TRANSGENIC PLANTS AND INSECTS Carabidae Population Dynamics and Temporal Partitioning: Response to Coupled Neonicotinoid-transgenic Technologies in Maize

1 2 3 3 T. W. LESLIE, D. J. BIDDINGER, C. A. MULLIN, AND S. J. FLEISCHER

Environ. Entomol. 38(3): 935Ð943 (2009) ABSTRACT Insecticidal Bt crops and seed treatments represent additional pest management tools for growers, prompting ecological studies comparing their impact on farm system inputs and effects to nontarget organisms compared with conventional practices. Using high taxonomic and temporal resolution, we contrast the dominance structure of carabids and dynamics of the most abundant species in maize (both sweet and Þeld corn) agroecosystems using pest management tactics deter- mined by the purchase of seed and application of pyrethroid insecticides. In the seed-based treat- ments, sweet corn contained Cry1Ab/c proteins, whereas Þeld corn contained the coupled technology of Cry3Bb1 proteins for control of corn rootworm and neonicotinoid seed treatments aimed at secondary soil-borne pests. The insecticide treatments involved foliar pyrethroids in sweet corn and at-planting pyrethroids in Þeld corn. The carabid community, comprised of 49 species, was dominated by four species, Scarites quadriceps Chaudoir, Poecilus chalcites Say, Pterostichus melanarius Illiger, and Harpalus pensylvanicus DeGeer, that each occupied a distinct temporal niche during the growing season. Two species, Pt. melanarius and H. pensylvanicus, exhibited differences between treatments over time. Only H. pensylvanicus had consistent results in both years, in which activity densities in Þeld corn were signiÞcantly higher in the control in July and/or August. These results, along with laboratory bioassays, led us to hypothesize that lower adult captures resulted from decrease in prey availability or exposure of H. pensylvanicus larvae to soil-directed insecticidesÑeither the neonicotinoid seed treatment in the transgenic Þeld corn or an at-planting soil insecticide in the conventional Þeld corn.

KEY WORDS Bt, Carabidae, Cry3Bb, Harpalus pensylvanicus, neonicotinoids

The use of genetically engineered (GE) crops has (among others) butterßies (Losey et al. 1999, Wraight risen steadily over the past decade, and adoption has et al. 2000), lacewings (Hilbeck et al. 1998, Guo et al. been highest in U.S. agriculture, where over 145 mil- 2008), ladybird beetles (Lundgren and Wiedenmann lion acres of GE crops were planted in 2008 (NASS 2002, Al-Deeb and Wilde 2003, Bai et al. 2006, Hoheisel 2008). Although most of the GE crop acreage consists and Fleischer 2007), and ground-dwelling beetles of herbicide-tolerant crops, insect-resistant (Bt) vari- (Duan et al. 2004, Ahmad et al. 2005, Mullin et al. 2005, eties of cotton and maize have established a Þrm foot- Leslie et al. 2007). hold in U.S. agriculture. In 2008, Bt maize represented Comparing population dynamics of nontarget or- 57% of total U.S. maize acreage and consisted of cul- ganisms between farm systems using transgenic versus tivars expressing Cry1- or Cry3-based endotoxins used conventional pest management practices may eluci- to control European corn borer and corn rootworm, date underlying interactions between the transgenes respectively (NASS 2008). The introduction of Bt and the ecology of the surrounding habitat. Groot and crops has been accompanied with concern for nega- Dicke (2002) noted that nontarget species could come tive effects to nontarget insects (Hails 2000, Wolfen- in contact with Bt toxins by feeding directly on Bt barger and Phifer 2000, Groot and Dicke 2002), espe- plants, feeding on target or nontarget herbivorous cially those in the same insect order at which the Cry insects, or through the environment (e.g., accumula- proteins are directed and important biological control tion of toxins in the soil). Introduced transgenes can agents found in agricultural Þelds. Numerous studies also alter pest management inputs, thereby indirectly in both the Þeld and the laboratory have examined affecting nontarget organisms and farmland biodiver- such effects for a variety of invertebrates, including sity (Hails 2000, Leslie et al. 2007). For example, lep- idopteran-speciÞc (Cry1-based) transgenic maize and 1 Corresponding author: Department of Biology, Long Island Uni- cotton can eliminate or reduce pyrethroid applica- versity, 1 University Plaza, Brooklyn, NY 11201 (e-mail: timothy. tions directed at European corn borer and pink boll- [email protected]). worm, respectively (Hutchison et al. 2004). Similarly, 2 Penn State University, Fruit Research and Extension Center, 290 coleopteran-speciÞc (Cry3-based) transgenic maize University Dr., Biglerville, PA 17307. 3 Penn State University, Department of Entomology, 501 ASI Build- may shift insecticide use patterns from at-planting ing, University Park, PA 16802. applications of soil insecticides toward seed treat-

0046-225X/09/0935Ð0943$04.00/0 ᭧ 2009 Entomological Society of America 936 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 3 ments (Smith et al. 2004). The efÞcient control of genes and seed treatments) and application of con- target pests by Bt crops can alter trophic relationships ventional insecticides during the growing season. as well: Riddick et al. (1998) found lower abundances Adding complexity to these agroecosystems, the man- of the carabid, Lebia grandis Hentz, a specialist pred- agement inputs can vary dramatically between both ator of Leptinotarsa decemlineata (Say), in transgenic types of maize. At-planting soil insecticides, primarily potato Þelds designed to control L. decemlineata, directed against corn rootworm, dominate inputs in whereas the abundance of the generalist predator, maize grown for animal feed. Foliar insecticide use Coleomegilla maculata DeGeer, was not affected be- later in the season is highest in sweet corn, where cause of its ability to feed on alternate prey. several ear-damaging insects can severely limit pro- Changes in pest management tactics are rarely in- duction as described in Crop ProÞles and Pest Man- troduced independently or in isolation. For example, agement Strategic Plans of states throughout the sweet all commercially available Cry3-based Þeld corn con- corn growing region of the United States (www.north- tains neonicotinoid seed treatments for control of sec- easternipm.org). These maize pest management in- ondary pests (Smith et al. 2004). Although the major- puts can be replaced or altered by the use of transgenic ity of studies have found little or no direct nontarget technologies and seed treatments. effects after exposure to Cry toxins (summarized by Here, we characterized the carabid community in Romeis et al. 2006, Marvier et al. 2007, Wolfenbarger central Pennsylvania maize Þelds over 2 yr and iden- et al. 2008), other technology associated with trans- tiÞed feasible candidates to test nontarget pest man- genics, such as seed treatments, could affect nontarget agement effects in maize. Candidates were chosen organisms. As part of a tiered approach (Dutton et al. based on their level of activity density (high numbers 2003) to determine the impact of Bt maize (and as- needed for statistical analysis purposes) and their sea- sociated seed treatments) on nontarget epigeal Cara- sonality to cover the range of times that pest manage- bidae, our current Þeld study was preceded by labo- ment events occur. Carabids were sampled weekly to ratory bioassays that identiÞed neonicotinoid seed look for Þner temporal partitioning than “spring” and treatments found on transgenic maize as a major mor- “autumn” breeders and to identify species active dur- tality factor for carabids, and alternatively, found no ing pest management events. We examined the pop- negative effects of Cry1Ab/c or Cry3Bb1 toxins de- ulation dynamics of the candidate species to compare livered to carabids in transgenic corn pollen (Mullin differences between current pest management strat- et al. 2005). egies appropriate for sweet corn and Þeld corn, re- Ground beetles, or Carabidae, have been used as spectively. For each type of maize, we designed a 2 ϫ bioindicators for agricultural practices because of 2 factorial experiment comparing systems with or their sensitivity to changes in the environment, abun- without seed-based insect control tactics and with or dance in agricultural settings, diversity of functional without conventional insecticide applications during roles, relative ease of identiÞcation to species level, the growing season. and ease of sampling using pitfall traps (Duelli et al. 1999). Many carabids are voracious feeders and can be Materials and Methods loosely grouped as generalist predators, granivores, or specialist predators, although a wide range of more Experimental Design. A randomized complete narrowly deÞned feeding guilds have been described block (RCB) factorial experiment was used to exam- (Toft and Bilde 2002). Therefore it is highly likely that ine the effects of seed-based inputs and insecticide carabids will directly or indirectly come into contact inputs on Carabidae in sweet corn and Þeld corn with Bt toxins in Bt crop Þelds. Indeed, Zwahlen and (Table 1). Experiments were conducted on the Penn Andow (2005) were able to detect Cry1Ab in carabids State research farms at the Russell E. Larson Agricul- collected from Þelds with Bt crops or crop residues. tural Experimental Station in Pennsylvania, Furnace, However, based on our bioassay results, it is unlikely PA, and spanned the 2003 and 2004 growing seasons. that carabid population dynamics in the Þeld would be The study site contained Hagerstown silt loam soils directly affected by exposure to Bt toxins present in with 0Ð3% slopes (HaA). In each year, we used 12 transgenic maize systems, even Cry3-based coleopter- experimental units (each 57.7 by 19.2 m) of sweet corn an-speciÞc toxins. Rather, neonicotinoid seed treat- and Þeld corn, representing four treatments replicated ments, conventional insecticide applications, or indi- three times. Each experimental unit underwent a min- rect trophic effects will likely have greater impacts on imal tillage regimen (mulch tiller) before planting. carabids than Bt corn. Snap beans were planted adjacent to experimental Northeastern U.S. agroecosystems, where this study units to provide a rotational crop for sweet corn in the was conducted, are characterized by a complex mix of second year, whereas Þeld corn was not rotated, as is numerous small farms nested in heterogenous land- common practice in this growing region. All experi- scapes, of which maize is often a component of dairy mental units included a 3-m alfalfa border. and vegetable production. Therefore, maize for ani- The four treatments (Table 1) were a 2 ϫ 2 factorial mal feed and sweet corn are prominent features of deÞned by presence/absence of seed technologies these landscapes and are often in close proximity, and presence/absence of conventional pyrethroid in- resulting in mosaics of varying types of maize. Cur- secticides. In sweet corn, the seed technology con- rently, insect management inputs are determined by sisted of a transgene expressing Cry1Ab/c toxins (Tra) two primary factors: purchase of the seed (i.e., trans- versus its isoline (Iso), and the conventional insecti- June 2009 LESLIE ET AL.: CARABIDAE POPULATION DYNAMICS IN TRANSGENIC MAIZE 937

Table 1. Pest management inputs defining the 2 ؋ 2 factorial experiment for both sweet corn and field corn farm systems

Type of Seed management (factor A) Pyrethroid applications (factor B) Treatment label maize Sweet corn Isoline None Iso Four foliar applications during silking stagea Iso/PyrSilk Transgene (Cry1Ab/c)b None Tra Four foliar applications during silking stagea Tra/PyrSilk Field corn Isoline None Iso At planting soil applicationc Iso/PyrSoil Transgene (Cry3Bb1)d and neonicotinoid None TraNeo seed treatmente At planting soil applicationc TraNeo/PyrSoil

Factor A refers to pest management inputs determined by the purchase of the seed and these seed treatments. Factor B refers to application of pyrethroids by growers and these insecticide treatments. a Lambda-cyhalothrin (Warrior; Syngenta, Greensboro, NC) 11.4% AI, 222 ml/ha. b Rogers Attribute WSS 0984 (Syngenta Seeds, Boise, ID). c Teßuthrin (Force 3G; Syngenta), 3% AI, 3.7 kg/ha. d DeKalb DKC60Ð12 YGRW (Monsanto, St. Louis, MO). e Imidacloprid (160 ␮g/seed) or clothianidin (250 ␮g/seed) (Bayer CropScience, Research Triangle Park, NC). cide management consisted of four pyrethroid appli- are expected to reduce broad-spectrum soil insecti- cations during the silking stage (PyrSilk). The four cides, but as mentioned above, these cultivars are treatments therefore consisted of combinations of the coupled with neonicotinoid seed treatments (160 ␮g presence or absence of the transgene and PyrSilk and imidacloprid/seed or 250 ␮g clothianidin/seed; Bayer were labeled as (1) Iso (i.e., control), (2) Tra, (3) CropScience, Research Triangle Park, NC) to control Iso/PyrSilk, and (4) Tra/PyrSilk. The conceptual additional damage to seeds, seedlings, and roots. All framework of the Þeld corn study was identical, except commercially available rootworm-directed Bt Þeld that the seed technology consisted of a neonicotinoid corn varieties contain neonicotinoid seed treatments; seed treatment and a transgene expressing Cry3Bb1 thus, this systems-based study contains a realistic eval- toxins (i.e., TraNeo) versus its isoline (Iso), and the uation of this coupled technology on Carabidae dy- conventional insecticide management consisted of a namics. In the Þeld corn experimental units that did soil-directed at-planting application of a pyrethroid not use seed-based insecticidal technology, we (i.e., PyrSoil). Therefore, the four treatments in Þeld planted the near isoline, DKC60Ð17, which does not corn consisted of the combination of the presence or contain neonicotinoid seed treatment. Additionally, absence of TraNeo and PyrSoil and were labeled as (1) all corn seed used was treated with a fungicide blend Iso, (2) TraNeo, (3) Iso/PyrSoil, and (4) TraNeo/ shown previously not to be directly toxic to Carabidae PyrSoil. in the laboratory (Mullin et al. 2005). In the conventional insecticide management treat- Insect Collection and Identification. Pitfall traps ments, sweet corn received four late-season foliar ap- were used to capture all epigeal coleopteran speci- plications of the pyrethroid lambda-cyhalothrin mens. The pitfall traps were made from plastic deli (11.4% [AI], 222 ml/ha, Warrior 1 EC; Syngenta, containers, 14.1 cm deep with 10.9 cm ID, and were Greensboro, NC), for control of lepidopteran ear- inserted ßush with the ground. Another small collec- feeding pests. Conventionally managed Þeld corn re- tion cup (5.5 cm deep, 8.2 cm ID) Þlled with ethylene ceived an at-planting soil application of the pyrethroid glycol was placed inside for removal of specimens. An teßuthrin (3% [AI], 3.7 kg/ha, Force 3G; Syngenta, inverted top of a 2-liter soda bottle was put in each deli Greensboro, NC), for control of corn rootworm and container to act as a funnel, limiting escape by beetles other seed- and root- feeding insects. These prede- and access of the ethylene glycol to small mammals. termined insecticide use patterns were consistent Ten traps, arranged in two transects of Þve, were with northeastern maize pest management. placed at 9, 18, 27, 36, and 45 m from the margins within Our choice of transgenes focused on those that were the rows of all Þeld corn and sweet corn plots for a total commercially available and most likely to inßuence of 240 traps. Each plot of Þeld corn and sweet corn had insecticide use patterns in the United States. In the 22 rows, and the traps were placed in rows 8 and 14 sweet corn, we used cultivars expressing Cry1Ab/c from the south side of the plot. In 2003, trapping toxins, aimed primarily at European corn borer, which consisted of 10 sampling dates between 12 June and 15 is expected to reduce broad-spectrum foliar insecti- September. In 2004, there were 11 trapping dates ex- cides. Syngenta Seeds (Boise, ID) WSS 0984 sweet tending from 5 June to 27 September. Trapping oc- corn expressing Cry1Ab/c endotoxins for control of curred every 7Ð14 d depending on weather conditions. European corn borer was used for the transgenic treat- For each sampling period, one row of Þve traps was ment, whereas Boreal F1 sweet corn was the near opened in each Þeld corn and sweet corn plot for a isoline. For Þeld corn, we used transgenic cultivars total of 120 open traps. The open rows were alternated (DeKalb DKC60Ð12 YGRW; Monsanto, St. Louis, each week to avoid oversampling a portion of the Þeld. MO) expressing Cry3Bb1 endotoxins, aimed at root- All traps were open for 72 h, after which all beetles feeding stages of Diabrotica spp. These Cry3 cultivars were transferred to 70% ethanol. Beetles were later 938 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 3

Table 2. Species list of Carabidae collected from sweet corn and field corn farm systems in Rock Springs, PA, during 2003 and 2004

Agonum cupripenne Say Diplocheila obtusa LeConte A. muelleri Herbst Dyschirius globulosus Say A. placidum Say Elaphropus anceps (LeConte) A. punctiforme (Say) Harpalus affinis Shrank Amara aenea DeGeer H. caliginosus F. A. exarata Dejean H. compar LeConte A. familiaris Duftschmidt H. erythropus Dejean A. impuncticollis Say H. faunus Say Anisodactylus harrisi LeConte H. herbivagus Say A. rusticus Say H. longicollis LeConte A. sanctaecrucis (F.) H. pensylvanicus DeGeer Bembidion affine Say H. rubripes Duftschmidt B. mimus Hayward Microlestes linearis LeConte B. quadrimaculatum oppositum Say M. pusio LeConte B. rapidum LeConte Patrobus longicornis Say Bradycellus rupestris Say Poecilus chalcites Say Calathus gregarius Say P. lucublandus Say Chlaenius tricolor tricolor Dejean Pterostichus melanarius Illiger Cicindela punctulata Olivier P. mutus Illiger C. sexguttata F. P. stygicus Say C. tranquebarica Herbst Scarites quadriceps Chaudoir Clivinia bipustulata F. Stenolophus comma F. C. impressefrons LeConte S. ochropezus (Say) Colliuris pensylvanica L. Trechus quadristriatus (Shr.) Cyclotrachelus furtivus LeConte

sorted, pinned, and identiÞed to species. IdentiÞca- tions were performed by Robert Davidson (Carnegie Museum of Natural History, Pittsburgh, PA), David Biddinger (Pennsylvania State University), and Tim Leslie (Pennsylvania State University), using several taxonomic keys (Downie and Arnett 1996, Ciegler 2000, Marshall 2006) and voucher specimens from Fig. 1. Dominance distribution of the Carabidae with previous studies (Hoheisel 2002, Leslie et al. 2007). highest activities densities collected in sweet corn and Þeld Voucher specimens are housed in the laboratory of corn farm systems in Rock Springs, PA, during 2003 (n ϭ S. J. Fleischer, Department of Entomology, Pennsyl- 2,748 carabids) and 2004 (n ϭ 4,518 carabids). Refer to vania State University. species list (Table 2) for full genus names. Data Analysis. Data were recorded as average ac- tivity density (no. of beetles/trap/72 h) for each spe- Results cies at the plot level. A complete species list was Over the 2-yr study, 7,256 Carabidae representing compiled, and species were ranked in order of highest 49 species (Table 2) were collected, a higher number to lowest activity densities. Species with the highest than is generally recorded (Ϸ 30 species) for temper- activity density (Ͼ200 individuals in each of the 2 yr) ate cropping regions (Luff 2002). In 2003, we collected were chosen to examine year-to-year temporal pat- 2,748 carabids (1,403 in Þeld corn, 1,345 in sweet terns and treatment effects on population dynamics. corn), and in 2004, we collected 4,518 carabids (2,426 All analyses of treatment effects were performed sep- in Þeld corn, 2,092 in sweet corn). Dominance distri- arately for each crop and year to avoid confounding bution was strongly skewed with 10 species account- effects of crop rotation and pest management inputs ing for Ͼ75% of the total abundance (Fig. 1). Scarites that differed between sweet corn and Þeld corn. A quadriceps Chaudoir and Pterostichus melanarius Il- mixed model repeated-measures procedure (SAS liger were the most abundant species in 2003 and v.9.1.3) was conducted on each species to examine the Harpalus pensylvanicus DeGeer, Poecilus chalcites Say, effect of date, seed technology, conventional insecti- and Bembidion quadrimaculatum oppositum Say were cide applications, and their interactions. An autore- the most abundant species in 2004 (Fig. 1). gressive covariance structure was used in the analysis, Of the species with the highest activity densities, H. because of the use of evenly spaced serial measure- pensylvanicus, S. quadriceps, Po. Chalcites, and Pt. mela- ments, resulting in higher correlation between ac- narius were the only species with Ͼ200 individuals tivity densities measured closer in time. Block was collected in each of the 2 yr. Date was signiÞcant included in the analysis as a random variable. Post (repeated-measures analysis of variance [ANOVA], hoc Tukey means separation tests were used to ␣ ϭ 0.05) for all four species in both years as depicted identify the direction of the treatment effects on by the shaded areas in Fig. 2. The four species exhib- activity densities. ited peak activity density during different times of the June 2009 LESLIE ET AL.: CARABIDAE POPULATION DYNAMICS IN TRANSGENIC MAIZE 939

Fig. 2. Population dynamics of the four carabid species with highest activity densities collected in sweet corn and Þeld corn farm systems at Rock Springs, PA (2003 and 2004). Shaded areas depict time of peak activity densities. season; S. quadriceps emerged Þrst, followed by Po. sities were signiÞcantly higher in Iso Þeld corn (0.96 Ϯ chalcites, Pt. melanarius, and H. pensylvanicus (Fig. 2). 0.14) than in the Iso/PyrSoil (0.44 Ϯ 0.08), TraNeo This pattern held true in both years except that H. (0.12 Ϯ 0.03), and TraNeo/PyrSoil (0.42 Ϯ 0.09) treat- ϭ ϭ pensylvanicus emerged earlier and remained active for ments (F1,86 9.36, P 0.003). Po. chalicites mean the remainder of the growing season in 2004 (Fig. 2). activity density also varied between insecticide man- ϭ The signiÞcant treatment and interaction effects for agement regimens in sweet corn in 2004 (F1,86 4.95, these carabids with the highest activity densities in P ϭ 0.0287), with a higher mean activity density re- each type of maize and year are summarized below. corded in the Tra/PyrSilk sweet corn (0.8 Ϯ 0.19) than Scarites quadriceps. Scarites quadriceps, a spring in the Iso (0.14 Ϯ 0.01), Iso/PyrSilk (0.19 Ϯ 0.06), and breeder, was consistently the Þrst species to emerge Tra (0.1 Ϯ 0.03) treatments. with activity densities highest in June and early July Pterostichus melanarius. Pterostichus melanarius, an and very few individuals trapped after mid-July (Fig. autumn breeder, peaked in activity density during 2). S. quadriceps did not respond to insecticide treat- August (Fig. 2). Treatment effects were only detected ments across dates, although mean activity density in 2003. Pt. melanarius exhibited a signiÞcant date by Ϯ ϭ ϭ was higher in Bt sweet corn (0.36 beetles/trap treatment interaction in sweet corn (F9,78 2.92, P 0.05 SE) than in isoline sweet corn (0.21 Ϯ 0.04) in 0.0049), with higher activity densities found in the Iso ϭ ϭ 2003 (F1,78 4.15, P 0.045). control treatment for three dates in August and Sep- Poecilus chalcites. Poecilus chalcites, another spring tember 2003 (Fig. 3, indicated with asterisks) based on breeder, reached peak activity density after S. quad- Tukey mean comparisons (␣ ϭ 0.05). No date by riceps with highest records from late June through the treatment interactions were signiÞcant in Þeld corn; end of July (Fig. 2). No signiÞcant treatment effects however, in 2003, mean activity density varied be- ϭ ϭ were detected in 2003; however, in 2004, Po. chalcites tween treatments (F1,78 6.89, P 0.0104), with mean activity density differed between treatments in highest activity densities in the Iso (0.49 Ϯ 0.1) and in both Þeld and sweet corn. In 2004, mean activity den- the TraNeo/PyrSoil (0.75 Ϯ 0.13) Þeld corn and low- 940 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 3

Fig. 4. 2003 and 2004 population dynamics of H. pensyl- vanicus in Þeld corn for each of four treatments: (1) isoline, i.e., control (Iso), (2) isoline with at-planting soil pyrethroid application (Iso/PyrSoil), (3) Cry3Bb1 transgenes with neo- nicotinoid seed treatment (TraNeo), and (4) Cry3Bb1 trans- genes with neonicotinoid seed treatment and at-planting soil pyrethroid application (TraNeo/PyrSoil). *Dates where ac- tivity density of H. pensylvanicus was signiÞcantly higher in Fig. 3. 2003 and 2004 population dynamics of Pt. mela- the Iso treatment than in other three treatments based on narius in sweet corn for each of four treatments: (1) isoline, Tukey means separation test (␣ ϭ 0.05). The soil pyrethroid i.e., control (Iso), (2) isoline with foliar pyrethroid applica- was applied in Iso/PyrSoil and TraNeo/PyrSoil treatments tions (Iso/PyrSilk), (3) Cry1Ab/c transgenes (Tra), and (4) during planting in mid-May. Cry1Ab/c transgenes with foliar pyrethroid applications (Tra/PyrSilk). *Date where activity density of Pt. melanarius was signiÞcantly higher in Iso treatment than in the other communities through direct or indirect effects (Lovei three treatments based on Tukey means separation test (␣ ϭ ¨ 0.05). Arrows indicate when foliar pyrethroid applications 2001, Dutton et al. 2002, Marvier et al. 2007). This were applied in Iso/PyrSilk and Tra/PyrSilk treatments. study identiÞed prominent carabid species in Penn- sylvania maize agroecosystems and provided Þeld evaluations of transgenes, some of which are coupled est activity densities in TraNeo (0.22 Ϯ 0.05) and with neonicotinoid seed treatments and conventional Iso/PyrSoil (0.13 Ϯ 0.03) Þeld corn. pest management practices (i.e., soil and foliar insec- Harpalus pensylvanicus. The autumn-breeding H. ticide applications) on these populations. Working in pensylvanicus was the species collected most often conjunction with laboratory bioassay studies (Mullin (Fig. 1), exhibited the highest activity density in Au- et al. 2005) that identiÞed neonicotinoid seed treat- gust and September (Fig. 2), and was rarely found ments present in Cry3-protected Þeld corn, but not before mid-July. H. pensylvanicus responded to insec- the Cry3 toxins directly (see also Duan et al. 2006), as ticide management inputs in Þeld corn in both 2003 a signiÞcant direct mortality factor for carabids, we ϭ ϭ ϭ ϭ (F9,78 2.54, P 0.0129) and 2004 (F10,86 2.01, P used a range of insecticide management options rel- 0.0419). H. pensylvanicus activity densities were sig- evant to current conditions. niÞcantly higher in the Iso control treatment for dates Over the 2-yr study, four species (i.e., S. quadriceps, in September 2003 and in July and September 2004 Po. chalcites, Pt. melanarius, and H. pensylvanicus) ex- (Fig. 4, indicated with asterisks) based on Tukey mean hibited high activity densities in each of the 2 yr (Ͼ200 comparisons (␣ ϭ 0.05). total individuals or 0.15 individuals/trap/72 h), and dominance distribution was highly skewed as the 10 carabid species (of the 49 total species) with highest Discussion activity densities accounted for Ͼ75% of all specimens Little evidence to date exists that suggests trans- captured. These results can be compared with other genes conferring the expression of Bt Cry toxins di- studies of carabids in different Pennsylvania agricul- rectly affects nontarget organisms (Romeis et al. 2006, tural systems. In a diversiÞed vegetable farm setting, Wolfenbarger et al. 2008). Instead, it is more likely that Leslie et al. (2007) found comparable species richness dynamic shifts in insecticide use patterns and delivery (i.e., 47 species), composition, and activity densities, systems caused, in part, by the deployment of trans- except for far fewer S. quadriceps. It is likely that fewer genic crops may inßuence nontarget populations and S. quadriceps were found in this earlier study at a June 2009 LESLIE ET AL.: CARABIDAE POPULATION DYNAMICS IN TRANSGENIC MAIZE 941 similar location because of the fact that pitfall trapping omnivorous tendencies, Pt. melanarius is better know began shortly after the period of peak activity density as a carnivore (Sunderland 2002), and the abundance for this species, highlighting the importance of tem- of grass seedsÑa preferred food source for H. pensyl- poral trapping considerations when studying carabid vanicusÑlikely reduced feeding competition between communities. A study examining carabid communities the two species. Therefore, the carabid species with in Pennsylvania grazed dairy pastures also reported the highest activity densities in this region seem to similar species richness (i.e., 44 species) but differed have transitioned toward segregating resources both in community composition (Byers et al. 2000). temporally and possibly by feeding preferences. This Whereas species such as Po. chalcites and Pt. melana- temporal partitioning highlights the importance of full rius were frequently found in both systems, H. pen- season sampling and species level identiÞcation. De- sylvanicus had the highest activity density in maize tailed knowledge of temporal partitioning can also be and Amara aenea DeGeer was collected in high num- useful in choosing appropriate species for examining bers in the grazed pasture (and was relatively scarce external inputs that occur at distinct times in the Þeld in maize). Both H. pensylvanicus and A. aenea are weed season (e.g., at-planting soil insecticide applications). seed predators, and the local weed communities, Treatment effects on the population dynamics of which can vary greatly between agricultural systems the most abundant carabids were only consistent for (Davis et al. 2005), may have selected for or against H. pensylvanicus. For several sampling periods in both each species based on their feeding preferences. years, H. pensylvanicus exhibited signiÞcantly higher Activity densities were noticeably higher in 2004 activity densities in isoline Þeld corn that had no (3.27 beetles/trap/72 h) than in 2003 (2.14 beetles/ insecticide inputs (Fig. 4). The other Þeld corn treat- trap/72 h), primarily because of a three-fold increase ments either contained an at-planting soil pyrethroid in H. pensylvanicus activity densities as well a three- to insecticide or the neonicotinoid seed treatments imi- four-fold increase in some smaller bodied carabids dacloprid or clothianidin found on the transgenic cul- such as B. quadrimaculatum oppositum and B. rapidum. tivar. Some carabids are tolerant of even the most toxic With the exception of H. pensylvanicus, more smaller- of the pyrethroids such as deltamethrin (Basedow et bodied carabids were found among the most abundant al. 1985, Wiles and Barrett 1998), in contrast to their beetles in the second year. Bu¨ chs et al. (2003) sug- susceptibility to neonicotinoids (Mullin et al. 2005); gested that smaller bodied insects may adapt better to thus, the soil teßuthrin or foliar lambda-cyhalothrin disturbed environments, and our Þndings partially treatments may not have exerted as much population support this trend. H. pensylvanicus most likely in- reduction impact as imidacloprid or clothianidin. creased in activity density because of higher weed However, deltamethrin sprays are known to cause densities, primarily giant foxtail (Setaria faberi reduction of other major epigeal insect groups (Base- Herrm.) and yellow foxtail (Setaria glaucai L.) in the dow et al. 1985), which could affect carabids indi- experimental Þelds during the second year (unpub- rectly. All Þeld corn insecticide management inputs lished data). The emergence of H. pensylvanicus adults occurred early in the season when the less-mobile H. is thought to coincide with the ripening of grass weed pensylvanicus larvae would have been in close prox- seeds, and feeding preference trials have shown that imity to the corn seed in the soil. The possible pres- foxtail is a preferred seed for H. pensylvanicus (Kirk ence of insecticide-induced mortality factors or a de- 1973, Best and Beegle 1977, Lund and Turpin 1977, crease in prey availability seems to be evident in the Brust and House 1988, Lundgren and Rosentrater lower trap captures of H. pensylvanicus adults later in 2007). the season. The four species abundant in both years exhibited Pt. melanarius was the only other species exhibiting unique temporal niches based on the period of their a date ϫ treatment effect on its population dynamics, highest activity density. Carabids are often general- with activity densities higher in isoline sweet corn ized as spring breeders and autumn breeders with without insecticides for three sampling periods in 2003 recognition of annual variation or species-speciÞc (Fig. 3). As with H. pensylvanicus, early-season treat- variation in life cycles (Thiele 1977, Loreau 1985, Hol- ments may have affected Pt. melanarius larval abun- land 2002). For example, it would be known a priori dance, or late season foliar sprays may have directly that S. quadriceps and Po. chalcites are spring breeders affected Pt. melanarius adults. This effect, however, and Pt. melanarius and H. pensylvanicus are autumn was not evident in 2004 (Fig. 3) when Pt. melanarius breeders before our study was conducted. However, activity densities were lower and the sweet corn had we established that, not only are these four species been rotated with snap beans. found in high numbers in central Pennsylvania agro- Treatment effects were evident when comparing ecosystems (see also Leslie et al. 2007), but that they mean activity density between the different pest man- seem to occupy temporal niches at a Þner resolution agement regimens, but these results were not consis- than the generalized seasonal depictions, resulting in tent and sometimes contradictory. For example, in a temporal succession. In general, this succession con- 2004, Po. chalcites exhibited a higher mean activity sisted of S. quadriceps, Po. chalcites, Pt. melanarius, and density in isoline Þeld corn unmanaged with insecti- H. pensylvanicus (Fig. 2). In one exception, Pt. mela- cides but in sweet corn had the highest mean activity narius and H. pensylvanicus overlap in abundant pe- density in Bt sweet corn managed with insecticides. In riods in 2004; however, these two species may occupy another study examining Cry3-protected Þeld corn different functional niches as well: although both have under different insecticide use regimens, Bhatti et al. 942 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 3

(2005) found lower activity densities of carabids in Best, R. L., and C. C. Beegle. 1977. Food preference of Þve maize treated with seed-, soil-, and foliar-applied in- species of carabids commonly found in Iowa cornÞelds. secticides (compared with no insecticide use), but Environ. Entomol. 6: 9Ð12. analyses were performed at the family level and results Bhatti, M. A., J. Duan, G. Head, C. Jiang, M. J. McKee, T. E. were also not consistent across all years and trap types. Nickson, C. L. Pilcher, and C. D. Pilcher. 2005. Field Lopez et al. (2005) suggested that spatial and temporal evaluation of the impact of corn rootworm (Coleoptera: Chrysomelidae)-protected Bt corn on ground dwelling variability can lead to such variability or lack of treat- invertebrates. Environ. Entomol. 34: 1325Ð1335. ment effects in results and insecticide inputs can cause Brust, G. E., and G. J. House. 1988. Weed seed destruction variation in behavior such as increased activity or by arthropods and rodents in low-input soybean agro- dispersal (Wiles and Jepson 1994, Singh et al. 2001), ecosystems. Am. J. Altern. Agric. 3: 19Ð25. which may affect trap captures. Additionally, H. pen- Bu¨ chs, W., A. Harenberg, J. Immermann, and B. Weiß. 2003. sylvanicus may have exhibited elevated numbers in Biodiversity, the ultimate agri-environmental indicator? the control treatment during the second year of our Potential and limits for the application of faunistic ele- experiment, when corn rootworm caused damage in ments as gradual indicators in agroecosystems. Agric. the nonrotated Þeld corn creating open areas for weed Ecosyst. Environ. 98: 99Ð123. invasion. Byers, R. A., G. M. Barker, R. L. Davidson, E. R. Hoebeke, and M. A. Sanderson. 2000. Richness and abundance of In conclusion, several carabid species exhibited Carabidae and Staphylinidae (Coleoptera) in northeast- high activity densities and occupied distinct temporal ern dairy pastures under intensive grazing. Great Lakes niches in Pennsylvania maize agroecosystems, making Entomol. 33: 81Ð105. all candidates for studies addressing maize manage- Ciegler, J. C. 2000. Ground beetles and wrinkled bark bee- ment in northeastern agroecosystems. Of these spe- tles of South Carolina. Clemson University, Clemson, SC. cies, H. pensylvanicus exhibited the most consistent Davis, A. S., K. A. Renner, and K. L. Gross. 2005. Weed response to maize insect pest management inputs in seedbank and community shifts in a long-term cropping the nonrotated Þeld corn. H. pensylvanicus activity systems experiment. Weed Sci. 53: 296Ð306. density was consistently higher in isoline Þeld corn Downie, N. M., and R. H. Arnett, Jr. 1996. The beetles of untreated with insecticides, whereas the lower pop- northeastern North America: vols. I and II. The Sandhill Crane Press, Gainsville, FL. ulation levels in the other treatmentsÑconventional Duan, J. J., G. Head, A. Jensen, and G. Reed. 2004. Effects insecticide use, transgenes with neonicotinoid seed of transgenic Bacillus thuringiensis potato and conven- treatment, or a combination of bothÑwere indistin- tional insecticides for Colorado potato beetle (Co- guishable from one another. These results suggest that leoptera: Chrysomelidae) management on the abun- both conventional insecticide management and neo- dance of ground-dwelling arthropods in Oregon potato nicotinoid seed treatments may represent a mortality ecosystems. Environ. Entomol. 33: 275Ð281. factor detectable in a Þeld setting for at least one Duan, J. J., M. S. Paradise, J. G. Lundgren, J. T. Bookout, C. carabid species, H. pensylvanicus. Jiang, and R. N. Wiedenmann. 2006. 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