Source: UNIV OF WISCONSIN submitted to
BIOLOGY AND ECOLOGY OF LYSIPHLEBUS TESTACEIPES, A NATIVE PARASITOID ATTACKING THE SOYBEAN APHID IN WISCONSIN
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
0223523
Grant No.
(N/A)
Project No.
WIS01534
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2010
Project End Date
Sep 30, 2012
Grant Year
(N/A)
Project Director
Hogg, D.
Recipient Organization
UNIV OF WISCONSIN
21 N PARK ST STE 6401
MADISON,WI 53715-1218
Performing Department
Entomology
Non Technical Summary
The soybean aphid is a native of Asia that was first discovered in Wisconsin in 2000 and has since spread throughout the northern soybean growing regions of North America. This aphid can build up to populations exceeding 1,000 per soybean plant and as a result can cause significant yield loss. In addition, the aphid is known to transmit several viruses that are pathogens of soybeans. Entomologists in the North Central Region of the U.S. responded quickly to this new soybean pest, and through cooperative research efforts established a management plan for this pest utilizing an economic threshold to guide decisions on insecticide applications. A major effort toward biological control of the soybean aphid was also launched, which has sought to import and establish "parasitoids" to help control soybean aphid populations. Parasitoids are tiny non-stinging wasps that lay their eggs in aphids, and the wasp larva devours the aphid and pupates within the aphid shell (known as a "mummy"). A new wasp then emerges and continues the cycle. There are two reasons parasitoids (rather than predators, the other type of natural enemy often used in biological control efforts) were targeted for importation and establishment against the soybean aphid: 1) parasitoids have a narrower range than predators and thus are very unlikely to result in unintended negative consequences; and 2) a number of predators, mainly lady beetles, are already providing some measure of control, but parasitoids of soybean aphid were largely absent in North America. However, we have observed an interesting phenomenon over the past few years in southern Wisconsin. Lysiphlebus testaceipes, a native parasitoid with an unusually broad host range of over 100 aphid species, has become increasingly abundant, to the point that in 2009 this parasitoid appeared to be limiting the increase of soybean aphid populations early in the growing season. Thus it is conceivable that Lysiphlebus testaceipes is adapting to take advantage of the availability of the recently introduced soybean aphid. However, little is known about Lysiphlebus testaceipes as a parasitoid of the soybean aphid. The goal of this project is characterize aspects of the biology of Lysiphlebus testaceipes in the north central U.S. (especially Wisconsin), and to assess the role the parasitoid plays in biological control of the soybean aphid. Specific objectives will investigate 1) the development and resulting sex ratio of Lysiphlebus testaceipes in relation to temperature, 2) the host range of Lysiphlebus testaceipes, including its preference for selected aphid hosts relative to the soybean aphid, 3) the dynamics of Lysiphlebus testaceipes field populations including the impact of the parasitoid on reducing soybean aphid populations, and 4) the aphid host species utilized by Lysiphlebus testaceipes to pass the winter (as a pupa within the aphid mummy).
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2151820113025%
2153110107050%
2161820113025%
Knowledge Area
215 - Biological Control of Pests Affecting Plants; 216 - Integrated Pest Management Systems;

Subject Of Investigation
1820 - Soybean; 3110 - Insects;

Field Of Science
1070 - Ecology; 1130 - Entomology and acarology;
Goals / Objectives
The overall goal of this project is to characterize aspects of the biology of Lysiphlebus testaceipes in the north central U.S., and to assess the role this parasitoid plays in biological control of the soybean aphid. To achieve this, four specific objectives will be addressed. Objective 1: Determine the developmental rate and resulting sex ratio of the immature stages of Lysiphlebus testaceipes in relation to temperature. Objective 2: Determine the host range of Lysiphlebus testaceipes and the preference of Lysiphlebus testaceipes for selected aphid hosts. Objective 3: Characterize the within-season dynamics of Lysiphlebus testaceipes field populations on soybean aphid, including the impact of hyperparasitoids. Objective 4: Determine the overwintering host(s) utilized by Lysiphlebus testaceipes.
Project Methods
Objective 1: Soybean aphids of mixed ages/instars on small soybean plants in individual cages will be exposed to mated female Lysiphlebus testaceipes for 8 hours at one of four constant temperatures (15, 20, 25, and 30 deg C), after which the parasitoids will be removed and the parasitized aphids allowed to develop. Time to mummy formation and to adult wasp emergence will be recorded, and the sex of each emerging parasitoid determined. Developmental rate at each temperature will be regressed against temperature, and the developmental threshold will be estimated. The developmental biology of Lysiphlebus testaceipes for the Wisconsin population will be compared with populations from Florida, Texas, Oklahoma & Nebraska. Objective 2: As many as thirteen aphid species will be tested to determine their acceptability and suitability as hosts of Lysiphlebus testaceipes. Many of these aphids are known to be hosts of the parasitoid in other locations. The aphids tested will include corn leaf aphid, English grain aphid, bird cherry oat aphid, green peach aphid, potato aphid, pea aphid, and a variety of other aphids in the genus Aphis, many of which occur on native prairie plants. Experimental protocols will follow those used by Desneux et al. (2009) for Binodoxys communis. Host preference tests will be conducted as pairwise choice experiments involving the soybean aphid and selected species based on the outcome of host suitability testing. Objective 3: Periodic sampling of soybeans will be conducted in various geographic regions in Wisconsin. At least one field will be used in each of 4 regions: south central, southwest, southeast, and east central. Each field will be sampled at weekly or biweekly intervals, with the following information recorded on at least 25 soybean plants: plant stage, number of aphids, number and species of natural enemies, and numbers of aphid mummies. All mummies will be collected and returned to the laboratory to be reared to determine for each mummy species (primary vs. hyperparasitoid), and sex for Lysiphlebus testaceipes. The dynamics of Lysiphlebus testaceipes in relation to aphid numbers and other natural enemies will be inferred from the patterns that emerge across the various sites. Objective 4: Lysiphlebus testaceipes likely does not overwinter in association with soybean aphid. Any mummies remaining in a soybean field would be crushed during the harvesting procedure, and the soybean aphid leaves soybean in the fall and colonizes buckthorn, where males and sexual females mate and the females lay overwinter eggs. It seems likely that Lysiphlebus testaceipes leaves soybeans late in the season and finds one or more species on which to overwinter. Our search for the overwintering aphid host will be guided by the results of the host range/preference experiments.

Progress 10/01/10 to 09/30/12

Outputs
OUTPUTS: 1) Soybean aphid (Aphis glycines) populations and natural enemies were surveyed in 5 commercial soybean fields and 3 agricultural research stations across southern Wisconsin during the summers of 2010, 2011, and 2012. 2) An experiment was conducted to compare the development of the parasitoid Lysiphlebus testaceipes in three aphid hosts: soybean aphid, greenbug (Schizaphis graminum), and bird cherry - oat aphid (Rhopalosiphum padi), across a range of temperatures. Parasitoids were reared at constant temperatures of 12, 16, 20, 24, or 28 degrees C. 3) An experiment was conducted to examine if the host aphid/plant complex from which the generalist parasitoid Lysiphlebus testaceipes develops influences future foraging behavior by the parasitoid. L. testaceipes were reared from soybean aphid on soybean or from bird cherry - oat aphid on barley. Both no-choice and choice assays were conducted. In no-choice assays, parasitoids were presented with 100 individuals of a single aphid species on the appropriate plant. In choice assays, parasitoids were presented with 50 aphids of each host aphid on their respective host plants in the same cage. PARTICIPANTS: Dr. David Hogg, UW Entomology Department, served as principal investigator for this project. Ms. Allison Dehnel, graduate student and research assistant, was responsible for the conduct of the research. We were assisted by personnel at two UW-CALS agricultural research station: Arlington and West Madison. In addition, we collaborated with farmers who graciously allowed us access to their soybean fields. This project provided the opportunity for Ms. Dehnel to obtain a Masters of Science degree. TARGET AUDIENCES: The overall objective of this research was to gain a better understanding of the behavior and ecology of a native aphid parasitoid, in hopes that we might better be able to utilize it for biological control of the the exotic soybean aphid. Thus the target audience includes soybean farmers, but only indirectly and in the long term. In the short term, the target audience includes others conducting research on soybean aphid management, including biological control, and those studying parasitoid behavior and ecology, and biological control of other aphid species. We also took advantage of several opportunities to report on this research at farmer field days. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
1) Average numbers of soybean aphids remained below the economic threshold of 250 aphids per plant all three summer, with the highest aphid populations occurring in 2010 and very few aphids occurring in soybeans during the drought conditions experienced in 2012. Thus, no useful data on aphid population dynamics were obtained during 2012. In 2010 and 2011, percent parasitism of soybean aphid was low, typically well below 5%, with a high of 5-20% recorded in 2011. The higher rate recorded in 2011 was due to low aphid densities as well as the contributions of an Aphelinus species (Hymenoptera: Aphelinidae)to the soybean aphid parasitoid guild previously dominated by Lysiphlebus testaceipes (Hymenoptera: Braconidae). 2) Estimates of the minimum temperature threshold and degree day (DD) requirements for parasitoid development were biologically similar for the aphid hosts, with thresholds between 7.5-7.8 degrees C and thermal constants between 154-176 DD. Development time was slower in soybean aphid than in the two cereal aphids at 12 & 28 degrees, which may have implications for the seasonal activity of L. testaceipes in the different aphid hosts. 3) In a no-choice assay, parasitoids from both host aphid/plant origins showed no difference in number of aphids parasitized, regardless of whether they foraged on a familiar or novel host/plant complex. In a choice assay, parasitoids reared from both host aphid/plant origins parasitized more bird cherry - oat aphids than soybean aphids. Evidence from this research suggests that the efficacy of L. testaceipes against soybean aphid is not improved by prior experience with this aphid.

Publications

  • No publications reported this period


Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: 1) Soybean aphid (Aphis glycines) populations and presence of soybean aphid parasitoids were monitored weekly in five commercial soybean fields and at three UW-CALS research farms scattered across southern Wisconsin. The parasitoid of primary interest in this survey was Lysiphlebus testaceipes. 2) Laboratory colonies of four aphid species were established, in addition to an existing soybean aphid laboratory colony: corn leaf aphid (Rhopalosiphum padi), English grain aphid (Sitobion avenae), greenbug (Schizaphis graminum), and cotton aphid (Aphis gossypii). All these aphids are known hosts of L. testaceipes. Colonies of corn leaf aphid and English grain aphid were initiated with early summer collections from local wheat fields. Colonies of greenbug and cotton aphid were initiated with individuals from established colonies in other laboratories. 3) A laboratory colony of L. testaceipes was established with individuals reared from soybean aphids collected in local soybean fields. The parasitoid colony will be maintained using soybean aphid as its host. 4) An experiment was conducted comparing L. testaceipes immature development on three different aphid hosts (soybean aphid, greenbug, and corn leaf aphid) at five constant temperatures (12, 16, 20, 24, & 28 degrees C). Soybean aphid was reared on soybean plants and both greenbug and corn leaf aphid were reared on barley plants. PARTICIPANTS: Dr. David Hogg, UW Department of Entomology, serves as principal investigator for this project. Ms. Allison Dehnel, graduate student and research assistant, has primary responsibility for the conduct of the research. We were assisted by personnel at three UW-CALS agricultural research stations: Arlington, Lancaster, and West Madison. In addition, we collaborated with the farmers who allowed us to survey for aphids and parasitoids in their soybean fields. TARGET AUDIENCES: The objective of this research is to gain a better understanding of the behavior and ecology of a native aphid parasitoid, in hopes that we might better be able to utilize it for biological control of the the exotic soybean aphid. Thus the target audience includes soybean farmers, but only indirectly and in the longer term. In the short term the target audience includes others conducting research on soybean aphid management, including biological control, and those studying parasitoid behavior and ecology, and biological control of other aphid species. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
1) Soybean aphid populations were at historic lows in the fields we monitored, with peak numbers less than 50 per plant. However, preliminary evidence suggests levels of parasitism by L. testaceipes were at historic highs, with a peak level of 18% parasitism recorded in mid-August for one of the fields. Samples are still being processed to determine final numbers. 2) The four aphid species will be used in experiments to assess host preference and host suitability for L. testaceipes, compared with preference for and suitability of soybean aphid as host. 3) All experiments involving parasitoid behavior and performance will be conducted using individuals from the newly established L. testaceipes colony. 4) Preliminary analysis of the parasitoid development experiment indicated no strong patterns in pupal mortality or sex ratio for the parasitoid, in relation to either aphid host or temperature. The highest level of pupal mortality recorded was 18%, at 12 deg C with soybean aphid as host. As expected, all sex ratios were female biased. The highest proportion of females recorded was 80%, at 12 deg C with corn leaf aphid as host. Parasitoid development was slightly slower in soybean aphid than in the other two aphid hosts at all temperatures.

Publications

  • No publications reported this period


Progress 01/01/10 to 12/31/10

Outputs
OUTPUTS: A project was initiated to characterize aspects of the biology of the native parasitoid (parasitic wasp) Lysiphlebus testaceipes in the north central U.S. (especially in Wisconsin), and to assess the role this parasitoid plays in biological control of the soybean aphid. Three complementary field surveys for L. testaceipes were carried out in Wisconsin during 2010. First, a survey for L. testaceipes parasitizing soybean aphids was conducted in 8 soybean fields in which the exotic parasitoid Binodoxys communis had been released in 2008 and 2009. These locations were visited and sampled biweekly from June through August to estimate densities of soybean aphids and L. testaceipes mummies. Second, a similar field survey was conducted in soybean plots at two UW-CALS agricultural research stations: West Madison and Lancaster, but in this case sampling was done on a weekly basis from mid-June through August. Third, a field survey was conducted at three prairie sites in or near Madison, each of which was visited on one to five occasions. At each visit a variety of native plants were examined for aphids and aphid mummies containing parasitoid pupae. Plants were identified using field guides, aphids were collected and returned to the laboratory for identification, and mummies were returned to the laboratory to hold for adult emergence and parasitoid identification. PARTICIPANTS: Dr. David Hogg, UW Department of Entomology, serves as principal investigator for this project. Ms. Allison Dehnel, graduate research assistant in Entomology, had primary responsibility for coordinating and conducting the research. She collaborated with personnel at the UW Arboretum and UW-CALS agricultural research stations at West Madison and Lancaster, and with six farmers and several UW-Extension agricultural agents. TARGET AUDIENCES: Organic and conventional farmers who grow field crops are a major target for the results of this research. Another target is the community of UW researchers and extension specialists with interest in soybean aphid management and in organic agriculture. A third target is entomology colleagues who reside in other states and regions and who have interests in insect pest management and biological control in field crops and organic cropping systems. PROJECT MODIFICATIONS: A field survey will again be conducted during 2011. A number of additional project objectives will be initiated during 2011, including: 1) Determine a threshold temperature of development for Lysiphlebus testaceipes (Wisconsin population) by taking a linear regression of development times across 5 temperatures (10, 15, 20, 25, 30 Celsius). 2) Compare developmental success across 5 temperatures for L. testaceipes by comparing adult emergence and sex ratio of emerged adults. 3) Attempt to find overwintering hosts for L. testaceipes: identify hosts used after soybean senescence, look for parasitoids around buckthorn and in prairies, etc. 4) Determine whether L. testaceipes has a host density preference on soybean aphid. 5) Determine host instar preference of L. testaceipes on soybean aphid. 6) Conduct host range testing of L. testaceipes with other common Wisconsin aphids: Test for differences in developmental time/success in different aphid hosts, as well as differences in ovipositional behavior among hosts.

Impacts
A total of 12 confirmed Lysiphlebus testaceipes were collected during 2010. These were found from mid-June through early July, and all at the Lancaster and West Madison locations. Soybean aphid numbers during 2010 were the lowest recorded since the discovery of the soybean aphid in Wisconsin in 2000, which helps explain the unusually low number of parasitoids. A small number of specimens tentatively identified as L. testaceipes were also collected parasitizing aphids on prairie plants; these identifications are being confirmed.

Publications

  • No publications reported this period