Northeast Region IPM Grants Projects Funded, FY 2001

Project Title:

Inoculative Releases of Trichogramma ostriniae for Control of European Corn Borer in Field Corn

*Award shown is total amount to be used over the course of the project term.

Executive Summary

Back to the top

European corn borer (ECB), Ostrinia nubilalis, is the most damaging pest of corn in the U.S. and Canada. The insect also attacks other important crops, such as sweet corn, sorghum, cotton, potatoes, peppers, and beans. Overall yield losses and control expenditures associated with ECB cost U.S. growers >$1 billion annually. Although several insecticides are available, timing is difficult to optimize spray timing and the consequently economic and environmental cost associated with insecticides exceeds the yield benefit for most growers.
Transgenic Bt-corn hybrids provide season-long protection against corn injury by ECB which insecticide programs cannot economically provide. The commercial availability of Bt-corn has the potential to provide for the first time an economically-viable strategy for managing ECB in the Northeast. However, although Bt-corn has several attractive features, the technology also has several negative aspects including the potential for the development of resistant ECB populations, possible impact on non-target species, and lack of consumer acceptance. These negative aspects may substantially limit the adoption of this technology and thus it is imperative that researchers continue to develop other management options for this pest.
One alternative tactic for managing ECB in field corn is biological control with inoculative releases of the egg parasitoid Trichogramma ostriniae, a species we have been working with for several years in fresh market sweet corn. Research since 1996 has provided impressive evidence that inoculative releases of T. ostriniae can successfully reduce ECB population levels and concomitant damage to sweet corn. The wasp has a strong host preference for ECB, and has been shown to disperse rapidly in fields and efficiently locate egg masses. Once an ECB egg mass is found by a female T. ostriniae, ˜90% of eggs will be parasitized. The wasp reproduces quickly and passes through multiple generations, resulting in season-long suppression of corn borer infestations and damage. Control of ECB would not necessarily be complete, but T. ostriniae would cause enough mortality to reduce damage below economic levels in most cases. In 2000, inoculative releases of T. ostriniae were made in 9 fields of sweet corn in New York. Approximately 47% of the total ECB eggs deposited over the season were parasitized. Furthermore, ECB damage to ears was reduced 50% compared with non-release fields.
We are proposing to evaluate early-season inoculative releases of T. ostriniae for suppression of ECB in field corn in New York, Pennsylvania, Delaware, and Virginia. We will also investigate the overwintering of T. ostriniae in each state and assess potential non-target effects of the parasitoid by evaluating parasitism of other lepidopteran eggs in and around release sites.
Successful inoculative releases and suppression of corn borer would provide an excellent biologically-based alternative to insecticides. Because of the much lower cost of Trichogramma releases compared with insecticide treatments, it is projected that nearly 60% of the field corn acreage in the Northeast might benefit economically from Trichogramma releases, while less than 13% would potentially benefit from the use of insecticides. The proposed release method of T. ostriniae is relatively simple, inexpensive, could be incorporated into existing IPM programs, and involves no risk to the grower. In addition, much of the proposed research will be conducted on-farm, which will greatly facilitate obtaining feedback from growers. Because the research will be conducted in four different states adoption by growers should be widespread. Because corn is planted throughout the northeastern U.S., results of this research will impact the entire region and they will have broad implications for other corn-growing regions and other cropping systems in which ECB is a pest.

THE PROBLEM, BACKGROUND, AND JUSTIFICATION

Back to the top

ECB Pest Status

Following its arrival from Europe early in this century, the European corn borer (ECB), Ostrinia nubilalis, spread quickly across the U.S. and Canada and became one the most serious pests of field corn and a number of vegetable crops. Nationally, ECB is the second most damaging pest of corn causing an estimated average annual loss to farmers of $1.2 billion (Calvin 1995). During outbreak years and in years when corn market value is high, economic losses can reach as high as $2.0 billion. In the Northeast and mid-Atlantic states, ECB is responsible for causing an estimated annual yield loss of $116.3 million (NASS 1995; Anonymous 1990 -1995). Field corn is the largest acreage crop grown in the northeastern U.S. Across the twelve northeastern states, corn for grain is produced on over 2.4 million acres, and is valued at nearly $750 million annually (Table 1). An additional 1.4 million acres of field corn is grown for silage production in the region. Management of European corn borer in field corn was identified by several 1996 statewide IPM needs assessments as a priority area that needs additional research (http://neipm.nysaes.cornell.edu:591/NE_Needs/FMPro).
Losses of this magnitude are still seen even though major advances in the pest's management have occurred since its introduction. As little as 40 years ago, it was not uncommon to have 20 or more ECB larvae feeding in one corn plant, causing a complete crop loss. The combined effect of cultural, biological, and genetic management tactics has been a lowering of the average ECB population density in corn fields. Today, it is uncommon to find a field with more than an average of 2.0 larvae per plant. According to state survey information summarized by the NC-205 Regional Research Project, almost 80% of corn fields have less than 0.5 first generation larvae per plant and 75% have less than 2.0 second generation larvae per plant (45% have less than 1.0 larvae per plant).
Although average ECB density levels have been significantly reduced, the pest still commonly causes 5 to 40 bushel per acre yield reductions in Northeast corn fields (Greg Roth, unpublished data). At a corn value of $2.50 per bushel, this means farmers are still losing anywhere from $12.50 to $100 per acre from this pest. The ECB's impact on yield is a function of crop yield potential, water availability, crop value, plant developmental stage when tunneling was initiated, crop health, plant population, and management intensity. On average, a single ECB larva tunneling into the plant at V10 and V16 (10th and 16th leaf stages) reduces yield by 5 to 6%. Second generation ECB larvae that attack the plant between R1 to R5 (blister to beginning dent stages) can reduce yield from 1.5 to 4.0% per larva per plant (Mason et al 1996; Calvin et al. 1988; Bode and Calvin 1990). When plants are under drought stress the impact of ECB stalk tunneling can be as high as 12% per larva per plant during the reproductive stages (Calvin unpublished data). Based on national average infestation levels (0.37 and 1.56 larvae per plant for first and second generation, respectively), crop yield (122.89 bushel per acre), and market value ($2.33 per bushel), first and second generation are responsible for a 2.1 and 4.3% yield reduction (6.4% total loss) in the average corn field (Anonymous 1994; Calvin 1995). Therefore, the average per acre loss caused by this pest is 7.86 bushels or $18.33 per acre. Although many farms in the Northeast may have average yields lower than 100 bushels per acre, top farmers commonly maintain average yields above 135 bushels per acre with some averaging over 150 bushels per acre. On these farms, the average per acre loss from the pest would be $20.13 (135 bushel per acre) and $22.37 (150 bushel per acre). These average losses per acre more than justify the use of Bt-corn hybrids which costs between $7.00 to $10.00 per acre or inoculative releases of Trichogramma which is projected to cost less than $10.00 per acre.

Table 1. Field corn production in the northeastern U.S. (Data taken from USDA - NASS 1997)

ECB Management

Over the last 40 years, a combination of cultural control, biological control and classically- bred resistant hybrids have greatly reduced overall levels of ECB damage. Although these methods have all made important contributions to the regulation and control of ECB populations, they do not reliably prevent yield losses caused by this pest. In spite of the impact this pest has had on corn production in the United States and the Northeast, few farmers attempt to protect their yield from the pest using insecticides (Calvin 1995). The main reasons that so few growers utilize insecticides are high costs and relatively low efficacy. The low efficacy of insecticides is due largely to the difficulty of timing the applications to correspond with the short window between larval hatching and boring into the stalk where they are relatively impervious to insecticides. In most cases, the cost of an insecticide application or applications exceeds the benefit derived from their implementation (Calvin 1995). Even if a viable insecticide control option were available, most farmers in the Northeast would not have the means to apply treatments to corn. Conventional on-farm spray equipment is inadequate and few commercial applicators are available. Aerial applications which are common in the Midwest are generally not cost-effective with the smaller field sizes of the Northeast, are risky to apply on rolling terrain, and are looked at unfavorably by the general public. For these reasons, most farmers have opted not to implement insecticide management programs despite the yield losses caused by ECB.
With the introduction of transgenic corn hybrids that produce the Bt toxin, the economics of ECB management was changed dramatically in the Northeast and throughout the United States. Research has shown that Bt-corn hybrids provide 95 to 100% control of first and second generation bivoltine and univoltine ECB larvae compared to 72% of first generation and 67% of second generation by insecticides. The cost to implement this technology is considerably lower than an insecticide based program and more reliable. The total per acre cost of Bt-corn ranges from $7.00 to $10.00 per acre depending of plant density compared to $30.00 to $40.00 per acre for both first and second generation control using an insecticide program. The result of this new technology entering the market place in 1996 and 1997 is a drop in the economic thresholds for the pest. Prior to the commercial release of Bt-corn hybrids, ECB exceeded economic thresholds only occasionally. Because of this new technology, ECB is expected to perennially exceed thresholds. The average economic thresholds for first and second generation ECB using an insecticide program were 1.39 and 3.2 larvae per plant, respectively, compared to the Bt-corn technology which lowered thresholds to 0.23 and 0.46 larvae per plant. With the introduction of the Bt-corn technology, 50 and 80% of corn fields in the Northeast have first and second generation ECB infestation levels, respectively, that exceed the economic threshold compared to 2.6 and 12.1% for an insecticide based program.
The Bt-corn technology that represents the most recent advance in ECB management, offers a highly effective, reliable, and affordable method to prevent yield losses from the pest. However, the history of pest management has demonstrated the danger of relying on any single tactic as a "silver bullet". There are several factors that could potentially limit the adoption and long-term viability of Bt-corn hybrids for ECB management. These factors include the potential selection for resistant populations, the possibility of non-target impacts, cross-pollination of organic corn, and lack of consumer acceptance. Thus it is imperative that researchers continue to develop other management tactics. One of the most promising alternatives to Bt-corn is the inoculative release of Trichogramma wasps. This strategy has already proven to be highly effective in sweet corn and the projected cost for commercial utilization is comparable to the use of Bt-corn (approximately $10/acre). This strategy represents the latest advance in the long history of biological control of this pest.

Biological Control of European corn borer:
Ever since its accidental introduction into North America, efforts have been made to introduce natural enemies of ECB (Clausen 1978). A number of parasitoids have been imported from Europe and Asia, but few have become established (Mason et al. 1996). A tachinid fly, Lydella thompsoni and two wasps, Macrocentrus grandii and Eriborus terebrans, are the major parasitoids attacking ECB in North America (Mason et al. 1994). These introduced parasitoids, and several natural predators may suppress ECB populations in some years and locations, but they generally do not control ECB populations below acceptable economic injury levels (Wressel 1973).
Augmentation of natural enemies, in particular releases of parasitoids may provide more predictable and effective control of ECB (Wang and Ferro 1998). Inundative releases of Trichogramma egg parasitoids have shown success at controlling European corn borer and the closely-related Asian corn borer, Ostrinia furnicalis Guenee, in Asia and Europe (Wang et al. 1984, Smith 1996). In inundative release programs, Trichogramma are released three to four times per season at ~240,000/acre/release (Smith 1996). Wasps are not directly released into the field rather parasitized eggs (containing developing Trichogramma) are placed in the field. As the wasps emerge from these eggs they are "released".
In the U.S., several Trichogramma spp. have been evaluated for controlling ECB. Among the native Trichogramma species, only T. nubilale Ertle and Davis may be effective (Losey and Calvin 1990, 1995, Losey et al. 1995). Unfortunately, this species is not commercially available and it is relatively expensive to mass produce (Wang and Ferro 1998).

Research with Trichogramma ostriniae:
Trichogramma ostriniae is endemic to China where it has been shown to parasitize 70-96% of eggs of O. furnicalis (Wang et al. 1984, Chiang et al. 1986). The parasitoid has been identified as a strong candidate for augmentative biological control of ECB (Wang et al., 1984; Chiu and Chen 1986, Zhang 1988, Hassan and Guo 1991, Pavlík 1993). In the first field release trials in the U.S., Charles Mason and colleagues in Delaware recorded >97% parasitism of naturally occurring ECB eggs in sweet corn when experimental releases were made at a density of 202,000 T. ostriniae per acre (Mason et al. 1996). Similar releases in New York, showed parasitism of sentinel ECB eggs to average ~60% (Hoffmann et al. 1992) and parasitism of naturally-occurring ECB eggs to range from 70 to 80% (Seaman et al. 1997).
Subsequent research on T. ostriniae has demonstrated proficient dispersal and host-finding abilities in corn (M. P. Hoffmann, unpublished data) and a density-dependent functional response to O. nubilalis in the field (Wang and Ferro 1998). Wang et al. (1999) found that T. ostriniae were more efficient at finding O. nubilalis egg masses and to provide higher levels of parasitism within the field than T. nubilale.
Also, T. ostriniae can successfully parasitize ECB eggs throughout most of their embryonic development (Hoffmann et al. 1995), and the wasp does not lose fitness even after many generations of being reared on alternate hosts. Given all of these reports, T. ostriniae appears to be a very promising species for mass production and biological control of ECB.
Two potential drawbacks of the inundative release method are cost and optimizing the timing of release. To overcome this in China, researchers attempted an inoculative release strategy with the parasitoid T. dendrolimi for control of Asian corn borer (Fucheng et al. 1986, Xiao-Cheng et al. 1986). Releases of 6,250 T. dendrolimi per acre during the first generation of corn borer were just as effective as a release of ten times that many later in the season.
In New York, Hoffmann (1998) demonstrated the potential of inoculative releases of T. ostriniae for control of ECB in sweet corn. In four fields of sweet corn, two releases of 15,000 T. ostriniae were made a week apart to coincide with the first generation ECB moth flight. Parasitism of egg masses was recorded throughout the season (79 days total). From 14 days after the inoculative release to the end of the season, a total of 78 naturally-occurring ECB egg masses were collected from the four fields. Of the egg masses collected, 47 (60.3%) were parasitized by T. ostriniae. The parasitism rate on the one organic farm was 76.9% versus 54.5, 66.6 and 43.8 on the conventional farms, where one or more insecticide applications was made to the test fields. Many of the parasitized egg masses were recovered at distances of 100 to 300 ft from release areas. This study demonstrated that inoculative releases of relatively few T. ostriniae can establish the parasitoid in a field allowing them to reproduce on eggs of ECB, increase their numbers, and disperse.
Further evaluations of T. ostriniae releases were made last season (2000) in commercial sweet corn fields in New York by M. P. Hoffmann, T. P. Kuhar, and Mark G. Wright to measure the impact of parasitism on ECB population levels and damage. Following the protocol outlined in the Hoffmann (1998) study, releases were made in nine fields. Nearby fields of the same variety and planting date served as non-treated controls for each of the fields. Egg populations of ECB were monitored twice weekly from early-whorl stage to harvest. Approximately 47% of the total ECB eggs deposited over the season were parasitized in the release fields compared with 3.6% in the non-release fields (Table 2). Trichogramma ostriniae accounted for >95% of the egg parasitism. ECB damage was reduced more than 50% in the release fields compared with the non-release fields (Table 2).

Table 2.  Evaluation of T. ostriniae inoculative releases on ECB damage in sweet corn planted in central, NY in 2000.

Numbers within columns followed by a different letter are significantly different, Fisher’s protected LSD at 0.05 level of significance.

Also in 2000, we (Hoffmann, Kuhar and Losey) evaluated inoculative releases of T. ostriniae in field corn. Six fields were sampled and analyzed using the same procedures as in the sweet corn study, except that yield was assessed as mass of grain (husked ears) per ha. Releases of T. ostriniae had a similar effect on ECB populations and reduced the number of stalk tunnels by 38% (Table 3).

Table 3.  Evaluation of T. ostriniae inoculative releases on ECB damage and yield in field corn planted in central, NY in 2000.

Numbers within columns followed by a different letter are significantly different, Fisher’s protected LSD at 0.05 level of significance.

Based on the aforementioned research studies, inoculative releases of T. ostriniae should be pursued as a biological control strategy for ECB in sweet corn and field corn. There are some important questions that still need to be answered. Based on our preliminary research over two years, T. ostriniae does not appear to overwinter in New York, but it may overwinter in Delaware (C. Mason, unpublished data). The overwintering ecology needs to be investigated. Gou (1985) showed that T. ostriniae enter diapause and can survive prolonged cold storage. However, the primary host, ECB, does not overwinter in the egg stage, other potential hosts with overwintering eggs must be assessed for T. ostriniae parasitism. Hoffmann et al. (1995) demonstrated that in the laboratory under no-choice conditions, T. ostriniae will parasitize a relatively wide range of lepidopteran hosts, particularly members of the Pyralidae, Noctuidae, and Plutellidae families. To our knowledge, T. ostriniae parasitism of hosts other than Ostrinia spp. has not been reported in the field. Host range of T. ostriniae needs further investigation, particularly in the field. Parasitism of non-target hosts could be beneficial, in that other hosts could serve as a reservoir for T. ostriniae when ECB eggs are scarce. Conversely, parasitism of non-target hosts could be detrimental if the non-target hosts are endangered species, or are considered beneficial organisms (Van Driesche and Bellows 1996).
We are confident that once shown to be effective and optimized, inoculative release of T. ostriniae will be widely adopted in sweet corn as well as field corn across the northeastern US and possibly in other regions. We have been assured that if the market for T. ostriniae is adequate, Beneficial Insectary Inc., Redding, CA is willing to mass produce and market this species for control of ECB. This would greatly facilitate adoption of the biological control program.

Objectives

Back to the top

1. Evaluate inoculative releases of Trichogramma ostriniae on ECB populations and damage in field corn in New York, Pennsylvania, Delaware, and Virginia
2. Construct a predator/prey simulation model for T. ostriniae-ECB
3. Investigate the potential overwintering of T. ostriniae in each state
4. Assess possible non-target effects of T. ostriniae releases by evaluating parasitism of other lepidopteran hosts in and around corn fields
5. Determine a cost benefit analysis of the release program
   

Back to the top

Links

Index of 2001 Northeast IPM Funded Projects

Northeast IPM Home

Integrated Pest Management (IPM): What Is It?:

Back to the top

About this Page

Credits: