Natural Enemies of Aphids

Exotic Natural Enemies Under Review: Progress 2007

Field cages were set up in aphid-infested fields for release of B. communis.

Soybean aphid parasitized by B. communis.

Binodoxys communis Field Cage Releases for Control of Soybean Aphid - Summer 2007
Permits to release Binodoxys communis were obtained by South Dakota, Iowa, Wisconsin, Illinois, Indiana, Michigan, and Minnesota. Field releases in soybeans were made in each of these states along with a monitoring program to document survival, numerical abundance and movement of the parasites in the field and at the landscape level. In Minnesota B. communis has also been released onto soybean aphid colonies found in buckthorn adjacent to soybean fields. As of late summer 2007, the parasitoid has been released in 3 locations in IN, 9 in MI, 1 in SD, 1 in IA, 2 in IL, 3 in WI, and 18 in MN.

Besides the goal of establishing B. communis, MN also investigated a number of release protocols and results including:

1. the best strategy for releasing B. communis in the field.
2. the extent to which B. communis disperses from release sites.
3. whether winged aphids carry B. communis eggs in the summer migrant and overwintering flights.
4. whether B. communis travel to the soybean aphid overwintering host, Rhamnus cathartica in the fall.

Overall, results indicated that

1. Caged reproductive releases is the best release method - cages are placed over plants with relatively few aphids (< 20 per plant) and parasitoids added 3 to 7 days later. Parasitoids are then allowed to reproduce for one or two generations and the cage is removed. About 500 mummies per cage are produced.
2. B. communis disperses rapidly from release sites.
3. B. communis is able to sting winged aphids, and also that these stung aphids leave the plants and mummify afterwards.
4. Travel of parasitized aphids from soybeans to buckthorn is currently under investigation.

Host specificity testing

Aphis monardae is an aphid species under study for potential non-target impacts. In prairie habitats, A. monardae populations aggregate in flower heads of their host plant, Monarda fistulosa

Host specificity testing of Binodoxys communis strains from both China and Japan indicate an intermediate level of host specificity. Soybean aphid is the most suitable host, with Aphis monardae showing slightly lower suitability on vegetative growth of the native prairie plant Monarda fistulosa.

Seven other species of aphids showed low suitability and a further 6 species were not used by B. communis at all. Aphis monardae is a native non-pest aphid that inhabits native prairie habitats and is therefore a non-target species that may be at risk if B. communis is released.

To evaluate this risk further, we have made observation of A. monardae in native prairie settings throughout Southern Minnesota. We found it abundant in both undisturbed prairie remnants and parkland meadows. During these observations, we also noticed that (i) this aphid tends to cluster in flower heads of its host plant, and that (ii) many of these aphid colonies are tended by ants (Lasius sp.). Both of these factors may decrease the risk of introduced B. communis to the native A. monardae. We are currently conducting studies to test the ability of B. communis to attack A. monardae that are clustered in M. fistulosa flowerheads, and being tended by ants. We believe that these tests, if they indicate a reduced level of risk, will facilitate the process of obtaining federal permission to release this parasitoid. Results of this work were recently published as Wyckhuys, K. A. G., R. L. Koch, and G. E. Heimpel. 2007. Physical and ant-mediated refuges from parasitism: implications for non-target effects in biological control. Biological Control 40: 306-313. Read abstract»

Identification of native natural enemies
An early season survey and collection of parasitoids of soybean aphid was conducted in the early summer of 2007 in Liaoning Province in northeastern China. Substantial collections of mummified aphids were made at several sites and were returned to the U.S. for evaluation. Two trips to Korea were undertaken to survey for parasitoids attacking pre-overwintering aphid populations on buckthorn.

Thirty-two populations in ten species of parasitoids from soybean aphid in several areas of northeast China, Korea, and Japan have been received and successfully established in quarantine at the USDA/ARS lab in Newark, Delaware. Host specificity evaluation has been completed on 21 parasitoid populations and culture of 13 populations has been discontinued because host range was too broad. However, two populations in the Aphelinus-varipes complex, two populations in the Aphelinus-mali complex, and a population of Binodoxys communis had narrow host ranges and may prove suitable for release. At the USDA lab, 19 cultures are now being maintained and host specificity testing is in progress with four populations of three species.

A graduate student at the University of Minnesota has initiated experiments to evaluate which of the parasitoids that are in culture are most compatible with resident natural enemies, in particular the multicolored Asian lady beetle, Harmonia axyridis.

To help determine the compatibility of released and U.S. natural enemies of soybean aphid, we assessed the extent to which Binodoxys vs. Aphelinus mummies were preyed upon in the field in the native home, China. We assessed predation by collecting mummies and examining whether or not they had been consumed by predators (attacked mummies have characteristic signs that indicate extensive chewing). Predation on B. communis was approximately half that on Aphelinus sp. Since the mummy state of Aphelinus is approximately twice as long of that of B. communis, this is consistent with a similar rate of predation on both species. From the standpoint of compatibility with predators though, these data suggest that B. communis escapes predation better by virtue of its shorter development time.

Data from the North Central Regional Soybean Aphid Suction Trap Network can be found on their website. The suction traps run from May through October and collect migratory aphids as they are flying.

Non-target research
In 2006, we initiated field study of potential non-target effects of Asian natural enemies. In this work, a group of 84 native (U.S.) aphids were chosen to focus field sampling that complements host specificity testing, and other studies. We measured the relative densities of theses aphids and those of their host plants. We reared their parasitoids and used sweep-net sampling to collect other natural enemies within the habitat.

Sampling for the second year of this study began in late May 2007. In WI, four prairies have been regularly sampled, with each site being visited on a bi-weekly basis. To date, 229 aphid colonies have been recorded from 25 plant species. Parasitoid load has been low, with parasitoids emerging from only 9 aphid colonies. In Iowa, 31 locations were sampled, 3 weekly, the rest monthly. As of August 2007 a total of 33,636 aphids of approximately 40 species have been collected. Natural enemy abundance and diversity are being determined. In Indiana, 6 locations were sampled twice monthly. To date 847 aphid colonies from 34 plant genera have been collected. Parasitized aphids were found in 97 colonies (11.5% of all colonies). Identification of parasitoids, aphids, and other natural enemies are ongoing.

North Central Regional Soybean Aphid Suction Trap Network
Suction traps were operational from May until late fall to document movement and relative abundance of the soybean aphid and native aphid species. New traps were located in South Dakota, Kentucky, Nebraska and Missouri in 2007, adding to the existing locations in Illinois, Indiana, Michigan, Wisconsin, Minnesota and Iowa. The distribution and relative abundance of native aphids will be used as part of the non-target research efforts.

Aphids in the genus Aphis and also Uroleucon are some of the most common non-target native species in the suction trap as well as in the collections made in Midwest natural areas.

Survey of the Aphis species in the midwest
A list of aphids (Aphidinae and Macrosiphinae) found in Illinois was developed along with their hosts and life cycle. Using this we are in the process of developing a matrix to place native aphid species based on their relative abundance, and host plant range. (We assume that a common aphid on a common host would have a higher chance of being utilized by a released exotic natural enemy than a rare aphid on a rare plant.). The matrix will be used to direct survey efforts and inform host-specificity research.

Recent Publications

Chacon, Jeremy M. and George E. Heimpel. Biotic interference of a classical biological control agent of the soybean aphid. Presented at the annual meeting of the Entomological Society of America, December 2007. Read abstract»

Heidel, T. H. and R. J. O’Neil. Survey of aphids of Indiana and their associated natural enemies as part of a study of nontarget effects of a classical biological control program of the soybean aphid. Presented at the annual meeting of the Entomological Society of America, December 2007. Read abstract»

Heimpel, George E. Classical biocontrol of soybean aphid: Risk assessment and releases. Presented at the Annual Meeting of the Entomological Society of America, December 2007. Soybean Aphid in the North Central US: Implementing IPM at the Landscape Scale.

Lagos, Doris and D. Voegtlin. A Survey of the Aphis spp. of the Midwestern States. Presented at the Annual Meeting of the Entomological Society of America, December 2006.

Loden, Anthony S. and George E. Heimpel. Phoretic association of Binodoxys communis (Hymenoptera: Braconidae) and the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae). Presented at the Annual Meeting of the Entomological Society of America, December 2007. Read abstract»

Wyckhuys, K. A. G., and G. E. Heimpel. 2007. Response of the soybean aphid parasitoid Binodoxys communis (Gahan) (Hymenoptera: Braconidae) to olfactory cues from target and non-target host-plant complexes. Entomologia Experimentalis et Applicata In press.

Wyckhuys, K. A. G., L. Stone, N. Desneux, K. A. Hoelmer, K. R. Hopper, and G. E. Heimpel. Parasitism of the soybean aphid, Aphis glycines, by Binodoxys communis (Hymenoptera: Braconidae): the role of aphid defensive behavior and parasitiod reproductive performance. Bulletin of Entomological Research: submitted.