols & D.J. Chessman. 1996. The biological control of field bindweed (Convolvulus arvensis L.) with the moth Tyta luctuosa and the gall mite Aceria malherbe. Proc. Weed Science Soc. America 36: 51.

Chessman, D.J., M.J. Horak & J.R. Nechols. Feeding preference, consumption, and growth of the biological control agent Tyta luctuosa on biotypes of field bindweed (Convolvulus arvensis L.) and hedge bindweed (Calstegia sepium (L.) R. Br.) Proc. Weed Science Soc. America 36: 52.

Nechols, J.R., M.J. Horak & D.J. Chessman. Environmental factors controlling seasonal development of the field bindweed (Convolvulus arvensis L.) biological control agent, Tyta luctuosa. Proc. Weed Science Soc. America 36: 52.

Journal articles

Chessman, D. J., M. J. Horak and J. R. Nechols. 1995. Host plant selection, consumption, growth, development and survival of Tyta luctuosa (Lepidoptera: Noctuidae) on biotypes of field bindweed and hedge bindweed. (Submitted to Environmental Entomology, pending)

Radio Show

Two 15-minute radio shows (August 4, 1994 and September 6, 1995) were taped for a daily farm program on KKSU (Kansas State University). The purpose was to disseminate knowledge about the biological control of field bindweed and to publicize our sustainable agriculture research program at Kansas State University.

Research conclusions:

The potential economic, social and environmental benefits of permanently establishing effective biological controls for a widespread, persistent weed such as field bindweed are enormous. The low-input, non-polluting, self-sustaining goals of biological control for exotic pest weeds match well with those of sustainable agriculture. However, projects of this nature are typically long-term. Therefore, even if we are successful in establishing one or both of the bindweed natural enemies in Kansas and other parts of the Midwest, we do not expect to see the impacts of our research for many years. Our findings will, however, contribute valuable information about whether or not the available natural enemies have promise for success and, therefore, warrant an investment of sustainable agriculture resources. They also should lead to a more efficient determination of where in the U.S.–where bindweed is virtually ubiquitous–these natural enemies can be used. The research problems we are investigating are crucial to both a short- and long-term evaluation of this project. Our specific contributions follow.

1. Overwintering survival

Documentation that bindweed moths have survived the winter at multiple sites in Kansas, and that some survival has occurred in two consecutive years, suggests that this natural enemy may be able to withstand winters in Kansas. This is important because the moth population we received was from a location (Rome, Italy) that has a milder climate than parts of Kansas. Our
findings may mean that this natural enemy can survive winters throughout a large part of the North Central Region and in other parts of the northern United States where field bindweed is a serious problem. Successful overwintering must occur before this new bindweed enemy can become permanently established in the United States. Our research with the gall mites was less promising. However, because this mite is established in the Texas High Plains and may also have colonized in eastern Washington State, the potential for establishment of this natural enemy under hot summer and cold winter conditions in the Midwest remains an open question.

2. Dispersal ability of T. luctuosa

Because field bindweed has such a broad range, a determination of within-season dispersal of the bindweed moth will help in developing models to predict rates of range expansion of this natural enemy assuming it becomes established in the U.S. North Central Region. Because of the known sensitivity of moths to trace odors of their highly specific sex attractant, we feel that sex attractant traps hold the most promise as a tool for monitoring the presence and movement of T. luctuosa.

3. Bindweed-Tyta interactions

Under natural field conditions, field bindweed exists as a mixture of biotypes. Therefore, our finding that Tyta caterpillars show no preference for different types of bindweed is important because it suggests that caterpillars likely will be able to apply equal pressure to all forms of bindweed throughout its total range. Because field bindweed has an extensive root system, and is capable of regrowth following defoliation, the direct and indirect impact of Tyta luctuosa on the weed is needed. Our studies suggest that repeated defoliation is needed to suppress bindweed growth. It also reveals that defoliation of younger, less vigorous, field bindweed plants early in the season will result in the greatest suppression with the lowest recovery of the weed.

4. Quantify field bindweed population reduction by T. luctuosa caterpillars

Our field studies showed which infestation levels of T. luctuosa caterpillars are necessary to defoliate bindweed. This information is important for planning releases of. More importantly, if this natural enemy becomes established, our findings will help to predict whether/when field populations of caterpillars are abundant enough to exert adequate biological control of field bindweed.

5. Train and involve farmers with on-farm releases, surveys of the biological control agent, and evaluation of success.

The benefits of this objective are to help in the dissemination of the knowledge gained through the funded research to farmers who are interested in the biological control of field bindweed. Benefits also include the distribution of the organisms to various parts of the state with the cooperators. Furthermore, knowledge of the research is spread through personal contacts of our cooperators with friends and colleagues.

6. Disseminate knowledge of the symptomology, ecology, and biology of moth to farmers, extension personnel, researchers, and others concerned with noxious weed control.

A key benefit is the opportunity to communicate to farmers and other end-users the importance of biological research towards applied goals. This education also enables farmers and extension personnel to identify the symptoms of weed damage and life stages of our natural enemies. This knowledge will allow these people to recognize when and where biological controls are present in their work and living environments. Added benefits of this "hands-on" training is that it reduces barriers towards adopting these alternative approaches for managing pests, and facilitates future cooperation with researchers.

Farmer Adoption

To date, neither natural enemy has become established in Kansas. Therefore, the program has not progressed to a point where farmers can adopt natural enemies as an alternative for field bindweed management.

Producer Involvement

Number of growers/producers/state weed personnel in attendance at:

Workshops: 24

Conferences & Tours: 280+
(County weed directors winter conference and summer tour at Kansas State University)

Other events: 8
(specify) On-site training for 2 growers and 6 others who cooperated in our overwintering survival research at various locations in Kansas.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

See Objective 6, above and attached copies. We expect to have scientific articles published within 18 months of the project’s termination date. We have compiled an extensive slide series of our research and plan to put together an autotutorial slide-audiocassette program to publicize our research efforts to evaluate and establish new natural enemies of field bindweed.

Project Outcomes

Recommendations:

Areas needing additional study

Four topics that deserve attention are:

1. Determining the effect (compatibility) of herbicides on the survival of bindweed natural enemies; and

2. Evaluating the impact of naturally-occurring predators and parasites on bindweed biological control agents.

3. Determining the combined effects of plant competition and insect herbivory on field bindweed.

4. Assessing whether either or both natural enemies we have released become established and, if so, measuring their rate of dispersal and long-term impact on field bindweed.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.