BIOLOGICAL CONTROLÐMICROBIALS Grower-Adoptable Formulations of the Entomopathogenic Fungus Metarhizium anisopliae (Ascomycota: Hypocreales) for Sugarbeet Root Maggot (Diptera: Ulidiidae) Management 1 2 3 4 5 L. G. CAMPBELL, M. A. BOETEL, N. B. JONASON, S. T. JARONSKI, AND L. J. SMITH Environ. Entomol. 35(4): 986Ð991 (2006) ABSTRACT Producers in many North American sugarbeet (Beta vulgaris L.) growing areas rely heavily on organophosphate insecticides to manage the sugarbeet root maggot, Tetanops myopaeformis Ro¨der. The threat of losing organophosphate options because of the potential for development of resistant root maggot strains or regulatory action has prompted a search for alternative control tools. American Type Culture Collection (ATCC) accession no. 62176, a strain of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin, was studied in Þeld trials as a bioinsecticidal option for control of T. myopaeformis larvae because of shown virulence in preliminary laboratory testing. The fungus was evaluated at four Þeld sites during 2001 and 2002 as a planting-time granule, an aqueous postemergence spray, or a combination of both. Three rates of M. anisopliae conidia, 4 ϫ 1012 (1ϫ), 8 ϫ 1012 (2ϫ), and 1.6 ϫ 1013/ha (4ϫ) were applied as granules, and the spray was tested at the 1ϫ rate. A signiÞcant linear response in sucrose yield in relation to M. anisopliae granule application rate conÞrmed its entomopathogenic capacity under Þeld conditions. Each multiple of M. anisopliae granules applied affected a yield increase of Ϸ171 kg sucrose/ha. The fungus was less effective than conventional insecticides at preventing stand loss from high root maggot infestations early in the season. It is concluded that, with additional research, mycoinsecticides could potentially be incorporated into management systems to complement chemical control tactics such as insecticidal seed treatments, soil insecticides (possibly at reduced rates), or postemergence materials for inte- grated control of T. myopaeformis adults or larvae. KEY WORDS Tetanops myopaeformis, mycoinsecticide, bioinsecticide, insect-pathogenic fungus, entomogenous fungus Few conventional chemical options are available to production in areas affected by this pest would be in North American sugarbeet growers for managing the jeopardy if an insecticide-resistant root maggot strain sugarbeet root maggot, Tetanops myopaeformis were to develop or, alternatively, if these insecticides (Ro¨der), a major insect pest of sugarbeet, Beta vulgaris became unavailable because of environmental con- L., in northern growing areas of the continent (Yun cerns and regulatory action. These possibilities, along 1986, Cooke 1993, Campbell et al. 1998). Most options with an increasing consumer demand for reduced available for T. myopaeformis management during the chemical pesticide use on food crops, stimulated a past three decades have involved organophosphate search for effective alternative control measures and carbamate insecticides. Both classes have the (Wozniak et al. 1993, Hodge et al. 1998, Campbell et same chemical mode of action (acetylcholinesterase al. 2000, Dregseth et al. 2003, Smigocki et al. 2003, inhibition) in insects. The proÞtability of sugarbeet Campbell 2005). The entomopathogenic fungus Metarhizium aniso- pliae (Metschnikoff) Sorokin has been evaluated as a This article reports the results of research only. Mention of a potential biological agent for managing insect pests in proprietary product does not constitute an endorsement or a recom- mendation by the USDA for its use. diverse crop and livestock production systems (Cilek 1 U.S. Department of AgricultureÐAgricultural Research Service, et al. 1991, Samson et al. 1994, Kaaya and Munyinyi Northern Crop Science Laboratory, Fargo, ND 58105. 1995, Kruger and Roberts 1997, Booth and Shanks 2 Corresponding author: Department of Entomology, 1300 Albrecht 1998, Ekesi et al. 1998, Campbell et al. 2000). Envi- Blvd., 202 Hultz Hall, North Dakota State University, Fargo, ND 58105 (e-mail: [email protected]). ronmental conditions that enhance the effectiveness 3 Department of Entomology, North Dakota State University, of the fungus also have been documented (Walstad et Fargo, ND 58105. al. 1970, Li and Holdom 1995). 4 U.S. Department of AgricultureÐAgricultural Research Service, Smith and Eide (1995) conducted bioassays on Northern Plains Agricultural Research Laboratory, Sidney, MT 59270. 5 University of Minnesota, Northwest Research & Outreach Center, American Type Culture Collection (ATCC) accession Crookston, MN 56716. no. 22099, a M. anisopliae strain from Israel. They 0046-225X/06/0986Ð0991$04.00/0 ᭧ 2006 Entomological Society of America August 2006 CAMPBELL ET AL.: Metarhizium anisopliae FOR MANAGING SUGARBEET ROOT MAGGOT 987 observed 94% mortality in third-instar T. myopaeformis 25 Ϯ 1ЊC and 150 rpm. The prepared cultures were within 15 d after exposure to the fungus (2.3 ϫ 107 used to inoculate autoclaved (103 KPa for 20 min/kg) conidia/ml), whereas 3% mortality occurred in non- pearled barley (Minnesota Grain, Eagan, MN) in ster- exposed larvae. Based on those laboratory trials, ilized, vented, plastic mushroom spawn bags (Unicorn ATCC 22099 was cultured on autoclaved whole-grain Implement and Manufacturing, Commerce, TX). Liq- barley to produce inoculum for Þeld testing. Data from uid cultures were hand-mixed with the substrate un- Þeld trials indicated that M. anisopliae was capable of der aseptic conditions at a ratio of 1:2 (vol:wt), and reducing root maggot damage under low to moderate the bags were heat-sealed. Solid substrate fermenta- root maggot pressure (Campbell et al. 2000). In sub- tion was conducted for8dat25Ϯ 1ЊC in constant sequent laboratory testing, Jonason et al. (2005) darkness. Cultures were observed daily and crumbled showed that ATCC 62176 was superior to ATCC by hand within spawn bags as needed to prevent 22099, several other M. anisopliae strains, and a Beau- binding and provide aeration throughout the culture veria bassiana (Balsamo) Vuillemin isolate. However, substrate. Whole cultures were transferred to paper information on the impacts of formulation, rate, or bags and dried for7dat24Ϯ 1ЊC. Conidia were application timing on the pest management potential harvested by mechanical sieving through 20- and 100- of M. anisopliae and, more speciÞcally ATCC 62176, is mesh sieves in an ultrasonic sieve shaker (AS200; lacking. Retsch, Newton, PA). Conidial fractions smaller than This study was designed to provide additional in- 100 mesh (0.15 mm) were retained. sight into the potential and limitations of M. anisopliae The granular formulation consisted of M. anisopliae as a biological control agent for protecting sugarbeet conidia bound to 16- to 20-mesh corn grit using 20% from feeding injury by the sugarbeet root maggot. monosorbitan oleate (Tween 20; Sigma, St. Louis, Furthermore, this study was carried out to determine MO) at 2% (vol:wt). Granules were prepared in 5-kg if granular and aqueous sprayable formulations, ap- batches by Þrst applying a coating of Tween binder to plied by placement methods and equipment com- corn grit using an artistÕs air brush while manually monly used by producers for conventional chemical mixing the carrier and then blending in a V-cone insecticide applications, could be used to effectively blender. The fungus was added to the carrier at 3.6 ϫ distribute infective units of the fungus for root maggot 1011 viable conidia/kg, and the combination was management. blended to form a homogeneous mixture. Fungal sprays consisted of conidia suspended in 0.1% aqueous Tween 80 (Sigma). Sprays were applied as 13-cm Materials and Methods bands centered over rows through three 4001E noz- Field trials were established near Crookston, MN zles (one centered above and two directed at plant (Wheatville very Þne sandy loam with 3.5% organic bases from each side of the row at 45Њ angles) at matter and 7.6 pH), and St. Thomas, ND (Bearded silt 2.8 kg/cm pressure, and incorporated into the top loam with 5.1% organic matter and 7.9 pH), in 2001, 1.5 cm of soil using 5-cm long rolling tines attached to and near Crystal (Glyndon silt loam with 4.9% organic a tractor-mounted toolbar. matter and 7.9 pH) and St. Thomas, ND (Glyndon silt The experiment was arranged in a randomized com- loam with 3.6% organic matter and 7.9 pH), in 2002. plete block design with four replications of the treat- Natural infestations of T. myopaeformis were relied on ments at each site. Six M. anisopliae treatments were at all study sites for this experiment. Experimental examined. Three rates of fungus granules, 1ϫϭ4 ϫ units were six-row, 10.6-m-long plots with rows spaced 1012 (11.2 kg formulation/ha), 2ϫϭ8 ϫ 1012 56 cm apart. The St. Thomas and Crookston trials were (22.4 kg/ha), and 4ϫϭ1.6 ϫ 1013 conidia/ha (44.8 planted 11 and 22 May, respectively, in 2001. The 2002 kg/ha), were applied using modiÞed in-furrow (MIF) trials were planted 28 and 29 May. All plots were placement (Boetel et al. 2006). This technique in- thinned to Ϸ76,500 seedlings/ha before colonization volved dropping granules through a conventional of the Þeld by T. myopaeformis adult ßies. Weeds were planter-equipped in-furrow insecticide application controlled by using herbicides, cultivation, and hand tube directed over the seed furrow in a 5- to 8-cm band weeding on an as-needed basis. near the rear press wheel. The tube was oriented Fungus conidia were applied as a corn meal-based backward toward the rear press wheel to allow some planting-time granule, a spray timed to coincide with soil to cover the seed before granules reached the peak adult ßy activity, or a combination of the two. furrow. This placement concentrated most of the ma- The M. anisopliae strain used (ATCC no. 62176) was terial over the row. The 2ϫ granular rate was also originally isolated from soybean cyst nematode (Het- applied by using the “spoon,” an alternative placement erodera glycines, Ichinohe) in Illinois (Carris and device consisting of an open-faced bander attached to Glawe 1989).