Progress 06/15/04 to 06/14/06
Outputs
We conducted field studies to 1) assess extant parasitoid and predatory fly species that may be adapting to prey upon the invasive Aphis glycines, soybean aphid, and 2) examine the role of predators in limiting parasitoid impacts via intraguild predation. For objective 1, in replicated large plots we detected parasitoids and predatory flies attacking sentinel A. glycines on potted soybean plants placed in soybean as well as other crops (alfalfa, corn, and wheat) and noncropped vegetation (early successional vegetation, poplar stands, and young forest). We also directly observed aphids and aphid enemies present on plants in the crop plots. In 2004 and 2005, we detected five species of parasitoids and eleven species of predatory flies parasitizing sentinel A. glycines. Most common (summed across all habitats) utilizing A. glycines were the parasitoids Aphelinus asychis, Lysiphlebus testaceipes, and a newly described species Binodoxys kelloggensis, and the flies
Aphidoletes aphidimyza, Allograpta oblique, and Sphaerophoria contigua. The other species were detected infrequently and in trace numbers, potentially only representing incidental use of A. glycines. Variation in habitat affinity was detected: L. testaceipes, A. oblique, and S. contigua utilized A. glycines placed in all crop and noncropped habitats; B. kelloggensis was principally found utilizing A. glycines placed in noncropped early successional vegetation and poplar stands; A. asychis most commonly utilized A. glycines placed in soybean; and A. aphidimyza was most common in soybean and other cropped plots. Overall, predatory flies were considerably less habitat specific than parasitoids. Percent field parasitism of A. glycines in soybean as measured by field inspection for mummies was disappointing, never exceeding 1% even among the most common species. Predatory flies were commonly found preying on A. glycines in soybean. For objective 2, a field experiment was aimed at examining
the role of predators in limiting parasitoid impacts via intraguild predation (IGP). Using tomato cage frames covered with mesh we differentially excluded all natural enemies (< 1 mm mesh, Aphid treatment) or only large predators (2 mm mesh, Mesh treatment), thus allowing natural parasitism to occur protected from IGP by large predators. We also included un-caged plants with and without A. glycines manipulation (Open and Field treatments), plants enclosed with a sham cage (Sham treatment) as a cage control, and plants caged without A. glycines (Plant treatment). All cages and the open treatment were enclosed by a plastic cylinder coated on the outside with Tanglefoot to prevent ants from entering and tending aphids. Our results showed strong impact from large predators (mainly Coccinellidae) but very low parasitism and predation achieved by extant parasitoid populations or small predators. Intraguid predation did not play a limiting role in parasitism. Large predator impacts on A.
glycines resulted in a trophic cascade that significantly increased soybean height, biomass, and yield to similar levels than plants in which aphids were excluded.
Impacts
There is a substantial complex of parasitoid and predatory fly species utilizing A. glycines, potentially supplementing other previously known predators of soybean aphid, particularly predatory flies which were commonly detected feeding on A. glycines in soybean. These data reflect challenges (most substantially habitat affinity) of parasitoid use of A. glycines, and bode well for predatory flies using A. glycines in soybean.
Publications
- Pike, K. S., P. Stary, M. J. Brewer, T. Noma, S. Langley, AND M. Kaiser. 2006. A new species of Binodoxys (Hymenoptera: Braconidae, Aphidiinae), parasitoid of the soybean aphid, Aphis glycines Matsumura, with comments on biocontrol. Proc. Entomol. Soc. Wash. In press.
- Costamagna, A.C. 2006. Do varying natural enemy assemblages impact Aphis glycines population dynamics? Ph. D. Dissertation, Department of Entomology, Michigan State Univ., East Lansing. 189 pp.
- Costamagna, A. C., and D. A. Landis. 2006. Predators exert top-down control of soybean aphid across a gradient of agricultural management systems. Ecological Applications. In press.
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Progress 01/01/05 to 12/31/05
Outputs
We conducted field studies to 1) assess extant parasitoid species that have adapted to prey upon Aphis glycines, the soybean aphid, and 2) examine the role of predators in limiting parasitoid impacts via intraguild predation. For objective 1, we sampled aphid parasitoids in soybean as well as other surrounding habitats (alfalfa, corn, wheat, and early successional vegetation). We periodically exposed sentinel A. glycines placed on potted soybean plants to detect parasitoids and predatory flies capable of attacking A. glycines. We also inspected individual plants in these crop plots to directly observe and identify aphids and aphid enemies present. From a series of four sampling dates, we detected 6 species of parasitoids and 7 species of predatory flies parasitizing sentinel A. glycines. The enemy fauna attacking A. glycines placed in soybean was about the same or only modestly lower in species number (4 parasitoids and 7 predatory flies) than in other crops (4
parasitoids and 7 predatory flies) and likely higher in species number than in early successional habitat (2 parasitoids and 2 predatory flies [data in noncropped habitat is still being processed]). Two parasitoids (Aphelinus asychis and Lysiphlebus testaceipes) and 3 predatory flies (Aphidoletes aphidimyza, Sphaerophoria contigua, Toxomerus marginatus) were found parasitizing and preying upon A. glycines only or A. glycines and other aphid species in alfalfa, corn, and wheat; while 2 other parasitoids (Aphelinus albipodus and Binodoxys new sp.) were limited to parasitizing aphid species other than A. glycines. Parasitoid variation in habitat affinity was also detected: L. testaceipes was more common in more habitats and Binodoxys new sp. was much more habitat specific to noncropped vegetation. Overall % field parasitism as measured by field inspection for mummies did not exceeding 1%. Predatory flies were less habitat specific than parasitoids were commonly found preying on A.
glycines in soybean. For objective 2, we replicated a 2004 field experiment aimed at examining the role of predators in limiting parasitoid impacts via intraguild predation (IGP). Using tomato cage frames covered with mesh we differentially excluded all natural enemies (< 1 mm mesh, Aphid treatment) or only large predators (2 mm mesh, Mesh treatment), thus allowing natural parasitism to occur protected from IGP by large predators. We also included un-caged plants with and without A. glycines manipulation (Open and Field treatments), plants enclosed with a sham cage (Sham treatment) as a cage control, and plants caged without A. glycines (Plant treatment). All cages and the open treatment were enclosed by a plastic cylinder coated on the outside with Tanglefoot to prevent ants from entering and tending aphids. Our preliminary results showed strong impact from large predators (mainly Coccinellidae) but very low parasitism and predation achieved by extant parasitoid populations or small
predators. Large predator impacts on A. glycines resulted in a trophic cascade that significantly increased soybean height, biomass, and yield to similar levels than plants in which aphids were excluded.
Impacts
As an alternative to insecticides, parasitoids can be integrated into the extant predator complex, as judged by a substantial complex of parasitoid species utilizing A. glycines and the lack of significant intraguild predation on parasitoids. Habitat affinity of some of the parasitoids will likely present additional challenges to utilization of A. glycines in soybean; whereas predatory flies were common among crops inspected. These data bode well for adaptation of predatory flies to A. glycines in soybean, and may add to the biosuppression of A. glycines by large predators.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
During the first year of this project, we conducted field studies in southern Michigan to address the following three objectives: 1) assess extant parasitoid species that have adapted to prey upon Aphis glycines, the soybean aphid, and 2) examine the role of predators in limiting parasitoid impacts via intraguild predation. For objective 1 (parasitoids adapting to prey on A. glycines), we sampled aphid parasitoids in soybean as well as other surrounding habitats (alfalfa, corn, and wheat-clover) to understand aphid-enemy-habitat interactions. We periodically exposed potted soybean plants infested with A. glycines to detect parasitoids attacking A. glycines in soybean and other crop plots. During the sampling with potted plants, we also inspected individual plants in these crop plots to directly observe and identify aphids and aphid enemies present. From a series of two sampling schemes, we detected a total of seven species of aphids and eight species of aphid
parasitoids in various crop plots in 2004. Of eight parasitoid species, six species were found parasitizing A. glycines only or A. glycines and other aphid species. Two other parasitoid species were limited to prey upon aphid species other than A. glycines, exhibiting no signs of adapting to A. glycines as a host. We are still in a process of assessing the relative importance of various crops as habitats of parasitoids relevant in soybean aphid control. The most abundant A. glycines parasitoid collected was Lysiphlebus testaceipes, a cosmopolitan species. Another soybean aphid parasitoid we sampled (Binodoxys sp.) was confirmed to be a new species to the science first discovered in this study. For objective 2 (intraguild predation), we conducted a cage experiment (1x1x1 meter) in which we manipulated mesh sizes to differentially exclude all natural enemies or only large predators from the cages. We also included un-caged plants with and without aphid manipulation, plants enclosed with
a sham cage as a cage control, and plants caged without aphids. Our preliminary results showed strong impacts from predators (mainly Coccinellidae). We observed direct evidence of intraguild predation (mummies being consumed).
Impacts
As an alternative to insecticides, we wish to identify optimal strategies to integrate parasitoids into the extant predator complex to increase biological suppression of soybean aphid. Integrating effective biological control into soybean management scheme will lessen SBA outbreaks and needs for chemical control. Such an IPM approach will benefit soybean industry by reducing spray costs, soybean damage, and risks of soybean pests developing insecticide resistance, thereby increasing productivity and environmental protection.
Publications
- No publications reported this period
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