Biological Control of Insect and Weed Pests in North Dakota Agriculture (continued - part 4 of 4)

E-1225, January 2002

Contents

Introduction
Biological Control
        - Parasites
        - Predators
        - Diseases
Maintaining Natural Order
        - Canola Insect Pests
        - Potato Insect Pests
        - Sunflower Insect Pests
        - Sugarbeet Insect Pests
        - Corn Insect Pests
       - Small Grain Insect Pests
Weeds
       - Leafy Spurge
       - Purple Loosestrife
Conclusions
Biological Control References

Sugarbeet Insect Pests

Sugarbeet root maggot, Tetanops myopaeformis, is probably the most destructive insect pest of sugarbeets in the Red River Valley of North Dakota and Minnesota. Damage depends on degree of infestation but can range from 10-50 percent if not managed. This native pest appears to have few natural enemies. Although no parasites have been reported, ground beetles and birds have been observed feeding on the root maggot. Research into the role of diseases may eventually assist in managing this pest.

A number of strains of entomopathogenic nematodes of the genus Steinernema (Figure 21) were effective in killing maggot larvae in the laboratory, but results were poor in field trials. A fungus, Syngliocladium tetanopsis, was discovered attacking the maggot larvae collected from sugarbeet fields in North Dakota. This species may be specific to the root maggot and killed 95-100 percent of newly hatched maggots in laboratory experiments, but more research is needed to discover if this disease could be developed into a biopesticide. Recent work with another entomopathogenic fungus, Metarhizium anisopliae, has shown promise in controlling the maggot in the field, but additional research is needed on the application rates, timing, and formulation.

Figure 21. Entomopathogenic nematodes released from the body cavity of killed larva. (USDA) (Click for a 14KB color photo of entomopathogenic nematodes.)

Corn Insect Pests

The European corn borer (Ostrinia nubilalis), corn rootworm (Diabrotica spp.), and corn leaf aphid (Rhopalosiphum maidis), are the most common insect pests of corn in the northern states. There are many infrequent pests such as cutworms, armyworm (Pseudaletia unipuncta), white grub (Phyllophaga spp.), wireworms and grasshoppers.

European corn borer (ECB) has many natural enemies. Predators that feed on eggs and larvae include lady beetles, lacewings, bigeyed bugs, damsel bugs, minute pirate bugs and others. There are numerous parasitic insects associated with European corn borer. The most significant parasitic wasps are Macrocentris grandii, a braconid larval parasite introduced from Europe, and the Trichogramma wasps which are egg parasites. Parasitization levels by M. grandii have been reported as high as 45 percent; Trichogramma levels are quite variable, ranging from less than 1 to 70 percent. Pathogens of ECB include Nosema pyrausta, Beauveria bassiana (Figure 22), Bacillus thuringiensis, the bacteria source for the gene inserted in genetically modified Bt-corn for producing an ECB toxin, and others.

Figure 22. Corn borer larva killed by Beauveria bassiana. (USDA) (Click for a 24KB color photo of a corn borer larva killed by Beauveria bassiana.)

Natural enemies fail to play a major role in affecting corn rootworm populations. The fungi B. bassiana and Metarhizuium anisopliae have been tested against rootworm larvae with poor results. A subspecies of the bacterium B. thuringiensis kills beetles and is a potential source of proteins useful in developing genetically modified corn resistant to rootworms.

Numerous predators and parasites help to regulate populations of the corn leaf aphid and other cereal aphids. Lady beetles, lacewings, and syrphid fly maggots feed on all species of aphids. The wasps Lysiphlebus testaceipes and Aphelinus mali are common aphid parasites that help regulate populations. Numerous fungal diseases affect aphids. Infected aphids take on a fuzzy appearance as the fungus grows outside the dead aphid's body (Figure 23). Rapid declines in aphid populations can occur when environmental conditions favor fungal infection.

Figure 23. Corn leaf aphids killed by a fungal pathogen. (Click for a 29KB color photo of corn leaf aphids killed by a fungal pathogen.)

Small Grain Insect Pests

The most important insect pests of wheat in the region are the cereal aphids, orange wheat blossom midge (Sitodiplosis mossellana), wheat stem sawfly (Cephus cincta), grasshoppers, and wireworms. Occasional pests include armyworms (P. unipuncta), cutworms, and wheat stem maggot (Meromyza americana).

Four cereal aphids, English grain (Macrosiphum avenae), greenbug (Schizaphis graminum), bird-cherry oat (Rhopalosiphum padi), and corn leaf (R. maidis), can be found in small grains. Lady beetles, lacewings, and syrphid fly maggots feed on all species. The parasitic wasps L. testaceipes, A. mali, and Aphidius avenaphis are common aphid parasites that help regulate populations. Numerous fungal diseases affect aphids. Infected aphids take on a fuzzy appearance as the fungus grows outside the dead aphid. Rapid declines in aphid populations can occur when environmental conditions favor fungal infection.

The orange wheat blossom midge is parasitized by the parasitic wasp Macroglenes penetrans (Figure 24), which is an egg-larval parasite. Eggs are laid in the egg of the wheat midge. The parasite larva develops in the midge larva, killing the larva in the late spring of the next year. This parasitic wasp controls about 40 percent of the overwintering midge larvae.

Figure 24. Macroglenes penetrans, egg-larval parasite of the wheat midge. (Saskatchewan Agriculture and Food) (Click for a 23KB color photo of an egg-larval parasite of the wheat midge.)

The wheat stem sawfly has four different parasitic wasps that attack it, but normally they do not kill enough sawfly larvae to have a great impact. The most common parasitic wasps are Bracon cephi, B. lissogaster, and Eupelmus allynii.

The armyworm is preyed on by ground beetles and many vertebrate predators. Important parasitic wasps include the redtailed tachinid fly, Winthemia quadripustulata, and the braconids Apanteles marginiventris and A. militaris. Activity by some of these parasites is apparent when clusters of the parasite's fuzzy, pupal cocoons are seen on wheat heads.

The wheat stem maggot has two parasitic wasps, Bracon meromyzae and Coelinidea meromyzae, that are important in maintaining the pest populations at low densities.

Weeds

The scope of biological control extends beyond the use of predators, parasites, and pathogens for management of insects. Herbivory is common among insects and many phytophagous insects feed exclusively on weed pests. Many noxious invasive weed species in the United States are being managed using herbivorous insects introduced through importation programs. Leafy spurge and purple loosestrife are two introduced noxious weed pests of the upper Midwest region including North Dakota and Minnesota. Insects that feed on these weeds have been located in the countries where the weeds originated and introduced into the United States to establish control.

Leafy Spurge

Nine insects have been released in the United States against leafy spurge. Six insects have become established in North Dakota, including a gall midge, a stem/root boring beetle and flea beetles (Aphthona spp., Figure 25). Of these, the flea beetles have been the most important in reducing leafy spurge density. Releases of five species of flea beetles (A. flava, A. czwalinae, A. lacertosa, A. abdominalis, and A. nigriscutis) began in 1985 in North Dakota. By 1996, A. lacertosa and A. nigriscutis had established in almost every county and are the most important in reducing leafy spurge infestations. Adult flea beetles feed on the foliage; however, it is larval feeding on the roots that results in the major damage to the plant. Small larvae feed on the fine root hairs, reducing water and nutrient absorption. Larger larvae feed on the root crown, destroying the root tissues directly and indirectly causing the plant to become more susceptible to herbicides and soil borne pathogens. Aphthona flea beetles have established throughout the north central Great Plains region and have substantially reduced spurge infestations at locations that provide the necessary environmental conditions for flea beetle development. Flea beetles do not always provide predictable and consistent levels of control. Under less than optimal conditions, they may take several years to establish and reduce a spurge stand to a tolerable level. When using flea beetles, land managers should not expect a "quick fix" and need to practice patience to ensure long term benefits. Flea beetles are collected and redistributed from mid-June to early July. Land managers interested in collecting and releasing flea beetles on their lands should contact the local county weed officer for information on date, time, and locations of flea beetle collection and redistribution programs in their area. Refer to NDSU Extension Service Circular W-1183, "Leafy Spurge Control Using Flea Beetles (Aphthona spp.)," for more information on Aphthona flea beetles for biological control of leafy spurge.

Figure 25. Aphthona flava, leafy spurge flea beetle. (USDA) (Click for a 15KB photo of a leafy spurge beetle.)

Purple Loosestrife

Four insects have been released in the United States for the control of purple loosestrife: two leaf feeding beetles, the black-margined loosestrife beetle (Galerucella calmariensis) and the golden loosestrife beetle (Galerucella pusilla, Figure 26); a root-boring weevil (Hylobius transversovittatus); and one flower-feeding weevil (Nanophyes marmoratus). The two leaf-feeding beetles and the root-boring weevil have recently been released on a few small areas in North Dakota. The two Galerucella species have established in two loosestrife infestations along the Sheyenne River at Valley City, and none of the biological control agents have yet established along the English Coulee in Grand Forks. Biological control has played a more important role in reducing loosestrife infestations in Minnesota, where this weed is a larger problem (several thousand acres infested at nearly 2,000 locations statewide) and herbicides are ineffective in areas of severe infestations (more than an acre with 75-100 percent loosestrife). Galerucella calmariensis and G. pusilla have been released on over 400 sites in Minnesota with an 85% establishment rate. The leaf-feeding beetles have significantly reduced the loosestrife infestation on many of these sites, including ones of up to 40 acres in size. There were approximately 20 sites that produced roughly 2 million beetles during the 2000 growing season. These sites serve as insectaries from which beetles can be collected and redistributed to other infested areas. A cooperative rearing program that enlists volunteers to rear the leaf-feeding Galerucella beetles has allowed Minnesota to rapidly expand the number of sites with biological control agents. A rearing method has recently been developed for the root weevil, and now this biological control organism can be produced on artificial diet. The Minnesota Department of Natural Resources will be releasing the loosestrife root weevil on only a few sites initially. As production increases, more sites will be established with this biological control agent.

Figure 26. Golden loosestrife beetle, an herbivore or purple loosestrife, Lythrum salicaria. (MN Dept. of Nat. Res.) (Click here for an 18KB color photo of the golden loostestrife beetle.)

Conclusions

The best approach to preserving effective biological control by natural enemies is a combination of management tactics. By conserving and protecting natural enemies, we provide an opportunity for them to operate at their full potential as naturally occurring sources of biological control in the agricultural environment.

Challenges for the future in biological control include additional studies to identify the complex of natural enemies in cultivated crops, understand the biology and population dynamics of the natural enemies associated with the major pest species, and determine how the different IPM practices can best be used to ensure their compatibility with the natural enemies. Also needed are studies to evaluate the impact of predators, parasites, and diseases to find ways to improve biological control through conservation, augmentation, and importation.

Biological Control References

Bellows, T. S. and T. W. Fisher (editors). 1999. Handbook of biological control. Academic Press, San Diego, CA. 1046p.

Flint, M. L. and S. H. Dreistadt. 1998. Natural enemies handbook — the illustrated guide to biological control. Univ. of California Press, Berkeley, CA. 154p.

Hunter, C.D. 1997. Suppliers of Beneficial Organisms in North America. California Environmental Protection Agency, Dept. of Pesticide Regulation, Environmental Monitoring and Pest Management Branch, 1020 N St., Rm 161, Sacramento, CA 95814-5624. www.cdpr.ca.gov

Lee, J. C. and D. A. Landis. 2001. Natural enemies in field crops: a guide to biological control. Michigan State Univ. Ext. Bull. 2721. 65p.

Mahr, D. L. and N. M. Ridgway. 1993. Biological control of insects and mites. North Central Regional Publication 481. Univ. of Wisconsin, Madison, WI. 92p.

Ryan, J. M., D. A. Landis, and E. J. Grafius. 1993. Biological control of insects. Michigan State Univ. Ext. Bull. E-2453. 8p.

Sloderbeck, P. E., J. R. Nechols, and G. L. Greene. 1996. Biological control of insect pests on field crops in Kansas. Kansas State Univ. Coop. Ext. Serv. MF-2222. 18p.

Van Driesche, R. G. and T. S. Bellows, Jr. 1996. Biological control. Chapman & Hall, New York, NY. 539p.

Biological Control News www.entomology.wisc.edu/mbcn/mbcn.html

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E-1225, January 2002