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

Abstract

We compared the economics of controlling European corn borer (Ostrinia nubilalis) in sweet corn by using the egg parasitoid, Trichogramma ostriniae, alone and integrated with insecticidal sprays. An initial experiment in 2003 compared T. ostriniae alone against insecticide alone and a second set of experiments conducted over 3 years (2006–2008) compared (1) insecticide alone [Insecticide]; (2) no insecticide, no T. ostriniae [Untreated Check]; (3) T. ostriniae alone [T. ostriniae 1X]; and (4) T. ostriniae + insecticide [Integrated]. In 2007 and 2008, a fifth treatment was added consisting of three approximately weekly releases of 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 insecticide on parasitism, O. nubilalis eclosion, or total O. nubilalis larvae at harvest time. Partial crop budgets were conducted for each treatment. In three of the 4 years, Untreated Checks had the highest sweet corn ear damage. Ear damage after a single release of T. ostriniae was statistically no different than using insecticides. In two of the three years, the Integrated treatment (T. ostriniae 1X + insecticide) generated the largest increase in profitability. The insecticide only treatment generated the second best increase in profitability. When comparing a single release of T. ostriniae to the insecticide only, the latter provided a better combination of efficacy and profitability. The breakeven costs of the T. ostriniae justified their use 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 of three years, suggesting again that conventional growers could benefit from integrating T. ostriniae with insecticidal treatments. Projected profitability based on ear packout obtained by combining data among years suggests that in general, for low prices and yields, the increase in profit is quite modest. In the lowest price-yield combination, the change in profit is T. ostriniae 3X > Integrated > Insecticide > T. ostriniae 1X ⩾ Untreated Check. At high prices and high yields, the differences between the management options when compared to Untreated Check are considerable. In the highest price-yield combination, the change in profit is T. ostriniae 3X > Integrated ≫ Insecticide > T. ostriniae 1X ≫ Untreated Check.

Introduction

Field-scale use of augmentative biological control in the US has lagged behind other countries, perhaps because of inadequate research investment in biological control and the widespread use of insecticides (Li, 1994). Other researchers have evaluated augmentative biological control in the US and concluded that broad-spectrum insecticides are unlikely to be replaced because biological control is frequently ineffective and there is little economic incentive relative to pesticides (Collier and Van Steenwyk, 2004). We attempt with this and other studies, to demonstrate that augmentative biological control with Trichogramma ostriniae can provide perhaps not a replacement of insecticides, but rather a reduction in their use.

Based on several studies, T. ostriniae (Pang et Chen) (Hymenoptera: Trichogrammatidae) was identified as a candidate to control European 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 parasitoid is believed native to China where it can parasitize 70–96% of eggs of 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 US in 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, Wright et al., 2002). In the first field trials in the US, >97% of naturally occurring O. nubilalis eggs in sweet corn were parasitized (Mason et al., 1996). More recent research has shown that despite pyrethroid applications to fields of sweet corn, T. ostriniae populations can persist from inoculative release until the crop is harvested (Gardner et al., 2007). This is not surprising given that adult Trichogramma are generally susceptible to most broad-spectrum insecticides but the immature stages of the parasitoid developing within a host egg are generally well protected from even the most toxic compounds (Bull and Coleman, 1985, Suh et al., 2000). Thus, we initiated studies to further assess not only the biological ramifications of integrating T. ostriniae and insecticides to control O. nubilalis in sweet corn, but the economics as well. Herein, we report the findings of our research.