Conventional and Seed-Based Insect Management Strategies Similarly Influence Nontarget Coleopteran Communities in Maize
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TRANSGENIC PLANTS &INSECTS Conventional and Seed-Based Insect Management Strategies Similarly Influence Nontarget Coleopteran Communities in Maize 1 2 3 4 T. W. LESLIE, D. J. BIDDINGER, J. R. ROHR, AND S. J. FLEISCHER Environ. Entomol. 39(6): 2045Ð2055 (2010); DOI: 10.1603/EN10049 ABSTRACT Seed-based pest management tools, such as transgenes and seed treatments, are emerg- ing as viable alternatives to conventional insecticide applications in numerous crops, and often occur as coupled technologies. Seed-based technologies have been readily adopted in maize, for which ecological studies are needed to examine effects to farmland biodiversity. We compared the response of nontarget coleopteran communities in Cry1Ab/c sweet corn and Cry3Bb Þeld corn to conventional pyrethroid applications and a control. Of particular interest was the Cry3Bb Þeld corn, which was coupled with a neonicotinoid seed treatment and was not rotated across years. A functionally diverse subset of the coleopteran community, consisting of three families (Carabidae, Chrysomelidae, and Nitidulidae) and 9,525 specimens, was identiÞed to species. We compared coleopteran diversity and dynamics using rarefaction and ordination techniques. There were no differences in species richness among treatments; however, higher activity densities were more common in the control. In the nonrotated Þeld corn, principal response curves showed a consistent pattern of treatment commu- nities deviating from the control communities over time, whereas crop rotation in the sweet corn negated treatment effects. Treatment effects could not be detected when beetles were grouped based on functional roles. Results indicate that neonicotinoid seed-based treatments may have effects on some nontarget coleopterans, but these effects are similar to conventional pyrethroid applications. KEY WORDS Bt maize, Coleoptera, neonicotinoid seed treatments, nontarget effects Many insect pest management decisions in agriculture and may promote or sustain on-farm biodiversity be- are now made during the purchase of seed. Options cause of reductions in insecticide use (Cattaneo et al. include an array of transgenic technologies and seed 2006, Leslie et al. 2007). treatments that can serve to augment, or even replace, Transgenic technology has been widely adopted in conventional insecticide applications. The ecological maize and cotton. In maize, Bt transgenes expressing ramiÞcations of these seed-based delivery mecha- Cry1- and Cry3-based proteins have been used for nisms, including effects to nontarget organisms and control of European corn borer [Ostrinia nubilalis biodiversity, are the topic of ongoing testing and de- Hu¨ bner (Lepidoptera: Pyralidae)] and corn root- bate. Much attention has been directed toward ge- worm [Diabrotica spp. (Coleoptera: Chrysomeli- netically engineered crops containing Bacillus thurin- dae)], respectively. Ecotoxicological studies have giensis (Bt) transgenes that encode for insecticidal concluded that, under Þeld conditions, adverse effects Cry proteins (Naranjo et al. 2005). Although this pest to nontarget organisms are nonexistent, minimal, or management approach is considered more localized cannot be detected for both Cry1 (Orr and Landis and/or target-speciÞc than conventional foliar or soil- 1997, Pilcher et al. 1997, Wraight et al. 2000, Floate et applied insecticides, numerous studies have been con- al. 2007, Hoheisel and Fleischer 2007) and Cry3 (Al- ducted to examine potential threats to nontarget in- sects. To date, most studies have shown that the use of Deeb and Wilde 2003, Ahmad et al. 2005, Bhatti et al. Bt crops can result in more efÞcient control of pest 2005) maize, except in instances in which the abun- taxa and less reliance on conventional insecticides dance of a specialist parasitoid of the target pest taxa (Musser and Shelton 2003, Brookes and Barfoot 2006), is reduced because of lack of prey (Pilcher et al. 2005). Broader conclusions have been drawn from nontarget studies in Bt crops by using meta-analyses (Marvier et 1 Department of Biology, Long Island University, 801 Metcalfe al. 2007, Naranjo 2009). In general, nontarget effects Building, 1 University Plaza, Brooklyn, NY 11201 (e-mail: timothy. [email protected]). have been negligible, even when examining speciÞc 2 Fruit Research and Extension Center, Pennsylvania State Univer- groups, such as biological control agents (Romeis et al. sity, 290 University Drive, Biglerville, PA 17307. 2006) and other functional guilds (Wolfenbarger et al. 3 Department of Biology (SCA 137), University of South Florida, 2008; but also see Lundgren et al. 2009 for a review of 4202 East Fowler Ave., Tampa, FL 33620. 4 Department of Entomology, Pennsylvania State University, 501 the interactions among ecological pathways and bio- ASI Building, University Park, PA 16802. logical control in transgenic crops). 0046-225X/10/2045Ð2055$04.00/0 ᭧ 2010 Entomological Society of America 2046 ENVIRONMENTAL ENTOMOLOGY Vol. 39, no. 6 Realistically, however, transgenic crops often come sumed to be at risk from direct or indirect effects of coupled with other seed-based technologies, includ- pest management strategies in maize. ing insecticidal seed treatments. For example, all com- Using a systems-based approach, we examined the mercially available Cry3-based transgenic corn seed is response of nontarget coleopterans to current insect treated with systemic neonicotinoids (Smith et al. pest management practices in sweet corn and Þeld 2004). Although much effort has been made to isolate corn in Pennsylvania, including Bt Þeld corn contain- and examine the effects of transgenes in Bt maize, ing neonicotinoid seed treatments. For each type of neonicotinoid seed treatments may pose a greater maize, we used a 2 ϫ 2 factorial experiment comparing threat to nontarget organisms than Bt toxins. Co- systems with or without seed-based insect control leopterans comprise a wide range of feeding guilds tactics, and with or without conventional pyrethroid (seed predators, omnivores, detritivores, predators, applications during the growing season. Carabidae ac- herbivores and even parasitoids) that may allow them tivity density and species richness were compared to come in direct or indirect contact with these toxins among treatments. To examine the effect to the in a Þeld setting. Seeding rates for maize vary with the broader coleopteran community, we analyzed the dy- yield potential of soil. In Pennsylvania, maize grown namics of species from three families (Carabidae, for grain range from 26,000Ð30,000 seeds per acre, and Chrysomelidae, and Nitidulidae) representing diverse reach 36,000 for silage corn; rates may be higher in soils functional roles. Seed-based technology in Þeld corn with greater yield potential. Thus, the potential for was of primary concern because of the presence of nontarget exposure could arise from the product neonicotinoid seed treatments shown to be highly leaching into the soil, direct feeding on the plant toxic to carabid beetles in laboratory bioassays (Mullin where the systemic insecticide is being expressed, or et al. 2005). indirectly by feeding on corn-feeding herbivores. In laboratory bioassays, Mullin et al. (2005) fed nontarget Materials and Methods carabids on transgenic (Cry3Bb and Cry1Ab/c) corn pollen and seedlings germinated from seeds treated Experimental Design. We used a randomized com- with systemic neonicotinoids. This study concluded plete block (RCB) factorial experiment to examine that neonicotinoid seed treatments, and not Cry3Bb, the effects of seed-based technologies and insecticide inputs on coleopteran communities in sweet corn and represent a major mortality factor for carabid beetles. Þeld corn. Earlier work (Leslie et al. 2009) describes Additionally, guttation drops collected from corn the population-level response of four dominant spe- seedlings germinated from neonicotinoid-coated cies within the Carabidae. Here we focus on overall seeds were recently shown to be toxic to honey bees carabid diversity and community-level response of in laboratory feeding trials (Girolami et al. 2009). Field species from three functionally diverse families. Thus, experimentation must consider the effects of these some details of Þeld plots, treatments and sample col- broader systems for realistic evaluation of currently lections are more extensively covered in Leslie et al. deployed transgenic crops. (2009). The experiment was conducted at the Russell Among the variety of approaches for examining E. Larson Agricultural Experimental Station in Rock community-level nontarget effects of pest manage- Springs, PA, and spanned the 2003 and 2004 growing ment practices, there remains a need for more studies seasons. The four treatments were a 2 ϫ 2 factorial with species-level resolution (Danks 1996). However, deÞned by presence/absence of seed technologies species-level identiÞcation often requires large invest- and presence/absence of conventional pyrethroid in- ments of time and money, which can be exacerbated secticides. In each year, we used 12 experimental plots by the current bottleneck in taxonomic expertise (each 57.7 ϫ 19.2 m) of sweet corn and Þeld corn, (Kim and Byrne 2006, Rohr et al. 2007). Because sam- representing the four treatments replicated three pling insect communities results in large numbers of times. Snap beans were planted adjacent to experi- specimens that often cannot all be identiÞed to spe- mental plots to provide a rotational crop for sweet cies, community analyses are often done