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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETICS OF HOST SPECIFICITY AND CLIMATIC ADAPTATION IN BIOLOGICAL CONTROL AGENTS INTRODUCED FOR CONTROL OF ARTHROPOD PESTS AND WEEDS

Location: Beneficial Insects Introduction Research

2007 Annual Report


1a.Objectives (from AD-416)
(1) Determine the genetic and evolutionary basis for host specificity of insect parasitoids and herbivores; (2) Determine the importance of climatic adaptation for establishment and growth of introduced populations of insects; and (3) Screen, introduce, and evaluate impact of candidates for biological control introductions, based on host specificity and climatic tolerances.


1b.Approach (from AD-416)
For the first objective, we will determine the genetic basis for a host shift in the specialist herbivore, Heliothis subflexa, and for differences in host specificity between species in the Aphelinus varipes complex using crosses, quantitative trait loci mapping, and differences in gene expression. We will confirm gene function by silencing with RNA interference. Climate matching is frequently used to decide where to collect biocontrol agents for introduction. However, three hypotheses can explain climatic adaptation:(1) populations in different regions are adapted to local climates, (2) single populations have the full range of genetic variation in traits affecting climatic adaption, and (3) physiological plasticity is sufficient for local adaptation. These hypotheses have very different implications for collection strategies. The second objective is to test these hypotheses using the A. varipes complex. In the third objective, we will use the knowledge and methods developed under objectives 1 and 2 to screen candidates proposed for introduction to control Diuraphis noxia and Aphis glycines, introduce the most promising candidates, evaluate their impact on target and non-target species, and determine whether the screening was useful in improving the success and safety of biocontrol introductions.


3.Progress Report
We continued with development of genetic maps for analysis of host specificity in APHELINUS species and HELIOTHIS species. We continued to establish laboratory cultures in quarantine and test host specificity of parasitoids of soybean aphid. We have started cultures of additional aphid species in the genus APHIS to more precisely determine the host specificity of promising candidates for introduction against soybean aphid. We searched for and found stands of European buckthorn infested with soybean aphid and we determined that soybean aphid was under attack by a variety of predators and parasitoids on this its overwintering host plant. We submitted four proposals to the USDA NRI competitive grants program; two of these proposal are pending.

1926 22000 017 02S - Specific Cooperative Agreement with the University of Delaware to conduct quarantine rearing and host range testing of parasitoids that are candidates for introduction against the soybean aphid, APHIS GLYCINES, a major new pest of soybeans in the U.S. Host range testing identified three species which are promising candidates for release against soybean aphid; one of these is now being released. Monitoring was achieved through oral discussions, telephone calls, written monthly reports, and emails. For a complete report on the progress of this agreement, see the report for 1926 22000 017 02S.

1926 22000 017 05R - Reimbursable Cooperative Agreement with Purdue University to conduct quarantine rearing and host range testing of parasitoids that are candidates for introduction against the soybean aphid, APHIS GLYCINES, a major new pest of soybeans in the U.S. Host range testing identified three species which are promising candidates for release against soybean aphid; one of these is now being released. Monitoring was achieved through telephone calls, written quarterly reports, emails, and conference calls. For a complete report on the progress of this agreement, see the report for 1926 22000 017 05R.

1926 22000 017 06R - Reimbursable Cooperative Agreement with the University of Minnesota to determine whether host specificity of parasitoids is behaviorly stable. We have identified a population of APHELINUS near GOSSYPII from China as appropriate for this research. Monitoring was achieved through frequent telephone calls and emails. For a complete report on the progress of this agreement, see the report for 1926 22000 017 06R.

1926 22000 017 07N – Non-funded cooperative agreement with North Carolina State University to determine the genetic architecture of host specifity in HELIOTHIS species. Markers for genetic mapping were developed using published sequences and integrated into a genetic map based on amplified fragment length polymorphisms. Monitoring was achieved through oral discussions, telephone calls, and emails. For a complete report on the progress of this agreement, see the report for 1926 22000 017 07N.


4.Accomplishments
“Source of parasitoids attacking Russian wheat aphid” - Determining the source of introduced biological control agents is necessary to evaluate the success and safety of biological control projects. A decade ago, parasitoids in the genus APHELINUS were released to control the Russian wheat aphid, a major pest of wheat and barley crops in the western states. Using DNA sequence data and morphological analyses, we determined that the APHELINUS species that now heavily parasitizes Russian wheat aphid in Colorado, Nebraska, and Wyoming is APHELINUS ATRIPLICIS from the Caucasus region of Russia and the Republic of Georgia. This knowledge not only shows that the introduction program was successful but also allows us to test whether host specificity has shifted since introduction of this parasitoid. This accomplishment relates to National Program 304 Problem Statements A - Understanding Complex Interactions under National Program Component III - Plant, Pest, and Natural Enemy Interactions and Ecology; and Problem Statement A - Traditional Biological Control under National Program Component V - Pest Control Technologies.

“Host specific parasitoids of soybean aphid” - Host specificity evaluation is crucial for safe biological control introductions. We have evaluated host specificity of 19 species/populations of biological control agents from China, Japan, and Korea that are candidates for introduction against the soybean aphid, APHIS GLYCINES, a major new pest of soybeans in the U.S. Although most populations of parasitoids differed in host range, 13 had broad host ranges and these have been eliminated from consideration for introduction and their culture in quarantine discontinued. A population of APHELINUS CERTUS from Korea, a population of APHELINUS near GOSSYPII from China, a population of BINODOXYS COMMUNIS from China had narrower host ranges. We are proceeding with releases of BINODOXYS COMMUNIS and additional research on the other two species because they are the most promising candidates for release against soybean aphid. This accomplishment relates to National Program 304 Problem Statements A - Understanding Complex Interactions under National Program Component III - Plant, Pest, and Natural Enemy Interactions and Ecology; and Problem Statement A - Traditional Biological Control under National Program Component V - Pest Control Technologies.

“Taxonomy of APHELINUS VARIPES complex” – Cryptic species of parasitic wasps look very similar but can have large differences in host specificity and climatic tolerances. Confounding cryptic species affects the success and safety of biological control introductions. We have identified five cryptic species in the APHELINUS VARIPES complex based on divergence in DNA sequences, reproductive compatibility, courtship behavior and morphometry. Associating these cryptic species with described species in the complex is a difficult taxonomic problem because molecular and behavioral data are not available for type specimens, and even morphometric data for some types would be difficult to obtain. However, using a phylogenetic tree based on morphological evidence from species descriptions, we associated named species with the cryptic species we have identified. This information is will be crucial for safe and effective introductions of species in this complex of parasitoids, which are major biological control agents. National Program 304 Problem Statement A - Traditional Biological Control under National Program Component V - Pest Control Technologies.

“Anchored genetic markers” - Markers for genetic mapping are important tools for analysis of genes involving host specificity, climatic adaptation, and other traits. Such markers are particularly useful if their location and homology can be determined. Using published sequences for known genes in HELIOTHIS VIRESCENS, we developed PCR primers for 30 genes that produce length differences between H VIRESCENS and H SUBFLEXA and we have integrated these into a genetic map based on amplified fragment length polymorphisms. The known genes map to 18 of the 31 chromosomes in HELIOTHIS VIRESCENS. Although we are using these markers in our analysis of the genetic architecture of host specificity, these primer sequences and gene locations will also be very useful to the scientific community working on these moths. This accomplishment to National Program 304 Problem Statement A - Understanding Complex Interactions under National Program Component III - Plant, Pest, and Natural Enemy Interactions and Ecology; Problem Statement A - Traditional Biological Control under National Program Component V - Pest Control Technologies; and Problem Statement A - Agent Discovery and Selection and Risk Assessment under National Program Component IX – Biological Control of Weeds.


5.Significant Activities that Support Special Target Populations
NONE


6.Technology Transfer

Number of non-peer reviewed presentations and proceedings3

Review Publications
Heraty, J.M., Woolley, J.B., Hopper, K.R., Hawks, D.L., Kim, J., Buffington, M. 2007. Molecular phylogenetics and reproductive incompatibility in a complex of cryptic species of aphid parasitoids. Molecular Phylogenetics and Evolution. doi:10.1016/j.ympev.2007.06.021.

Wyckhuys, K.A., Hopper, K.R., Wu, K., Straub, C., Gratton, C., Heimpel, G.E. 2007. Predicting potential ecological impact of soybean aphid biological control introductions. Biocontrol News and Information. 28(2):30-34

Last Modified: 4/16/2014
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