Biological Control 56 (2011) 9–16

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Biological Control

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Integrating insecticides and Trichogramma ostriniae to control European cornborer in sweet corn: Economic analysis

Jeffrey Gardner a,⇑, Michael P. Hoffmann a, Sylvie A. Pitcher a, Jayson K. Harper b

a Cornell University Department of Entomology, Ithaca, NY 14853, USAb Pennsylvania State University Department of Agricultural Economics and Rural Sociology, University Park, PA 16802, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 19 January 2010Accepted 31 August 2010Available online 6 September 2010

Keywords:Trichogramma ostriniaeOstrinia nubilalisZea maysBiological controlEconomicsPartial budgetBreakeven costSweet corn

1049-9644/$ - see front matter � 2010 Elsevier Inc. Adoi:10.1016/j.biocontrol.2010.08.010

⇑ Corresponding author. Fax: +1 607 255 1720.E-mail address: jg48@cornell.edu (J. Gardner).

We compared the economics of controlling European corn borer (Ostrinia nubilalis) in sweet corn by usingthe egg parasitoid, Trichogramma ostriniae, alone and integrated with insecticidal sprays. An initial exper-iment in 2003 compared T. ostriniae alone against insecticide alone and a second set of experimentsconducted over 3 years (2006–2008) compared (1) insecticide alone [Insecticide]; (2) no insecticide, noT. ostriniae [Untreated Check]; (3) T. ostriniae alone [T. ostriniae 1X]; and (4) T. ostriniae + insecticide [Inte-grated]. In 2007 and 2008, a fifth treatment was added consisting of three approximately weekly releasesof T. ostriniae [T. ostriniae 3X]. Parasitism of O. nubilalis eggs was higher in plots receiving T. ostriniae;O. nubilalis eclosion was lower with T. ostriniae; there was no interaction of T. ostriniae and insecticideon parasitism, O. nubilalis eclosion, or total O. nubilalis larvae at harvest time. Partial crop budgets wereconducted for each treatment. In three of the 4 years, Untreated Checks had the highest sweet corn eardamage. Ear damage after a single release of T. ostriniae was statistically no different than using insecti-cides. In two of the three years, the Integrated treatment (T. ostriniae 1X + insecticide) generated the larg-est increase in profitability. The insecticide only treatment generated the second best increase inprofitability. When comparing a single release of T. ostriniae to the insecticide only, the latter provideda better combination of efficacy and profitability. The breakeven costs of the T. ostriniae justified theiruse relative to the Untreated Check treatment, but not when compared to the Insecticide treatment.The breakeven costs for T. ostriniae in the Integrated treatment exceeded the actual cost in two out ofthree years, suggesting again that conventional growers could benefit from integrating T. ostriniae withinsecticidal treatments. Projected profitability based on ear packout obtained by combining data amongyears suggests that in general, for low prices and yields, the increase in profit is quite modest. In the low-est price-yield combination, the change in profit is T. ostriniae 3X > Integrated > Insecticide > T. ostriniae1X P Untreated Check. At high prices and high yields, the differences between the management optionswhen compared to Untreated Check are considerable. In the highest price-yield combination, the changein profit is T. ostriniae 3X > Integrated� Insecticide > T. ostriniae 1X� Untreated Check.

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1. Introduction

Field-scale use of augmentative biological control in the US haslagged behind other countries, perhaps because of inadequateresearch investment in biological control and the widespread useof insecticides (Li, 1994). Other researchers have evaluatedaugmentative biological control in the US and concluded thatbroad-spectrum insecticides are unlikely to be replaced becausebiological control is frequently ineffective and there is little eco-nomic incentive relative to pesticides (Collier and Van Steenwyk,2004). We attempt with this and other studies, to demonstrate thataugmentative biological control with Trichogramma ostriniae can

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provide perhaps not a replacement of insecticides, but rather areduction in their use.

Based on several studies, T. ostriniae (Pang et Chen) (Hymenop-tera: Trichogrammatidae) was identified as a candidate to controlEuropean corn borer (Ostrinia nubilalis) (Hübner) (Lepidoptera:Crambidae) in the US (Wang et al., 1984; Chiu and Chen, 1986;Zhang, 1988; Hassan and Guo, 1991; Pavlík, 1993). The parasitoidis believed native to China where it can parasitize 70–96% of eggsof the closely related Ostrinia furnacalis Guenée (Lepidoptera:Crambidae) (Wang et al., 1984; Chiang et al., 1986; Zhang, 1988)and a strain from Jilin Province, China, was imported into the USin 1990 (Hoffmann et al., 1995).

T. ostriniae has been shown to be fairly effective in reducing O.nubilalis infestations in sweet corn when released augmentatively(e.g., Mason et al., 1996; Seaman et al., 1997; Wang et al., 1999;Wright et al., 2001; Hoffmann et al., 2002; Kuhar et al., 2002;

Table 1Dates of T. ostriniae releases and insecticide applications for sweet corn exposed to (1)insecticide alone [Insecticide]; (2) no insecticide, no T. ostriniae [Untreated Check]; (3)Trichogramma ostriniae alone [T. ostriniae 1X]; (4) Trichogramma ostriniae alone [T.ostriniae 3X]; and (5) T. ostriniae + insecticide [Integrated].

Year Treatment T. ostriniae release dates Insecticide spray date

2003 T. ostriniae 1X 22-Jul –Insecticide – 14-Aug

2006 T. ostriniae 1X 13-Jul –Integrated 13-Jul 4-AugInsecticide – 4-Aug

2007 T. ostriniae 1X 22-Jul –T. ostriniae 3X 22-Jul, 30-Jul, 10-Aug –Integrated 22-Jul 3-Aug and 14-AugInsecticide – 3-Aug and 14-Aug

10 J. Gardner et al. / Biological Control 56 (2011) 9–16

Wright et al., 2002). In the first field trials in the US, >97% of natu-rally occurring O. nubilalis eggs in sweet corn were parasitized(Mason et al., 1996). More recent research has shown that despitepyrethroid applications to fields of sweet corn, T. ostriniae popula-tions can persist from inoculative release until the crop is har-vested (Gardner et al., 2007). This is not surprising given thatadult Trichogramma are generally susceptible to most broad-spec-trum insecticides but the immature stages of the parasitoid devel-oping within a host egg are generally well protected from even themost toxic compounds (Bull and Coleman, 1985; Suh et al., 2000).Thus, we initiated studies to further assess not only the biologicalramifications of integrating T. ostriniae and insecticides to controlO. nubilalis in sweet corn, but the economics as well. Herein, we re-port the findings of our research.

2008 T. ostriniae 1X 29-Jul –T. ostriniae 3X 29-Jul, 5-Aug, 11-Aug –Integrated 29-Jul 7-Aug and 14-AugInsecticide – 7-Aug and 14-Aug

2. Materials and methods

2.1. Experimental design, T. ostriniae colony maintenance and releasemethods

In 2003 and 2006–2008 we conducted experiments to comparethe relative economic impacts of using T. ostriniae alone and com-bined with insecticidal control. In all years, plots were approxi-mately 25 � 30 m and were planted on the same dates and withthe same varieties of sweet corn at a nominal rate of 54,340seeds/ha. Plots were spatially separated by approximately 100 mto minimize T. ostriniae movement among plots. Prior to plantingall plots were treated with Lumax� herbicide (S-metolachlor, atra-zine, mesotrione; Syngenta Crop Protection, Greensboro, NC, USA)at 2.9 L/ha plus atrazine at 1.2 L/ha, and fertilized with approxi-mately 337 Kg/ha of 1:1 blend of urea:ammonium sulfate. In2003, sweet corn cv. ‘Seneca Spring’ (Petoseed, Saticoy, CA), a66 day se bicolor was planted. In 2006 and 2008, ‘Obsession’(Seminis Inc., Saint Louis, MO USA), a 79 day shQ bicolor, wasplanted. In 2007, we used ‘Ambrosia’ (Crookham Seeds, Caldwell,ID) a 75 day se bicolor. Plots were scouted for O. nubilalis eggmasses and when initially found, T. ostriniae were released at thecenter of the appropriate replicates.

In 2003, T. ostriniae alone was compared to insecticide treat-ment alone. The experiment was conducted as a completely ran-domized design with eight replicates of the insecticide treatmentand nine replications of the T. ostriniae treatment. In 2006, thestudy used a randomized complete block design and was expandedto include the following treatments: (1) insecticide alone [Insecti-cide]; (2) no insecticide, no T. ostriniae [Untreated Check]; (3)T. ostriniae released once [T. ostriniae 1X]; and (4) T. ostriniae (1X)+ insecticide [Integrated]. In 2007–2008, it was further expandedto include a 5th treatment, T. ostriniae with three approximatelyweekly releases (T. ostriniae 3X). Dates of T. ostriniae releases arepresented in Table 1.

The T. ostriniae for this research were from colonies that wehave maintained since 1992 without documented loss of fitness(Hoffmann et al., 2001). The colonies have been maintained onirradiated Ephestia kuehniella (Zeller) (Lep., Pyralidae) eggs (Benefi-cial Insectary, Redding CA, USA) under nominal conditions of16L:8D, 25 �C, and �80% RH. Before each field season, the waspswere reared for four generations on O. nubilalis and then switchedto E. kuehniella for mass production.

Release packets consisted of parasitized E. kuehniella eggs gluedinto polyethylene coated poster-board envelopes that were stapledclosed in a manner allowing parasitoid egress while preventingpredator access. Because we were concerned that emigration ofT. ostriniae from such small plots might substantially render theeffective release rate to well below the 74,000 per hectare that isour standard, we opted to increase the release rate by using

15,000 wasps per plot, effectively delivering approximately202,500 T. ostriniae/ha.

We anticipated some background parasitism from extantTrichogramma, so sub-samples of Trichogramma from field-col-lected O. nubilalis egg masses were identified as T. ostriniae ornot-T. ostriniae by using molecular methods for differentiatingITS-2 region base pair lengths and sequences (Stouthamer et al.,1999; and Silva et al., 1999). Egg masses used to assess backgroundparasitism were only taken from Insecticide and Untreated Checkplots.

Each week of the study after parasitoid release, all plots weresequentially sampled to determine the need for sprays (Hoffmannet al., 1996; Cornell Cooperative Extension, 2009). Dates of insecti-cide sprays are presented in Table 1. In 2003, Insecticide alonetreatments were sprayed once with Warrior (k-cyhalothrin) at31 g active ingredient/ha, by a commercial pesticide applicatorusing a Patriot (Case IH) high clearance sprayer equipped with Tee-Jet Twin Fan (Spraying Systems Co., Wheaton, IL) nozzles to deliver236 L/ha. In 2006, Lannate (methomyl) was applied at 511 g activeingredient/ha to all Insecticide and Integrated replicates (a singleplot that was over threshold was also sprayed on 29-July). In2007, plots were similarly sampled but the decision to spray wasbased on timing the spray to coincide with anticipated O. nubilalislarval emergence after sequential sampling indicated an increasein the number of egg masses. A second spray was applied at earlysilking to further protect the crop during a particularly susceptiblephase of growth (Spangler et al., 2003). Thus, in 2007, Warrior(k-cyhalothrin) was applied twice at 31 g active ingredient/ha torecipient plots using the method described above. In 2008, meth-ods were the same as for 2007, with Warrior applied twice. Thedecision to conduct a second application of insecticide in 2007and 2008 was not triggered by a threshold being exceeded, butwas made to better protect the corn during the fruiting stage(Spangler et al., 2003) and to insure against any shortcomings ofthe first sprays.

2.2. O. nubilalis egg and larval fate

In 2003, parasitism rates by Trichogramma were evaluated bysampling the corn plots for O. nubilalis eggs every 3–4 days fromTrichogramma release until harvest. Egg masses were, removedfrom the plots, transferred to the laboratory, and observed forapparent and latent parasitism. Egg number was determined foreach egg mass and egg fate was categorized as parasitized, dead,or viable with O. nubilalis eclosion occurring. At harvest, approxi-

J. Gardner et al. / Biological Control 56 (2011) 9–16 11

mately 100 plants were dissected and number of establishedO. nubilalis larvae was recorded.

In 2006 and 2007, all plots, regardless of treatment, had 200 focalplants in the first year of the study and 160 focal plants in the secondyear that were delineated from the rest of the plot and inspected forO. nubilalis egg masses. Any egg masses found, rather than removingthem from the plot, were flagged for subsequent observation andeach egg mass was digitally photographed for egg counting. Theplots were sampled every 3–4 days from release until harvest andany egg masses that were flagged during the previous samplingevents were again photographed and subsequently each egg withinan egg mass was observed using NIH ImageJ software to assist withvisual counting of the digitized image. Within an egg mass, eachegg’s status was recorded as viable and eclosed, or parasitized.Observation and photography of a given egg mass was terminatedwhen its fate had manifested. At harvest, the focal corn plants wereexamined to estimate larval establishment in the plant, so that thedata could be correlated with egg mortality on the very same plants.

In 2008, parasitism levels were evaluated during sequentialsampling for insecticide spray decisions (described previously). Inthis case, O. nubilalis egg masses were evaluated for apparent par-asitism during sequential sampling, but the number of individualeggs and egg fate other than parasitism were not determined. NoO. nubilalis larval data were recorded at harvest.

For 2003, the data were analyzed using a general linear modelanalysis of variance for each of the response variables as a propor-tion of the total O. nubilalis eggs. In 2006, 2007 and 2008, the po-tential interaction of T. ostriniae with insecticide on the responsevariables was analyzed as an RCBD design with a 2 � 2 factorialarrangement to test for an interaction of T. ostriniae and insecticide.Because the addition of the 3X T. ostriniae treatment in 2007 unbal-anced the factorial arrangement, data from 2007 were analyzed forinteractions by excluding the 3X T. ostriniae treatment. In 2008, thedata were also analyzed using a general linear model AOV for RCBDdesign with a 2 � 2 factorial arrangement, as above (SAS Institute,2008). Subsequently the data were analyzed as a simple RCBD withfour treatments in the first year and five treatments in the secondyear. Means separations were conducted using Tukey’s adjust-ment. Exploratory analyses indicated that there was a significanteffect of year, so data were analyzed for each year.

2.3. Harvest ear evaluation

At harvest, approximately 100–200 (depending on year) pri-mary ears of sweet corn per plot were examined for O. nubilalislarvae and damage. In 2003 and 2008, random primary ears wereselected; in 2006 and 2007 only focal plants were sampled. Differ-ences in percentage marketable (undamaged) ears among treat-ments and within years were determined using a general linearmodel on untransformed proportional data (SAS Institute, 2008).The percentage of marketable ears was then used to constructpartial budgets for each treatment each year.

2.4. Individual year partial budgeting analysis

Economic analysis of biological control of O. nubilalis in sweetcorn production involved comparing the input costs of conventionalspray programs with those of biological control practices and byevaluating the quality (percentage marketable ears) of the sweetcorn harvested from each system. Input costs for the number ofapplications and the quantity of insecticides, T. ostriniae, labor re-quired to apply release packets, etc., were generated for those insectmanagement programs evaluated during a given year. Pesticideapplication costs were published values (Pike, 2009). Pesticide costsrepresent the average of several price quotes for 2009 that were ob-

tained from several agri-chemical dealers. For T. ostriniae, costs werebased on a 1.6 ha release using the prevailing commercial cost of $14for 30,000 per 0.4 ha, with Federal Express ground shipping costsadded. While cost of the insect management program is a criticalconsideration, the most important economic factor from a pro-ducer’s perspective is the difference in the percentage of marketableears among the various treatments.

The overall economic impact of a change from conventionalpest management practices to biological control or integratedmethods was evaluated using partial budgeting. The partial bud-gets contained only those income and cost items that changeddue to a particular management practice. For this study, the newor additional costs were any additional inputs, labor, and manage-rial time. The final result estimated the increase or decrease inprofit attributable to the change. Decreased revenues and in-creased costs were subtracted from increased revenues and de-creased costs to identify the net effect of the change.

2.5. Breakeven cost analyses

Another way to gauge the economic benefit of releases ofT. ostriniae compared to the other treatments (i.e., Untreated Checkor Insecticide) is to calculate the breakeven cost. This is the maxi-mum cost for T. ostriniae that is justified based on differences insweet corn packout (i.e., marketable ears), T. ostriniae release costs,and cost of insecticides (spray materials plus application costs). Aslong as the breakeven cost exceeds the actual cost, use of T. ostri-niae is economically justified. The equations for calculating thebreakeven cost for T. ostriniae are:

Comparison of T. ostriniae (1X or 3X) treatments to UntreatedCheck treatment:Ctost ¼ P � ðPOtost � POUntreated CheckÞ � Y � Ctapp

Comparison of T. ostriniae (1X or 3X) treatments to Insecticidetreatment:Ctost ¼ P � ðPOtost � POinsecticideÞ � Y þ Cins þ Cinsapp � Ctapp

Comparison of Integrated treatment to Untreated Checktreatment:

Ctost ¼ P � ðPOIntegrated � POUntreated CheckÞ � Y � Cins � Cinsapp � Ctapp

Comparison of Integrated treatment to Insecticide treatment:

Ctost ¼ P � ðPOIntegrated � POinsecticideÞ � Y � Ctapp

where:Ctost = breakeven cost of T. ostriniae ($/ha)P = price of sweet corn ($/dozen ears)POtost = packout for T. ostriniae treatment (% marketable ears)POinsecticide = packout for Insecticide treatment (% marketableears)POIntegrated = packout for Integrated treatment (% marketableears)POUntreated Check = packout for Untreated Check (% marketableears)Y = sweet corn yield (dozen ears/ha)Cinsecticide = cost of insecticide spray materials ($/ha)Cinsapp = cost of insecticide application ($/ha)Ctapp = cost of T. ostriniae application ($/ha)

Additionally, the breakeven cost of the Insecticide treatmentcompared to the Untreated Check treatment were calculated as:

Cinsecticide ¼ P � ðPOinsecticide � POUntreated CheckÞ � Y � Cinsapp

where:

Cinsecticide ¼ breakeven cost of insecticide spray materials ð$=haÞ

12 J. Gardner et al. / Biological Control 56 (2011) 9–16

3. Results

3.1. O. nubilalis egg and larval fate

3.1.1. O. nubilalis ovipositionIn 2003, we observed 302 O. nubilalis egg masses representing

5496 eggs. We tracked the fate of 783 egg masses in 2006(14,603 eggs) and 584 egg masses (10,645 eggs) in 2007. In 2008,we recorded 314 egg masses during sequential sampling but num-ber of eggs was not determined.

In 2003 there was no difference between treatments for totalnumber of O. nubilalis eggs (Tables 2 and 3). Total egg number alsodid not differ among treatments for either 2006 or 2007 (Tables 2and 3), indicating relatively uniform pest pressure among thetreatments, but there were more eggs in 2006 than in 2007. In2008, there were differences among treatments for number ofegg masses found (Tables 2 and 3), with Untreated Check havingthe fewest egg masses.

3.1.2. ParasitismIn 2003, parasitism of O. nubilalis eggs was greater in the T. ostri-

niae 1X treatment than in the Insecticide treatment (Tables 2 and3). In 2006, parasitism of O. nubilalis eggs was also higher in plots

Table 2O. nubilalis egg fate, total larvae at harvest, and crop packout for sweet corn exposed to (1)Trichogramma ostriniae alone [T. ostriniae 1X]; (4) T. ostriniae + insecticide [Integrated]; andare expressed as a percentage of total eggs.

Year Treatment Total eggs % Pa

2003 Insecticide 344.1 ± 43.3 ac 22.2T. ostriniae 1X 304.8 ± 45.1 a 60.9

2006 Untreated Check 745.6 ± 110.0 a 4.2Insecticide 652.6 ± 133.5 a 2.6Integrated 723.8 ± 143.3 a 24.7T. ostriniae 1X 688.6 ± 134.1 a 22.9

2007 Untreated Check 351.8 ± 60.2 a 20.6Insecticide 498.8 ± 67.5 a 25.5Integrated 417.6 ± 60.8 a 50.8T. ostriniae 1X 378.4 ± 129.5 a 45.3T. ostriniae 3X 482.4 ± 101.7 a 53.7

2008a Untreated Check 5.8 ± 1.1 c 15.0Insecticide 10.0 ± 1.2 ab 12.1Integrated 17.0 ± 2.8 a 40.5T. ostriniae 1X 13.0 ± 0.8 ab 38.1T. ostriniae 3X 17.0 ± 2.6 a 55.6

Combined yearsb Untreated Check – –Insecticide – –Integrated – –T. ostriniae 1X – –T. ostriniae 3X – –

a In 2008, O. nubilalis egg masses were enumerated, but not the total number of eggsb Used for profitability projections in Table 7.c Within a year and within combined years, values followed by the same letter are n

Table 3F and P values associated with analysis of variance conducted on data summarized in Tab

Year df Total eggsa % Parasitized

F P F P

2003 1, 15 0.39 0.5412 22.22 0.0003

2006 3, 12 0.20 0.8929 16.91 0.0001

2007 4, 16 0.73 0.5854 4.2 0.0164

2008 4, 16 6.31 0.0030 6.93 0.0020

Combined years 4, 80 – – – –

a In 2008, O. nubilalis egg masses were enumerated, but not the total number of eggs

receiving T. ostriniae than in plots not receiving the wasps (Tables 2and 3), and was not affected by insecticide, or by the interaction ofT. ostriniae � insecticide (Table 4). In 2007 only T. ostriniae 3X hadsignificantly greater parasitism than Untreated Checks (Table 2).Parasitism was greater with T. ostriniae present, but there was nointeraction with insecticide (Table 4). In 2008, the number of eggmasses parasitized varied among treatments (Tables 2 and 3).Again, parasitism was greater where T. ostriniae was present, butthere was no interaction of insecticide and T. ostriniae (Table 4).Of the subsample of egg masses used to evaluate parasitism byother Trichogramma species (n = 12, 2006; n = 28, 2007), parasitismby species other than T. ostriniae was approximately 8% in 2006and 21% in 2007.

3.1.3. O. nubilalis eclosionThe percentage of O. nubilalis larvae that eclosed was generally

lower in the presence of T. ostriniae (Tables 2 and 3). Eclosion wasclearly reduced by T. ostriniae, but it was not affected by insecticideor the interaction of T. ostriniae � insecticide (Table 4). This findingwas reinforced by a negative correlation between percent parasit-ism and percent larval eclosion for both 2006 (n = 20, R = �0.79,P < 0.0001) and 2007 (n = 16, R = �0.83, P < 0.001) and when bothyears were combined (n = 36, R = �0.79, p = 0.0001). The pattern

insecticide alone [Insecticide]; (2) no insecticide, no T. ostriniae [Untreated Check]; (3)(5) Trichogramma ostriniae alone [T. ostriniae 3X]. Parasitism, eclosion and total larvae

rasitized % Eclosed % Total larvae % Ear packout

± 5.3 b 65.9 ± 3.8 a 4.6 ± 2.1 a 91.2 ± 4.0 a± 6.1 a 29.3 ± 6.8 b 15.7 ± 6.8 a 88.1 ± 2.8 a

± 1.3 b 59.4 ± 8.9 a 15.7 ± 0.5 a 85.0 ± 2.7 a± 1.0 b 54.3 ± 2.1 ab 10.3 ± 1.7 bc 89.8 ± 2.1 ab± 2.6 a 43.0 ± 6.2 ab 5.9 ± 1.5 c 92.6 ± 2.1 b± 5.2 a 35.0 ± 3.3 b 10.8 ± 0.9 b 89.4 ± 3.2 ab

± 4.9 b 49.4 ± 4.3 a 10.0 ± 1.9 a 96.3 ± 0.9 a± 9.8 ab 50.8 ± 9.2 a 0.9 ± 0.2 b 99.7 ± 0.2 d± 4.6 ab 22.6 ± 5.0 b 0.4 ± 0.2 b 99.5 ± 0.3 cd± 7.6 ab 28.6 ± 7.0 ab 8.0 ± 3.6 ab 97.7 ± 0.7 ab± 8.6 a 7.0 ± 2.3 b 1.2 ± 0.4 b 98.9 ± 0.2 bc

± 12.1 b – – 87.0 ± 4.1 a± 5.2 b – – 96.9 ± 0.9 bc± 6.6 ab – – 98.3 ± 0.8 c± 4.2 ab – – 90.9 ± 1.7 ab± 4.0 a – – 94.3 ± 1.2 abc

– – 89.4 ± 2.0 a– – 94.6 ± 1.2 b– – 96.8 ± 1.1 b– – 91.7 ± 1.2 ab– – 96.9 ± 1.0 b

within the egg masses.

ot significantly different.

le 2.

% Eclosed % Total larvae % Ear packout

F P F P F P

20.70 0.0004 2.22 0.1573 0.89 0.3592

3.63 0.0450 14.26 0.0003 3.82 0.0394

11.16 0.0002 6.18 0.0033 8.45 0.0007

– – – – 5.29 0.0073

– – – – 4.14 0.0042

within the egg masses.

Table 4Main effects and interactions for O. nubilalis egg and larval fates from mixed model AOV, RCBD design with factorial arrangement for sweet corn exposed (1) insecticide alone[Insecticide]; (2) Trichogramma ostriniae alone [T. ostriniae 1X]; and (3) T. ostriniae + insecticide [Integrated]. In 2008, only egg masses were enumerated and not eggs, eclosion ortotal larvae. Data from 2003 are omitted because the design was not suitable for factor interaction analyses.

Egg and larval fate Effect 2006 2007 2008

F1,12 P F1,12 P F1,12 P

Parasitism T. ostriniae 49.83 <0.0001 11.99 0.0047 11.26 0.0057Insecticide 0.03 0.8684 0.35 0.5655 0.00 0.9740T. ostriniae � insecticide 0.67 0.4295 0.02 0.8916 1.01 0.4415

Eclosion T. ostriniae 9.44 0.0097 18.00 0.0011 – –Insecticide 0.04 0.8464 0.20 0.6636 – –T. ostriniae � insecticide 1.30 0.2759 0.40 0.5414 – –

Total larvae T. ostriniae 13.98 0.0028 1.56 0.2359 – –Insecticide 18.90 0.0009 37.35 <.0001 – –T. ostriniae � insecticide 0.09 0.7661 0.05 0.8199 – –

J. Gardner et al. / Biological Control 56 (2011) 9–16 13

of reduced eclosion where T. ostriniae was present was fairly con-sistent among the years, but in 2006, the Integrated treatmentwas no different than treatments receiving insecticide alone or T.ostriniae alone, nor was it statistically different than UntreatedChecks (Table 2).

3.1.4. Total larvaeThere were differences among the treatments for percentage

larval survival for 2006 and 2007, but not for 2003 (Tables 2 and3); larval data were not recorded in 2008. T. ostriniae and Insecti-cide, alone or Integrated, generally caused a reduction in the num-ber of O. nubilalis present at harvest, relative to Untreated Checks.In 2007, however, there was no difference between T. ostriniae 1Xand the Untreated Check; T. ostriniae 3X provided control equal toInsecticide. The reduction in larval numbers at harvest was attrib-utable to both T. ostriniae and Insecticide in 2006, but not due totheir interaction (Table 4). In 2007, Insecticide had a pronouncedeffect on larval numbers, but T. ostriniae did not. In general, thedata suggest that a reduction in O. nubilalis larval numbers at har-vest were associated with both T. ostriniae induced egg mortalityand insecticide induced larval mortality.

3.2. Harvest evaluation

There were generally differences in the percentage of harvest-able ears within years; as expected, plots receiving neither T. ostri-niae nor insecticide (Untreated Checks) generally had the lowestnumber of harvestable ears, while plots receiving interventionwith insecticides, biological control, or both, had greater numbersof marketable ears (Tables 2 and 3). In 2003, there was no differ-ence in packout between Insecticide and T. ostriniae 1X, indicatingthat biological control was as good as insecticidal control, and in

Table 5Change in profitability ($/ha) for T. ostriniae and Integrated treatments versus Untreatedvalues.

Year: 2003 2006

Price (per doz): $2 $3 $5 $2 $3

Yield (doz ears/ha): 1250 2500 3750 1250 2500

Untreated Check versus:Insecticide – – – 50 268T. ostriniae 1X – – – 46 246T. ostriniae 3X – – – – –Integrated – – – 63 409

Insecticide versus:T. ostriniae1X (68) (209) (544) (4) (22)T. ostriniae 3X – – – – –Integrated – – – 13 141

three of the 4 years, a single release of T. ostriniae was not statisti-cally different from insecticidal control (Table 2). IntegratingT. ostriniae + insecticide (Integrated) had no statistical effect onmarketable ears relative to Insecticide (Table 2).

3.3. Individual year partial budgeting analysis

Partial budgets were developed for every year under two sce-narios: (1) adoption of a O. nubilalis management program (Insec-ticide, T. ostriniae 1X, T. ostriniae 3X, or Integrated) where none hadbeen used previously i.e., some intervention vs. none, or (2) elimi-nation of an insecticide only program in favor of those containing T.ostriniae (T. ostriniae 1X, T. ostriniae 3X, or Integrated). In Table 5,the annual partial budgeting results are given for each comparisonfor a low yield/low price grower (1250 doz. yield/ha; $2/doz. price),medium price/medium yield grower (2500 doz. yield/ha; $3/doz.price), and a high price/high yield grower (3750 doz. yield/ha; $5/doz. price).

3.3.1. Untreated Check vs. Insecticide, T. ostriniae 1X, T. ostriniae 3Xand Integrated

In general, except for the low yield/low price combination in2007, some form of control for O. nubilalis would generate a posi-tive change in profit compared to Untreated Check (Table 5). Intwo of the three years (2006 and 2008) the Integrated treatmentgenerated the largest increases in profitability. The Insecticide onlytreatment generated the second best profitability changes, beinghighest in 2007 and second highest in 2006 and 2008. For growerswho do not use insecticides and who do not fall in the lowest yieldand price combination, use of either T. ostriniae 1X or T. ostriniae 3Xwould improve their profitability over Untreated Check.

Check or Insecticide treatments, 2003 and 2006–2008. Parentheses indicate negative

2007 2008

$5 $2 $3 $5 $2 $3 $5

3750 1250 2500 3750 1250 2500 3750

787 (19) 136 503 111 562 1632722 (15) 48 200 36 213 635– (79) 40 320 18 350 11391230 (67) 78 424 96 610 1831

(65) 4 (87) (303) (76) (349) (997)– (60) (96) (183) (94) (212) (493)281 (48) (57) (79) (15) 48 200

14 J. Gardner et al. / Biological Control 56 (2011) 9–16

3.3.2. Insecticide vs. T. ostriniae 1X, T. ostriniae 3X and IntegratedWhen comparing the Insecticide treatment to the T. ostriniae 1X

and T. ostriniae 3X treatments it is clear that the Insecticide treat-ment provides a good combination of both efficacy and profit(Table 5). It is also very clear that conventional growers can benefitfrom integrating T. ostriniae into their O. nubilalis managementprogram, in particular when yields and price are high.

3.4. Breakeven costs

The results of the breakeven cost calculations for T. ostriniae arepresented in Table 6 for a 2500 doz./ha yield and $3.00/doz. price.Breakeven costs are presented for mean packout (% marketableears) levels and also for packout levels ± 1 standard deviation fromthe mean. The breakeven prices for the packout levels (±1r) fromthe mean can be either higher or lower than the mean dependingon the relative variability and costs of the comparison (see Table 6).If the breakeven cost is higher than the actual cost of T. ostriniae(which was $42.35/ha per application during the study period),then it was economically justified to apply T. ostriniae to controlO. nubilalis. The T. ostriniae 1X and 3X treatments were economi-cally justified relative to the Untreated Check, but were not whencompared to the Insecticide treatment. If breakeven costs are lessthan the actual cost, a grower would be economically justified inapplying T. ostriniae only if they were subsidized to make up thedifference. The Integrated treatment was also economically justi-fied relative to the Untreated Check. When comparing the Inte-grated treatment to the Insecticide treatment, the breakevencosts for the T. ostriniae component exceeded the actual cost in

Table 6Breakeven cost per T. ostriniae application for the T. ostriniae 1X, T. ostriniae 3X, and Integrata yield of 2500 doz. ears/ha of sweet corn and price of $3.00/doz. Parentheses denote neg

Comparison Year PO1 (%) PO2 (%) Cinsecticide + Cinsapp ($)

T. ostriniae 1X vs 2006 89.40 85.00 0.00Untreated Check 2007 97.70 96.30 0.00

2008 90.90 87.00 0.00

T. ostriniae 1X vs 2003 88.10 91.20 38.79Insecticide 2006 89.40 89.80 48.13

2007 97.70 99.70 87.712008 90.90 96.90 90.43

T. ostriniae 3X vs 2007 98.90 96.30 0.00Untreated Check 2008 94.30 87.00 0.00

T. ostriniae 3X vs 2007 98.90 99.70 87.71Insecticide 2008 94.30 96.90 90.43

Integrated vs 2006 92.60 85.00 48.13Untreated Check 2007 99.50 96.30 87.71

2008 98.30 87.00 90.43

Integrated vs 2006 92.60 89.80 0.00Insecticide 2007 99.50 99.70 0.00

2008 98.30 96.90 0.00

a Breakeven cost calculated at mean values for packout (marketable ears), rounded tob Calculated for breakeven cost for ± 1 r from the mean packout values for the treatm

Table 7Breakeven cost for Insecticide treatment materials compared to the Untreated Check trea

Comparison Year PO1 (%) PO2 (%)

Insecticide vs 2006 89.80 85.00Untreated Check 2007 99.70 96.30

2008 96.90 87.00

a Breakeven cost calculated at mean values for packout (marketable ears), rounded tob Calculated for breakeven cost for ± 1 r from the mean packout values for the treatm

two out of three years. This suggests that conventional growersmay benefit from adding T. ostriniae to their O. nubilalis manage-ment programs. Breakeven costs could be calculated for other priceand yield combinations. At lower prices and yield combinations,the breakeven cost for T. ostriniae will decline since it would beused to protect a less valuable crop. Conversely, at higher priceand yield combinations the breakeven cost will increase.

The results of breakeven cost calculations for Insecticide com-pared to Untreated Check are presented in Table 7 for a2500 doz./ha yield and $3.00/doz. price. Because the breakevencost exceeds the actual cost of insecticides per application($26.88 in 2006, $39.29 in 2007, and $41.51 in 2008), it was eco-nomically justified to apply insecticides to control O. nubilalis dur-ing every year of the study at this price and yield combination.

4. Discussion

It is apparent from the preceding partial budget analysis thatadditional profit can be generated for most growers by controllingO. nubilalis in sweet corn. Projecting forward, a partial budget canbe constructed to take into account anticipated treatment costsand mean observed differences in the percentage of marketableears. By varying prices and yields, a table can be constructed thatcan be used by a variety of growers with different production sys-tems (conventional vs. organic), soil productivities (yields), andmarkets (prices). In Table 8 such an analysis is presented for a lim-ited range of sweet corn prices and yields for the four treatmentalternatives (based on 2008 costs). More detailed tables could bedeveloped for a range of costs for each treatment option and a

ed treatments compared to the Untreated Check and Insecticide treatments, assumingative value.

Ctapp ($) Breakeven costa ($) Breakeven �1r ($) Costb + 1r ($)

1.14 358 312 4041.14 113 98 1281.14 317 152 483

1.14 (212) (308) (15)1.14 19 (61) 991.14 (68) (108) (28)1.14 (392) (447) (337)

3.41 70 52 883.41 198 132 264

3.41 9 9 93.41 (39) (46) (32)

1.14 673 644 7011.14 357 311 4031.14 1022 795 1249

1.14 227 222 2321.14 (18) (26) (10)1.14 113 106 120

the nearest dollar.ent comparison, rounded to nearest dollar.

tment, assuming a yield of 2500 doz. ears/ha of sweet corn and price of $3.00/doz.

Cinsapp ($) Breakeven costa ($) Breakeven costb

�1r ($) +1r ($)

21.25 369 335 40224.21 251 197 30624.46 782 562 1002

the nearest dollar.ent comparison, rounded to nearest dollar.

Table 8Projected change in profitability ($/ha) compared to Untreated Check for various treatment options containing insecticide and/or T. ostriniae for control of O. nubilalis in sweetcorn, assuming observed packout differences and 2008 treatment costs.

Treatment option 2008 cost ($) Average packout differencea (%) Yield (doz. ears/ha) Price (per dozen)

$2 $3 $4 $5

Insecticide 90.43 5.2 1250 38 103 167 2322500 167 297 426 5553750 297 491 685 879

T. ostriniae (1X)b 43.49 2.3 1250 13 41 70 982500 70 127 183 2403750 127 212 297 382

Integrated 133.92 7.4 1250 49 141 233 3252500 233 418 602 7863750 418 694 971 1247

T. ostriniae (3X) 130.46 7.5 1250 55 148 242 3352500 242 429 616 8023750 429 709 989 1270

a Compared to Untreated Check; mean packouts were 89.4% for Untreated Check (3 years of data), 94.6% for Insecticide (4 years of data), 91.7% for T. ostriniae 1X (4 years ofdata), 96.8% for Integrated (3 years of data), and 96.9% for T. ostriniae 3X (2 years of data) (see Table 2).

b Trichogramma ostriniae shipping costs based on one shipment per 1.6 ha.

J. Gardner et al. / Biological Control 56 (2011) 9–16 15

wider range of prices and yields. In general, it can be seen that forlow prices and yields, the increase in profit is quite modest. In thelowest price-yield combination, the change in profit is T. ostriniae3X > Integrated > Insecticide > T. ostriniae 1X P Untreated Check.At high prices and high yields, the differences between themanagement options when compared to Untreated Check areconsiderable. In the highest price-yield combination, the changein profit is T. ostriniae 3X > Integrated� Insecticide > T. ostriniae1X� Untreated Check.

T. ostriniae is an economically viable management option formanagement of O. nubilalis in sweet corn. It has applicability toboth organic and conventional production conditions and a widerange of sweet corn prices and yields. The breakeven cost of T.ostriniae indicates its potential to improve grower profitability atcurrent prices. If even modest reductions in the cost of producingT. ostriniae could be realized and passed onto growers, it could leadto significant improvement in quality for organic growers and re-duce the use of insecticides for O. nubilalis management in sweetcorn.

Role of funding agency

This research was supported in part by the NIFA, USDA PestManagement Alternatives Program award number 2006-34381-16995, and by Cornell University Agricultural Experiment Stationfederal formula funds, Project Nos. NYC-139332 and NYC-139841received from NIFA, USDA. Any opinions, findings, conclusions, orrecommendations expressed in this publication are those of theauthor(s) and do not necessarily reflect the view of the US Depart-ment of Agriculture. The funding source had no role in study de-sign; collection, analysis or interpretation of data; in the writingof the report; or in the decision to submit the paper for publication.

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