The Composition of Wireworm Species in Montana Wheat

THE COMPOSITION OF WIREWORM SPECIES IN MONTANA WHEAT

AND BARLEY FIELDS AND ITS EFFECT ON

DEVELOPING IPM PROGRAMS

Anuar Morales-Rodriguez

A dissertation submitted in partial fulfillment of the requirements for the degree

Doctor of Philosophy

Plant Science

Montana State University Bozeman, MT

August, 2014

©COPYRIGHT

Anuar Morales – Rodriguez

2014

DEDICATION

I dedicate this work to the engine of my life, Arcacely, Isabella, Nathalia and Carolina, my family.

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ACKNOWLEDGEMENTS

I would like to take this opportunity to thank everyone who has helped me throughout the entire process of my research from the beginning to its completion. First of all, thank you to my advisor, Dr. Kevin W. Wanner, for his invaluable guidance, advice, and support. To my committee members, Drs Michael A. Ivie, David K. Weaver and Robert K. D. Peterson, thank you for all your advice.

A huge thank you to our Wanner’s laboratory team who helped me so much including Aracely Ospina – Lopez, Peggy Bunger, and Ruth O’Neill, and our summer helpers Emily Rohwer, Hannah Johnson, Alix Bold, Branden Brelsford, Ammiel

Branson, Meghan McGauley, Laura Morales and Diana Florian.

Thank you to the superintendents David Wichman, CARC at Moccasin, MT,

Grant D. Jackson and Gadi V.P. Reddy, WTARC at Conrad and Dave Gettel, Post Farm at Bozeman for allowing us to collect and conduct wireworm research at their facilities.

Also I want to thank John Miller for his invaluable help seeding and harvesting all the different field trials.

Thank you to all the helpful people of the Department of Plant Science and Plant

Pathology Jim Berg, Ron Ramsfield, Jeff Johnston for all their help in different aspects of my work. A special thank you for all the help and support to Irene Decker, Tamara

Parnell and Jill Scarson.

Finally, thank you to all my friends and colleagues at Montana State University for making my stay here a memorable. iv

VITA

Anuar Morales Rodríguez was born in Bogotá, D.C., Colombia on January 8, 1966. He is the eldest of three siblings. After graduation in 1985 from the Instituto Nacional de Educación Media Diversificada, INEM Santiago Pérez El Tunal-Bogotá, he attended the Universidad Distrital “Francisco José de Caldas” in Bogotá, and received his B.S. in Biology with a major in Education in 1995. His undergraduate thesis was titled “Biological control of the coffee berry borer Hypothenemus hampei Ferrari (Coleoptera: Scolytidae) with different propagules of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill.” Before and after his graduation from the university, he worked with different agrochemical companies in Colombia until 1995. From 1995 to 2004, he worked at the International Center for Tropical Agriculture (CIAT), Colombia in the beans, forage and IPM entomology programs. From 2000 to 2001, he attended the Universidad del Valle in Cali, Colombia to obtain a “Specialization in Entomology.” He moved to the United States in 2004 as a Visiting Scholar in the Department of Entomology at the New York State Agricultural Experimental Station (NYSAES) of Cornell University in Geneva, NY. In 2006, he was accepted into the graduate program (M.S.) in the Field of Entomology at Cornell University, and conducted his work at the NYSAES. His master thesis was titled “Variation in the Susceptibility of Turf-infesting White Grubs to Different Control Agents and Opportunities for Synergistic Combinations of Biologicals and Neonicotinoids.” In January of 2009, he graduates from his Master in Entomology. In the same year, he was accepted into the graduate program (Ph.D.) in Plant Science and Plant Pathology Department at Montana State University in Bozeman, MT.

TABLE OF CONTENTS

1. GENERAL INTRODUCTION ...... 1

2. A BRIEF REVIEW OF THE WIREWORM IN NORTH AMERICA ...... 3

Wireworm Distribution ...... 5 Wireworm as a Pest of Field Crops ...... 7 Life History ...... 8 Taxonomy ...... 12 Sampling ...... 13 Larvae ...... 13 Adults ...... 16 Management ...... 18 Conventional ...... 18 Cultural ...... 20 Trap Crops ...... 21 Physical Barriers ...... 21 Light Traps ...... 21 Biological ...... 21 Common Species in Montana Wheat and Barley Fields ...... 22 Limonius californicus (Mannerheim 1843)...... 22 Limonius infuscatus Motschulsky 1859...... 23 Limonius canus LeCount 1853...... 23 Hypnoidus bicolor (Eschscholtz 1829)...... 24 Aeolus mellillus (Saylor 1836)...... 24 Selatosomus aeripennis (Kirby 1837)...... 25 References ...... 33 References Cited in the Table 1 ...... 43

3. AN EVALUATION OF FOUR DIFFERENT BAIT TRAPS FOR SAMPLING WIREWORMS (COLEOPTERA: ELATERIDAE) INFESTING CEREAL CROPS IN MONTANA ...... 49

Contribution of Authors and Co-Authors ...... 49 Manuscript Information Page ...... 50

TABLE OF CONTENTS - CONTINUED

Abstract ...... 51 Introduction ...... 52 Materials and Methods ...... 55 Insect Sampling ...... 55 Data Analysis ...... 57 Results ...... 57 Total Caches...... 57 Bozeman ...... 58 Conrad ...... 60 Denton ...... 61 Toston ...... 62 Relative Variation ...... 63 Species Diversity ...... 64 Discussion ...... 65 Acknowledgements ...... 72 References ...... 86

4. DESCRIPTION OF THE LARVAL ACTIVITY OF THREE SPECIES OF WIREWORMS IN THREE COMMERCIAL CEREAL FIELDS IN MONTANA ...... 90

Introduction ...... 90 Methodology ...... 92 Data Analysis ...... 92 Results ...... 93 Bozeman ...... 94 Conrad ...... 95 Denton ...... 96 Discussion ...... 97 Acknowledgments ...... 100 References ...... 106

5. A SURVEY OF WIREWORM (COLEOPTERA: ELATERIDAE) SPECIES INFESTING CEREAL CROPS IN MONTANA ...... 108

Contribution of Authors and Co-Authors ...... 108 Manuscript Information Page ...... 109 Abstract ...... 110

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TABLE OF CONTENTS - CONTINUED

Resumen ...... 110 Introduction ...... 112 Material and Methods ...... 115 Results ...... 116 Discussion ...... 118 Acknowledgments...... 123 References ...... 128

6. DETERMINING THE POTENTIAL FOR CEREAL CROP INJURY BY WIREWORM SPECIES COMMONLY FOUND INFESTING CROPLAND IN MONTANA ...... 130

Contribution of Authors and Co-Authors ...... 130 Manuscript Information Page ...... 131 Abstract ...... 132 Introduction ...... 132 Methodology ...... 134 Field Experiments ...... 134 Greenhouse Experiments ...... 135 Two-Choice Test ...... 135 No-Choice Test ...... 136 Data Analysis ...... 137 Results ...... 137 Field Experiments ...... 137 Greenhouse Experiments ...... 139 Two-Choice Test ...... 139 No-Choice Test ...... 139 Discussion ...... 140 Acknowledgments...... 144 References ...... 150

7. EFFICACY OF THIAMETHOXAM AND FIPRONIL, APPLIED ALONE AND IN COMBINATION, TO CONTROL Limonius californicus AND Hypnoidus bicolor (COLEOPTERA: ELATERIDAE) ...... 153

Contribution of Authors and Co-Authors ...... 153

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TABLE OF CONTENTS – CONTINUED

Manuscript Information Page ...... 154 Abstract ...... 155 Background ...... 155 Results ...... 155 Conclusions ...... 155 Introduction ...... 156 Experimental Methods ...... 158 Insects ...... 158 Insecticide Treatments ...... 158 Laboratory Trials ...... 159 Greenhouse Trials ...... 160 Field Trials ...... 160 Data Analysis ...... 162 Results ...... 163 Laboratory Trials ...... 163 Insecticide Interactions ...... 163 Dose Response ...... 164 Greenhouse Trials ...... 165 Field Trials ...... 165 Discussion ...... 168 Acknowledgements ...... 172 References ...... 179

8. EVALUATION OF THE EFFECTS OF DIFFERENT CULTURAL PRACTICES ON THE WIREWORM POPULATION AND DAMAGE IN CEREAL FIELDS ...... 182

Contribution of Authors and Co-Authors ...... 182 Manuscript Information Page ...... 183 Abstract ...... 184 Introduction ...... 185 Methodology ...... 188 Tillage Effect ...... 188 Tillage and Crop System Effect ...... 189 Seed Density ...... 191 Data Analysis ...... 192 Results ...... 193 ix

TABLE OF CONTENTS - CONTINUED

Tillage Effect ...... 193 Tillage and Crop System Effect ...... 194 Seed Density ...... 196 Discussion ...... 198 Acknowledgements ...... 206 References ...... 218

9. GENERAL CONCLUSIONS ...... 222

GENERAL REFERENCES ...... 226

LIST OF TABLES

Table Page

2.1. Distribution of wireworm species economically important in agricultural fields in North America...... 27

2.2. Wireworm species have been reported in the literature to damage crops representing 16 different plant families. Numbers in the table correspond to the sources in the literature citation section ...... 29

3.1. Wireworm sampling location in Montana. Elevation in meters above sea level ...... 73

3.2. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Bozeman, MT in 2010 ...... 73

3.3. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Bozeman, MT in 2011...... 73

3.4. Average number of wireworms collected (mean ± standard deviation) using four different types of baited trap placed in a field near Bozeman MT, at four sampling dates during 2010 and 2011 ...... 74

3.5. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Conrad, MT in 2010 ...... 75

3.6. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Conrad, MT in 2011 ...... 75

3.7. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Conrad, MT in 2012 ...... 75

3.8. Average number of wireworms collected (mean ± standard d eviation) using four different types of baited traps placed in a field near Conrad MT, at five sampling dates during 2010 to 2012. H.b = H. bicolor; L.c = L. californicus ...... 76

LIST OF TABLES – CONTINUED

Table Page

3.9. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Denton, MT in 2010 ...... 78

3.10. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Denton, MT in 2011 ...... 78

3.11. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Denton, MT in 2012 ...... 78

3.12. Average number of wireworms collected (mean ± standard deviation) using four different types of baited trap placed in a field near to Denton, MT in 2010 to 2012 ...... 79

3.13. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Toston, MT in 2010...... 79

3.14. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Toston, MT in 2011...... 79

3.15. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Toston, MT in 2012...... 80

3.16. Average number of wireworms collected (mean ± standard deviation) using four different types of baited trap placed in a field near Toston, MT at four sampling dates during 2010 to 2011 ...... 81

3.17. Percentage of the three main species collected with four different bait traps polled in open (stocking and pitfall) and close (canister and pot) in small cereal fields in Montana. Chi square value = 94.91 p= 0.001 ...... 83

5.1. Incidence of wireworms in 214 crop fields surveyed across Montana, 2011–2013. The number of fields positive for wireworms (at least 1 wireworm / trap set) is tabulated separately based on producer-reported field history. Each trap set contained five canister traps ...... 124

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LIST OF TABLES – CONTINUED

Table Page

6.1. Wireworm sampling locations in Montana. Elevation is in meters above sea level. Crops planted or managed for each given year...... 145

6.2. Number of wireworms by species collected with soil core and stocking in 2011 and 2012 in four different small grain fields at Montana ...... 146

6.3. Chi- square contingence table analyzing the dependence of sampling method (stocking and soil core) on the proportion of wireworm species collected at four locations in Montana. L. californicus and L. infuscatus were the two main species collected in 2011; all minor species were pooled under the c ategory of “others” ...... 147

6.4. Chi- square contingence table analyzing the dependence of sampling method (stocking and soil core) on the proportion of wireworm species collected at four locations in Montana. L. californicus and H. bicolor were the two main species collected in 2012; all minor species were pooled under the category of “others” ...... 147

6.5. Host plant preference of three wireworm species, H. bicolor, L. californicus and L. infuscatus, for wheat and barley in a potted greenhouse study. Number of wireworms on the side of the pot planted with barley or wheat plants ...... 147

6.6. Damage to wheat and barley plants by three different wireworm species, H. bicolor, L. californicus and L. infuscatus, in a two-choice potted greenhouse bioassay. The number of living plants and dryweight was recorded 14 days after infestation ...... 148

7.1 Percentage of mortality of L. californicus and H. bicolor in laboratory bioassays 30 DAT with insecticide treated wheat seeds. Bioassays were replicated with larvae collected in two different years ...... 173

7.2. Laboratory mortality (mean ± SE) of two species of wireworms and the interaction with two doses combinations of fipronil and thiamethoxam insecticides at 30 DAT in 2011 and 2012 ...... 174 xiii

LIST OF TABLES – CONTINUED

Table Page

7.3. Probit for mortality of L. californicus with wheat seed treated with fipronil...... 175

7.4. Percentage of mortality of H. bicolor and L. californicus and wheat seedlings 30 DAT in greenhouse bioassays with different doses of fipronil applied as seed treatments. Untreated check that was not infested with insects was included as a control for seedling mortality ...... 175

7.5. Total number of wireworms collected from treatment plots in 2012 and identified to species, and the average number of all wireworms combined. Each plot was planted with treated wheat seed in 2011, and in 2012 all plots were overplanted with untreated seed...... 176

7.6. Stand density, dry weight, yield and grain density in treated field plots planted in 2011...... 177

7.7. Stand density, dry weight, yield and grain density in treated Field plots over planted with untreated wheat seed in 2012 ...... 178

8.1. Wireworms, stand counts, dry weight and seed density bunk (mean ± SD) by soil till system and year of plots under two different tillage practice in Moccasin, MT ...... 207

8.2. Wireworms, stand counts, dry weight and seed density bunk (mean ± SD) by soil till system and year of plots under four different treatments of tillage and crop system practice in Moccasin, MT ...... 208

8.3. Barley seeding density trial results. Plant density expressed as a % of the seeding density at two assessment dates, plant biomass measured as dry weight, yield and seed density (mean ± SD) at three different locations in Montana...... 209

8.4. Spring wheat seeding density trial results. Plant density expressed as a % of the seeding density at two assessment dates, plant biomass measured as dry weight, yield and seed density (mean ± SD) at three different locations in Montana ...... 210 xiv

LIST OF FIGURES

Figure Page

2.1. Number of publications (5 year moving average) listed on the Web of Knowledge (Thomson Reuters. 2010) using the search terms “wireworm” and “Elateridae” and “click beetle”, from 1920 to 2010...... 32

3.1. Four bait traps used (top) see methodology for the description and display of the traps in the field (bottom) ...... 83

3.2. Average (LC 95) of wireworm by bait trap collected during 2010 to 2012 in Bozeman, Conrad, Denton and Toston Montana ...... 84

3.3. Relative variation values for each location during 2010 to 2012 intensive sampling (all dates of each year combine), n=total wireworms collected for the given year and locality ...... 85

4.1 Total Limonius infuscatus (Li) collected by date and average soil temperature at 7.5 cm deep in 2010 in a cereal filed in Bozeman, MT...... 102

4.2. Total Limonius infuscatus (Li) collected by date and average soil temperature at 7.5 cm deep in 2011 in a cereal filed in Bozeman, MT...... 102

4.3 Total Limonius californicus (Lc) and Hypnoidus bicolor (Hb) collected by date and average soil temperature at 7.5 cm deep in 2010 in a cereal filed in Conrad, MT...... 103

4.4. Total Limonius californicus (Lc) and Hypnoidus bicolor (Hb) Collected by date and average soil temperature at 7.5 cm deep in 2011 in a cereal filed in Conrad, MT ...... 103

4.5. Total Limonius californicus (Lc) and Hypnoidus bicolor (Hb) collected by date and average soil temperature at 7.5 cm deep in 2012 in a cereal filed in Conrad, MT...... 104

4.6. Total Limonius californicus (Lc) collected by date and average soil temperature at 7.5 cm deep in 2010 in a cereal filed in Denton, MT...... 104

LIST OF FIGURES - CONTINUED

Figure Page

4.7. Total Limonius californicus (Lc) collected by date and average soil temperature at 7.5 cm deep in 2011 in a cereal filed in Denton, MT ...... 105

4.8. Total Limonius californicus (Lc) collected by date and average soil temperature at 7.5 cm deep in 2012 in a cereal filed in Denton, MT ...... 105

5.1. Number of fields surveyed for wireworms by county and year in Montana. The number of fields surveyed each year within each county is indicated numerically within symbols used to represent survey year ...... 124

5.2. Incidence of wireworms trapped in 31 counties across Montana during 2011–2013. At least eight species of wireworms were collected from the 95 cereal fields surveyed, with the five major species shown here. Each field positive for a wireworm is represented by a colored symbol, the shape of the symbol denotes the survey year and the color denotes the species caught. A field infested by more than one species is represented by overlapping and hollow symbols. The approximate location of the Continental Divide is shown in purple ...... 125

5.3. Abundance of each species of wireworm sampled from 95 cereal fields across Montana. The number of wireworms collected from a field (a set of five traps) is presented categorically on the x-axis. The y-axis displays the number of fields in each category, for each of the five species collected in the survey. Data from the three year survey is pooled ...... 126

6.1. Linear regression of wheat plant damage by L. californicus to the number of larvae infested into no-choice potted greenhouse bioassay. A) Number of seedlings destroyed/lost vs the number of larvae infested, B) Dry weight of seedlings vs the number of larvae infested. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 149

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LIST OF FIGURES - CONTINUED

Figure Page

8.1. Penetration resistance measurement in four fields under different management in Moccasin, Montana. Red line at 300 PSI mark indicate the compaction level of the data above the line...... 211

8.2. Regression percentage of barley plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Kalispell’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 212

8.3. Regression percentage of wheat plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Kalispell’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 213

8.4. Regression percentage of barley plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Conrad’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 214

8.5. Regression percentage of wheat plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Conrad’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 215

8.6. Regression percentage of barley plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Fort Ellis’s seed density trial Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 216

8.7. Regression percentage of wheat plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Fort Ellis’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits ...... 217

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ABSTRACT

Wireworms, the larvae of click beetles, are the most important soil-insect pest of small grain fields in Montana. Worldwide, there are about 9,300 species of elaterids in 400 different genera, and in North America 885 species in 60 genera have been identified. In Montana, 166 species were identified, among them, 21 species have been identified as possible pests in small grain fields and some are serious pests of a wide variety of crops. My research focused on three main objectives related to wireworm IPM: first, the identification of the species causing damage in the field and their geographic and seasonal distribution in Montana; second, establishing the potential of different baited traps to monitor pest wireworm populations; and third, evaluating chemical and cultural management alternatives. To complete the first objective a statewide wireworm survey was conducted for three years as well as an intense sampling of four cereal fields season for three consecutive years. To complete the second objective, the effectiveness of four baited traps were assessed: traditional pitfall compared to pot, stocking and canister type traps, in four cereal fields for three years. To complete the last objective, laboratory, greenhouse and field studies were conducted to evaluate new insecticides, crop injury, tillage practices and seeding density. 5,097 wireworms were collected from the four sites during 2010 – 2012 including four common species, Aeolus mellillus, Hypnoidus bicolor, Limonius californicus and L. infuscatus, and three minor species, Agriotes spp., Dalopius spp. and Selatosomus aeripennis. Peak wireworm activity at the soil surface was found to coincide with cereal crop germination and establishment. While all trap types can be used to detect wireworm activity and estimate population levels, pitfall and stocking were more efficient than pot and canister traps. Thiamethoxam does not kill wireworms but its ability to suppress wireworm populations in the field can be improved by the addition of fipronil. Increasing seeding density is one of the most common cultural recommendations for managing wireworms, but my studies did not support its benefit to higher crop yields. Significantly, species-specific crop injury and seasonal movement in the soil support the need for species-specific IPM research. 1

CHAPTER ONE

GENERAL INTRODUCTION

Wireworms are the larval stage of click beetles and are the most important soil- dwelling pest of wheat, barley, small grain and several other crops grown in the northwestern region of the US. During the last decade, producers in the region have noticed an increase in wireworm populations and damage to their crops. Prior to the last decade wireworms were effectively controlled using inexpensive insecticidal seed treatments. However, the EPA has banned and removed from the market many of the original insecticides, because of serious environmental concerns, and producers have found the newer insecticides to lack efficacy. Furthering this problem, little is known about the biology and ecology of wireworms infesting cereal crops in Montana and the northwestern region. For example, basic information such as the identity of the species infesting and damaging crops, a cornerstone of integrated pest management (IPM) is unknown.

The goal of this project is to provide a foundation of knowledge required to develop future IPM programs for crops grown in Montana. First, the complex of species infesting cereal crops was investigated and Limonius californicus, L. infuscatus and H. bicolor were identified as common pest species. The geographic and seasonal distribution of these key pest species was established by a statewide survey and an intensive survey of four cereal fields in Montana. Second, I evaluated four different types of bait traps for 2 monitoring pest wireworm populations. Third, laboratory, greenhouse and field studies were conducted to evaluate the effectiveness of insecticidal and cultural IPM tactics. New

IPM approaches are required to mitigate crop losses from wireworms in Montana. With this research I expect to contribute to the knowledge of wireworms as crop pests in

Montana and provide the knowledge needed to develop future control options. The research will also provide a knowledge base for researchers in the northwestern region and nationally.

CHAPTER TWO

A BRIEF REVIEW OF THE WIREWORM IN NORTH AMERICA

Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are the most significant soil-dwelling pests of a wide variety of field crops worldwide (Comstock and

Slingerland 1891; Seal et al. 1992; Parker and Howard 2001; Toba and Turner 1983;

Kohno and Miyai 1993). Larvae of some species of Elateridae are fitophagous and are important agricultural pests; larvae of other species are predaceous, often living in soil, subcortical habitats, or rotten logs (Johnson 2002).

However, little is known about the biology of most species. Wireworms seem to be an increasing threat to the sustainable production of small grains, potatoes, and other crops since the de-registration of lindane, an effective and inexpensive insecticidal seed treatment. Although new insecticides have been registered as seed treatments, their efficacy is not satisfactory (Vernon et al. 2008 and 2009; Van Herk and Vernon 2007) and new IPM tools are required to manage wireworm populations. Before its de- registration, lindane effectively controlled wireworm damage to grains for more than 50 years at low cost (Toba and Turner 1983). During this period, little wireworm research was conducted and this deficit is reflected in the low number of publications between

1960 and 2010 (Figure 1). The peak observed in 1960 includes papers describing the use of first generation insecticides developed in the 1950s. More recently the number of wireworm publications has increased, reflecting their changing pest status.

The first cornerstone of IPM, pest identification, remains largely unclarified for wireworms, particularly for the damaging larval stage (Pedigo 1989 and Norris et al.

2003). The effectiveness of many IPM tactics is specific to a set of related species

(Morales et al. 2009).

Click beetles are a large group with about 10,000 described species in 400 different genera worldwide (Johnson 2002). In Europe, the most important pest species are in the genus Agriotes Eschscholtz 1829, including A. lineatus L., A. sputator L., A. obscurus L., A. brevis C and., L. ursinus Van Dyke and A. ustulatus Schall (Benefer et al,

2012). In North America (not including Mexico), 921 species in 99 genera have been reported (Johnson 2009); similar numbers (965 species in 91 genera) have been reported by Marske and Ivie (2003), ranking elaterids as the seventh-most species rich family in

North America. However, the larvae are described in less than 10% of the North

American species and of those 95% are of a single larval instar (Becker and Dogger

1991).

A total of 369 species and subspecies have been reported from Canada and Alaska

(Bousquet 1991), 30 of which are reported as economically important in Canada (Benefer et al. 2012b). In Montana, 164 species of click beetles in 43 genera have been identified of which 23 are potential crop pests in small grains (Seibert 1993). However, most of these listed species can only be identified using adult males, and their actual distribution and abundance in cropland remains largely unknown; there is a potential for significant under-estimation of the diversity of wireworm species infesting cropland in Montana.

Wireworm Distribution

Wireworms are a diverse group with a worldwide distribution. Although several studies have described species of economic importance to agriculture, little or nothing is known about non-economically important species.

The distribution of the most economically important species is very well known:

A. lineatus is found in all European countries, Kazakhstan, Mongolia, Brazil, Haiti, New

Zealand, Kyrgyzstan, Israel, Laos, and introduced populations in Canada and the United

States; A. obscurus is found in all European countries, Korea, China, Japan, and

Mongolia, with introduced populations in Canada and the United States; A. sputator is found in all European countries, Kazakhstan, countries within the Caucasus, Siberia,

North Africa, Asia Minor, Canada, the United States, China, and Iran; A. ustulatus is found in all European countries, countries within the Caucasus, North Africa, Mongolia,

Iran, Asia Minor, the Balkans, Canada, and the United States (Ritter and Richter 2013,

Elateridae.com 2012). Other economically important species include the genera Ampedus

Dejean, Athous Eschscholtz, Conoderus Eschscholtz, Ctenicera (under revision; Majka and Johnson 2008; Johnson 2009), Dalopius Eschscholtz, Hypnoidus Dillwyn, Limonius

Eschscholtz, Melanotus Eschscholtz, and Selatosomus Stephens, mainly distributed in the

Holarctic region. In North America, native and introduced species that are economically important are summarized in Table 2.1.

In the Pacific Northwest (PNW) region of North America, the most economically important wireworm species thus far reported belong to six genera, Aeolus, Agriotes,

“Ctenicera1”, Dalopius, Limonius, and Melanotus. Ctenicera pruinina (Horn) is reported to be the predominant dryland species in northern Oregon, followed by L. californicus,

M. longulus oregonensis (LeC.), and L. infuscatus (Mots) (Toba and Campbell 1992). In

2008, the five most important species reported in the PNW belonged to two genera,

Limonius and “Ctenicera”, with L. canus, L. californicus, L. infuscatus, L. subauratus

LeC. reported on irrigated land and C. pruinina on dry land (Andrews et al. 2000, 2008).

In central Montana Athous spp. historically were the most important crop pests overall (Hastings and Cowen 1954) although L. canus was the main pest in irrigated areas

(Mail 1932). In 1981, a complex of A. mellillus, C. glauca, and C. destructor was reported from wheat fields in North Central Montana (Morrill 1983). Limonius californicus and L. canus have been listed as most important on irrigated land in

California (Stone and Campbell, 1933 and Campbell 1942), southwest Idaho (Shirck

1945), and the Yakima Valley (Gibson 1939). In 1925, Ludius [Ctenicera] inflatus Say

[=L. glaucus (Germar)], L. [C.] noxius Hyslop, and Pheletes [Limonius] occidentalis

Cand were reported as the principal wireworm species of economic importance in

Washington, Oregon, and Idaho (Lane 1925), but these species were no longer considered economically important by 1950 (Glen 1950). In 1997, Agriotes obscurus and

A. lineatus were first reported in northern Washington State (Vernon and Päts 1997) asintroduced species from Europe. In 2005, these species were found in southern

Washington (LaGasa et al. 2006), Oregon (Andrews et al. 2008), and in the Fraser Valley

1 We are going to use “Ctenicera” under quotations to refer to this genus. The genus is undergoing taxonomic review and generic transfer (Johnson, 2009) and with the literature published it is unclear as to the actual status. 7 of British Columbia where these species have become major pests of small fruit, vegetable, ornamental, and forage crops (Vernon et al. 2001). It is important to note that these reports do not represent comprehensive surveys, but simply reports from isolated field sites. The literature from North America suggests that the current complex of pest species has changed compared to early records.

Wireworms as Pests of Field Crops

Knowing the species of wireworm(s) present in a field and their ecology is of fundamental importance to develop effective management strategies (Pedigo 1989;

Morales et al. 2009). However, wireworms are soil insects with diverse feeding habits and their role in the ecosystem is not always clear. For example, in Canada 30 species are reported as economically important (Benefer et al. 2012b), but the larvae of some of these species were found abundantly in crop fields without causing damage. MacLeod and

Rawlins (1935) found large populations of H. abbreviatus larvae in close proximity to potato (Solanum tuberosum L.) plants, but no damage was done to the tubers, suggesting that this species was not a pest of potato. In the Czech Republic, Jedlička and Frouz

(2007) have found saprophagous species such as Athous niger (L.), A. subfuscus (Müller) and A. vittatus (Fab.) and carnivorous species such as Dalopius marginatus (L.) and

Agrypnus murinus (L.) in the same field with A. obscurus, one of the most important pests damaging crops in Europe.

The pest status of a particular species of wireworm may depend on the type of crop planted in the field and may also vary by geographical region. Glyphonyx bimarginatus Schaeffer is the second most important wireworm pest of sugarcane

(Saccharum officinarum L.) in Florida, but is not considered economically important to potato (Deen and Cuthbert 1955). Larvae of A. sputator L. and A. niger, both serious pests of vegetables in Europe, entered the United States with nursery stock in the 1920s

(Sasscer 1924) but have not been reported as pests in the United States. A wireworm species may also be a pest in one location but beneficial in another. Stirrett (1936) lists A. mellillus as a pest in Ontario, Canada while Doane (1977a) reports that it might reduce populations of C. destructor and H. bicolor by feeding on their eggs. One of the main wireworm pests of California, L. californicus, is an effective predator of root maggots

(Stone 1941).

Mostly a generalist herbivore in nature, wireworms have been reported as a serious economic pest in at least 40 different field and specialty crops in 16 different plant families (Table 2.2). Several species have been reported to damage a specific crop worldwide, for instance, 39 species in 21 genera have been reported in potato (Jansson and Seal 1994).

Life History

Wireworms have shiny golden brown, tough, firm exoskeletons and are cylindrical in shape. Their body has three parts: the head, the thorax with three pairs of

9 short legs, and the abdomen comprised of nine segments. The morphology of the last abdominal segment is often used for species identification, which may include elaborate urogomphi (dorsal processes, often hooked) (e.g., Limonius, Ctenicera, Aeolus,

Selatosomus) or a conical tip with or without strong hairs (a.i.; Agriotes, Dalopius)

(Etzler et al 2014).

Female beetles lay eggs singly or in small clusters just below the soil surface in humid or fresh soil, in grassy or weedy areas. Eggs are translucent, spherical and small, ranging in diameter from 0.5 to 0.8 mm. The embryonic development time depends on the species and the meteorological conditions. Furlan (1996) reported that the embryonic development time of A. ustulatus was 45 days at 15°C, 14 days at 25°C and only 13 days at 29°C. Conversely, the development time of A. sordidus varied from 11 to 17 days at

25°C to 9 to 11 days at 29°C based on populations collected in northern Italy; while southern populations varied from 11 to 25 days at 25°C and 11 to 20 days at 29°C.

Hatching success ranged between 90 and 100% for both populations. In the field, mortality of eggs can be very high if soil conditions are dry, as they are very prone to desiccation (Doane 1969; Rabb 1963). Edwards and Evans (1950) reported an incubation period of about 34 days for eggs of Corymbites cupreus F and Cohen (1942) reported 36 to 59 days for A. obscurus, and Rawlins (1940) reported an incubation period between 22 to 28 days for A. mancus; however, they did not report how the calculation was done or the ambient conditions. Eggs of C. destructor, C. aeripennis and H. bicolor normally hatched between 13 to 14 days at 24.5°C (Doane 1966), but three years later for C. destructor, Doane (1969) reported an embryonic development time of 14, 22.5, and 52 10 days at 25, 20, and 15°C, respectively. For C. vespertinus, Rabb (1963) reported an incubation period of 8 to 11 days at 30°C, 9 to 16 days at 26.7°C and 15 to 20 days at

23.9°C. The incubation period of M. communis reported by Wilson (1940) is between 12 and 17 days.

The total length of the larval life cycle may vary considerably between different genera and species and can be influenced by site-specific soil conditions. The larval stage of Agriotes spp. may have as many as 14 instars. Agriotes ustulatus has been reported to have 12 instars (Furlan 1998), A. sordidus 13 (Furlan 2004), and A. mancus 9-13

(Rawlins 1940). Stone (1941) reported 10 to 13 instars for L. californicus under laboratory conditions; one male completed development in 13 instars and a female in 10.

Strickland (1939) recorded 10 to 24 instars using field cages artificially infested with C. aeripennis destructor. Seal (2011) reported three instars for Conoderus rudis (Brown).

Agriotes spp. wireworms in the U.K. spend from four to as many as seven years in the soil before pupating (Benefer 2012a). Melanotus communis and M. pilosus Blatch require as many as six years to complete their larval stage (Fenton 1926), A. ustulatus, A. sordidus five to seven years (Furlan 1998; 2004), L. californicus four to eleven years

(EPPO 2005b) and C. aeripennis destructor four to nine years (Strickland 1939). Other species have shorter development times and fewer instars. Conoderus bellus Say completes its larval stage in approximately 30 days (Jewett 1945), A. melillus and C. bellus in one year (6-7 instars) (Jewett 1940, 1945) and C. rudis averaged of 93.7 days

(range, 70-98 days) (Seal 2011). Conoderus falli in the southeastern US have a larval

11 period of 3.5 to 12 months and are capable of completing two generations per year

(Baumler 2008; Day et al. 1971; Norris 1957).

The size of larvae from different species also varies. Newly emerged larvae are small, only 1.0 to 1.5 mm long. Transparent white, neonate wireworms hatch after about a month and feed on both dead and living plant material in the soil. Depending on the species, the size of fully developed larvae varies from 6 mm to 40 mm. Fully-developed larvae of L. californicus and L. infuscatus are 25 to 30 mm, H. bicolor 10 to 12 mm, and

C. rudis 8.4 mm (Seal 2011). Kulash and Monroe (1955) reported variation in the size of three of the more common species found in North Carolina corn fields: Glyphonyx recticollis (Say) grow to 12 to 14 mm and M. communis and Conoderus lividus (De G) grow to 25 to 30 mm.

As wireworms mature, they feed to a greater extent on living plant material below the soil surface. They feed for two, maybe three, short periods, with March to May and

September to October being the most intense periods. Soil conditions and resources can influence both the number of larval instars and the larval development time. Evans and

Gough (1942) reported a faster growth of A. obscurus fed with wheat compared to carrots

(Daucus carota L.) and potatoes, with wheat-fed larvae doubling their weight in 25 weeks; larvae fed with carrots increased their body weight by 10%, and larvae fed with potatoes did not grow. Mail (1932) reported a wider soil pH range tolerance of L. canus under laboratory (4.8 to 8.2) and field (6.1 to 7.7) conditions in Montana, but he concluded that “the pH value of the soils in Montana which are suitable for and are used

12 to grow agricultural products, has no influence on the presence of wireworms, and that other factors must be considered in seeking an answer to this problem”.

Wireworms usually reach maturity in July to September, at which point they burrow in the soil and hollow out small pupation cells 5 to 30 cm below the soil surface

(Comstock and Slingerland 1891). After three to four weeks, they become adults, but usually remain in the cell for hibernation unless disturbed (Comstock and Slingerland

1891, Parker and Howard 2001; Rawlins 1940). Selatosomus aeripennis begins spring activity mid-April to mid-July, with males becoming active two to three weeks before females. Doane (1961) collected 2,534 adults in 1959 and 4,328 in 1960 from wheat fields at the University of Saskatchewan, and the sex ratio was 6:1 and 8:1 m:f for each year, respectively. Hypnoidus bicolor become active from late April until the end of July.

Both sexes were active at the same time, with a sex ratio of 1:2 m:f where both genders are present (Doane 1961).

Taxonomy

Less than 10% of North American wireworms are currently described, and of those 95% are described from a single larval instar. This is a worldwide trend, where only the economically important species that damage the crop have thorough taxonomic descriptions, and even related species found in association have not been studied. Adding to the taxonomic confusion, several groups are under revision and have or will be relocated, split, or reassigned to new genera (eg. “Ctenicera group”) (Johnson 2009). The

13 most recent reviews of the Elateridae have been conducted by Johnson (2009) for

Nearctic genera, and Bousquet (1991) for the Canadian Elateridae. Other reviews were completed early in the 1900s and include wireworms of economic importance in Canada

(Glen et al. 1943); contributions to knowledge of the larval Elateridae (Glen 1944);

Limonius spp. (Lanchester 1941, 1946); Dalopius spp. (Brown 1934a, 1934b);

Cordiophorus spp. (Douglas 2003); tribe Lepturoidini (Glen 1950); Nearctic species of

Agriotes (Becker 1956); the North American elaterid types of Otto Schwarz, with a revision of C. bivittata (Melsheimer) (Becker 1961).

Sampling

Larvae

Insects with a subterranean habitat are especially difficult to monitor and control.

Wireworms may burrow and live as deep as 1.5 m below the soil surface (Andrew et al.

2008). Vertical movements in the soil depend on the species and related cycles of feeding and molting, as well as extrinsic variables such as geography, temperature, moisture, amount of ground cover (e.g., grass vs. fallow) (Elateridae.com), and location of food

(Zacharuk 1962; Doane et al. 1975; Toba and Turner 1983; Parker 1996). Assessments of wireworm populations in the soil can vary radically in terms of both spatial and temporal distributions (Parker 1996; Simmons et al. 1998; Horton 2006). Selecting the best type of sampling method, including timing and spatial sampling protocols, depends specifically on the objective, be it simple detection, species census/survey, population estimation, or

14 threshold-based monitoring. The realities and limitations of wireworm sampling need to be considered carefully when used to provide management recommendations.

Wireworm population assessments can be separated into ‘absolute’ and ‘relative’ sampling methods (Southwood 1979). Absolute sampling methods such as soil coring, which measures the number of larvae in a given volume of soil to extract wireworms in situ, typically involve a higher level of expertise, time, infrastructure, and associated expense. The main objective of absolute sampling for wireworms has historically been to estimate the population size, spatial distribution (horizontal and vertical), and temporal activities of wireworms in a field. This has typically involved removing field soil in layers (Gibson 1939; Salt and Hollick 1944) or by soil coring (Yates and Finney 1942;

Anon. 1948) at various depths and at enough locations in a field over time that wireworm population estimates can be made with reasonable accuracy.

Howard 2001) that depend upon CO2 production to attract wireworm larvae (Doane et al.

1975) such as germinating seeds, respiring plants, and decomposing plant material. Of the large number of CO2-producing baits tested, including fruits and vegetables (melons

[Cucumis melo L.], carrot [Daucus carota L.], potato [Solanum tuberosum L.) and

15 processed cereals (bran, rolled oats, flour), baits containing germinating cereal seed

(wheat [Triticum spp.], barley [Hordeum vulgare L.]) and/or other seeds (e.g. corn [Zea mays L.], sorghum [Sorghum spp]), several have been found most effective and are now most commonly used (Bynum and Archer 1987; Jansson and Lecrone 1989; Parker 1994,

1996; Simmons et al. 1998; Parker and Howard 2001; Horton and Landolt 2002; Vernon et al. 2003, Furlan et al. 2010). Wireworms can detect distinct CO2 gradients from different distances. Doane et al. (1975) found that wireworms (C. destructor) can detect and orient to CO2 sources from as far away as 20 cm (the limit of their soil bioassay arena), and Vernon et al. (2000) showed that the majority (83%) of wireworms (A. obscurus) in field plots will orient to trap crops of wheat spaced 1 m apart.

Among the more important characteristics of wireworm trapping systems for use in research and especially in management programs are consistency among traps, control over CO2 production, ease of trap assembly and deployment, and rapid, accurate methods of wireworm extraction. Of the methods developed, we have found that traps similar to those described by Chabert and Blot (1992) adequately meet these criteria (Vernon et al.

2009). These consist of 450 ml plastic pots filled with medium grade vermiculite, and with 100 ml each of untreated corn and hard red spring wheat spread in layers in the middle of the pots. The traps are soaked with warm water, placed within 24 hours in 15 cm deep holes, and covered with soil on all sides. A 20 cm diameter inverted tray is positioned 5 cm above the trap and level with the ground. Traps are generally left for 12 to 14 d, and then removed from the field without the surrounding soil. The trap contents

(vermiculite and germinated wheat and corn seed) are sorted by hand to find larger 16 wireworms (> 1 cm), and/or are placed in Tullgren/Berlese funnels which effectively extract all instars (Vernon et al. 2009). Other bait trapping systems, including the various food baits mentioned, are inconsistent in CO2 production among baits, and wireworm counts are highly variable because variable amounts of soil surrounding the baits often have to be sampled as well.

Various methods of improving the efficacy of bait traps have been developed, such as covering the baits at the soil surface with black plastic (Ward and Keaster 1977;

Chabert and Blot 1992; Simmons et al. 1998) or charcoal dust (Ward and Keaster 1977;

Bynum and Archer 1987). These approaches increase soil temperature and thus CO2 production by encouraging the germination of living baits (wheat and corn seed) or the microbial respiration in non-living baits (bran, rolled oats, flour). This has facilitated earlier trapping and greater catches for some species (Ward and Keaster 1977; Bynum and Archer 1987), but has also increased the time and cost of sampling, which may not be feasible for all monitoring strategies.

Either approach, absolute or relative, is problematic as a monitoring tool for determining action thresholds in spring-planted grain crops because of early planting dates. At these early dates, wireworm activity can be suppressed due to cool soil temperatures, making it difficult for producers to make population assessments and select treatment options before planting.

Adults

The adult activity of several click beetle species has been studied by trapping with

17 baits, pitfall traps, light traps, pheromones, or by collection from underneath various types of covers (Hawkins 1936; Comstock and Slingerland 1891; Campbell and Stone

1939; Cohen 1942; Tóth 2012; Tóth et al. 2003; Benefer et al. 2012). Comstock and

Slingerland (1891) observed larvae and adults attracted to sliced potatoes, wads of green clover (Trifolium spp.), and corn meal dough. Traps baited with clover yielded 500 adults, mostly A. mancus (Comstock and Slingerland 1891). Doane (1961) evaluated the population of C. aeripennis and H. bicolor infesting the same field using pitfall traps; in

1959 an average of 180.8 males/trap of C. aeripennis were collected from April 14 to

May 18, and in 1960 an average of 322 males/trap were collected from April 20 to July

13. For H. bicolor, in 1959 an average of 37.8 males/trap were collected from April 27 to

July 24 and in 1960 and average of 19 males/trap were collected from May to August 7.

A portable trench barrier originally designed to prevent walking Colorado potato beetles, as a modified pitfall trap (Hunt and Vernon 2001), has been use to intercept adults of A. obscurus entering fields (Vernon and van Herk 2013). Pheromones and attractant compounds of different species have been isolated and identified (see Table 1 in Tóth

2012). Cherry and Hall (1986) successfully collected high numbers of C. cummins in sugar cane fields in Florida using black light traps, but in North Carolina, black light traps failed to capture C. vespertinus (Baumler 2008). Traps baited with pheromones of

A. obscurus, A. lineatus, and A. ustulatus are used in Europe and Canada to evaluate their population and distribution (Tóth 2012; Sufyan, et al. 2011; Szarukán et al. 2005, Tóth et al, 2003; Vuts et al. 2012; Hicks and Blackshaw 2008; Vernon and Tóth 2007; Vernon and Päts 1997; Vernon et al. 2001; Vernon 2004). LaGasa et al. (2006) used pheromones 18 of two introduced species, A. obscurus and A. lineatus, to survey the distribution of invasive populations in Washington State.

Campbell and Stone (1939) collected 666 to 3,102 click beetles per acre using traps composed of a pile of malva (Malva spp.), thick-stemmed mustard, and other coarse plants. This type of trap, however, gives no assurance that the beetles will stay under the refuge for any definite period of time, and does not permit a quantitative estimate of the population (Doane 1961). Also, the cover loses its attractiveness when it becomes dry

(Campbell and Stone 1939).

Adult populations do not necessarily reflect the density of larval infestation in a specific field. Adults usually move from adjacent fields or grassy areas. As noted by

Blackshaw and Vernon (2008), there are two unsubstantiated assumptions necessary for legitimizing trap counts of adults as predictors of larval activity. The first is that there is a spatial relationship between the catches of adult male click beetles in pheromone traps and wireworms in soil. The second is that each species is attracted to its pheromone trap to a similar degree.

Management

Conventional

In most crops, wireworm management has relied on conventional seed treatment insecticides. Typically, if wireworms have been scouted on-site in previous years, an

19 insecticidal seed treatment will be used prophylactically in ensuing years. Cyclodiene insecticides provided effective control of wireworms in the 1960s to 1980s until they were eventually banned because of their long persistence in the soil, a characteristic that made them so efficacious against wireworms. Since then, organophosphates or carbamates have been used for wireworm control in potatoes (Kuhar et al. 2008) and synthetic pyrethroids, neonicotinoids, and organophosphate insecticides have been largely used to control wireworms in corn (Kuhar et al. 2003). However, concerns associated with human and environmental health have arisen and it is expected that in future years many of these will also be delisted by the EPA. For example, benzene hexachloride (BHC) insecticides (e.g., lindane) were used for more than 50 years to control wireworms in small grain crops, but were later removed from the market. The currently available replacements are based on neonicotinoid active ingredients, and do not give satisfactory control (Vernon et al. 2008). These new neonicotinoids

(imidacloprid, clothianidin and thiamethoxam) do not suppress populations of neonate and larger wireworms in the soil (Vernon et al. 2009), but can protect wheat stands by inducing temporary morbidity.

In most cases, published damage thresholds are nominal (based on a practitioner's experience) and not based on objective criteria and data used to calculate an “economic injury level” (EIL) (Pedigo et al. 1986). However, in the case of potatoes, more research has been conducted to establish firm thresholds. Cranshaw (2002) established an

“economic threshold” (ET) for control in potatoes using a screen method (screening soil samples through ¼-inch hardware mesh) and using bait stations. The ET thus established 20 is 0.4 wireworms per square foot (screen method) or one larva per bait station deploying two bait stations per acre. These thresholds correspond to an estimated 17,000 and

20,000 wireworms/acre, respectively. This ET does not consider the market value of the crop or costs of control. When considering the variable behavior of wireworms in the soil, the real accuracy of these thresholds would require future evaluation.

Cultural

Due to the broad feeding habits and long life cycles of wireworms, crop or fallow rotations have not proved to be an effective management tactic (Comstock and

Slingerland 1891). It may reduce the population but not in an efficacious or cost effective manner. Increased seeding density to compensate for damage is the most commonly used cultural practice adopted by wheat and barley producers. Another recommended practice is to delay spring planting for a few weeks to reduce the amount of time that the most susceptible crop stage (seeds and small seedlings) is exposed to wireworm feeding.

However, little research has evaluated different cultural practices on wireworm populations. Bryson (1930) reported a higher incidence of injured corn plants planted early in April than those planted in late May. Other cultural practices include trap crops, physical barriers, light traps, and soil preparation such as till and no-till. In the past, soil compaction was recommended (Comstock and Slingerland 1891) but this is not consistent with modern practices.

Some commonly-used cultural practices to improve soil conditions (no-till production) and to maximize profit (irrigation and continuous cropping) appear to actually favor wireworms. 21

Trap Crops. The mortality of strawberry plants observed by Vernon et al (2000) was significantly less when wheat was planted between the rows in fields infested with A. obscurus. In the lower Fraser Valley of British Columbia, inter-planting with wheat has been used to manage wireworm damage in new strawberry fields (Vernon et al. 2003).

Physical Barriers. Vernon and van Herk (2013) used a portable trench barrier to intercept adults of A. obscurus from entering fields using a modified pitfall trap (Hunt and Vernon 2001).

Light Traps. Black light traps collected high numbers of adults of C. cummins in sugar cane fields in Florida (Cherry and Hall 1986), but this practice needs to be evaluated for each species present in the field since not all respond. For example, in

North Carolina, C. vespertinus was not captured in black light traps (Baumler 2008).

Biological

Entomopathogenic fungi (Metarhizium anisopliae (Metschnikoff) Sorokin,

Beauveria bassiana (Balsamo) Vuillemin and nematodes (families Steinernematidae and

Heterorhabditidae) have shown promise for the control of soil pests (Ansari et al. 2009;

Morales-Rodriguez and Peck 2009). However, just a few studies with wireworms have been published. Kabaluk et al. (2007) have identified Canadian strains of M. anisopliae which are pathogenic to A. obscurus infesting corn fields in British Columbia. The strains

V1002 and LRC181A of M. anisopliae caused 90 and 100% mortality of A. lineatus, 21

DAA under laboratory conditions. Other M. anisopliae strains caused mortality ranging between 10 and 70%, whereas strains of B. bassiana and Paecilomyces fumosoroseus 22

(Wize) were non-pathogenic to A. lineatus. However, biological agents have not yet been demonstrated to be effective in field trials.

Common Species in Montana Wheat and Barley Fields

Based on preliminary surveys and historical data we suspect several species to be found in Montana crops and in the next section, I will review species-specific information.

Limonius californicus (Mannerheim 1843)

Sugarbeet Wireworm. This species is polyphagous, its main hosts being potatoes, sugarbeets, cereals, beans, maize, and red clover (EPPO 2005b). Limonius californicus is found in the Pacific northwest of North America on irrigated land or where annual rainfall exceeds 460 mm. It has been reported from Alberta, British Columbia, Manitoba, and Saskatchewan in Canada; and from California, Idaho, Oregon, and Washington in the

United States (Al Dhafer 2009; Johnson 2009; Bousquet 1991).

The larval stage lasts 4 to 11 years. Older larvae are usually found feeding in the top 15 cm of soil. During early summer, individual female beetles lay 200–1400 eggs in loose or cracked soil and under lumps of soil. Pupation occurs during summer, at depths of 5 – 10 cm in the soil.

The larvae are white when they first hatch, but change to shiny yellow and then to brown as they mature, growing to 25 mm long. The last abdominal segment is flattened and elongated with short, stout appendages on the end (EPPO 2005b). Limonius californicus can be distinguished by the bulbous parameres having the lateral margins 23 gradually narrowing from apical 1/5 toward apical blades, the apical blades triangular with lateral angle pointed apically, and the aedeagus gradually narrowing to tip, extending beyond parameres by less than 1/5 length of apical blades. In L. canus the parameres have the lateral margin gradually narrowing toward apical blades, with the apical blades being triangular, the aedeagus gradually narrowing to tip, and extending beyond parameres by less than 1/5 length of apical blades. Moreover, the anterior clypeal margin of L. californicus is entire, whereas, in L. canus the clypeal margin is concave medially (Al Dhafer 2009). Adults are slender, black beetles, 8–12 mm long.

Limonius infuscatus Motschulsky 1859

Western Field Wireworm. This species is polyphagous and its reported host range is the same as L. californicus. It is a common and apparently widespread species across

North America. Limonius infuscatus is most similar to L. agonus and L. subauratus and can be identified by the male genitalia. There is no specific information about its biology, morphology or life history.

Limonius canus LeCount 1853

Pacific Coast Wireworm. This species is polyphagous, and its reported host range is the same as L. californicus. This species is found in western North America, especially abundant along the Pacific Coast from Washington south to California (Al Dhafer 2009;

Johnson 2009; Bousquet 1991). Adults of L. canus are about 8 to 12 mm long, reddish brown to black, with a prothorax that has pointed posterior tips. There is no specific information about its biology, morphology or life history. 24

Hypnoidus bicolor (Eschscholtz 1829)

[No common name]. This species is polyphagous, its main hosts being cereals, potatoes and sugarbeet. This species has one of the widest ranges and distributions of any of the known species of Hypnoidinae. In western North America (excluding Mexico), it is present from Alaska to California including Arizona, Nevada, Utah, Idaho and

Montana. In the northeastern United States is present in Massachusetts, New York,

Maine and New Hampshire. In the northcentral states, it is found in North and South

Dakota, Minnesota, Wisconsin, Illinois, Indiana, Michigan and Ohio. Hypnoidus bicolor has been detected in all Canadian provinces and the Yukon and Northwest Territories

(Johnson 2009; Bousquet 1991). Where both sexes occur, adults of both sexes are active at the same time, April to July. Doane (1961) using pitfall traps, captured more females than males in a 2:1 ratio. Populations in some areas are apparently parthenogenetic.

Adults are small (4-6 mm in length), bicolored reddish and brown-black click beetles with most of the pronotum black and the hind angles of the pronotum and all of the elytra reddish-brown. Larvae are cylindrical, elongate, somewhat flattened, and at later stages, are 4.8-8.4 mm in length and 1.2 mm in width.

Aeolus mellillus (Saylor 1836)

Flat Wireworm. This species is generally distributed in North America, mostly in the east and south (Johnson 2009; Bousquet 1991). Jewett (1940) reported the overwintering stages are adults and larvae. It appears from rearing records that the adult group is composed in part of adults from the previous season mixed with the emerging spring-brood adults. The spring-brood adults are those that develop from overwintering 25 larvae. These included both first- and second- generation larvae of the previous season.

The time of the whole life cycle varied considerably from 53 to 108 days for the first generation of the year: 7 to 16 days in the egg stage, 36 to 82 days as larvae, and 8 to

23 days as pupae. For overwintering larvae, the total life cycle was 276 to 369 days: 9 to

20 days as eggs, 248 to 350 days as larvae, and 8 to 18 days as pupae (Jewett 1940).

Bryson (1930) and Stirrett (1936) report a life cycle of one year and Forbes (1892) reported a life cycle of two years. Forbes (1891, 1892) also suggested that the adults do not overwinter in the pupal cells because he found adults under different kinds of litter in the field. Aeolus mellillus is parthenogenetic, several authors having collected only females in different places (Jewett 1940; Forbes 1891, 1892; Stirret 1936). However,

Brown cited by Stirret (1936) reported a collection of males in Kansas State. Adults emerge in May and live for several weeks. The eggs are oviposited in highly aggregated batches (Doane 1977b).

The larva is distinguished from other common wireworms by its flatness, small size, softness of texture and light yellow color (Jewett 1940). The adults are small, 5–8 mm in length, reddish-orange and black with a variably-sized black patch on the pronotum and a variable amount of black on the elytra. Tarsal claws have a basal seta, tarsal segments lack ventral lobes and the frontoclypeal carina is complete (Jewett 1940).

Selatosomus aeripennis (Kirby 1837)

Prairie Grain Wireworm. This wireworm is best known as a wheat pest. Barley, canola, flax, oats, rye, sugarbeet, and sunflower crops can also be injured. In addition, they have a wide host range including many vegetables: bean, carrot, corn, lettuce, lima 26 bean, onion, potato, tomato, and probably many others. Selatosomus spp. also feed on other insects, such as fly larvae (Zacharuk, 1962).

These native species are cool weather wireworms, and principally western in distribution. They cause damage in the United States from Oregon and Washington east to the northcentral states. In Canada, S. aeripennis is destructive in British Columbia, the

Prairie Provinces, and north into the Northwest and Yukon Territories.

Duration of the egg stage is about 30 days, with hatching occurring in June.

Young larvae are white, but soon turn yellow. When larvae hatch they measure about 1.5 mm long, but eventually attain a length of about 18-20 mm. Larvae feed on rootlets and roots, usually molting twice per year with a range of 1-5 molts per season (Johnson

2002). Pupation occurs in the soil at a depth of 15-25 cm, in a small cell formed by the larva. Duration of the pupal stage is only about 10 days, but beetles remain in the cell until the following spring when they dig to the surface. The adults become active in the spring, usually May, when the soil attains a temperature of at least 10˚C and air temperature reaches 18-20˚C. Males are active earlier than females and the m:f ratio is

6:1 and 8:1 (1959 and 1960, respectively) (Doane 1961). Adults are relatively short lived, usually perishing after 3-4 weeks. The adults seem not to feed or, if they do, will feed only slightly. The average number of eggs per female ranged from 261.0 to 946.0 (Doane

1961). Young larvae are white, but soon turn yellow. The head, thorax, and anal plate are yellowish brown. As is the case with most wireworms, they are shiny in appearance and the thoracic legs are not pronounced (Zacharuk 1962). The adults are small- to medium- sized (8-16 mm in length) black or black and iridescent green-blue click beetles with few 27 setae. The elytra are black or iridescent and the pronotum is black. The tarsal segments lack ventral lobes, tarsal claws lack setae, frontoclypeal carina is incomplete (appearing as carinae above the antennal socket), and the pronotum and elytra lack conspicuous setae

(Zacharuk 1962).

Table 2.1. Distribution of wireworm species that are economically important in agricultural fields in North America. Species Distribution Author

Agriotes lineatus Canada: BC, NS, NF, PE Bousquet 1991; Vernon and Päts 1997; LaGasa et al. 2006; United States: WA, OR Andrews et al. 2008; Vernon et al. 2001

A. obscurus Canada: BC, NS, PE, NF Bousquet 1991; Vernon and Päts 1997; LaGasa et al. 2006; United States: WA, OR Andrews et al. 2008; Vernon et al. 2001

A. sputator Canada: AB, NB, NS, PEI, SK Bousquet 1991; Vernon and Van Herk 2013b

A. mancus Canada: AB, SK, MB, ON, PQ, NB, Bousquet 1991 NS, PE, LB.

United States: ME, NY, PA, NJ, MI

Limonius californicus Canada: BC, AB, SK, MB Al Dhafer 2009; Bousquet 1991 United States: CA, ID, MT, OR, WA.

L. canus Canada: BC, AB, SK, MB Al Dhafer 2009; Bousquet 1991 United States: CA, ID, MT, OR, WA.

L. infuscatus Canada: BC, AB Al Dhafer 2009; Bousquet 1991 United States: CA, FL, ID, IL, IN, IA, MA, MO, MT, NE, NH, OR, PA, RI, SD, UT, WA 28

Table 2.1. continued

L. ectypus Canada: SK, MB Majka et al. 2011; Bousquet 1991 United States: CT, MA, ME, NH

Ctenicera Canada: AK, YK, NT, BC, AB, SK, Bousquet 1991 destructor/aeripennis MB

United States: all continental states

C. lobata Canada: AK, NT, BC, AB, SK, MB, Bousquet 1991 ON, PQ, QC, NB, NS, NF

C. glauca Canada: BC, AB, SK Bousquet 1991; Morrill 1984; Toba and Campbell 1992 United States: OR

C. pruinina Canada: BC. Bousquet 1991; Toba and Campbell 1992 United States: OR, ID

Aeolus melillus Canada: NT, BC, AB, SK, MB, ON, Doane 1977b; Downie and PQ, QC Arnett 1966; Bousquet 1991

United States: CT, IN, ME, MD, NH, OR, PA, RI

Melanotus communis Canada: ON, PQ EPPO 2005a; Bousquet 1991

United States: AL, AZ, AR, CO, FL, GA, IL, IN, IA, LA, MO, NE, NY, NC, OH, PA, SC, SD, TX, VA

Hypnoidus abbreviatus Canada: AK, YK, BC, AB, SK, Bousquet 1991 MB,ON, PQ, NB, NS, PE, NF United States: IA, ME

H. bicolor Canada: AK, YK, NT, BC, AB, Bousquet 1991 SK, MB,ON, PQ, NB, NS, LB

H. impresicollis Canada: AK, YK, NT, BC, AB, Bousquet 1991 MB,ON, PQ, LB, NF

H. leei Canada: AB Bousquet 1991

7 2 7 4 1 2 3 8

Total Total Citations 4 4

6,37

40,65

Melanotus

2 4 6

42 16 11

Limonius 6

6 6 6 6 6

Ctenicera 6

6 6

6,21,

22,37,66

Conoderus 6

6 3 6

Agriotes 6 6

Aeolus 6

47 17 18

,58

17,18,52

No ID No 18 18

Celery

Crop Beets Chard Spinach Onion Carrot Lettuce Escarole Guayule Sunflower Broccoli Cabbage Cauliflower Gladiolus Horseradish Turnip Sweet potato

2. Wireworm species have been reported in the literature to damage crops representing 16 different plant plant families. representing 16 different to damage species crops have been 2. Wireworm reported literature in the

Table Table in the section. correspondcitation to literature in the table the sources Numbers Plant Family Amaranthaceae Amaryllidaceae Apiaceae Asteraceae Brassicaseae Convolvulaceae

4 4 4 9 3 1 4 2 1 1

2 12 2,6 33,34 45

6 45 6

6 6 6

6 6

28,29

17,63 17,27,35 13,15 17,23,30 57 17 17,46 17

Cantaloupe Cantaloupe watermelon Cucumber Cucurbits Gladiolus beans Dry Soybeans Chick pea Lentil Garden pea Green Beans Peas Mint Flax Okra Cotton,

continued continued

Table 2 Table Cucurbitaceae Iridaceae Fabaceae Lamiaceae Linaceae Malvaceae

8 6 5 2

11 13 1

6 6

6,8,20

,25,26,31

6,65 6,65

2,6,11

6,38 2,6,49,56

6 6 6

9, 56

6 6,4

6 6 6

6,60 6

6 6

6,14

6 6

8,25

5,9,17

17,43,44 17,32,53

18,19,59 50,61 41

Barley Wheat Wheat Barley Rye Oates Milo Sorghum Corn Field Strawberry Tomatoes, Pepper Potato Grape Wine

continued continued

Table 2 Table Poaceae Rosaceae Solanaceae Vitaceae 32

Figure 2.1. Number of publications (5 year moving average) listed on the Web of Knowledge (Thomson Reuters. 2010) using the search terms “wireworm” and “Elateridae” and “click beetle”, from 1920 to 2010.

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CHAPTER THREE

AN EVALUATION OF FOUR DIFFERENT BAIT TRAPS FOR SAMPLING WIREWORMS (COLEOPTERA: ELATERIDAE) INFESTING CEREAL CROPS IN MONTANA

Contribution of Authors and Co-Authors

Manuscript in Chapter 3

Author: Anuar Morales-Rodriguez

Contributions: Conceived and implement the study design the data collection and analysis. Collected and analyzed data. Wrote the manuscript.

Co-Author: Kevin W. Wanner

Contributions: Provided feedback in the study design, data analysis and comments to the manuscript.

Manuscript Information Page

Anuar Morales-Rodriguez, Kevin W. Wanner Journal of Economic Entomology. Status of Manuscript: X Prepared for submission to a peer-reviewed journal Officially submitted to a peer-review journal Accepted by a peer-reviewed journal ____ Published in a peer-reviewed journal

Published by Entomological Society of America.

Abstract

Wireworm population assessments can be separated into absolute and relative sampling methods. Absolute sampling methods, such as soil coring to extract wireworms in situ from their soil habitat, typically involve a higher level of expertise, time, infrastructure and associated expense. Selecting the best type of sampling protocol depends specifically on the sampling objective, be it simple detection, species census/survey, population estimation, or threshold-based monitoring. The efficacy of four different types of baited trap was evaluated in four commercial cereal fields in Montana.

Pitfall and stocking traps were the most efficient, followed by pot and canister type traps.

A total of 5,097 wireworms were collected from the four sites during 2010 – 2012 including seven species: Aeolus mellillus, Agriotes spp., Dalopius spp., Hypnoidus bicolor, Limonius californicus, L. infuscatus, and Selatosomus aeripennis.

KEY WORDS: Aeolus mellillus, Agriotes spp., Dalopius spp., Limonius californicus, L. infuscatus.

Introduction

Wireworms, the larval stage of click beetles (Family Elateridae), are becoming a serious soil pest of many different field crops. A multiyear larval stage and broad host range can make wireworms a perennial problem for crop production, where they can feed on and damage the seeds and developing seedlings, as well as underground tubers and aboveground fruit in contact with the soil. Historically wireworms were common pests of a wide variety of field crops worldwide (Comstock and Slingerland 1891, Toba and

Turner 1983, Seal et al. 1992, Kohno and Miyai 1993, Parker and Howard 2001). With the exception of some species of economic importance to agriculture, little is known about their biology.

Wireworms, regardless of species, were managed effectively for many decades with inexpensive insecticides applied to the soil or as seed treatments (Toba et al. 1985).

However, most of these original insecticides have been removed from the market in favor of newer and safer alternatives, such as the neonicotinoid class of insecticide.

Unfortunately, the efficacy of these new insecticides can be poor and producers are still in need of effective management tools (Vernon et al. 2013). New alternative approaches based on the principles of Integrated Pest Management (IPM) are needed, but the first critical step, pest species identification, remains largely unknown. For example, in

Montana, a survey of adult beetles found 155 species (Seibert 1993), but no surveys of the damaging larval stage have been completed. Sampling protocols for IPM are required

53 to monitor and identify the pest as well as establish thresholds for treatment (Furlan

2005).

Insects with a subterranean habitat are especially difficult to monitor and control.

Wireworms may burrow and live as deep as 1.5 m below the soil surface (Andrew et al.

1962, Doane et al. 1975, Toba and Turner 1983, Parker 1996). Selecting the best type of trapping, timing and sampling protocols depends specifically on the sampling objective, be it simple detection, species census/survey, population estimation, or threshold-based monitoring. Assessments of wireworm populations in the soil can vary radically both spatially and temporally (Parker 1996, Simmons et al. 1998, Horton 2006). The realities and limitations of wireworm sampling need to be considered carefully when being used to provide management recommendations.

Wireworm population assessments can be separated into “absolute” and “relative” sampling methods (Southwood 1979). Absolute sampling methods, such as soil coring to extract wireworms in situ from their soil habitat, typically involve a higher level of expertise, time, infrastructure and associated expense. The main objective of absolute sampling for wireworms has historically been to estimate the population size, spatial distribution (horizontal and vertical) and temporal activities of wireworms in a field.

This has typically involved removing field soil in layers (Gibson 1939, Salt and Hollick

1944) or by soil coring (Yates and Finney 1942, Anon. 1948) at various depths and at 54 enough locations in a field over time that wireworm population estimates can be made with reasonable accuracy.

Relative sampling methods, including the use of attractive baits or traps to draw wireworms from variable distances in the soil, are also used for research purposes, but have mostly been developed with the intention of providing indications of wireworm presence and relative abundance for use in management programs. The time required to examine soil samples, and the large number of samples required to accurately estimate wireworm populations in fields, has led to the development of several attractant-based sampling methods in North America and Europe (Parker and Howard 2001). Wireworm larvae are attracted to sources of CO2 production (Doane et al. 1975) such as germinating seeds, respiring plants, and decomposing plant material. Of the large number of CO2 - producing baits tested, including fruits and vegetables (eg., melons, carrot, potato) and processed cereals (eg., bran, rolled oats, flour), germinating cereal seed (eg., wheat, barley) and/or other seeds (eg., corn, sorghum) have been found most effective and are now most commonly used (Bynum and Archer 1987, Jansson and Lecrone 1989, Parker

1994, 1996; Simmons et al. 1998, Parker and Howard 2001, Horton and Landolt 2002,

Vernon et al. 2003, Furlan et al. 2010). Wireworms can detect distinct CO2 gradients from different distances. Doane et al. (1975) found that wireworms C. destructor (= S. aeripennis) can detect and orient to CO2 sources from as far away as 20 cm, and Vernon et al. (2000) showed that the majority (83%) of wireworms (A. obscurus) in field plots will orient to trap crops of wheat spaced one meter apart.

Various methods of improving the efficacy of bait traps have been developed, such as covering the baits at the soil surface with black plastic (Ward and Keaster 1977,

Chabert and Blot 1992, Simmons et al. 1998, Esser 2010) or charcoal dust (Ward and

Keaster 1977, Bynum and Archer 1987). These approaches raise soil temperature and thus CO2 production by encouraging the germination of living baits (eg., wheat and corn seed) or the microbial respiration in non-living baits (eg., bran, rolled oats, flour). This has facilitated earlier trapping and higher catches for some species (Ward and Keaster

1977, Bynum and Archer 1987), but has also increased the time and cost of sampling, which may not be feasible for all monitoring strategies.

As a first step towards identifying the economically important wireworm species infesting wheat and barley cropland in Montana, this study will compare the efficiency of four different types of bait traps in four commercial small grain fields in Montana.

Materials and Methods

Insect Sampling

Four different bait traps were compared: 1) A 1.3 liter plastic canister with 6 mm diameter holes evenly distributed over the surface and separated by ~25 mm, 2) A 1-liter plastic planting pot with eight holes (10 mm diameter) on the bottom, 3) A small pantyhose stocking (Foot Sox®, Montana Leather, Billings, MT), and 4) A traditional baited pitfall trap 25 cm deep and 20 cm wide. Each trap, with the exception of the stocking, was filled with peat moss (Sunshine®) and baited with 120 g of a 1:1 mix of

56 wheat and barley seed placed between two layers of peat moss. Stockings were filled with 120 g of the seed mixture only (Figure 3.1.). The seed mixture (traditional pitfall and planting pot traps), or the whole trap (canister and stocking traps), was soaked in water for 24 hours prior to field placement, to facilitate seed germination. All traps were buried

5 cm below ground surface. With the exception of the canister, all traps were covered with a 0.093 m2 black plastic sheet secured with four sod staples. Each of the four traps was placed within 30-45 cm of each other in an arbitrary order and each set replicated 10 times, in a line with each set separated by 4-5 meters (Figure 3.1.). The traps were recovered 14 days after being deployed and stored at 4˚C. Sampling began when the soil temperature reached 7-10˚C at a depth of 5 cm and continued until the end of the summer. Each sampling date a new parallel line of traps was deployed approximately 5 meters distant from the line of traps that was removed. In this way, a season with 9 sampling dates occupied an area of about 60 meters in length and 40 meters in width. The sampling was repeated for three years at four different field sites. The same area was used each of the three years that the study was conducted, with exception of the Bozeman field in 2012. Larvae were sorted from the traps, labeled, and preserved in 95% ethanol for future identification. Species were identified by the authors using the morphological characteristics describes by Etzler (2013) and personal consultation with Frank Etzler, a wireworm taxonomist resident at the Montana Entomology Collection. The four locations are located in commercial fields and were selected for their wireworm history, different elevation and soil types, listed in Table 3.1.

Data Analysis

Total number of larvae per trap, date and site were evaluated for normality and transformed with log(X). Relative variation values determined the precision of each trap using mean larvae counts pooled for location, year and month. The formula RV = (SEM / mean) x 100, where SEM = standard error of the mean. Data were analyzed by Proc Mix procedure using SAS 9.3, as least-square means (LSMEANS statement), where repetition was treated as a random factor and treatment and species were treated as fixed factors within a repeated-measures design, for each field site and year. For each location and year the effect was evaluated for the main species present and the minor species were pooled as “others”. Limonius californicus was the main species infesting the commercial fields located near Denton and Toston and L. infuscatus for Bozeman. At the Conrad site there were two main species co-infesting the field, L. californicus and H. bicolor.

Results

Total Catches

From spring to the end of summer, 880 baited traps were processed from four different fields in Montana during 2010, and 840 in 2011 and 2012. Pitfall and stocking traps caught more total wireworms (n =1625 and 1575 larvae, respectively) compared to pot and canister type traps (n = 1173 and 725 larvae, respectively). Average catches for each trap type ranged from 2.46 to 1.16 and were significantly different (F3, 2560 = 11.41;

P < 0.0001) (Figure 3.2) when all field sites, years, sampling dates and species were

58 pooled together. Average trap catches using pooled data support an efficiency relationship where: pitfall = stocking  pot > canister (Figure 3.1.). However, ANOVA analysis detected significant interaction effects between trap*species (F15, 15364 = 3.11; P <

0.0001), location*year (F3, 15364 = 73.75; P < 0.0001), location*sample date (F3, 15364 =

33.75 P < 0.0001), location*specie (F15, 15364= 84.48 P < 0.0001), year*sample date (F1,

15364 = 63.19; P < 0.0001), species*year (F5, 15364= 157.4; P < 0.0001) and sample*species

(F5, 15364 = 37.47; P < 0.0001). The data was further analyzed separately for each field site and year using a Proc Mix as described in the methods section (Tables 3.2, 3.3, 3.5, 3.6,

3.7, 3.9, 3.10, 3.11, 3.13, 3.14 and 3.15). For all field sites and years, trap type was a significant factor (Tables 3.2, 3.3, 3.5, 3.6, 3.7, 3.9, 3.10, 3.11, 3.13, 3.14 and 3.15), with exception of Denton in 2011 (F3, 351 = 1.43; P = 0.22) and 2012 (F 3, 351 = 1.47; P = 0.22) and Toston 2010 (F3, 288 = 1.39; P = 0.25).

The collection dates varied between years and location. Each year sampling started when the soil temperature reached about 7 -10˚C, which varied by location and year. In some cases the sampling date was also influenced by the production practices

(planting date, tilling, irrigation etc.) carried out in the commercial field. For the

Bozeman and Toston sites four collection dates were analyzed, and five dates for the

Conrad and Denton sites.

Bozeman. Limonius infuscatus was the predominant species trapped at this location (Table 3.4). Average trap catches of L. infuscatus were generally higher in 2011 compared to 2010 and higher during the first two sampling dates of both years. A total of

1095 wireworms were collected from traps deployed in Bozeman, 216 in 2010, 866 in

2011 and 13 in 2012. Of the 216 wireworms collected in 2010, 50.9% were collected on the first date, 26.9% on the second, 16.7% on the third and 5.6% on the fourth date. Of the 823 wireworms collected in 2011, 35.7% were collected on the first date, 51.0% on the second, 12.2% on the third and 1.6% on the fourth date. The 2012 sampling year was not analyzed since the trap catches were very low.

In both 2010 and 2011, trap (F3, 279 = 22.34; P < 0.0001 and F3, 279 = 25.43; P <

0.0001, respectively for each year) and sampling date (F3, 279 = 45.38; P < 0.0001 and F3,

279 = 88.50; P < 0.0001, respectively for each year) were significant factors affecting total catches of L. infuscatus and “other” species. There was a significant interaction between the factors trap*sampling date (F9, 279 = 5.39; P= 0.0012 and F9, 279 = 2.57: P < 0.0075) for

2010 and 2011, respectively, and trap*species (F3, 279 = 10.87; P < 0.0001) for 2011 but not for 2010 (Tables 3.2 and 3.3). Because of this interaction, the average catches displayed in Table 3.4 are calculated separately for each sampling date and each species.

Statistically significant differences (Tukey’s test) between average catches of L. infuscatus for the four different trap types was detected during the first of four sampling dates in 2010 and the first 3 of 4 sampling dates in 2011 (Table 3.4). The general pattern of efficacy between the four trap types was the same as that observed using pooled data

(Figure 3.2), pitfall = stocking  pot > canister. Catches of “other” species never exceeded an average of 0.8 and statistical differences between trap types were not detected.

Conrad. At this location, two wireworm species dominated the trap catches, L. californicus and H. bicolor (Table 3.8). Trap catches were generally highest in 2010. 966 wireworms were collected from the four traps types deployed in Conrad, 610 in 2010,

211 in 2011 and 143 in 2012). Of the 189 wireworms collected in 2010, 30.2% were collected on the first date, 46.0% on the second, 14.3% on the third, 2.1% on the fourth and 7.4% on the fifth date. During 2011, 3.4% of the total number of wireworms was collected on the first date, 0.7% on the second, 25.4% on the third, 38.5% on the fourth and 32.3% on the fifth date. In 2012, 22.0% were collected on the first date, 0.7% on the second, 46.1% on the third, 22.0% on the fourth and 9.2% on the fifth date.

During all three sampling years trap type was a significant factor affecting catches

(F3, 540 = 15.16; P < 0.0001 for 2010, F3, 540 = 15.16; P < 0.0001 for 2011 and F3, 540 =

9.67; P < 0.0001 for 2012) (Tables 35-3.7). A significant interaction between the factors trap*sampling date and trap*species was also detected for all three years. The last 3 of 5 sampling dates in 2010, first 2 of 5 dates in 2011 and the third sampling date in 2013 yielded higher averages in general. During 2010, the last two sampling dates yielded statistically significant differences between trap types for average catches of L. californicus, H. bicolor and “other” species (Table 3.8). The general pattern of trap efficacy was the same as that established in Figure 3.2, pitfall = stocking  pot > canister.

Significant differences between traps types were only detected for H. bicolor in

2011, during the first three sampling dates. During these sampling dates, the pattern of trap efficacy was more variable, possibly due to lower total trap catches. During the second sampling date, the stocking, pitfall and pot type traps were all equally effective 61

(Table 3.8). The canister trap was as effective as the pitfall and pot traps during the first sampling date. In 2012, significant differences between trap types were detected only for

H. bicolor at the first and third sampling dates. A general trend of higher catches in stocking and pitfall traps and fewest catches in canister traps was observed.

Denton. Limonius californicus was the dominant wireworm infesting this location

(Table 3.12). Trap caches was generally highest in 2010. 2403 wireworms were collected from the four traps types deployed in Denton, 2120 in 2010, 132 in 2011 and 151 in

2012. Of the 2120 wireworms collected in 2010 51.6% was collected on the first date,

6.3% on the second, 10.1% on the third, 19.3% on the fourth time and 12.8% was collected on the fifth date. During 2011 20.5% was collected on the first date, 2.3% on the second, 34.8% on the third, 26.5% on the fourth time and 15.9% was collected on the fifth date. In 2012 0.0% was collected on the first date, 43.8% on the second, 36.2% on the third, 11.5% on the fourth time and 8.5% was collected on the fifth date.

Trap type was a significant factor affecting catches in 2010 (F3, 359 = 5.31; P =

0.0014) and 2012 (F3, 359 = 8.67; P < 0.0001), but was not significant in 2011 (F3, 359 =

1.47; P = 0.2225) (Tables 3.9-3.11). There was not a significant interaction between the factors trap*sampling date and trap*species was observed for any of the three sampling years (Tables 3.9-3.11). Because of the lack of interaction, average catches displayed in

Table 3.12 are pooled for species and sampling date. ANOVA analysis of the pooled data found trap type was significant factor affecting catches in 2012 (F3, 239 = 4.80; P =

0.0029), but not in 2010 (F3, 279 = 1.13; P = 0.264) or 2011 (F3, 239 = 1.92; P = 0.127). In

2012, socking traps caught more wireworms followed by pitfall, pot and canister type traps (Table 12).

Toston. Limonius californicus was the dominant wireworm infesting this location

(Table 16).Trap caches were highest in 2011 and 2010 than in 2012. 663 wireworms were collected from the four traps types deployed in Toston, 217 in 2010, 351 in 2011 and 95 in 2012. Trap type was a significant factor affecting catches in 2011 and 2012 (F3, 279 =

4.09; P = 0.0073 and F3, 279 = 6.40; P < 0.003 for each year respectively), but was not significant in 2010 (Tables 3.13-3.15). Of the 217 wireworms collected in 2010, 29.9% was collected on the first date, 21.9% on the second, 31.6% on the third, and 16.7% on the fourth sampling date. During 2011 20.5% was collected on the first date, 2.3% on the second, 34.8% on the third, 26.5% on the fourth time and 15.9% was collected on the fifth sampling date. During 2012, 32.9% was collected on the first date, 46.1% on the second, 10.5% on the third, and 10.5% on the fourth time sampling date.

During the first two years of sampling 2010 and 2011 was not a significant interaction between the factors trap*sampling date and trap*species for any of the three sampling years, was observed. Data were pooled for species and sampling date, however, no effect was detected for 2010 (F3, 159 = 0.1812; P= 0.1812) and in 2011 differences among the traps (F3, 39 = 4.802; P= 0.0065) were only found in at the first collection date

(05/19/2011 to 06/02/201) for L. californicus (Table 3.16). Pitfall traps were more efficient followed by stocking, canister and pot. With the other group of wireworm

Species, no differences were observed (Table 3.16). Trap type was a significant factor affecting catches only in 2012 (F3, 199 = 3.40; P = 0.0187). Differences among the traps were found in the first (05/11/2012 to 05/23/2012) collection date for L. californicus.

Pitfall traps were more efficient followed by stocking and canister and the less efficient were the pot traps. With the other group of wireworm species, no differences were observed (Table 16).

Relative Variation

Precision of insect traps is most commonly measured by relative variation were variability is expressed as a percentage of the ratio of the standard error of the means to the mean (Buntin 1994). Lower relative variation values were observed for all traps in all locations during 2010 and 2011, while in 2012 higher values were observed for canister

(38-70) and pot traps (21-100) in all locations (Figure 3.5). During all three years, lower values were observed for stocking and pitfall traps and the low values were consistent for location, sampling time, repetition and year. However, in 2012 high relative values were observed in Bozeman, because number of wireworms collected was low (13). Relative variation across values changed as the growing season progressed. For example, in 2010 in Bozeman relative variations was lower (20-45%) for the first collection time and higher (30-55%) for the second through fourth collection dates. In Conrad during 2010, higher relative variations were observed for the first collection date (35 to 70%) but from the third through the fifth collection dates relative variations declined, increasing again

64 during last two collection dates. In Denton relative variations values were generally lower compared to the other three sites, but trends in relative variations was similar. At early sampling dates relative variations was 13 – 22%, increasing slightly during the middle of the season (30 – 40%) and decreasing slightly at the last collection time (20 – 30%). In

Toston, the relative variation was high for all collection dates (40 to 60%) (Figure 3.5).

Species Diversity

A total of 5097 wireworms were collected from the four sites during 2010 – 2012.

In 2010, 3135 wireworms comprised of five species were collected; 1560 wireworms comprised of 5 species in 2011; and 402 wireworms comprised of 6 species in 2012.

Aeolus mellillus, Agriotes spp. Dalopius spp., Hypnoidus bicolor, Limonius californicus and L. infuscatus were the six species collected. Limonious californicus, L. infuscatus and

H. bicolor were the most common species collected. Limonius californicus was the dominant species in Denton (97.4, 85.2 and 77.1% of the total of wireworm population, respectively, for 2010, 2011 and 2012) and Toston (99.3, 96.8 and 97.5% of the total of wireworm population, respectively, for 2010, 2011 and 2012). Limonius infuscatus was the dominant species in Bozeman (83.8 and 89.0% of the total of wireworm population, respectively for 2010 and 2011). At the Conrad site, two wireworm species were co- dominant. Hypnoidus bicolor was slightly more prevalent during the last two years of the study (53.7 and 52.4% of the total of wireworm population, respectively, for 2011 and

2012), while L. californicus was more prevalent in the first year (60.4% of the total of wireworm population in 2010). Aeolus mellillus was collected at all four locations as a minor component of the total catches. Agriotes spp. and Dalopius spp., collected in

Bozeman, Conrad and Denton, were uncommon.

The percent distribution of each species was tabulated for each trap from data pooled from all sites and all years. ANOVA results reported for canister and pot traps were similar, but different from the pitfall and stocking traps that were also similar to each to other (Figure 3.1). Based on this observation, an a priori 3x2 contingency table of pooled data (canister and pots pooled =close and pitfall and stoking pooled = open) was analyzed (in this analysis the other species making up a minority of the total catches were not included). The distribution of the three species caught was not independent of trap type (Chi-square = 94.91; P <0.0001) (Table 3.17). Open traps combined caught a smaller proportion of L. californicus (13.3% fewer) and higher proportions of H. bicolor

(3.7%) and L. infuscatus (9.8%), compared to canister and pot traps.

Discussion

Four different baited traps were evaluated for relative sampling of wireworms infesting cereal crops in Montana. Each trap differed in its design, related to ease of use and ability to trap wireworms. Two trap types were an open design (traditional pitfall and stocking traps), one was closed (canister) and one was semi-closed (pot). The semi-closed pot design has a total surface area of 478.1 cm2, with 23.5% of the surface area open,

1.3% in holes at the bottom of the pots and 22.4% on the open top that is buried 5 cm below the soil surface. The closed canister trap design has a larger surface area (751.5

2 cm ) and only 0.8% of the surface area is open for attractive CO2 to leave and wireworms to enter. Open style traps released attractive CO2 from the germinating seed freely from all directions, and wireworms could enter and leave the trap from any direction. The canister released CO2 from holes drilled through the side, through which wireworms could enter, but would have much less probability of leaving, because of limited exit points and the lack of external attractant. A canister trap can be considered a cumulative trap; wireworms enter but are unlikely to exit. Pot traps are semi-closed, with eight larger open holes on the bottom, and an open top buried 5 cm below the soil surface, through which CO2 can exit and wireworms can enter.

Important characteristics of baited traps used for research or pest management decisions are: consistency among traps; some control over CO2 production; ease of trap assembly and deployment; and rapid, accurate methods of wireworm extraction. Of the methods developed, Vernon et al. (2009) have found that traps similar to those described by Chabert and Blot (1992) adequately meet these criteria. These consisted of 450 ml plastic pots filled with medium grade vermiculite, and with 100 ml each of untreated corn and hard red spring wheat spread in layers in the middle of the pot. The traps were soaked in warm water and within 24 hours placed in 15 cm deep holes, covered with soil on all sides and retrieved after 12-14 d. Vernon et al. (2009) found that all sizes of Agriotes spp. wireworms could be extracted effectively using Tullgren funnels. The potted traps used in this study were similar with the exception that corn was not used as bait. In this study, 67 traps with an open design (traditional and stocking traps) consistently caught the most wireworms, followed by a semi-open design (pots) while the closed design, canisters, caught the fewest. These results are consistent with the hypothesis that greater CO2 release will attract more wireworms, and that open designs may be more effective at detecting wireworms when their populations are low. However, Parker (1996) perforated the surface of plastic pots (350 ml size) with 24 evenly spaced holes (4 mm diameter) and filled the traps with a mix of soil and cereals. This custom pot design caught the same number of wireworms as the traditional design. The additional holes may have released more attractive CO2 and the wireworms can enter through the open top, compared to our canister design.

A second variable associated the bait trap design is the amount of surrounding soil that is collected with the trap. The open traps used in this study collected the largest volume of soil, because the germinating bait was free to expand, and surrounding soil adhered to the developing roots. This was not the case for bait that was enclosed within a plastic pot or canister, soil did not adhere to the outside and the volume sampled was smaller and always consistent in size. However, the larger volume of soil sampled by the pitfall and stocking traps does not appear to explain their higher trap catches. While pot and canister traps were similar in size and the volume of soil sampled, the potted traps caught more wireworms. In a previous study Kifman et al. (1986) showed no significant differences in wireworm’s caches among different traps with pot and when in the analysis include the wireworms from the soil around the pot trap significant differences were found. These results suggest that the degree of open design, for attractive CO2 to exit and 68 wireworms to enter, was the most important variable influencing total trap catches. We cover the traps with a black plastic sheet to increase temperature (very important especially early in the spring), to increase germination rate and CO2 production and also provide a refugee to the insects once they localize the trap. Several other authors used the same strategy covering traps with black plastic (Ward and Keaster 1977, Chabert and

Blot 1992, Simmons et al. 1998, Esser 2010) or charcoal dust (Ward and Keaster 1977,

Bynum and Archer 1987). Canister traps was the only trap of the four that was not cover with the black plastic sheet and could explain in part the differences in caches with the other traps especially early in the spring.

Trap consistency is another important variable to consider. One suggestion is that traps used for pest management decisions should have a relative variation value less than

25% (Pedigo 1990). We calculated relative variation values for each trap type at each of the four locations and three sampling years (Figure 3.2). With one exception, the relative variation of each trap type at all four sites was below 25% during 2010 and 2011. During

2012 the relative variation exceeded 25% from more than half of the observations, and was particularly high at the Bozeman site. With the exception of Denton in 2011, these four experimental sites in 2012 caught the fewest number of wireworms, only 13 or all four traps types in Bozeman. These results are consistent with the fact that the relative variation decreases with increasing trap catches (Simmons et al. 1998). The lowest relative variation values were observed at Conrad and Denton in 2010, and Bozeman in

2011 that had the highest trap catches (Figure 3.2). This trend is confirmed when the relative variation is calculated for all sites combined within a sampling year. In 2010, 69

3135 wireworms were collected and the relative variation was 20.7%, in 2011, 1560 wireworms were collected and the relative variation was 18.5%, and in 2012 only 402 wireworms were collected and the relative variation was 41.5%. Simmons et al. (1998) also noticed that the accuracy of each relative sampling method improve when wireworm population was high and also suggested to improve precision levels more samples should be taken by area.

At least six different species of wireworm have been found infesting Montana’s cropland in various combinations (Morales et al. 2014; Chapter 2). Species-specific wireworm biology and ecology is not well known, but differences in larval behavior between the species are expected. An ideal wireworm trap would catch all pest species equally, but studies comparing trap efficiency as a function of wireworm species have not been reported. In this study a total of 6 species were identified among the wireworms caught by the four different trap types: Limonius californicus, L. infuscatus, Hypnoidus bicolor, Aeolus mellillus, Agriotes spp and Dalopius spp. The distribution of wireworm species between trap types was analyzed for all catches pooled between sites and years.

Aeolus mellillus, Agriotes spp and Dalopius spp. were pooled into a single group that constituted only 3 – 6% of the species caught (Table 17). The distribution of wireworm species among trap types was not independent of trap type (P<00001). Interestingly, the proportion of L. californicus, L. infuscatus and H. bicolor caught by the closed and semi- closed style traps (canister and pot traps) was almost identical, and the open style traps

(pitfall and stocking traps) differed by no more than 2% (Table 3.17). Rather, the open style traps caught proportionally more H. bicolor and L. infuscatus and less L. 70 californicus compared to the closed and semi-closed style. These proportional results could be explained by an increased attractiveness of the open trap to some species, or, by differential species-specific movement into and out of the open style trap. Since the canister traps should reflect a cumulative catch, two hypothesis are likely: 1) H. bicolor and L. infuscatus have a higher threshold for CO2 attraction, and proportionally are more attracted to the open style traps that releases more CO2, or 2) L. californicus is leaving the open traps at a higher frequency compared to H. bicolor and L. infuscatus. This is the first study to demonstrate the potential for species specific wireworm catches based on trap design.

Desirable factors associated with sampling methods include minimum implementation and labor cost, maximum sample precision and reliability and maximum sample efficiency (Kirfman et al. 1986). Based on these criteria stocking traps are the best choice for the sampling wireworms in small grains fields in Montana. The disposable stocking are inexpensive to purchase, easy to assemble and deploy, and they contain the germinating bait in a single ball. Traditional traps are similarly easy to use, but are much messier to collect since germinating seed is not contained. Pot style traps also contain the germinating seed, but take more time to deploy and collect and provide no advantage over stocking traps. Plastic canister traps were the most expensive trap to construct, and caught the fewest wireworms, but their closed design may be better suite for certain research trials and surveys. They are easily mailed to and from collaborating producers and they contain the wireworms in a cumulative catch.

Our research evaluated different traps baited with the same mix of cereal grains, and previous works evaluated the efficiency of different baits with the same type of traps, usually pitfall (Doane 1961, Brown and Keaster 1986, Horton and Landolt 2002). The wireworms move toward the bait oriented by the different gradients of CO2 (Doane

1961). The CO2 resource could be germination of living baits (e.g., sorghum, wheat and corn seed), the microbial respiration in non-living baits (e.g., bran, rolled oats and flour), vegetable pieces (e.g., carrots and potatoes) or fruits (e.g., melon). Cereal mixture of wheat and barley or wheat and corn soaked for 24 are the most effective in many crops

(e.g., corn, potato, wheat) (Onsager et al. 1975, Jansson and Lecrone 1989), and with many species (e.g., Melanotus cummins, Conoderus falli, C. amplicollis, C. rudis,

Agriotes spp. and Limonius spp.) (Parker 1994, 1996).

On average, all four sites exceeded the economic threshold (1 – 2 larvae per trap) and according Bechinski et al. (1994), Bozeman and Toston are in 50:50% of risk of economic damage and Conrad in "probably more than 50:50% risk of damage ", Denton will be in "Extreme Risk of Economic damage”, and it was always detected with pitfall, pot and stocking. Since canister was the least efficient of the four traps, the levels of the wireworm population detected could be sub estimated. However, they recognized that the economic threshold calculated is arbitrary and the recommendations are very conservative (Bechinski et al. 1994).

Acknowledgements

We thank Mark Grubb (Conrad, Pondera Co), Richard Barber (Denton, Fergus

Co) and Brian Tutvedt (Kalispell, Flathead Co) for allowing us to collect wireworms and plant field trials on their cropland. We also thank John Miller for his hard work planting and harvesting our field assays. We thank Emily Rohwer, Alix Bold, Branden Brelsford,

Ammiel Branson, Meghan McGauley, Ruth O’Neill, Diana Florian, Hannah Johnson, and

Laura Morales for their help in conducting this work. Paul S. Robbins provided comments to improve the manuscript. This study was supported in part by funds from the

Montana Wheat and Barley Committee, Montana Seed Potato Producers Association and

USDA Crops at Risk Grant 2010-51100-21547.

Table 3.1. Wireworm sampling location in Montana. Elevation in meters above sea level.

Location Elevation Crops (2010-2011-2012)* Irrigation Type soil Bozeman 1495 SW - SW – SW Non irrigated Clay-Sandy Conrad 1080 Barley – SW- SW Irrigated Clay Denton 1096 SW – WW- Lentils Non irrigated Clay-Sandy Tolston 1232 SW – WW – SW Irrigated Sandy * SW = Spring wheat, WW = winter wheat

Table 3.2. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Bozeman, MT in 2010.

Source Num df Den df F value Pr > F Trap 3 279 22.34 < 0.0001 Species 1 279 0.0 1.000 Time 3 279 45.38 < 0.0001 Trap*species 3 279 0.0 1.000 Species*time 3 279 5.47 < 0.0001 Trap*time 9 279 5.3975 0.0012 Trap*species*time 9 279 0.0 1.000

Table 3.3. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Bozeman, MT in 2011.

Source Num df Den df F value Pr > F Trap 3 279 25.43 < 0.0001 Species 1 279 361.41 < 0.0001 Time 3 279 88.50 < 0.0001 Trap*species 3 279 10.87 < 0.0001 Species*time 3 279 86.35 < 0.0001 Trap*time 9 279 2.57 0.0075 Trap*species*time 9 279 2.29 0.0173

Table 3.4. Average number of wireworms collected (mean ± standard deviation) using four different types of baited trap placed in a field near Bozeman MT, at four sampling dates during 2010 and 2011.

2010a 2011 Trap L. infuscatusb Others L. infuscatus Others

Time 1 Canister 0.6 ± 0.8C 0.0 ± 0.0 3.2 ± 3.1B 0.0 ± 0.0 Pitfall 3.3 ± 2.2AB 0.0 ± 0.0 9.6 ± 6.1A 0.1 ± 0.3 Pot 1.3 ± 1.8BC 0.1 ± 0.3 5.3 ± 4.2AB 0.4 ± 0.5 Stocking 5.6 ± 5.7A 0.1 ± 0.3 10.1 ± 5.4A 0.3 ± 0.5

Time 2 Canister 0.1 ± 0.3 0.0 ± 0.0 5.1 ± 4.2C 0.2 ± 0.4 Pitfall 2.1 ± 2.0 0.6 ± 1.0 15.3 ± 6.9A 0.6 ± 0.7 Pot 0.6 ± 1.3 0.3 ± 0.7 7.3 ± 4.7BC 0.2 ± 0.4 Stocking 1.9 ± 3.4 0.2 ± 0.7 12.8 ± 6.1AB 0.5 ± 0.5

Time 3 Canister 0.4 ± 0.5 0.0 ± 0.0 0.3 ± 0.5B 0.1 ± 0.3 Pitfall 0.4 ± 0.7 0.5 ± 1.0 4.5 ± 2.1A 0.8 ± 1.3 Pot 0.0 ± 0.0 0.3 ± 0.5 1.0 ± 1.3B 0.3 ± 0.6 Stocking 1.6 ± 2.7 0.4 ± 0.7 2.8 ± 1.3A 0.2 ± 0.4

Time 4 Canister 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.1 ± 0.3 Pitfall 0.2 ± 0.4 0.7 ± 1.3 0.0 ± 0.0 0.6 ± 0.7 Pot 0.0 ± 0.0 0.3 ± 0.5 0.0 ± 0.0 0.3 ± 0.7 Stocking 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.3 ± 0.5 a Collection dates. 2010: Time 1 = 05/10/2010 to 05/24/2010, Time 2 = 06/24/2010 to 06/08/2010 Time 3 = 06/08/2010 to 06/22/2010 and Time 4 = 06/22/2010 to 07/08/2010. 2011: Time 1 = 05/19/2011 to 06/02/2011, Time 2 = 06/02/2011 to 06/17/2011 Time 3 = 06/17/2011 to 06/30/2011 Time 4 = 06/30/2011 to 07/20/2011. b Means followed by the same letter are not significantly different, Tukey’s test (P= 0.05).

Table 3.5. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Conrad, MT in 2010.

Source Num df Den df F value Pr > F Trap 3 540 15.16 < 0.0001 Species 2 540 102.31 < 0.0001 Time 4 540 69.40 < 0.0001 Trap*species 6 540 2.55 0.0191 Species*time 8 540 29.20 < 0.0001 Trap*time 12 540 5.94 < 0.0001 Trap*species*time 24 540 1.34 0.1290

Table 3.6. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Conrad, MT in 2011.

Source Num df Den df F value Pr > F Trap 3 531 15.16 < 0.0001 Species 2 531 102.31 < 0.0001 Time 4 531 69.40 < 0.0001 Trap*species 6 531 2.55 0.0191 Species*time 8 531 29.20 < 0.0001 Trap*time 12 531 5.94 < 0.0001 Trap*species*time 24 531 1.34 0.1290

Table 3.7. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Conrad, MT in 2012.

Source Num df Den df F value Pr > F Trap 3 540 9.67 < 0.0001 Species 2 540 30.51 < 0.0001 Time 4 540 16.87 < 0.0001 Trap*species 6 540 4.23 0.0004 Species*time 8 540 6.20 < 0.0001 Trap*time 12 540 2.18 0.0115 Trap*species*time 24 540 1.40 0.0973 76

Others

0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.3 0.1±0.3 0.0±0.0 0.0±0.0

H. b

0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.3

2012

0.1±0.3B 0.0±0.0B

1.5±1.8A 1.5±1.5A 1.4±1.5A

0.6±1.3AB 0.9±1.7AB 0.4±0.5AB

L. californicus

L.c

;

L. c

0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.2±0.4 0.9±1.2 0.6±0.7 1.5±2.1

H. bicolor

0.0

Others

0.0±0.0 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.0± 0.1±0.3 0.0±0.0

H.b

H. b

2011

0.5±1.1B 0.2±0.4B 0.0±0.0B 0.0±0.0B

1.9±2.0A 1.9±3.0A 1.3±2.2A 1.0±1.1A 1.2±2.2A

0.6±1.2AB 0.8±1.3AB 0.3±0.7AB

L. c

0.0±0.0 0.6±1.6 0.7±1.6 0.5±1.0 0.8±0.0 1.5±0.0 1.1±0.0 0.7±0.0 0.0±0.0 0.4±0.0 0.4±0.0 0.3±0.0

Others

0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.0 0.0±0.3 0.0±0.0

ive sampling during 2010 to 2012. dates

H. b

0.8±1.0 0.2±0.6 0.2±0.4 0.3±0.6 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 2.5±2.2 2.0±1.3 2.2±2.2 3.0±2.3

L. c

0.0 ± 0.0 0.1 ± 0.3 0.3 ± 0.5 0.0 ± 0.0 0.1 ± 0.3 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.4 ± 0.5 1.0 ± 1.3 1.2 ± 1.9 1.6 ± 1.6

2010

Average number of wireworms collected (mean ± standard deviation) using four different types of baited traps traps of baited types collected ± standard number different wireworms deviation) four using of Average (mean

Table 3.8. Table f Conrad MT, at in a field near placed Trap 1 Time Canister Pitfall Pot Stocking 2 Time Canister Pitfall Pot Stocking 3 Time Canister Pitfall Pot Stocking

0.0±0.0 0.0±0. 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

Time 1 = Time 1 =

0.0±0.0 0.4±1.0 0.5±0.5 1.0±1.6 0.0±0.0 0.0±0.0 0.1±0.3 0.4±0.7

0.0±0.0 0.4±0.8 0.1±0.3 0.7±1.9 0.1±0.3 0.2±0.4 0.4±0.5 0.1±0.3

0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.3 0.0±0.0 0.1±0.3 0.1±0.3 0.2±0.4

0.0±0.0 0.1±0.3 0.0±0.0 0.1±0.3 0.1±0.3 0.2±0.4 0.1±0.3 0.2±0.6

0.0±0.0B 0.0±0.0B 0.0±0.0B 0.0±0.0B

0.1±0.0A 0.1±0.3A 0.1±0.3A 0.2±0.4A

0.0±0.0 0.2±0.4 0.0±0.0 0.1±0.3

0.1±0.3B 0.0±0.0B

1.2±1.4A

0.5±0.8AB

04/30/2012 to 05/18/2012 Time 4 = 05/18/2012 to 06/01/2012, Time 5 = 5 = 04/30/2012 Time 05/18/2012 to 05/18/2012 to 06/01/2012, Time 4 =

0.0±0.0B 0.2±0.4B

2.0±1.7A 1.4±1.1A 2.0±2.4A

0.7±0.8AB 1.6±1.1AB 0.4±0.5AB

3.1A

1.4±1.1B 0.9±1.3B

5.6±5.0A 4.7±3.4A 5.2±

3.6±2.5AB 4.1±2.6AB 3.1±2.3AB

Continued

Means followed by the same letter are not significantly different Tukey’s test Tukey’s 0.05) (P= different not significantly are by the followed letter same Means

Collection dates. 2010: Time 1 = 03/26/2010 to 04/12/2010, Time 2 = 04/12/2010 to 04/26/2010 Time 3 = 03/26/2010Time 3 = 04/12/2010 to 04/12/2010, 1 = 2010: Time to 04/26/2010 Time 2 = Collection dates.

Table 3.8 Table 4 Time Canister Pitfall Pot Stocking 5 Time Canister Pitfall Pot Stocking a 05/12/2010 2011: 05/21/2010 to 05/21/2010, 4 = to 06/04/2010. Time Time04/26/2010 5 = to 05/12/2010 05/27/2011Time 4 = 06/13/2011 to 06/13/2011 2 = to 06/29/2011 Time Time05/17/2011 3 = to 05/27/2011, 03/27/2012 to 04/10/2012, 1 = 07/13/2011 Time 2 = to 07/26/2011. 5 = Time 2012:06/29/2011 Time to 07/13/2011, 3 = Time 04/10/2012 to 04/30/2012 06/01/2012 to 06/15/2012. b 78

Table 3.9. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Denton, MT in 2010.

Source Num df Den df F value Pr > F Trap 3 351 5.31 0.0014 Species 1 351 567.71 <0001 Time 4 351 39.00 <0001 Trap*species 3 351 1.97 0.1177 Species*time 4 351 39.74 <0001 Trap*time 12 351 0.52 0.9037 Trap*species*time 12 351 0.65 0.7945

Table 3.10. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Denton, MT in 2011.

Source Num df Den df F value Pr > F Trap 3 351 1.47 0.2225 Species 1 351 46.24 < 0.0001 Time 4 351 6.21 < 0.0001 Trap*species 3 351 0.47 0.7047 Species*time 4 351 11.33 < 0.0001 Trap*time 12 351 1.12 0.3432 Trap*species*time 12 351 1.93 0.0295

Table 3.11. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Denton, MT in 2012.

Source Num df Den df F value Pr > F Trap 3 351 8.67 < 0.0001 Species 1 351 33.68 < 0.0001 Time 4 351 12.96 < 0.0001 Trap*species 3 351 1.76 0.1536 Species*time 4 351 10.44 < 0.0001 Trap*time 12 351 1.14 0.3293 Trap*species*time 12 351 0.56 0.8704

Table 3.12. Average number of wireworms collected (mean ± standard deviation) using four different types of baited trap placed in a field near to Denton, MT in 2010 to 2012.

Trap 2010 2011 2012a Canister 5.36 ± 8.77 0.38 ± 0.63 0.28 ± 0.92 B Pitfall 8.54 ± 11.44 0.66 ± 1.21 0.73 ± 1.33 AB Pot 8.04 ± 12.41 0.70 ± 1.09 0.40 ± 1.01 B Stocking 8.37 ± 10.84 0.90 ± 1.31 1.10 ± 1.76 A a Means followed by the same letter are not significantly different Tukey’s test (P= 0.05).

Table 3.13. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Toston, MT in 2010.

Source Num df Den df F value Pr > F Trap 3 288 1.39 0.2453 Species 1 288 107.41 < 0.0001 Time 3 288 1.41 0.2392 Trap*species 3 288 1.73 0.1616 Species*time 3 288 1.34 0.2613 Trap*time 9 288 0.48 0.8901 Trap*species*time 9 288 0.39 0.9382

Table 3.14. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Toston, MT in 2011.

Source Num df Den df F value Pr > F Trap 3 279 4.09 0.0073 Species 1 279 139.73 < 0.0001 Time 3 279 11.72 < 0.0001 Trap*species 3 279 1.14 0.3351 Species*time 3 279 10.89 < 0.0001 Trap*time 9 279 1.76 0.0766 Trap*species*time 9 279 0.59 0.8027

Table 3.15. PROC MIX of number of wireworms collected with four baited traps in small grain fields in Toston, MT in 2012.

Source Num df Den df F value Pr > F Trap 3 279 6.40 0.0030 Species 1 279 0.04 0.8375 Time 3 279 10.56 < .0001 Trap*species 3 279 0.04 0.9885 Species*time 3 279 0.01 0.9977 Trap*time 9 279 2.30 0.0166 Trap*species*time 9 279 0.01 1.000

0.0±0.0 0.6±0.8 0.2±0.4 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

Others

2012

1.0±1.5 2.1±2.6 2.4±2.8 3.5±2.6 0.3±0.6 0.4±0.5 0.2±0 0.2±0.4

0.6±0.7B

2.5±2.5A

0.7±1.3AB 0.7±0.8AB

L. californicus

0.0±0.0 0.6±0.8 0.2±0.4 0.1±0.3 0.0±0.0 0.2±0.6 0.0±0.0 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

Others

2011

1.0±1.2 2.1±1.7 2.4±2.8 3.5±2.7 0.3±0.7 0.4±0.5 0.2±0.4 0.2±0.4

0.6±0.7B

2.5±2.5A

0.7±1.3AB 0.7±0.8AB

L. californicus

ling dates during 2010 to 2011. during ling dates

0.0±0.0 0.0±0.0 0.0±0.0 0.1±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

Others

2010

, MT at four samp four , MT at

0.7±1.3 1.1±1.4 2.5±3.8 1.2±1.6 0.8±1.5 1.8±2.5 1.1±1.7 0.4±0.7 1.6±1.6 2.1±2.1 1.1±1.2 1.1±1.8

Toston

L. californicus

. Average number of wireworms collected (mean ± standard deviation) using four different types of baited trap trap ± standard different of baited deviation) four types using collected number wireworms (mean of . Average

Table 3.16 Table in a field near placed Trap 1 Time Canister Pitfall Pot Stocking 2 Time Canister Pitfall Pot Stocking 3 Time Canister Pitfall Pot Stocking

0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

Time 2 Time

Time 1 Time

Time 4 Time

Time 3 Time

1.3±1.3 1.5±1.4 2.0±2.6 1.8±1.6

= 05/19/2011 to 06/02/2011, 05/19/2011 to 06/02/2011, =

0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

= 06/11/2012 to 06/25/2012=

= 07/05/2011 to 07/19/2011. 2012: 07/05/2011 to 07/19/2011.= 2012:

Time 1 Time

= 06/02/2010 to 06/02/2010=

2011: 3 Time

4 Time

Time 2 Time

.3±1.3

1 1.5±1.4 2.0±2.6 1.8±1.6

012 to 06/11/2012

0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0

= 05/23/2 =

= 06/28/2010 to 07/17/2010.= 06/15/2011 to 07/05/2011=

= 05/17/2010 to 06/02/2010,=

Time 2 Time

Time 4 Time 3 Time

Time 1 Time

0.8±1.3 1.1±1.5 0.6±1.0 0.6±1.1

Continued

/2010 to 06/28/2010

Means followed by the same letter are not significantly different Tukey’s test Tukey’s 0.05). (P= different not significantly are by the followed letter same Means

Collection dates. 2010: Collection dates.

Table 3.16. Table 4 Time Canister Pitfall Pot Stocking a 06/02 06/02/2011 to 06/15/2011 05/11/2012 to 05/23/2012, 06/25/2012 to 07/12/2012. b

Table 3.17. Percentage of the three main species collected with four different bait traps polled in open (stocking and pitfall) and close (canister and pot) in small cereal fields in Montana. Chi square value = 94.91 p= 0.00001.

H. bicolor L. californicus L. infuscatus N = total # wireworms Open 10.6% 62.7% 26.7% 3030 Close 6.9% 76.1% 16.9% 1836

Figure 3.1. Four bait traps used (top) see methodology for the description and display of the traps in the field (bottom).

Figure 3.2. Average (LC 95) of wireworm by bait trap collected during 2010 to 2012 in Bozeman, Conrad, Denton and Toston Montana.

Figure 3.3. Relative variation values for each location during 2010 to 2012 intensive sampling (all dates of each year combine), n=total wireworms collected for the given year and locality.

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CHAPTER FOUR

DESCRIPTION OF THE LARVAL ACTIVITY OF THREE SPECIES OF WIREWORMS IN THREE COMMERCIAL CEREAL FIELDS IN MONTANA

Introduction

Detailed studies of wireworm biology, seasonality and ecology are rare, mostly because wireworms are difficult to collect in large numbers and have extremely prolonged life cycles, thereby making them difficult to study (Keaster et al.1975).

However, understanding the seasonal population dynamics of wireworms in a crop may be important for predicting damage. For example, Bynum et al. (1949) reported that wireworm damage was more severe in fall compared to summer planted sugarcane in

Louisiana. Also, Burrage (1963) noted that wireworm damage to potatoes increased with rising soil temperatures in the spring, peaking during June at the study site in Canada.

Cherry (2007) noted that seasonal population dynamics of wireworms damaging sugarcane in Florida remains unknown and this information is important to understanding the basic biology of these important pests.

Seasonal activity can depend on the species of wireworm, their developmental stage, the type of crop, soil type and geographic location. In Florida for example, wireworms infesting sugarcane crops can be active during the entire growing season

(Cherry 2007) with some differences between species. Conoderus spp. are more abundant in the sugar cane fields during the summer when M. cummunis is less abundant (Cherry

2007). In general wireworms have two intense periods of activity near the soil surface

91 that may result in significant crop damage during a calendar year in the Northern hemisphere, that relate to suitable temperature and moisture conditions in the different soil layers. A spring period generally occurs from March through to May and a fall period in September and October (Barsics et al. 2013). Early in the spring wireworms that overwintered deep in the soil return to the surface to feed when soil temperatures reach about 10°C, coinciding with the time that early season crops are planted and begin to germinate. Later, during the summer season, when soil temperatures reach about 25°C at the surface, wireworms move deeper to seek favorable soil moisture and temperature conditions. In North Carolina’s sweet potato fields, Conoderus vespertinus was most abundant in August and September (Willis 2010). In contrast, in sweet potato fields in

Georgia, C. scissus and C. rudis abundance decrease successively from July to November

(Seal et al. 1992). In potato fields in the United Kingdom, two seasonal activities of

Agriotes spp. have been reported, one early in the spring (March to May), and the second during the fall (September to October) (Gratwich 1989). Three peaks of activity in one year have been reported for C. destructor (= S. aeripennis), one in June, August and

September (Doane 1981). The August activity peak may be related to molting and pupation, as has been reported for Agriotes species (Evans and Gough 1942).

In order to develop new IPM tools that target the damaging larval stage, their seasonal activity in crop fields needs to be characterized. In this study the activity of wireworms at the soil surface was monitored throughout the growing season in four fields representing different geographic locations in Montana over a three year period.

Methodology

Wireworms were collected from two commercial cereal fields in Montana and one research station field: the first field was located at the Arthur H. Post Research Farm,

Gallatin Co. Bozeman, MT in a dry land wheat field; the second field was located at

Mark Grubb Ranch Inc., Pondera Co. Conrad, MT in a irrigated wheat and barley field; and the third field was located at Barber Seed Services Inc., Fergus Co. Denton, MT in a dry land wheat and barley seed production field. Wireworms were collected with four different bait traps described in Chapter 3. Each year the goal was to deploy traps as early as possible to have a sampling period that preceded the anticipated movement of wireworms to the soil surface that is thought to occur when average soil temperatures reach 7-10˚C. Traps were then successively deployed every two weeks throughout the growing season. However, weather conditions often restricted the date of first trap deployment. The sampling was repeated for three years (2010 – 2012) at Conrad and

Denton and two years (2010 – 2011) at Bozeman. The same area was used each year that the study was conducted. Larvae were sorted from the traps, labeled, and preserved in

95% ethanol for future identification. At each site a data logger (WatchDog 1400 series,

Spectrum® Technologies, Inc.) was installed to monitor soil temperature at a depth of 7.5 cm.

Data Analysis

Catches from the four trap types were pooled for each collection date. Catches of the predominant species at each site were analyzed: Bozeman (L. infuscatus), Denton (L.

93 californicus), and Conrad (L. californicus and H. bicolor). The data is analyzed descriptively using a graphical presentation to illustrate seasonal trap catches and soil temperature at 7.5 cm deep. Traps remained in the soil for 14 days, total trap caches are reported as the date midway between trap deployment and trap collection.

Results

A total of 4190 wireworms were collected from the three sites during 2010 –

2012. In 2010, 2011 and 2012, 2811, 1088 and 291 wireworms were collected, respectively. Three species were predominantly represented: L. californicus, L. infuscatus and H. bicolor. Other minor species collected and not included in this analysis are:

Aeolus mellillus, Agriotes spp. and Dalopius spp. Limonius californicus was the dominant species at the Denton site; L. infuscatus was the dominant species at the Bozeman site and at the Conrad site, two wireworm species were co-dominant: Hypnoidus bicolor and

L. californicus. Aeolus mellillus was collected at all three locations as a minor component of the total catches. Agriotes spp. and Dalopius spp., collected in Bozeman, Conrad and

Denton, were uncommon.

Considerable variation in the total number of wireworms trapped was observed among the different locations, years and species. Significant more wireworms were collected in Denton followed by Bozeman and Conrad. Forty-nine percent of all wireworms were collected in Denton in 2010 and 18.5% in Bozeman in 2011. Heavy precipitation and flooding experienced in Montana during spring of 2011 likely affected movement of the wireworms and numbers collected. Fifty-six counties experienced

94 flooding and 31 were classified as disasters by the USDA Farm Service Agency (2011).

The Denton plot suffered the most flooding and was covered with water for two weeks after the first set of traps was deployed in the first week of May. During April and May rainfall accumulation was 354 mm, twice the long-term average of 179 mm.

Bozeman

Soil temperatures approached 7-10˚C during the middle of April in 2010 and

2011. However, traps were not deployed until May 10 in 2010 and May 19 in 2011, because of heavy precipitation and/or snowfall that occurred (Figures 4.2 and 4.3). At the first sampling date in 2010 (05-10 to 05-24), 108 L. infuscatus were collected and the average soil temperature for the same period was 10.7˚C (9.4 – 12.3˚C). During the next three sampling dates trap catches declined sequentially as the soil temperature increased.

By the fourth sample encompassing the last week of June and first week of July (06/23 to

07/06), only two L. infuscatus were collected, the average soil temperature for this period was 19.7˚C (18.2 – 21.5 ˚C). After July 6th soil temperatures were consistently near or above 20˚C for the remainder of the growing season (Figure 4.1). Larger numbers of L. infuscatus were trapped in 2011, all on three sampling dates spanning six weeks. A total of 282 were collected on the first sampling date (05/19 to 06/02) when the average soil temperatures were 12.9˚C (11.8 – 14.8 ˚C), increasing to 405 on the second sampling date

(06/02 to 06/17) and decreasing to 86 on the third sampling date on (06/17 to 06/30)

(Figure 4.2). After July 1 average soil temperatures were above 20˚C for the remainder of the growing season (Figure 4.2).

Conrad

Average soil temperatures reached 7-10˚C during the middle of April in 2010, 3rd week of April in 2011 and by the first week of April in 2012. Traps were deployed during the last week of March in 2010 and 2012 and not until the second week of May in 2011 due to heavy precipitation (rain and/or snowfall). For the first sampling date in 2010

(03/24 to 04/08), 15 L. californicus and 4 H. bicolor were collected and the average soil temperature for this period was 5.4˚C (2.1 – 10.5˚C). During the first half of the next sampling period (04/08 to 04/24) average soil temperatures dropped below 5˚C and only one wireworm of each species was collected. Interestingly, average soil temperatures fluctuated above and below 5˚C and did not exhibit a clear trend of continued warming, but wireworm trap catches increased dramatically. Between May 7 and June 4 average soil temperatures exhibited sustained warming from about 7˚C to 15˚C, and these two sampling periods yield the largest wireworm catches. After this date average soil temperatures approached or exceeded 20˚C and trap catches declined.

During 2011 sampling was delayed because of heavy precipitation and flooding, and total catches were lower compared to 2010. The first date (05-17 to 05-27) yielded 38

L. californicus and 18 H. bicolor collected while average soil temperature were 11.3˚C

(7.6 – 16.2˚C). Catches of L. californicus (n = 45) remained consistent at the next sampling date (05/27 to 06/13) while numbers of H. bicolor (n = 41) increased.

Interestingly, average soil temperatures ranged from 22 – 25˚C during the last sampling date in August (8/14 to 8/27), and 13 L. californicus and 10 H. bicolor were collected

(Figure 4.4). This was the only observation of wireworm activity during August in this this study.

In 2012 soil temperatures warmed much earlier, averaging 6.7˚C (3.2 – 11.7˚C) during the first sampling date (03/27 to 04/10), and 31 L. californicus but no H. bicolor were collected (Figure 4.5). Oddly, wireworm catches decreased dramatically during the second sampling date (04-16 to 04-30), only a single L. californicus larva was collected, while average soil temperatures warmed. The first catches of H. bicolor were recorded at the third sampling date, and they were the highest catches for this species in 2012. L. californicus was trapped at approximately equal numbers to H. bicolor on the third sampling date. In a typical pattern, trap catches of both species declined sequentially during the next two sampling dates and no wireworms were trapped during July and

August when average soil temperatures exceeded 20˚C. The Conrad site is unique in that it was co-infested by two wireworm species, allowing a direct comparison of seasonal activities under the same soil conditions. During all three sampling years, peak catches of

L. californicus occurred at earlier dates compared to H. bicolor (Figures 4.3 – 4.5).

Denton

Average soil temperatures reached 7 – 10˚C during the first week of April in 2010 and 2012 and the 2nd week of April in 2011. Traps were deployed later in 2011 because of heavy precipitation and flooding. The first sampling date in 2010 (4/17 to 4/27) yielded astounding numbers, 1031 L. californicus were trapped while the average soil temperature for the period was 7.0 ˚C (1.7 – 12.1˚C) (Figure 4.6). Average soil temperatures decreased during the second sampling date and trap catches declined

97 successively during the next two sampling dates, although the soil temperatures increased for the third sampling date (Figure 4.6). Interestingly, there was a second period of activity later in the growing season at the 5th and 6th sampling dates.

During 2011 peak wireworm activity was later compared to 2010, possibly the result of earlier season flooding. At the first sampling date (4/19 to 4/29) 27 L. californicus were collected and the average soil temperature for the same period was

12.9˚C (7.3 – 17.7˚C) (Figure 4.7). Numbers decreased to only 3 at the second sampling date (4/16 to 4/30) although soil temperatures remained favorable. Trap catches increased again during the last week of June and first week of July, when average soil temperatures ranged from 15-25˚C (Figure 4.7).

During 2012 average soil temperatures reached 7 – 10˚C during the first week of

April (Figure 4.8). However, trap catches peaked later, during the middle and end of

May, and continued until July 17 (sampling date 07/3 to 07/20). The average soil temperatures ranged from about 20 to 24 ˚C during this sampling period. Earlier sampling dates (04/27 and 05/09) failed to catch wireworms.

Discussion

In this study wireworms were caught during April when average soil temperatures ranged from only 5 to 10˚C (Conrad during 2010 and 2012; Denton 2010). However, higher catches that indicate greater activity were more common during May and early

June when soil temperatures averaged 10 to 20˚C. In general the majority of the wireworms were trapped during three successive sampling dates representing 6 weeks of

98 the growing season. This period of activity occurred most commonly during the month of

May and the first half of June. This pattern in general supports a single period of peak wireworm activity in Montana’s cropland, during the spring when soil temperatures become favorable for activity. Cereal crops are typically planted in Montana during April or early May, so the period of peak wireworm activity coincides with crop seed germination and seedling establishment, the stages most vulnerable to wireworm feeding.

Insecticidal seed treatments are expected to persist for about one month after the crop is planted. If a cereal crop is planted during the middle of April, by the middle of May, a period that can coincide with peak wireworm activity, the developing seedlings are no longer protected by the insecticide treatment. Our results are contrary to published reports of two peaks of wireworm activity, one in the spring and one in the fall (Doane 1981;

Gratwich 1989). Although our study did not deploy traps during September and October, reports of damage to fall seeded cereal crops in Montana are very rare. The lack wireworm activity near the soil surface during the fall season is likely related to the dry soil conditions experienced across much of Montana’s cereal cropland.

Wireworm activity observed in this study was not always consistent with soil temperature, suggesting additional variables may influence their vertical movements in the soil. Their need for food early in the spring, and their physiological status, may explain some apparently anomalous observations from this study. In several cases the first observed trap catches were among the highest trap catches for the season, even though they coincided with cooler soil temperatures that are less conducive to activity.

This trend was strong for L. californicus during the first sampling dates at the Conrad site

99 in 2012 and the Denton site in 2010, suggesting a concerted movement and effort to secure food resources after a dormant winter season. If satiated early in the spring, the wireworms may not need to immediately return to surface to feed even if minimum soil temperatures enable activity, as was observed at the Conrad site at the second sampling date in 2012. Although soil temperatures were conducive to activity during the April in

Denton during 2012, wireworms were not caught during the first two sampling periods.

In this case a peak of activity may have occurred before the first sampling date. For half of the observed growing seasons smaller numbers of wireworms continued to be trapped during July and August. The Conrad site during 2011 provides the most striking example, where both H. bicolor and L. californicus were caught at the end of August. Heavy rainfall and flooding earlier in the season may have inhibited their feeding activity near the surface, necessitating additional feeding later in the season despite warm soil conditions. Trap catches during July and August could also represent opportunistic feeding as mature larvae return to top six inches of the soil surface to pupate. Finally, at one site infested by two wireworm species, the results suggested that peak activity of H. bicolor might occur later compared to L. californicus, reinforcing the need for species– specific studies.

The merits of absolute and relative methods for sampling wireworms were discussed generally in Chapter 3. The study conducted in this chapter provides valuable insights into the seasonal movements of wireworms in Montana and a foundation for future studies. Absolute sampling methods such as soil cores should be incorporated in conjunction with attractive bait samples. Soil core samples will be valuable early in the

100 spring season when cool inclement weather can interfere with the deployment and germination of bait traps. Also, soil cores are independent of insect physiological status and developmental stage, and can collect wireworms that are not feeding or inactive life stages such as the pupae. A further concern of relative bait samples is the consistency of their activity during the growing season. A bait trap may catch more relative numbers of larvae early in spring when there is no crop to produce CO2 as a competing attractant.

However, at low population densities, bait traps that can attract wireworms from a distance are more effective at sampling populations compared to sampling smaller volumes of soil. Results presented in Chapter 6 demonstrate that three core samples yield only 1/3 of the wireworms compared to a single stocking trap. Soil core samples incorporated into future studies will need to be used judiciously.

Peak activities of wireworms early in the spring season need to be confirmed using absolute sampling methods. If these patterns of activity observed in this study do in fact accurately represent their vertical movements in the soil, it may provide a window of opportunity for their control using insecticidal baits. Baits can be used to deliver conventional biological insecticides designed to suppress their populations in a field.

Such baits should be more effective when wireworms first return to the soil surface after overwintering, and few competing food sources are present.

Acknowledgments

We thank Mark Grubb (Conrad, Pondera Co), Richard Barber (Denton, Fergus

Co) and Brian Tutvedt (Kalispell, Flathead Co) for allowing us to collect wireworms and

101 plant field trials on their cropland. We thank Alix Bold, Branden Brelsford, Ammiel

Branson, Meghan McGauley, Ruth O’Neill, Diana Florian, Hannah Johnson, and Laura

Morales for their help in conducting this work. This study was supported in part by funds from the Montana Wheat and Barley Committee, Montana Seed Potato Producers

Association and USDA Crops at Risk Grant 2010-51100-21547.

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Figure 4.1. Total Limonius infuscatus (Li) collected by date and average soil temperature at 7.5 cm deep in 2010 in a cereal filed in Bozeman, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

Figure 4.2. Total Limonius infuscatus (Li) collected by date and average soil temperature at 7.5 cm deep in 2011 in a cereal filed in Bozeman, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

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Figure 4.3. Total Limonius californicus (Lc) and Hypnoidus bicolor (Hb) collected by date and average soil temperature at 7.5 cm deep in 2010 in a cereal filed in Conrad, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

Figure 4.4. Total Limonius californicus (Lc) and Hypnoidus bicolor (Hb) collected by date and average soil temperature at 7.5 cm deep in 2011 in a cereal filed in Conrad, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

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Figure 4.5. Total Limonius californicus (Lc) and Hypnoidus bicolor (Hb) collected by date and average soil temperature at 7.5 cm deep in 2012 in a cereal filed in Conrad, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

Figure 4.6. Total Limonius californicus (Lc) collected by date and average soil temperature at 7.5 cm deep in 2010 in a cereal filed in Denton, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

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Figure 4.7. Total Limonius californicus (Lc) collected by date and average soil temperature at 7.5 cm deep in 2011 in a cereal filed in Denton, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

Figure 4.8. Total Limonius californicus (Lc) collected by date and average soil temperature at 7.5 cm deep in 2012 in a cereal filed in Denton, MT. Light blue line = maximum soil temperature; light green line = average soil temperature and light red line = minimum soil temperature.

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References

Barsics, F., E., Ahubruge, F. Verheggen. 2013. Wireworms’ Management: An Overview of the Existing Methods, with Particular Regards to Agriotes spp. (Coleoptera: Elateridae). Insects. 4(1): 117-152.

Burrage, R. 1963. Seasonal feeding of larvae of Ctenicera destructor and Hypolithus bicolor (Coleoptera: Elateridae) on potatoes placed in the field at weekly intervals. Annals Entomology Society of America. 56: 306-313.

Bynum, E., J. Ingram, and L. Charpentier. 1949. Control of Wireworms Attacking Sugarcane in Louisiana. Journal Economic Entomology. 42: 556-557.

Cherry, R. 2007. Seasonal Population Dynamics of Wireworms (Coleoptera : Elateridae) in Florida Sugarcane Fields. Florida Entomologist. 90(3): 426-430.

Doane, J. F. 1981. Evaluation of a Larval Trap and Baits for Monitoring the Seasonal Activity of Wireworms (Coleoptera, Elateridae) in Saskatchewan. Environmental Entomology. 10(3): 335-342.

Evans, A. C. and H. C. Gough. 1942. Observations on Some Factors Influencing Growth in Wireworms of the Genus Agriotes Esch. Annals of Applied Biology. 29(2): 168-175.

Gratwick, M., 1989. Potato Pests. Ministry of Agriculture, Fisheries and Food Reference Book 187.HMSO, London, 104 pp.

Jedlička, P. and J. Frouz. 2007. Population Dynamics of Wireworms (Coleoptera, Elateridae) in Arable Land after Abandonment. Biologia (Bratislava). 62(1): 103-111.

Keaster, A., G. Chippendale, and B. Pill. 1975. Feeding Behavior and Growth of the Wireworms Melanotus depressus and Limonius dubitans: Effect of Host Plants, Temperature, Photoperiod, and Artificial Diets. Environmental Entomology. 4: 591-595.

Lefko, S. A., L., Pedigo, W. D., Batchelor, and M. E. Rice. 1998. Spatial Modeling of Preferred Wireworm (Coleoptera: Elateridae) Habitat. Environmental Entomology. 27(2): 184-190.

Seal, D.R., R. McSorley, and R.B. Chalfant. 1992. Seasonal Abundance and Spatial Distribution of Wireworms (Coleoptera: Elateridae) in Georgia Sweet Potato Fields. Journal of Economic Entomology. 85:1802-1808.

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USDA Natural Resources Conservation Service Montana http://www.nrcs.usda.gov/wps/portal/nrcs/detail/mt/newsroom/?cid=nrcs144p2_056232 [accessed 06-19-2014]

Willis, R.B., G.G. Kennedy, and M.R. Abney. 2010. Survey of Wireworms (Coleoptera: Elateridae) in North Carolina Sweetpotato Fields and Seasonal Abundance of Conoderus vespertinus. Journal of Economic Entomology. 103(4):1268-1276.

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CHAPTER FIVE

A SURVEY OF WIREWORM (COLEOPTERA: ELATERIDAE) SPECIES INFESTING CEREAL CROPS IN MONTANA

Contribution of Authors and Co-Authors

Manuscript in Chapter 5

Author: Anuar Morales-Rodriguez

Contributions: Conceived and implemented the study design. Collected and analyzed data. Wrote the manuscript.

Co-Author: Ruth P. O’Neill

Contributions: Contacted producers and extension agents for the survey in 2012 and 2013, helped with the data collection and analysis, creation of the figures and tables. Provided valuable feedback to the manuscript.

Co-Author: Kevin W. Wanner

Contributions: Provided feedback in the study design, data analysis and comments

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Manuscript Information Page

Anuar Morales-Rodriguez, Ruth P. O’Neill and Kevin W. Waner Pan-Pacific Entomologist. Status of Manuscript: ____ Prepared for submission to a peer-reviewed journal ____ Officially submitted to a peer-review journal X Accepted by a peer-reviewed journal ____ Published in a peer-reviewed journal Published by the Pacific Coast Entomological Society Submitted on January 2014. Accepted for publication June 2014.

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Abstract

Wireworms are an increasing threat to the sustainable production of cereal, potato and other crops in Montana since the delisting of lindane, an effective and inexpensive insecticidal seed treatment. With this study, we have initiated long term research to investigate the diversity of wireworm species infesting Montana’s cropland. Canister- type bait traps were mailed to collaborating producers who buried them in established cereal fields for 10 – 14 days, and then returned them to Montana State University where the wireworms were identified to species. A total of 61 cereal fields in 12 counties were surveyed during 2011; 67 fields in 24 counties during 2012; and 66 fields in 16 counties during 2013. Wireworms were caught in 36.8% (46/125) of cereal fields with no prior known history of wireworms, averaging 0.5 larvae per trap. Wireworms were caught in

62.7% (37/59) of fields with a reported history of wireworms, averaging 4.1 larvae per trap. The prairie grain wireworm, Selatosomus aeripennis (Kirby, 1837), was thought to be the most common species in the region. However, Limonius californicus

(Mannerheim, 1843), L. infuscatus Motschulsky, 1859, Hypnoidus bicolor (Eschscholtz,

1829) and Aeolus mellillus (Saylor, 1836) were identified as the most common species in this study. Additionally, 2–3 different species often infested the same field.

Resumen

Desde la exclusión del mercado de lindano, un insecticida eficaz y barato para el

111 tratamiento de semilla, los gusanos alambre se han convirtiendo en una amenaza creciente para la producción sostenible de cereales, papas y otros cultivos en el estado de

Montana. En este estudio, hemos iniciado un programa de investigación a largo plazo para establecer la diversidad de especies de gusanos alambre que infestan tierras cultivables en Montana. Trampas cebadas fueron enviadas a los agricultores para que fueran enterradas durante 10 a 14 días en campos de cereales recién sembrados. Las trampas fueron devueltas a la Universidad Estatal de Montana, donde las diferentes especies de gusanos alambre fueron identificadas. Un total de 61 campos de cereales en

12 condados en el 2011; 67 campos en 24 condados en el 2012, y 66 campos en 16 condados en el 2013 fueron evaluados. Los gusanos alambre fueron capturados en 36,8

% (46 /125) de los campos sin historia conocida de gusanos alambre, con un promedio de

0.5 larvas por trampa. Larvas fueron capturadas en el 62,7 % (37 /59) de los campos con una historia previa de gusanos alambre, con un promedio de 4.1 larvas por trampa. Se creía que Selatosomus aeripennis (Kirby, 1837) era la especie más común en la región.

Sin embargo, Limonius californicus (Mannerheim, 1843), L. infuscatus Motschulsky,

1859, Hypnoidus bicolor (Eschscholtz, 1829) y Aeolus mellillus (Saylor, 1836) fueron identificadas como las especies más comunes. Adicionalmente, se observó que a menudo

2–3 especies diferentes infestan el mismo campo.

Keywords. Bait traps, Selatosomus aeripennis, Limonius californicus, L. infuscatus,

Hypnoidus bicolor, Aeolus mellillus, click beetle

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Introduction

During the past decade the pest status of wireworms in agriculture has increased significantly (Vernon et al. 2013). Wireworms are the soil-dwelling larval stage of click beetles in the insect family Elateridae. With larval stages lasting as long as 11 years and broad phytophagous, saprophagous and predaceous feeding habits, wireworms can damage a wide diversity of crops by feeding on the seeds, developing seedlings, underground tubers and above-ground fruits in contact with soil (Comstock &

Slingerland 1891, Thomas 1940). For 40 years wireworm damage was effectively and inexpensively managed by the first generation of highly toxic and persistent pre-planting insecticides applied to soil and seeds (e.g. organochlorines and organophosphates) (Toba et al. 1985, Vernon et al. 2013). During this period their pest status was low, and little research was conducted towards understanding the pest species’ diversity and biology.

Neonicotinoid-class insecticides (e.g. imidacloprid, thiamethoxam and clothianidin) currently used as seed treatments in agriculture do not kill or suppress wireworm populations infesting cropland (Vernon et al. 2008, Morales-Rodriguez & Wanner, personal observation). While they can provide crop protection in moderately infested fields, the wireworm populations can continue to increase until they reach severe levels where damage cannot be prevented by any treatment. Further understanding of basic wireworm biology and ecology is required to develop alternative management strategies based on integrated pest management (IPM).

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Montana commonly ranks 3rd nationally in barley and wheat production. The

1,000,000 acres of barley and 5,770,000 acres of wheat harvested in 2012 in Montana was valued at 0.25 and 1.1 billion U.S. dollars, respectively (USDA National Agricultural

Statistics Service, http://www.nass.usda.gov/). In central Montana, Athous spp. historically were considered important pest species (Hastings & Cowen 1954), but

Limonius canus LeConte, 1853 was considered more important on irrigated cropland

(Mail 1932). In 1981, a complex of Aeolus mellillus (Saylor, 1836), Ctenicera glauca

(Germar, 1843) [= Hadromorphus glaucus (Germar, 1843)], and C. destructor (Brown,

1853) [= Selatosomus aeripennis (Kirby, 1837)] was reported from wheat fields in northcentral Montana (Morrill 1983). In Washington, Oregon, and Idaho, Ludius inflatus

(auct. nec Say, 1825) [=H. glaucus (Germar, 1843)], L. noxius Hyslop, 1914 [= S. pruininus (Horn, 1871)], and Pheletes occidentalis Candeze, 1860 [= L. californicus

(Mannerheim, 1843)] were reported as the principal species of economic importance

(Lane 1925). Two and half decades later, these species were not considered economically important in the region (Glen 1950). More recently, C. pruinina (Horn,

1871) [= S. pruininus] has been reported as the predominant species infesting dryland fields in northern Oregon, followed by Limonius californicus (Mannerheim, 1843),

Melanotus longulus oregonensis (LeConte, 1853), and L. infuscatus Motschulsky, 1859

(Toba & Campbell 1992). Andrews et al. (2000, 2008) reported L. canus, L. californicus,

L. infuscatus and L. subauratus LeConte, 1853 as common pests of irrigated crops in the

Pacific Northwest region of the U.S. A current survey of pest wireworm species infesting

Montana’s cereal crops is a clear research priority.

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More regionally, there are two invasive pest species of interest from Europe,

Agriotes obscurus (Linnaeus, 1758) and A. lineatus (Linnaeus, 1767), that have been reported from Washington State (Vernon & Päts 1997, LaGasa et al. 2006), Oregon

(Andrews et al. 2008) and in the Fraser Valley of British Columbia, where they have become major pests of small fruit, vegetable, ornamental and forage crops (Vernon et al.

2001). These species have not been collected in Montana.

One cornerstone of IPM is the accurate species-level identification of the organism causing damage. Species-specific knowledge of the pest biology and ecology is necessary to develop cultural, biological and chemical IPM tactics. In general, the immature stages of insects are more difficult to identify to species-level, and wireworms are no exception.

In many cases, species-level identification of pest wireworms has relied on the aboveground adult stage, which does not cause damage. With long multi-year larval stages that can span several crop rotations, the aboveground fauna does not necessarily correlate with the belowground larval species that damage the crop (Blackshaw &

Vernon 2008). The most recent survey of the adult-stage click beetle fauna in Montana identified 152 different species (Seibert 1993). Of these, 22 were listed in the literature as potential pests of agricultural crops. Six different elaterid genera were represented:

Agriotes Eschscholtz, 1829, Conoderus Eschscholtz, 1829, Ctenicera [= Selatosomus]

Stephens, 1830, Hypnoidus Dillwyn, 1829, Limonius Eschscholtz, 1829 and Melanotus

Eschscholtz, 1829 (Seibert 1993). Here we report the results of a 3-year survey of wireworm species infesting and damaging Montana’s cereal crops.

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Materials and Methods

For broad statewide survey coverage we recruited collaborating wheat and barley producers through press releases, telephone calls, and extension “AgAlert” emails.

Cooperators agreed to survey 1 to 4 fields each by deploying a set of five bait stations per field. The traps consisted of 1.3-liter plastic canisters with 33 6-mm-diameter holes evenly distributed over the surface to allow wireworms access. The bait consisted of a

125 g wheat and barley seed mixture packed lightly between two layers of dry peat moss

(Sunshine®). Water was used to stimulate seed germination before burying the traps, by adding 1 – 2 cups of water or immersing the whole canister in water. Cooperators were instructed to deploy the canister-traps shortly after the crop was planted (typically late

April or early May). The top of the trap was 2.5 cm below ground level. After 10 to 14 days the traps were retrieved and mailed to the Cropland Entomology Laboratory at

Montana State University. Along with the traps, producers returned a sheet with field history information, including history of wireworm infestation. In 2011, wireworms were sorted from the traps by hand. In 2012 and 2013, an array of Berlese funnels was used to expedite the process. The wireworms were stored in 95% ethanol and subsequently identified to species. Species were identified by the authors using the morphological characteristics describes by Etzler (2013) and personal consultation with Frank Etzler, a wireworm taxonomist resident at the Montana Entomology Collection. Additionally, collaborating producers were asked to complete an information sheet that included: field location, crop history, cropping practices, and history of wireworm infestation.

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Results

A total of 213 cereal fields in 31 counties located across the state of Montana were successfully surveyed for wireworms over three years (Figure 5.1). Initially, a total of

1375 traps (275 sets) were mailed to potential collaborators and 77.5% of these sets were returned. A field was considered to be successfully surveyed if at least one of the five traps per set was returned to us. The overall trap return rate was 64.7% in 2011 (275 sets),

80.3% in 2012 (520 sets) and 86.8% in 2013 (270 sets). Some traps were lost or destroyed in the field, particularly in 2011 when two weeks of heavy rain flooded parts of central and western Montana. In other cases producers simply forgot to deploy or retrieve the traps or were unable to locate some or all of them. Overall, the canister traps were in good condition when they arrived at Montana State University and the wheat/barley mix had sprouted inside the trap, indicating sufficient moisture when activated. However, in some cases excess moisture resulted in poor seed germination, fouling the traps; in other cases the traps were too dry, and no seeds germinated. Field history was reported for

86.0% of the fields surveyed. The majority of collaborating producers reported no history of wireworms in the fields they surveyed (58.4%), while 27.6% reported a positive history and 14.0 % did not provide field history information (Table 5.1). Wireworms were collected from 62.7% of the fields that had reported a history of wireworms. In these fields positive for wireworms, average catches were high; 4.1 per trap. Wireworms were collected from 36.8% of the fields that reported no history of wireworms (Table

5.1). In these fields fewer wireworms were trapped; an average of 0.5 per trap.

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Here we present results for five major species collected in this survey: Aeolus mellillus, Hypnoidus bicolor, Limonius californicus, L. infuscatus and S. aeripennis. A few additional elaterid larvae in other taxa were trapped at such low numbers (1.7% of total catch) that they are not included in the present description: Aeolus sp. (1),

Hemicrepidius sp. (4), Limonius spp. (8), and three elaterids that were not identified to the genus level. Qualitative trap catches are presented in Figure 5.2 as the number of fields positive for each species. Measured as the incidence of each species, L. californicus

(37 fields), H. bicolor (31 fields) and A. mellillus (22 fields) were the most common species, followed by L. infuscatus (12 fields) and S. aeripennis (5 fields).

West of the Continental Divide that separates the Atlantic and Pacific watersheds of North America, 33 crop fields were surveyed (Flathead, Lake and Ravalli Counties) and 23 were positive for wireworms. This region was dominated by L. californicus (17 fields) and L. infuscatus (8 fields). Hypnoidus bicolor was recorded from only one field and none of the other three species were collected (Figure 5.1). In addition, the highest trap catches were reported from this region, ranging from 0 to 97 per trap. In the central region of Montana, bounded in the east by Blaine, Fergus, Wheatland and Sweet Grass

Counties, 137 crop fields were surveyed and 53 were positive for wireworms. All five wireworm species were recorded from this region: H. bicolor (27 fields), L. californicus

(19 fields) and A. mellillus (14 fields) were the most common, followed by S. aeripennis

(4 fields) and L. infuscatus (2 fields) (Figure 5.1). In eastern Montana, 43 fields were surveyed and 15 were positive for wireworms: A. mellillus (8 fields), H. bicolor (3

118 fields), L. infuscatus (2 fields), L. californicus (1 field) and S. aeripennis (1 field).

Combinations of different wireworm species were found infesting the same crop field. In

14 crop fields that were surveyed, as many as three species were found to co-occur

(Figure 5.2): H. bicolor + L. californicus (6 fields); H. bicolor + A. mellillus (2 fields); H. bicolor + S. aeripennis (1 field); H. bicolor + L. infuscatus (1 field); L. californicus + L. infuscatus (2 fields); H. bicolor + L. californicus + A. mellillus (1 field); and, L. californicus + A. mellillus + S. aeripennis (1 field).

Wireworms were collected from a total of 95 (44.6%) of the successfully surveyed fields. Figure 5.3 displays the frequency of different trap counts for each species. At low levels of 1-5 wireworms per field (an average of 0.2 – 1.0 per trap), A. mellillus, H. bicolor and L. californicus were the most common species, followed by L. infuscatus and S. aeripennis. At higher levels of 11 – 40 or >40 per field, L. californicus was clearly the most common of the four species sampled. While less common at high levels, A. mellillus and S. aeripennis were found in at least two fields at numbers higher than the economic threshold, an average of 1 – 2 per trap (Figure 3.5).

Discussion

A three-year survey of wheat and barley fields in 31 different counties across

Montana yielded five different wireworm species. The sugarbeet wireworm, L. californicus, was the most common species caught and also yielded the highest trap

119 catches. Limonius californicus was first reported as a pest of alfalfa and sugar beets in

California (Graf 1914), and now is commonly known from the Pacific Northwest region of North America (British Columbia to California and Idaho and Montana) and east to the

Canadian province of Manitoba (Al Dhafer 2009, Johnson 2009, Bousquet 1991). In our survey, L. californicus was the most common species sampled from the Flathead Valley west of the Continental Divide (Figure 5.2) and was also common just east of the

Continental Divide. One infested field was located in the northeast corner of Montana

(Daniels County). The adult beetles are slender, black, and 8 – 12 mm long. The larvae reach a length of 25 mm after 4 – 11 years in the soil, before pupating (EPPO 2005b).

Limonius californicus has been reported to damage wheat, barley, sugar beet and several other vegetable crops (EPPO 2005b, Al Dhafer 2009). During the last three years, visits to infested farm fields have supported the common pest status of L. californicus in

Montana, where they have been observed damaging wheat, barley, canola, lentil and potato crops (Wanner & Morales-Rodriguez, personal observations).

Hypnoidus bicolor (no common name) was the second most common species in

Montana, yet was trapped only once west of the Continental Divide. This species is distributed widely in North America from Alaska to California in the West (including

Arizona, Nevada, Utah, Idaho and Montana); Massachusetts, New York, Maine and New

Hampshire in the Northeast; and North and South Dakota, Minnesota, Wisconsin,

Illinois, Indiana, Michigan and Ohio in the central U.S. (Jonhson 2009, Bousquet 1991).

Hypnoidus bicolor has been detected in all Canadian provinces and the Yukon and

Northwest Territories (Bousquet 1991). Adult beetles are small (4 – 6 mm in length) and

120 bicolored reddish and brown-black. The larvae are also smaller, only reaching 4.8 – 8.4 mm in length at later stages (Stibick 1968). The duration of the larval stage before pupation is 1 – 2 years. Interestingly, both sexual and parthenogenetic populations have been reported in North America (Stibick 1968). In Montana, we have observed economic populations in wheat, barley and potato fields (Wanner & Morales-Rodriguez, personal observations).

The remaining species caught in this survey, L. infuscatus (the Pacific Coast wireworm), A. mellilus (the flat wireworm) and S. aeripennis (the prairie grain wireworm), were much less common. Limonius infuscatus is more widely distributed than L. californicus, having been reported from central and northeastern U.S. states in addition to the Pacific Northwest (Al Dhafer 2009, Bousquet 1991). Little is known about biological or ecological differences from L. californicus. In Montana, L. infuscatus was trapped as far east as Custer County but was found more commonly west of the

Continental Divide in the Flathead Valley. Aeolus mellillus was trapped only east of the

Continental Divide in Montana. This species is generally distributed in North America, mostly in the east and south (Johnson 2009, Bousquet 1991). Bryson (1930) and Stirrett

(1936) reported a life cycle of one year and Forbes (1892) reported a life cycle of two years. Aeolus mellillus is parthenogenetic, several authors having collected only females in different regions (Forbes 1891, 1892, Stirrett 1936, Jewett 1940). The adults are small,

5 – 8 mm in length, reddish-orange and black. The larva is distinguished from other common wireworms by its flatness, small size, softness of texture and light yellow color

(Jewett 1945).

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A surprising result of this survey was the near lack of the prairie grain wireworm,

S. aeripennis. Of 214 cereal fields surveyed it was caught in only five, all east of the

Continental Divide. Selatosomus aeripennis is distributed throughout the northwestern portion of North America and is best known as a pest of wheat in cool climates (Zacharuk

1962). In addition to wheat, barley, canola, corn, flax, oats, rye, sugarbeet, and sunflower crops, many vegetable crops can be injured as well, including bean, carrot, lettuce, lima bean, onion, potato, tomato, and probably many others (Glen 1935). The adults are small to medium-sized (8 – 16 mm in length), black or black and iridescent green-blue click beetles, and the larvae can reach a length of about 18 – 20 mm (Zacharuk 1962).

The five different wireworm species identified in this survey were found to co- occur in various combinations. Since the biology and ecology of each species can vary

(size, duration of larval stage, sexual vs. parthenogenetic reproduction, for example), identifying the infesting species and developing species-specific IPM strategies will be important. In Montana, future IPM research will focus on L. californicus and H. bicolor as the two key species infesting cereal fields.

Modern wireworm research is scarce because until recently conventional insecticides effectively controlled their damage, resulting in a low pest status. As a result, some contemporary knowledge is based on historical observations rather than quantitative data. Furthermore, wireworms are a complex of many different species that can have diverse life histories. For example, L. californicus has been widely reported as an important pest of irrigated fields or areas with more than 460 mm of annual rainfall

(EPPO 2005b). However, in the current survey we found L. californicus in areas of

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Montana with an average annual rainfall less than 305 mm, both in irrigated and dryland fields.

Wireworms are a complex of many different species that can have diverse life histories. A better understanding of the biology and ecology of crop-infesting wireworm species is needed, yet is currently difficult because only about 10% of cropland species are described for the larval stages. As a result, previous taxonomic summaries of wireworms in Montana cropland have probably been inaccurate. Hastings & Cowan

(1954) collected 49 Elateridae larvae from a heavily infested field near Denton, Montana.

Identifications were only made to genus, one as Limonius sp. and 48 as “probably Athous sp.” Mail (1932) reported L. canus as the most common pest of irrigated land in Montana.

The current survey is much broader geographically, yet did not find any Athous sp. or L. canus infesting cereal cropland. Long-term changes to cropping systems, such as

Montana’s adoption of minimum tillage practices, may shift the composition of pest species over time. However, a deeper understanding of wireworm species complexes will certainly expand our understanding of how farming practices as well as geographic and climatic factors can affect cropland wireworm distribution.

A surprising result of this survey was the large percentage of small grain producers that had fields infested with low numbers of wireworms in fields with no known prior history of this pest. If producers reported a history of wireworms in their field, trap catches from those fields were high (average of 4.1 per trap). However, low numbers of wireworms (an average of 0.5 per trap) were caught in 36.8% of fields with no reported history of wireworms. This result may indicate that wireworm populations

123 are becoming established more broadly in Montana’s cropland, and their populations may continue to grow over the next decade. However, specific surveys need to be designed to test this hypothesis, as these low numbers may also represent endemic populations.

Acknowledgments

We would like to thank all the producers who participated in the 2011–2013

Montana surveys and Frank Etzler for his assistance with identifying wireworm larvae.

We also would like to thank Emily Rohwer, Hannah Johnson, Alix Bold, Branden

Brelsford, Ammiel Branson, Meghan McGauley, Laura Morales and Diana Florian for assistance preparing and sorting the traps. Thanks to David Gettel for providing space at the MSU Post Farm for the Berlese funnel array. This study was supported in part by funds from the Montana Wheat and Barley Committee, Montana Seed Potato Producers

Association and USDA Crops at Risk Grant 2010-51100-21547.

124

Table 5.1. Incidence of wireworms in 214 crop fields surveyed across Montana, 2011– 2013. The number of fields positive for wireworms (at least 1 wireworm / trap set) is tabulated separately based on producer-reported field history. Each trap set contained five canister traps. Known History of Subset of Traps With Larval Count > 1 # Fields Wireworms in # Larvae/Trap Set Surveyed # Fields (%) Field? Range Mean+S.D. Yes 59 37 (62.7) 1–224 20.57+43.89 No 125 46 (36.8) 1–10 2.61+2.18 No Answer 30 12 (40.0) 1–15 4.83+4.62 Total 214 95 (44.4) 1–224 9.82+28.59

Figure 5.1. A. Number of fields surveyed for wireworms by county and year in Montana. The number of fields surveyed each year within each county is indicated numerically within symbols used to represent survey year.

125

Figure 5.2. Incidence of wireworms trapped in 31 counties across Montana during 2011– 2013. At least eight species of wireworms were collected from the 95 cereal fields surveyed, with the five major species shown here. Each field positive for a wireworm is represented by a colored symbol, the shape of the symbol denotes the survey year and the color denotes the species caught. A field infested by more than one species is represented by overlapping and hollow symbols. The approximate location of the Continental Divide is shown in purple.

126

Figure 5.3. Abundance of each species of wireworm sampled from 95 cereal fields across Montana. The number of wireworms collected from a field (a set of five traps) is presented categorically on the x-axis. The y-axis displays the number of fields in each category, for each of the five species collected in the survey. Data from the three years survey is pooled.

127

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Bryson, H. R. 1930. A study of field practices as related to wireworm infestations (Elateridae). Journal of Economic Entomology 23:303–315.

Comstock, J. H. & M. V. Slingerland. 1891. Wireworms. Bulletin 33 Cornell University Agricultural Experiment Station.

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Forbes, S. A. 1891–1892. Eighteenth Report of the State Entomologist on the noxious and beneficial insects of the state of Illinois. Springfield, Illinois, 149 pp.

Etzler, F. E. 2013. Identification of Economic wireworms using traditional and molecular methods. Unpublished M.S. thesis, Montana State University, Bozeman, 287 pp.

Glen, R. 1935. Contributions to the morphology of the larval Elateridae (Coleoptera) No. I: Ludius aeripennis destructor Brown. The Canadian Entomologist 67:231–238.

Glen, R. 1950. Larvae of the elaterid beetles of the tribe Leptuoidini (Coleoptera: Elateridae). Smithsonian miscellaneous collections 111(11):1–246.

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Jewett, H. H. 1940. Observations on life history of Aeolus mellillus. Journal of Economic Entomology 33(5):816–816.

Jewett, H. H. 1945. Life history of the wireworm Conoderus bellus (Say). Kentucky Agriculture Experiment Station Bulletin 472:1–8.

Johnson, P. J. 2009. Classification of the Nearctic genera of Elateridae. Available from http://www.sdstate.edu/ps/Severin-McDaniel/project-elater/canada- contintentalus/loader.cfm?csModule=security/getfile&PageID=688179 (accessed 20 August 2011).

LaGasa, E. H., S. Welch, T. Murray, and J. Wraspir. 2006. 2005 Western Washington delimiting survey for Agriotes obscurus and A. lineatus (Coleoptera: Elateridae), exotic wireworm pests new to the United States. Washington State Department of Agriculture Publication 805, 144 pp.

Lane, M. C. 1925. The economic wireworms of the Pacific Northwest (Elateridae). Journal of Economic Entomology 18:90–95

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Morrill, W. L. 1983. Early history of cereal grain insect pests in Montana. Bulletin of the Entomological Society of America 29(4):24–28.

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Vernon, R. S., W. Van Herk, J. Tolman, H. O. Saavedra, M. Clodius & B. Gage. 2008. Transitional sublethal and lethal effects of insecticides after dermal exposures to five economic species of wireworms (Coleoptera : Elateridae). Journal of Economic Entomology 101:365–374.

Vernon, R. S., W. G. van Herk, M. Clodius & C. Harding. 2013. Crop protection and mortality of Agriotes obscurus wireworms with blended insecticidal wheat seed treatments. Journal of Pest Science 86:137–150.

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CHAPTER SIX

DETERMINING THE POTENTIAL FOR CEREAL CROP INJURY BY WIREWORM SPECIES COMMONLY FOUND INFESTING CROPLAND IN MONTANA

Contribution of Authors and Co-Authors

Manuscript in Chapter 6

Author: Anuar Morales-Rodriguez

Contributions: Conceived and implement the study design the data collection and analysis. Collected and analyzed data. Wrote the manuscript.

Co-Author: Kevin W. Wanner

Contributions: Provided feedback in the study design, data analysis and comments to the manuscript.

131

Manuscript Information Page

Anuar Morales-Rodriguez and Kevin Wanner Canadian Entomologist. Status of Manuscript: X Prepared for submission to a peer-reviewed journal Officially submitted to a peer-review journal Accepted by a peer-reviewed journal ____Published in a peer-reviewed journal

Published by Cambridge University Press.

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Abstract

Click beetles are the adult stage of wireworms comprised of a large number of insects with about 10,000 described species in 400 different genera worldwide. Little is known about the varying ecological roles of wireworms and their impact in agriculture.

Some species are abundant in crop fields without causing damage or are reported only as regionally important. A species complex is more complicated to understand and manage.

Using baited traps and soil cores, we determined which species are causing damage in cereal crops within the complex of species present in Montana’s fields. In greenhouse trials the potential of H. bicolor, L. californicus and L. infuscatus to injure both wheat and barley plants was quantified and in the field their association with crop plants was confirmed. Our results suggest that L. californicus has the greatest damage potential among the three species.

Introduction

Identifying the species of wireworm present in a field and understanding their different ecological roles is fundamental in the development of effective management strategies (Pedigo 1989; Morales et al. 2009). Wireworms occur most often as a complex of soil dwelling insects with diverse feeding habits and thus, their role in this ecosystem is not always clear. For example, in Canada 30 species are reported as economically important (Benefer et al. 2012). However, the larvae of some of these species were found abundantly in crop fields without causing damage and their pest status is not clear.

MacLeod and Rawlins (1935) found large populations of Hypnoidus abbreviates (Say)

133 larvae in close proximity to potato (Solanum tuberosum L.) plants, but damage to the tubers was not observed, suggesting this species was not a pest of potato. In fact, a number of species of elaterid larvae are saprophagous and feed on plant litter and soil organic matter (Hemerik and de Fluiter 1999; Langenbuch 1932; Schaerffenberg 1942).

In the Czech Republic, Jedlička and Frouz (2007) have found saprophagous wireworms such as Athous niger (L.), A. subfuscus (Müller) and A. vittatus (Fab.) and carnivorous wireworms such as Dalopius marginatus (L.) and Agrypnus murinus (L.) in the same field with Agriotes obscurus L., one of the most important crop damaging wireworm species in Europe. Carnivorous species such as A. murinus L. also occur in arable soils

(Schimmel 1989). Stirrett (1936) lists A. mellillus as a pest in Ontario, Canada while

Doane (1977a) reports that it might reduce populations of the phytophagous species

Ctenicera destructor (= Selatosomus aeripennis (Brown)) and H. bicolor (Eschscholtz) by feeding on their eggs. One of the main wireworm pests of many crops in California,

Limonius californicus (Mannerheim), is an effective predator of sugar beet root maggots

(Stone 1941).

The pest status of a single species of wireworm may depend on the type of crop grown and this may also vary by geographical region. Glyphonyx bimarginatus Schaeffer is the second most important wireworm pest of sugarcane (Saccharum officinarum L.) in

Florida, but is not considered of economic importance to potato (Deen and Cuthbert

1955). Larvae of Agriotes sputator L. and A. niger, both serious pests of vegetables in

Europe, entered the United States with nursery stock in the 1920s and have not been reported as pests of vegetables in the U.S. Most elaterid larvae are generalist herbivores

134 and wireworms have been reported as serious economic pests of at least 40 different field and specialty crops in 16 different plant families (Table 2, Chapter 1). Several species have been reported to damage specific crops worldwide. For example, 39 species representing 21 elaterid genera have been reported to damage potato globally (Jansson and Seal 1994).

Three species of wireworm were found commonly infesting cereal crops in

Montana: H. bicolor, L. californicus and L. infuscatus (Morales et al. 2014; Chapters 2 and 3). A mixture of germinating wheat and barley seed was used as an attractive bait to sample potential pest species from the cropland. With such diverse life histories represented by a complex of wireworm species, germinating seed that emits CO2 might also attract species that are not herbivorous. Two obvious examples are saprophagous species attracted to emissions from microbes that decompose plant material and predaceous species attracted by the respiration of other insects. To characterize the pest status of wireworms sampled from cropland in Montana, it is important to determine their potential to injure those crops. In this study, the potential of H. bicolor, L. californicus and L. infuscatus to injure wheat and barley plants was confirmed by demonstrating an association of these species with the crop plants in the field and by their potential to damage plants in greenhouse trials.

Methodology

Field Experiment

The composition of wireworm species associated with wheat and barley plants in

135 the field was determined by soil core samples centered on a row of crop plants. The species found in soil core samples was compared to the species caught in attractive bait traps. A stocking trap consisting of disposable pantyhose stocking (Foot Sox®) filled with 125 ml of a 50:50 mixture of wheat and barley grain was used as an attractive bait trap. After soaking the stocking trap in water for 24 hours, the traps were buried 10 cm below the soil surface in commercial small grain fields infested with wireworms.

Detailed methods are described in described in Chapter 2. Soil core samples were taken with a cup cutter (Golf Hole Cutter, Doyle Golf Cedar Falls, IA) within two meters of the stocking bait traps, on the date that the stocking traps were retrieved. Each soil core had a volume of 1.57 liters (10 cm diameter x 20 cm height). On each sampling date bait trap and soil core samples were taken from 10 replicated locations at several different times over the growing season, in four commercial small grain fields located near Denton,

Conrad, Townsend, and Bozeman (Table 1). During 2011 a single soil core (1.57 liters) was sampled at the location of a bait trap, while in 2012, three core samples were taken at the location of each bait trap (4.71 liters of soil). Wireworms from the soil samples were extracted using an array of 200 Berlese funnels. Larvae collected from each sample were preserved in 95% alcohol for identification.

Greenhouse Experiments.

Two-Choice Test. A row of 5 hard red spring wheat (variety ‘Bullseye’) seeds was planted parallel to a row of 5 barley (variety Conrad) seeds. ‘Bullseye’ (B02-0081)

(Agripro®, Syngenta Cereals, Berthoud, CO) is a Pacific Northwest-adapted hollow stem

136 wheat with good disease and Hessian fly resistance and ‘Conrad’(B5057) (Busch

Agricultural Resources, Inc. Idaho Falls, ID) is a Pacific Northwest-adapted two-row malting barley. Seed were sown in a 0.5 liter pot filled with “Montana soil mix” commonly used in the MSU’s greenhouse. The Montana mix is a combination of mineral soil, Canadian sphagnum peat moss and washed concrete sand blended to a ratio of 1:1:1 by volume. Individual seeds were spaced 1.0-1.5 cm apart and the two parallel rows were

5.0 cm apart. Twenty-four hours after planting, a single wireworm larva was released at the center of the space between the two rows. Larger wireworms were selected by weight,

> 500 mg for L. californicus and L. infuscatus and > 200 mg for H. bicolor, a smaller species. Wireworms were held at room temperature for 24 h prior to infestation.

Wireworms that had not burrowed into the soil one hour after their release were replaced with a new insect. Twenty replicated pots were evaluated for each wireworm species in 2012 and 2014. The pots were held in a greenhouse with constant temperature

(25˚C ± 2˚C) and photoperiod of 12:12 h (dark: light). Damage was evaluated 14 days after infestation (DAI), as the number of plants per pot and dry weight of above ground stem and leaf tissue. The plant tissue was dried in an oven (38˚C) for 8 days prior to weighing. The pots were divided between the two rows prior to recovering the wireworms and their position noted.

No-choice Test. Using similar methodology as described above for the two-choice test, a no-choice experiment was conducted. Ten seeds of spring wheat (variety Bullseye) were planted in two parallel rows in a 0.5 liter pot. Twenty-four hours after seeding the pots, one, three or five large wireworm larvae were infested between the rows as

137 described for the two-choice test. The number of plants per pot and dry plant weight was recorded 14 DAI. Ten replicated pots were evaluated for L. californicus in 2012 and

2014.

Data Analysis.

The composition of wireworm species from soil cores and stocking bait traps was analyzed using a contingency table and chi-square test on pooled data. A paired sample t- test was used to analyze differences in damage to wheat and barley plants in the two- choice experiment. Simple linear regression of the number of plants and the plant dry weight (g per pot) versus number of insects per pot was performed using SAS 9.3 2002-

2010 SAS Institute Inc., Cary, NC, USA. and/or JMP®, Version 10.0.2. 2012 SAS

Institute Inc., Cary, NC.

Results

Field Experiment.

In 2011, 478 wireworms were collected from the stocking traps deployed in four different fields over three sampling dates and only 47 from the adjacent soil cores, a ratio of 10:1. Seven species were identified from the combined 525 samples: L. californicus

(53.5% of the total), L. infuscatus (29.5%), H. bicolor (10.5%), A. mellillus (5.5%),

Dalopius spp. (0.6%), Agriotes spp. (0.2%) and S. aeripennis (0.2%). The three species with a frequency of less than 1.0% were pooled into a single category termed “others”

(Table 2). All four species and the “other” category were represented in both of the sample collections (bait traps and soil core samples, Table 2). For statistical analysis, the

138 other category was expanded to include A. mellillus and H. bicolor to avoid having too many cells in the contingency table with an expected frequency less than 5. The frequency of wireworm species caught in 2011 was independent of the method used for their collection, stocking bait traps versus soil core samples (Table 3, X2-test P = 0.76).

In 2012, 158 wireworms were collected from the stocking traps deployed in four different fields over three sampling dates and 57 from the adjacent three soil core samples, a ratio of 2.8:1. Six species were identified from the combined 215 samples: L. californicus

(62.8% of the total), H. bicolor (27.4%), A. mellillus (7.0%), Agriotes spp. (0.9%),

Dalopius spp. (0.9%) and L. infuscatus (0.9%). Agriotes spp. and Dalopius spp. were combined in Table 2 as “others”. All four species and the “other” category were represented in both of the sample collections (bait traps and soil core samples, Table 2).

For statistical analysis, the other category was expanded to include A. mellillus and L. infuscatus to avoid having too many cells in the contingency table with an expected frequency less than 5. The frequency of wireworm species caught in 2012 was dependent on the collection method, (Table 4, X2-test P < 0.0001). Inspection of expected frequencies revealed that the “other” category yielded atypically greater deviations from expected. An a priori 2 X 2 contingency table of H. bicolor and L. californicus found no dependence of the frequency of wireworm species on the method used for sampling (P =

0.22, Yates chi-square, corrected for continuity).

139

Greenhouse Experiments.

Two-choice Test. In 2012 a preference of the three species of wireworm for wheat over barley seeds and seedlings was observed. At 14 DAI, 85% of L. californicus,

80% of H. bicolor and 75% of L. infuscatus were found in the soil on the side of the pot planted with wheat. (Table 5). For all three species, there was a difference in the amount of damaged wheat versus damaged barley, measured as the number of living plants and the stem and leaf dry weight. In all cases wheat plants were more heavily damaged but the lesser damage caused by L. infuscatus was significant at P > |t| = 0.053 for number of plants and at P > |t| = 0.059 for dry weight (Table 6).

In 2014 fewer wireworms were located on the wheat side of the bioassay pot at 14

DAI, 55% of H. bicolor, 55% of L. californicus and 70% of L. infuscatus. No preference of the three species of wireworm for wheat compared to barley seeds and seedlings was observed (Table 5). Differences in damage to wheat vs barley caused by the three different species were also not detected in 2014 with the exception of the number of plants for H. bicolor (P > |t| = 0.0016) and dry weight for L. infuscatus (P > |t| = 0.037).

The limited detectable differences in 2014 was due to reduced feeding activity compared to experiments conducted in 2012. Overall seedling mortality was also higher in 2012 than in 2014.

No-choice Test. Experimental data from 2012 and 2014 were pooled to perform simple linear regression of damage to the number of wireworms infested. The number of dead seedlings increased with greater numbers of L. californicus in the pots. The

140 relationship was linear, plants lost = 0.57 + 1.68 wireworms, R2 = 0.90. Total stem plus leaf dry weight decreased with greater numbers of L. californicus in the pots. The relationship was linear, dry weight loss = 0.84 + 1.47 wireworms, R2 = 0.72 (Figure 1).

Discussion

Field and greenhouse experiments conducted in this study confirm the potential pest status of H. bicolor, L. californicus and L. infuscatus previously found infesting cereal fields in Montana. Four other species collected less frequently, A. mellillus,

Agriotes spp., Dalopius spp. and S. aeripennis, were found using both sampling methods

(bait traps and soil cores). In 2012 however, their proportions were found to be dependent on sampling method. While all seven species collected in this study were listed by Seibert (1993) as potential pests of cereal grains, further study of the four minor species is required to establish their pest status.

Parker (1994; 1996) while evaluating techniques to assess wireworm populations in arable crops such as potato fields compared different attractive food baits with soil core samples. No difference in the species composition between the bait traps and core samples was detected when the total number of wireworms trapped was analyzed.

Overall, baits captured more wireworms than soil cores. Similar to Parker (1994; 1996), our study captured more wireworms in the bait traps compared to the soil core samples.

Stockings traps deployed for 14 days collected 10 times as many wireworms compared to a soil core taken on the day that the stocking traps were collected. This general ratio

141 appeared accurate, since increasing the soil cores by a factor of 3 in 2012 resulted in a bait trap to soil core ration of 2.8:1.

A soil core sample centered over a crop plant provides a sample of the species directly associated with the crop plant, but it does not demonstrate feeding damage. Due to the high frequency of zero counts in core samples, these absolute measures could not be correlated with catches from the relative (stocking) samples at specific sites and sampling dates. After pooling all absolute and relative samples a contingency table analysis revealed no difference between the proportion of the three main species associated with the crop-plants and those caught with the attractive bait. Similar results were presented by Onsager (1969) and Parker (1994). Parker reported no significant relationship of the any of baited techniques used with the soil core. Onsager suggested taking a very large number of core samples to compare to the baited technique to solve the inconsistency. In this study the soil cores were sampled within 2 m of the bait trap.

Future studies could include soil cores sampled at increasing distances from the bait trap, to avoid confounding effects of wireworms attracted to the bait. In 2011, one single core

(10 cm diameter) collected an average 0.39 wireworms and in 2012, the average was 0.48 wireworms per three-soil cores. The proportion of total wireworms collected using soil cores increased when the number of core samples was increased: 8.95% of the total was collected with a single soil core in 2011 and 26.51% of the total catche was collected with three soil core samples in 2012, approximately three times greater than the previous year. Yates and Finney (1942) suggested that slight biases in wireworm surveys are not so important. On the other hand, the cost of sampling could influence the decision,

142 because collect more or bigger samples requires more time and effort, and hand sorting the wireworms in the field or even when using Berlese funnels increases the processing time and cost.

Wireworms are mostly generalist herbivores and have been reported as a serious economic pest in at least 40 different field and specialty crops in 16 different plant families (Table 2, Chapter 1). Little is known about their host preferences. Using a no- choice test three varieties of potatoes were significantly more susceptible to damage caused by Agriotes spp. (A. obscurus and A. lineatus mix) (Johnson et al. 2008). In the same study, wireworms fed more on the susceptible varieties of potato, consuming more tissue and gaining more weight. When given a choice, A. obscurus and A. lineatus always preferred the susceptible varieties over the less-susceptible (Johnson et al. 2008).

In the field, wireworms have been observed to prefer cereal crops over other crops. For example, field experiments showed a preference of wheat over strawberries (Vernon et al.

2000) and peas over wheat or oilseed or radish crops (Landl and Glauninger 2013) when these crops were planted as trap crops, however, the mechanism of preference was not studied.

In this study all three species of wireworm studied caused more injury to wheat compared to barely in two-choice tests. Field observations (data not published) are consistent with these lab results, less damage to barley plots compared to wheat plots planted within the same field (infested with L. californicus and H. bicolor) have been observed. First, this confirms the pest status and ability of each of these species to injure cereal crops. Second, it demonstrates that the degree of injury can vary with the type of

143 crop plated, even among similar plat species. No-choice tests using only L. californicus found that measures of damage were correlated to the number of wireworms in the pot, providing evidence that correlations may be used to help develop economic damage thresholds. All three species tested strongly preferred wheat over barley in 2011 two- choice tests, but no difference was observed in 2012. Limonius canus preferred wheat and barley over other baits and no difference was detected between wheat and barley (Horton and Landolt 2002). Wireworms orient towards CO2 production zones or gradients

(Doane et al. 1975) but little to no research is has been conducted to understand the role of other plant cues such as soil volatiles in the attraction and preference of wireworms to their host. Recently, Gfeller et al (2013) isolated 21 volatile organic compounds from young barley roots and evaluated them in an olfactometer assays with A. sordidus. Only slight differences in wireworm attraction to blends of volatile organic compounds were detected and specific chemical stimuli could not be identified. Clearly, the chemical ecology of wireworms and their hosts is an important area of future study that may help illuminate host plant preference and injury, and lead to IPM strategies based on olfactory cues, such as attractive baits and traps.

We demonstrate that three species commonly infesting Montana cropland, H. bicolor, L. californicus and L. infuscatus, are found in the soil near growing wheat and barley plants. Using potted greenhouse bioassays their ability to injure and damage wheat and barley crop plants is evident. Further studies are needed to fully clarify and quantify wireworm injury and damage to barley, wheat and other Montana crops to develop crop- specific economic injury levels to facilitate IPM decision making.

144

Acknowledgments

We thank Frank Etzler, Meghan McGauley, Hannah Johnson, and Laura Morales for their help in conducting this work. David Weaver to provide comments to improve the manuscript. This study was supported in part by funds from the Montana Wheat and

Barley Committee, Montana Seed Potato Producers Association and USDA Crops at Risk

Grant 2010-51100-21547.

145

Table 6.1. Wireworm sampling locations in Montana. Elevation is in meters above sea level. Crops planted or managed for each given year. Place Elevation Crops 2011 and 2012 Irrigation Type soil Spring Wheat-Spring Non Clay- Bozeman 1495 Wheat irrigated Sandy Spring Wheat- Spring Conrad 1080 Irrigated Clay Wheat Non Clay- Denton 1096 Winter Wheat-Lentils irrigated Sandy Winter Wheat -Spring Tolston 1232 Irrigated Sandy Wheat

146

47 57

478 158

Total

(11.1%)

4 1 2 2

Other

1 1

139

Selatosomus aeripennis

L. infuscatus

24 32

257 103

spp. (66.7%) and and spp. (66.7%)

L. californicus

Dalopius

51 40 19

spp. (22.2%),

H. bicolor

2 3

27 12

Agriotes

A. mellillus

Number of wireworms by species collected with soil core and stocking and 2012 in four in of by 2011 and species collected soil with Number core wireworms

2011 2012

Others correspond to correspond Others

Table 6.2. Table small grain fields Montana at different Trap Stocking Soil core Stocking Soil core a

147

Table 6.3. Chi- square contingency table analyzing the relationship between sampling methods (stocking bait traps and single soil cores) on the overall proportion of wireworm species pooled across four locations in Montana in 2011. L. californicus and L. infuscatus were the two main species collected in 2011; all minor species were pooled under the category of “others”.

Trap L. californicus L. infuscatus Others Total Stocking Count 257 139 82 478 Expected 255.8 141.1 81.0 Soil core Count 24 16 7 47 Expected 25.2 13.9 8.0 Total Count 281 155 89 525 Expected 281.0 155.0 89.0

Table 6.4. Chi- square contingency table analyzing the relationship between sampling method (stocking bait trap and three soil cores) on the proportion of wireworm species pooled for four locations in Montana in 2012. L. californicus and H. bicolor were the two main species collected in 2012; all minor species were pooled under the category of “others”.

Trap H. bicolor L. californicus Other Total Stocking Count 40 103 6 149 Expected 40.9 93.6 14.6 Soil core Count 19 32 15 66 Expected 18.1 41.4 6.4 Total Count 59 135 21 215 Expected 59.0 135.0 21.0

Table 6.5. Host plant preference of three wireworm species, H. bicolor, L. californicus and L. infuscatus, for wheat and barley in a potted greenhouse study. Number of wireworms on the side of the pot planted with barley or wheat plants.

Species Wheat Barley Z-value P > |Z| 2012 H. bicolor 16 4 -2.6833 0.0073 L. californicus 17 3 -3.1305 0.0017 L. infuscatus 15 5 -2.2361 0.0253 2014 H. bicolor 9 11 -0.4472 0.6547 L. californicus 9 11 -0.4472 0.6547 L. infuscatus 14 6 -1.7889 0.0736

148

0.91 0.37

0.059 0.037

test

0.0002

Pr>|t|

< 0.0001 <

36 ± 0.30

0.37 ± 0.35 0. 0.11 ± 0.26 0.01 ± 0.20 0.08 ± 0.39 0.09 ± 0.19

- - -

Difference

. californicus and and . californicus

Dry weight Dry

Wheat

0.39 ± 0.17 0.45 ± 0.18 0.36 ± 0.22 0.38 ± 0.17 0.43 ± 0.18 0.34 ± 0.22

Barley Barley

0.77 ± 0.31 0.80 ± 0.24 0.47 ± 0.23 0.37 ± 0.17 0.42 ± 0.10 0.25 ± 0.12

0.37 0.67

0.053

test

0.0008 0.0016

Pr>|t|

< 0.0001 <

0.80 ± 0.89 1.60 ± 1.23 0.55 ± 1.19 0.50 ± 0.60 0.31 ± 1.49 0.05 ± 0.51

Difference

Plants

Wheat

3.9 ± 0.79 3.3 ± 1.03 4.1 ± 1.02 4.5 ± 0.60 3.8 ± 0.83 4.9 ± 0.37

0 ± 0.22

Barley

choice potted greenhouse bioassay. The number of living plants and dry weight was recorded 14 days after weight recorded bioassay. number living and dry plants greenhouse was potted The of choice

4.7 ± 0.57 4.9 ± 0.30 4.7 ± 0.59 5. 4.0 ± 1.00 4.9 ± 0.31

2012 2014

Damage to wheat and barley plants by three different wireworm species, H. bicolor, L wireworm bicolor, H. plants by to wheat different and barley species, Damage three

, in a two

Table 6.6. Table infuscatus infestation Species H. bicolor L. californicus L. infuscatus H. bicolor L. californicus L. infuscatus

149

Figure 6.1. Linear regression of wheat plant damage by L. californicus to the number of larvae infested into no-choice potted greenhouse bioassay. A) Number of seedlings destroyed/lost vs the number of larvae infested, B) Dry weight of seedlings vs the number of larvae infested.

150

References

Deen, O. T. and Cuthbert, F. P. 1955. The distribution and relative abundance of wireworms in potato-growing areas of the southeastern states. Journal of Economic Entomology 48: 191-193.

Doane, J. F. 1977b. The Flat Wireworm, Aeolus mellillus: Studies on seasonal occurrence of adults and incidence of the larvae in the wireworm complex attacking wheat in Saskatchewan. Environmental Entomology 6: 818-820.

Gfeller A., Laloux M., Barsics F., Kati D.E., Haubruge E., du Jardin P., Verheggen, F. J., Lognay, G., Wathelet, J. P., and Fauconnier, M. L. 2013. Characterization of volatile organic compounds emitted by barley (Hordeum vulgare L.) roots and their attractiveness to wireworms. Journal of Chemical Ecology 39, 1129–1139.

Hemerik L, de Fluiter R. 1999. No preference of the wireworm, Agriotes lineatus (L.), for four grass species. Proceedings of the Section Experimental and Applied Entomology of the N.E.V. 10:175–181.

Horton, D. and Landolt, P. 2002. Orientation response of Pacific Coast Wireworm (Coleoptera: Elateridae) to food baits in laboratory and effectiveness of baits in field. The Canadian Entomologist 134: 357-367.

Jackson, M. D., Harrison, H. F., Ryan-Bohac, J.R. 2012. Insect Resistance in Sweetpotato Plant Introduction Accessions. Journal of Economic Entomology. 105(2): 651-658.

Jedlička, P. and J. Frouz . 2007. Population dynamics of wireworms (Coleoptera, Elateridae) in arable land after abandonment. Biologia (Bratislava) 62(1): 103-111.

151

Landl, M. and Glauninger, J. 2013. Preliminary investigations into the use of trap crops to control Agriotes spp. (Coleoptera: Elateridae) in potato crops. Journal of Pest Science 86(1): 85-90.

Ladell, W. R. S., Cochran, W. G. 1938. Field experiments on the control of wireworms. Annals of Applied Biology 25(2):341-382.

Langenbuch, R. 1932. Beiträge zur Kenntnis der Biologie von Agriotes lineatus L. und Agriotes obscurus L. Zeitschrift für Angewandte Entomologie 19(2): 278-300.

MacLeod, G. F. and. Rawlins, W. A. 1935. A comparative study of wireworms in relation to potato tuber injury. Journal of Economic Entomology 28: 192-195.

Morales-Rodriguez, A., O’Neill, R., and Wanner, K. W. Accepted. A survey of wireworm (Coleoptera: Elateridae) species infesting cereal crops in Montana. Pan-Pacific Entomologist.

Onsager, J. A. 1969. Sampling to Detect Economic Infestations of Limonius spp. Journal of Economic Entomology 62(1):183-189.

Parker, W. E. 1994. Evaluation of the use of food baits for detecting wireworms (Agriotes spp., Coleoptera: Elateridae) in fields intended for arable crop production. Crop Protection 13: 271-276.

Pedigo, L. P. 1989. Entomology and Pest Management. MacMillan, New York & Collier Macmillan, London. 646 pp.

Sasscer, E. R. 1924. Important foreign insect pests collected on imported nursery stock in 1923. Journal of Economic Entomology 17: 443-444.

Schaerffenber, B. 1942. Elateridenlarven der Kiefernwaldstreu. – Z. angew. Entomology 29: 85-115.

Schimmel, R. 1989. Monographie der rheinland-pfälzischen Schnellkäfer (Insecta: Coleoptera: Elateridae). – Pollichia, Bad Dürkheim, Germany.

152

Seibert, C. E. 1993. A faunal survey of the Elateroidea of Montana. Montana State University, Department of Plant Science and Plant Pathology. MSc Thesis. Bozeman, MT. 320 pp.

Stirrett, G. M. 1936. Notes on the “flat wireworm,” Aeolus mellillus Say. The Canadian Entomologist 68: 117-118.

Stone, M. W. 1941. Life history of the sugarbeet wireworm in southern California. Technical Bulletin of the U.S. Department of Agriculture No. 744.

Yates, F., Finney, M. A. 1942. Statistical problems in field sampling for wireworms. Annals of Applied Biology 29(2): 156-167.

153

CHAPTER SEVEN

EFFICACY OF THIAMETHOXAM AND FIPRONIL, APPLIED ALONE AND IN COMBINATION, TO CONTROL Limonius californicus AND Hypnoidus bicolor (COLEOPTERA: ELATERIDAE)

Contribution of Authors and Co-Authors

Manuscript in Chapter 7

Author: Anuar Morales-Rodriguez

Contributions: Conceived and implemented the study design, the data collection, and analyses. Collected and analyzed data. Wrote the manuscript.

Co-Author: Kevin W. Wanner

Contributions: Provided feedback in the study design, data analysis and comments to the manuscript.

154

Manuscript Information Page

Anuar Morales-Rodriguez; Kevin W. Wanner Pest Management Science Status of Manuscript: Prepared for submission to a peer-reviewed journal Officially submitted to a peer-review journal X Accepted by a peer-reviewed journal ____ Published in a peer-reviewed journal

Published by John Wiley & Sons, Inc. Submitted on November 2013

155

Abstract

Background: Wireworms, the larval stage of click beetles (Family Elateridae), are significant soil pests of wheat and barley crops in the Pacific Northwest. At present, few pest management alternatives exist. For several decades, wireworms were effectively controlled by first generation insecticides applied to the soil or as seed treatments.

Currently used neonicotinoid insecticides protect crop seeds and germinating seedlings by temporary toxicity but limited mortality. As a result, field populations may increase, reaching levels too high for crop protection. In this study we investigated the combination of two insecticides to achieve crop protection as well as insect mortality in wheat fields.

Results: Laboratory bioassays using wheat seed treated with fipronil at 1.0 and 5.0 grams AI 100 kg-1 of seed resulted in 72-90% mortality of two wireworm species,

Limonius californicus and Hypnoidus bicolor. At a rate of 39 g AI 100 kg-1 kg of seed, eight times higher than the high rate of fipronil, thiamethoxam caused only 10-31% larval mortality in the bioassays, but did protect developing wheat stands from damage in field trials. Field plots planted with wheat seed treated with both 5.0 g AI of fipronil and 39.0 g

AI of thiamethoxam 100 kg-1 of seed had 83% fewer wireworms the following year compared to untreated check plots. No reduction in population was observed in plots treated with 39.0 g of thiamethoxam alone.

Conclusions: Fipronil and thiamethoxam can be combined as a seed treatment to protect wheat crops from wireworm damage and reduce larval populations in the field.

Keywords: Wheat, insecticide interactions, Neonicotinoids, Synergism.

156

Introduction

Wireworms, the larval stage of click beetles (Family Elateridae), are historically significant pests of field crops in the United States with few to no effective management techniques1. Wireworms live in the soil for one to nine years before completing development2,3,4,5, development time being species-dependent. During this time larvae feed on seeds, germinating seedlings, and roots and stems of many different crops, causing thin and/or patchy stand development and reduced yields. Effective control was not achieved until the insecticide era that began in the 1950s, and resulted in inexpensive and effective broad-spectrum insecticides for crop protection6. For example, lindane was used as an insecticidal seed treatment to manage wireworm damage in many affected crops for more than 50 years7,8,9. Recently, crop damage by wireworms has been increasing in the Pacific Northwest region of North America. This resurgence in pest status has been attributed in large part to the recent removal of many conventional insecticides that were used to control them, as well as the ineffectiveness of their second- generation replacements9, 10. Neonicotinoid insecticides with active ingredients (AI) such as imidacloprid (eg. Gaucho®) and thiamethoxam (eg. Cruiser®) are current standards for seed treatment of a wide variety of field crops. However, research has demonstrated that neonicotinoid-class insecticides typically kill only 0-30% of the wireworm population and protect crops from damage through a mechanism of intoxication, where the larvae become sick and stop feeding but subsequently recover9, 10, 11. As a consequence, populations in the soil can continue to increase and repeatedly attack crop plants10.

157

Vernon et al. (2013)12 reported better stand protection and wireworm mortality with a combination of thiamethoxam + fipronil (10 g and 1 or 5 g AI 100kg-1 seed, respectively) compared to fipronil and thiamethoxam applied alone, in fields infested with Agriotes obscurus. Based on LD50 values from contact toxicity studies, the insecticide fipronil is 100 times more toxic to wireworms compared to neonicotinoid- class insecticides.13 Low application rates of fipronil were investigated by Vernon et al.

(2013) to reduce the risk of residues accumulating in the soil as this insecticide has a relatively long half-life.

Montana is a major producer of wheat and barley crops in the US, commonly ranking 3rd nationally in barley and wheat production (USDA National Agricultural

Statistics Service, http://www.nass.usda.gov/). The 1,000,000 acres of barley and

5,770,000 acres of wheat planted in Montana during 2012 were valued at 0.25 and 1.1 billion dollars, respectively. Producer reports of wheat and barley crop damage by wireworms have increased in Montana during the last five years, coinciding with the delisting of lindane, the most commonly used insecticidal seed treatment. In this study we investigated thiamethoxam and fipronil applied to wheat seeds alone and in combination to control Limonius californicus (Mannerheim) and Hypnoidus bicolor (Eschscholtz), two common wireworm species in Montana. The intoxication of wireworms by thiamethoxam could reduce the amount of fipronil ingested, causing antagonistic interactions in mortality. We tested thiamethoxam in laboratory, greenhouse and field trials at its highest labeled rate of 39 g AI 100kg-1 seed (Crusier 5FS®) in order to detect potential antagonistic interactions when combined with fipronil.

158

Experimental Methods

Insects

Wireworm larvae used for the laboratory experiments were collected using stockings filled with 125 ml of a 50:50 mixture of wheat and barley grain as bait. After soaking in water for 24 hours, traps were buried 15-20 cm below the soil surface in commercial small grain fields infested with wireworms. The trap location was marked and covered with a one square foot piece of black plastic to warm the soil. After three weeks the traps were collected from the field and stored in a walk-in cooler at 4˚C. In

2011 larvae were sorted from the traps by hand, and in 2012 they were collected using

Berlese funnels. During May and June of 2011 L. californicus larvae were collected from commercial fields near Denton, MT (Barber Seed Services Inc., Fergus Co.) and Conrad,

MT (Mark Grubb Ranch Inc., Pondera Co.). During May of 2012 larvae were collected from a field near Kalispell, MT (Tutvedt Livestock Co., Flathead Co.). Hypnoidus bicolor larvae were collected in Conrad, MT (Mark Grubb Ranch, Pondera Co.) during

May and June of 2011 and 2012.

Insecticide Treatments

Spring wheat seed, Triticum aestivum L. variety Chouteau, was treated with two different insecticides, fipronil and thiamethoxam. Fipronil was formulated as an experimental insecticide at a rate of 500 g AI liter-1 (BASF 350 23 I, lot number 84051,

BASF Corporation, Research Triangle Park, NC). Thiamethoxam was formulated as

Cruiser® 5 FS, Syngenta Crop Protection Inc., Greensboro, NC. Fipronil was applied at a

159 rate of 1.0 and 5.0 g AI 100 kg-1 of seed and thiamethoxam at 39.0 g AI 100 kg-1 of seed.

The fungicides difenoconazole and mefenoxam (Dividend Extreme ®, Syngenta Crop

Protection Inc., Greensboro, NC) were added to all treatments at 15.0 g per100 kg-1 of seed.

Laboratory Trails

A single wireworm larva was placed in a 30 ml plastic cup (CometwareTM City of

Industry, CA) filled with approximately 28.0 g of greenhouse soil, a 50:50 combination of Montana and Sunshine mixes, raised to 12.0% moisture (w/w). The Montana mix was a combination of mineral soil, Canadian sphagnum peat moss and washed concrete sand blended to a ratio of 1:1:1 by volume. The Sunshine mix was a blend of Canadian sphagnum peat moss and horticultural grade Perlite. A single treated wheat seed was planted into each cup 2.0 cm deep 24 h prior to infestation. Larvae were selected by weight, > 500 mg for L. californicus and > 200 mg for H. bicolor. Wireworms were held at room temperature for 24 h prior to infestation. Wireworms that had not burrowed into the soil one hour after their release were replaced with a new insect. Bioassay cups were capped and stored in trays within plastic bags containing a damp sponge to maintain moisture levels. In the first experiment, an untreated control, one rate of thiamethoxam

(39.0 g AI 100 kg-1), two rates of fipronil (1.0 and 5.0 g AI 100 kg-1), and thiamethoxam plus the two rates of fipronil were tested. Each treatment consisted of ten bioassay cups that were replicated five times (n = 50 bioassay cups per treatment) for each wireworm species. For the dose response experiment, six rates of fipronil (0.001, 0.01, 0.1, 1.0, 5.0 and 10.0 g AI 100 kg-1 seed) as well as an untreated check were tested. The dose response

160 experiment was infested only with L. californicus. Bioassay cups were kept in a growth chamber set at 28˚C, 90 % relative humidity and a 24 h dark cycle. Mortality was assessed 30 days after treatment (DAT). Larval death was confirmed by either probing the thoracic and head areas to observe for body, leg, or mouthpart movement and/or by noting changes in body color to dark brown or black.

Greenhouse Trails

Greenhouse experiments were conducted at the Montana State University Plant

Growth Center. The average day/night greenhouse temperatures were 22.2˚C / 18.3˚C and the photoperiod was set at 14:10 h L:D. Assay units were 250 ml plastic pots filled with greenhouse soil as described for the laboratory assays. Five treated wheat seeds (at rates of either 1.0, 5.0 or 10.0 g fipronil 100 kg-1 of seed) were added to each pot 24 h prior to infestation. Seeds were planted 2.0 cm apart and 2.5 cm deep. Each treatment was replicated 10 times. After being held at room temperature for 24 h, five larvae of L. californicus or H. bicolor were released into each pot, and any that did not burrow into the soil within 1 h were replaced. After infestation, pots were kept in the greenhouse for four weeks, arranged in a completely randomized design. To each pot, 50 ml of water were added every other day. Wireworm mortality and plant mortality were assessed 30

DAT.

Field Trials

The field trial was conducted in a commercial small grain field near Conrad, MT with a history of wireworm infestation (Mark Grubb Ranch Inc.). During the spring of

161

2011 treated spring wheat seed (variety Chouteau, Northern Seed LLC, Conrad, MT) was planted in plots measuring 4 m x 4 m, with 0.66 and 0.5 m separating repetitions and plots, respectively. Each treatment was replicated four times. The plots were planted on

April 14, 2011 with an experimental plot drill (composed of a custom 4 row seeder with 4 cones) at a density of 90 seeds m-1 and 30 cm row spacing. Five treatments were planted in a randomized complete block design: 1) Untreated control, 2) Dividend Extreme®, 3)

Dividend Extreme® + 39.0 g thiamethoxam 100 kg-1 seed, 4) Dividend Extreme® + 5.0 g fipronil 100 kg-1 seed, and 5) Dividend Extreme® + 39.0 g thiamethoxam + 5.0 g fipronil 100 kg-1 seed. The following year, on May 10, 2012, the experimental plot was planted with untreated Clearfield® variety spring wheat (AP604CL, Barber Seed Service

Inc., Denton, MT at a density of 90 seeds m-1 and 30 cm row spacing. Plant stand counts

(number of plants m-1) were recorded 3, 7 and 11 weeks after planting in 2011 and 2012, from the center two rows, to avoid edge effects. A destructive 1 m row section was sampled from the center two rows to record dry weight (plants dried in an oven for 10 days) 11 weeks after planting. After maturing the grain was harvested from each plot using a Hege 140 plot combine (Hege Maschinen GmbH Hohebuch 5 D-74638,

Waldenburg). The grain was cleaned using an ASC-3 seed cleaner (Agriculex Inc.,

Guelph, Ontario, Canada), weighed, and the density evaluated using a filling Hopper and stand with a pint cup (SEEDBURO Equipment Company, Des Plaines, IL). Wireworm populations within treated plots were assessed using a single stocking trap deployed in the center of each plot 2 and 6 weeks after planting in 2012. After two weeks the traps were collected and stored in a walk-in cooler at 4˚C until they were sorted for wireworms

162 using a series of Berlese funnels. Collected larvae were preserved in 95% alcohol for identification.

Data Analysis

Mean mortality rates for each treatment were calculated after correcting for mortality in untreated checks (laboratory and greenhouse trials)14. Percent mortality was normalized using a square root transformation. Plant stand, yield and grain density data from the field experiments were normalized using a square root transformation. Data were subjected to analysis of variance (GLM). If treatment effects were significant,

Tukey’s test was employed to detect differences between treatment means. Synergistic, additive and antagonistic interactions between insecticides tested alone and in combination were determined using the X2 test15,16,17. The expected interaction mortality value, ME, for combined agents was calculated using the formula ME = MF + MT (1 –

MF/100), where MF and MT are the observed percent mortalities caused by the fipronil and thiamethoxam products alone, respectively. Results from the X2 tests were compared

2 2 2 to the X table value for one degree of freedom, using the formula X = (MFT - ME) /ME, where MFT is the observed mortality for the fipronil-thiamethoxam combinations. A non- additive effect between the two agents was inferred when the X2 value exceeded the table

17 value (3.841) . A positive or negative MFT - ME value was considered synergistic or antagonistic, respectively. The dose response mortality was analyzed by log-probit regression analysis to estimate lethal concentrations for 50% mortality (LC50). All statistical analyses were performed using SAS ver. 9.3 18.

163

Results

Laboratory Trials

Insecticide Interactions. Although wireworms were collected during two different years using different methods, mortality of both species tested was low in the untreated controls, ranging from 2 - 6% (Table 7.1). Furthermore, the bioassay results were consistent between the two test years. Although the year the bioassay was conducted was not a significant factor in treatment mortality (F1, 29 = 0.523; P = 0.5623), each year was analyzed separately rather than pooling the data.

In 2011, there was a significant effect of treatment for both species (F5, 29 = 49.39;

P < 0.0001 for L. californicus and F5, 29 = 43.19; P < 0.0001 for H. bicolor) on mortality at 30 DAT. Higher mortality was observed with the fipronil 5.0 g rate (89.8 and 85.6% for H. bicolor and L. californicus, respectively); followed by the fipronil 1 g rate (79.8 and 72.6% for H. bicolor and L. californicus, respectively) (Table 7.1). The mortality observed for seed treated with thiamethoxam alone was lower, 28.2% for H. bicolor and

10.0% for L. californicus. A non-additive effect on mortality was observed for both species when thiamethoxam was combined with fipronil at the 1.0 g rate (X2 = 11.71 and

6.26 for H bicolor and L. californicus, respectively) and the negative MFT - ME value indicates an antagonistic interaction between the two insecticides. The X2 analysis did not support a statistically significant non-additive effect when thiamethoxam was combined with fipronil at the 5.0 g rate (Table 7.2).

164

In 2012, there was a significant effect of treatment for both species (F5.29 = 20.61;

P < 0.0001 for L. californicus and F5, 29 = 10.73; P < 0.0001 for H. bicolor) on mortality at 30 DAT. Highest mortality was observed at the 5.0 g rate of fipronil (89.3 and 85.6% for H. bicolor and L. californicus, respectively), followed by the 1.0 g rate of fipronil

(77.1 and 72.6% for H. bicolor and L. californicus, respectively) (Table 7.1). Mortality from thiamethoxam alone was much lower, 31.4% for H. bicolor and 10.0% for L. californicus (10.0%). An antagonistic interaction between the two insecticides was observed for L. californicus (X2 = 6.395) when thiamethoxam was combined with 1 g of fipronil, and additive for H. bicolor. The interaction was additive for both species when thiamethoxam was combined with fipronil at the 5.0 g rate (Table 7.2).

Dose Response. Dose response experiments were completed in 2012 using L. californicus only. Sufficient numbers of H. bicolor were not available. The probit analysis revealed that wheat seed treated with fipronil had a dose-dependent effect on the mortality of wireworms in a bioassay cup. The LC50 of fipronil to L. californicus was

0.082 AI 100 kg-1 wheat seed (Table 7.3). Seventy percent mortality is predicted at a 1.8 g AI of fipronil 100 kg-1 wheat seed, corresponding well to mortality of L. californicus observed in Table 7.1. However, observed mortality at the 25 and 50 g rates of fipronil was only 78 and 90%. This levelling off of mortality at higher rates of fipronil reflects the reliance on feeding to ingest a lethal dose, and variation in the behavior of wireworms in the bioassay (feeding and molting status for example). A more accurate estimate of oral toxicity would be obtained by forced ingestion on the insecticide.

165

Greenhouse Trials

Seedling mortality in the absence of wireworms ranged from 2.0 – 6.0% (Table

7.4). Seedling mortality was 32.0 and 48.0% in pots planted with untreated seed and infested with H. bicolor and L. californicus, respectively. Fipronil treated seeds reduced seedling mortality and increased wireworm mortality in a dose dependent trend (F3, 39 =

213.26; P = < 0.0001 and F3, 39 = 95.74; P = < 0.0001 for H. bicolor and L. californicus, respectively) (Table 7.4). Higher mortality of H. bicolor (48.0%) was observed at the 1.0 g rate of fipronil compared to L. californicus (28.0%). However, at the 5.0 g rate similar mortality was observed for both species (91.5% and 90.5% for H. bicolor and L. californicus, respectively). At the 10.0 g rate of fipronil, mortality of H. bicolor was

100% while it was only 88.5% for L. californicus. Complete seedling protection was achieved at the 1.0 g rate in pots infested with H. bicolor, and at the 5.0 g rate for L. californicus, compared with the untreated control (F4, 49 = 18.0; P = < 0.0001 and F4, 49 =

47.33; P = < 0.0001 for H. bicolor and L. californicus, respectively) (Table 7.4).

Wireworm mortality at the 5.0 g rate was similar to that observed in the laboratory assay, however, at the 1.0 g rate mortality in the pots was lower (Tables 7.1 and 7.4).

Field Trials

Three species of wireworms were identified infesting the plots in 2012: Aeolus mellillus, H. bicolor and L. californicus (Table 5). Hypnoidus bicolor was the most common species followed by L. californicus, and A. mellillus. At the first sampling date

(May 21, 2012) no significant differences among the treatments were observed in the total numbers of wireworms collected (F4, 19 = 0.71; P = 0.595), although the treatments

166 containing fipronil had the lowest counts. Higher numbers were collected from the untreated plots at the second sampling date (June 23, 2012) and a significant treatment effect was observed (F4, 19 = 3.11; P = 0.047) (Table 7.5). Experimental plots planted with seed treated with thiamethoxam (39.0 g AI 100 kg-1 wheat seed) averaged almost twice the number of seedlings per meter row compared to untreated check plots (approximate

1.8 fold increase, May12 and June3, respectively) (Table 7.6). However, wireworm populations in the thiamethoxam treated plots were not suppressed in 2012 compared to the untreated check plots (Table 7.5). Thiamethoxam treated plots yielded an average of

7.5 wireworms per trap on June 23 compared with an average of 6.0 from traps in untreated plots. In contrast, plots planted with fipronil treated seed, or fipronil mixed with thiamethoxam, only yielded an average of 1.0 wireworm per bait trap on June 23 (Table

7.7). Plots planted with fungicide treated wheat seed yielded fewer wireworms compared to the untreated check, but the counts were also more variable.

Wheat crop stand densities during 2011, within the insecticide treated plots, were significantly higher during all three post treatment sampling dates compared to the untreated and fungicide only plots (F 4,19 = 7.84; P = 0.0013, F4,19 = 7.52; P = 0.0016 and

F4, 19 = 3.40; P = 0.0363 for each the stand density count, respectively) (Table 7.6). The average number of plants counted per meter row in fungicide-treated plots was not significantly different from untreated plots, indicating that the majority of the stand damage was caused by insects. On May 12, 2011, 28 days after planting, stand densities were significantly higher in all plots planted with insecticide-treated seed (Table 7.6).

Seed treated with thiamethoxam and thiamethoxam + fipronil had significantly increased

167 stand densities (1.8X) compared to the untreated control. While average stand counts decreased for all treatments by the second assessment date, some averages increased at the third assessment date of June 29, 2011. This increase could reflect the development of tillers (new shoots from the parent plant) that is common in some grass crops. No significant differences in plant dry weight (F4, 19 = 2.44; P = 0.0920), yield (F4, 19 = 2.48;

P = 0.0890) or grain density (F4, 19 = 2.22; P = 0.1275) were observed. However, the fipronil treatment produced the highest average yield (3315.7 kg ha-1) and the thiamethoxam + fipronil treatment produced the highest average biomass (151 g m-1 row)

(Table 7.6). Untreated wheat seed was planted over all plots during 2012. No significant differences in stand density, biomass and yield were detected between plots that were planted with treated seed the year previous (Table 7.7). However, plots that were planted with fipronil or fipronil + thiamethoxam treated seed in 2011 produced the highest average yields in 2012 (3497.3 ha-1). The lack of stand damage in 2012 may be attributed to the variable nature of wireworm movement in relation to soil conditions. Bait traps deployed on May 10 2012, when the crop was planted, yielded lower numbers of wireworms when they were sampled two weeks later on May 21. By the second sampling date of June 23, when the wheat plants were larger, twice as many wireworms were trapped. Peak wireworm activity near the soil surface did not appear to coincide with the most vulnerable crop stage.

168

Discussion

Limonius californicus and H. bicolor commonly infest wheat and barley crops in

Montana, causing stand thinning and yield loss (Morales-Rodriguez, unpublished observations). H. bicolor (no common name) is a small wireworm species with a 1-2 year life cycle and it is distributed widely in the western, northeastern and central US states19,

20, 21 22, 23, 24. The sugarbeet wireworm, L. californicus, is an averaged-sized wireworm with a 4-11 year life cycle and it is commonly found throughout the Pacific Northwest region of North America19, 20, 21 22, 23, 24. Vernon et al. (2013) clearly demonstrated the ability of thiamethoxam mixed with fipronil to reduce wheat stand damage caused by the dusky wireworm, Agriotes obscurus, an invasive pest species introduced from Europe, as well as reduce its populations in the field. We extended this research by demonstrating the efficacy of similar insecticide mixtures against two pest wireworm species native to

North America.

Vernon et al. (2013) reported 85.9 to 93.6% stand protection and 17.5 to 65.2% wireworm mortality from thiamethoxam (10 g AI 100 kg-1 of seed) compared to the untreated control, under low A. obscurus pressure. However, under high wireworm pressure, the same level of stand protection and wireworm mortality was not achieved

(stand protection was 20.2% and wireworm mortality was 31.3% compared to untreated controls). By combining thiamethoxam (10 g AI 100 kg-1 of seed) and fipronil (5 g AI

100 kg-1 of seed) stand protection (91.7 to 94.8%) and wireworm mortality (90.5 to

93.5%) were both very high at sites with low wireworm pressure. Again, under high wireworm pressure, the same level of stand protection and wireworm mortality was not

169 achieved (65.0% stand protection and 74.7% wireworm mortality), but the thiamethoxam

+ fipronil mixture performed better than thiamethoxam alone. Compared to Vernon et al.

(2013), our experiments used a higher rate of thiamethoxam; 10 g compared to 39 g AI

100kg-1 seed, respectively. We achieved an 83% reduction of field populations of L. californicus and H. bicolor using a mixture of 39 g thiamethoxam and 5 g fipronil AI

100kg-1 seed. Our results suggest that fipronil can be combined with higher rates of thiamethoxam to improve stand protection under high wireworm pressure without compromising mortality.

Antagonistic interactions on mortality between the two insecticides when mixed together, is a potential concern of this strategy. Van Herk et al. (2008) observed that A. obscurus and Limonius canus spend significantly less time in contact with wheat seeds treated with a combination of thiamethoxam (Cruiser 350 FS) and a pyrethroid

(Tefluthrin 20 CS) than with wheat seeds treated with each insecticide alone, resulting in decreased mortality when both insecticides were applied together19. Intoxication by thiamethoxam might reduce wireworm feeding and the amount of fipronil ingested.

Supporting this hypothesis, wireworm mortality in laboratory bioassays was always lower when the 1.0 or 5.0 g rate of fipronil was combined with thiamethoxam at its highest label rate, compared to fipronil alone (Table 7.1). When analyzed statistically, this interaction was antagonistic for the 1.0 g fipronil rate for both species in 2011 and for

L. californicus in 2012 (Table 7.2), but it was only additive at the 5.0 g rate. These results are consistent with a reduction in feeding caused by thiamethoxam; less feeding is required to ingest a lethal dose of fipronil when the fipronil rates are higher. However, in

170 greenhouse studies using sugar beets, mortality of A. brevis and A. ustulatus was equally high for imidacloprid (45.0 g of AI per 100,000 seeds) and fipronil (15.0 g of AI. per

100,000 seeds) mixed together, and for fipronil alone (25 g of AI per 100,000 seeds) 22.

While antagonistic interactions were noted in our laboratory study at the 1.0 g rate of fipronil, in all cases fipronil boosted mortality rates compared to thiamethoxam alone, and suppression of L. californicus and H. bicolor in the field at the 5.0 g rate of fipronil was not affected. However, further studies would be required to test for interactions between this high rate of thiamethoxam and lower rates of fipronil under field conditions.

Our laboratory and field results confirmed that thiamethoxam applied to wheat seed even at a high rate does not cause significant mortality of L. californicus and H. bicolor. When tested in a one ounce bioassay cup with a single treated wheat seed as the sole food source, the high rate of thiamethoxam resulted in only 10% mortality of L. californicus and 28-31% mortality of H. bicolor (Table 7.1). Field plots planted with thiamethoxam-treated wheat seed the year previous had an average of 7.5 wireworms per plot (all species combined) compared to an average of 6.0 in the untreated plots (Table

7.5). While thiamethoxam did not reduce field populations of L. californicus and H. bicolor, it did protect the spring wheat crop from wireworm damage (Table 7.6).

Controlling wireworms in cropland fields is a current challenge and priority recognized by producers, researchers and the agricultural industry during the recent

Pacific Branch - Entomological Society of America meeting (Symposium: Wireworms in the west: what is known, what has been done and what needs to be done. April 7 – 10,

2013. Pacific Branch- Entomological Society of America. Lake Tahoe, NV.). Older first

171 generation insecticides, such as lindane, were used for decades as inexpensive seed treatments because wheat seed treated with lindane can reduce soil wireworm populations by about 50% 9. Like thiamethoxam in this study, the neonicotinoid-class insecticides in general do not reduce wireworm populations in the soil, and wireworm numbers can continue to increase in a crop field. The pyrethroid insecticide tefluthrin applied to wheat seed alone or in combination with thiamethoxam also provided crop protection, but like the neonicotinoids, it did not reduce field populations of A. obscurus10. Fipronil was the only insecticide that effectively reduced the A. obscurus population. The topical LC50 of fipronil to A. obscurus is 1,000 fold lower compared to thiamethoxam23, likely explaining its effectiveness at suppressing this species in field trials. However, this high toxicity and relatively long half-life in the soil raises concerns about potential soil persistence and non-target effects. In response, minimal rates of fipronil blended with thiamethoxam have been investigated, and have been demonstrated to reduce field populations of A. obscurus in British Columbia and in our study of L. californicus and H. bicolor in Montana. In addition to minimizing the rate of fipronil used, annual applications are not necessary for wireworm species with long life cycles as larvae in the soil (Vernon et al. 2013). To broaden the scope of future studies, biorational and microbiological agents such as fungi, nematodes and bacteria will be investigated alone or in combination with conventional insecticides. For example, Ansari et al. (2009)24 suggests that strain V1002 of M. anisopliae has considerable potential for the control of the wireworms. Jossi et al.

(2008)25 recognize that the efficacy of this strain of fungus is limited by poor residual activity, and suggest the possibility of using a more suitable isolate of M. anisopliae to

172 achieve long term control. Efficacy and persistence could potentially be improved with combined applications of neonicotinoids at low doses and M. anisopliae15,16,17.

Acknowledgements

We thank Mark Grubb (Conrad, Pondera Co), Richard Barber (Denton, Fergus

Ammiel Branson, Meghan McGauley, Ruth O’Neill, Diana Florian, Hannah Johnson, and

Laura Morales for their help in conducting this work. Paul S. Robbins provided comments to improve the manuscript. This study was supported in part by funds from the

Montana Wheat and Barley Committee, Montana Seed Potato Producers Association and

USDA Crops at Risk Grant 2010-51100-21547.

173

6.0 ± 5.5 B

2012*

85.3 ± 6.0 A 62.4 ± 9.1 A

10.0 ± 22.4 B

72.0 ± 25.7 A 66.0 ± 18.6 A

different years.different

L. californicus

4.0 ± 5.5 C

2011*

66.4 ± 6.3 B

85.6 ± 9.4 A

10.0 ± 17.3 C 62.4 ± 12.5 B

followed by different letters letters followed are by different

72.6 ± 10.4 AB

in laboratory bioassays 30 DAT bioassays in laboratory with

± 1.1 A

H. bicolor

6.0 ± 8.9 C

and

2012*

89.3

77.1 ± 23.8 A

31.4 ± 12.3 BC

66.8 ± 25.6 AB 59.5 ± 34.8 AB

% Corrected Mortality ± SD) (Mean % Corrected

H. bicolor

L. californicus L. californicus

2.0 ± 5.1 E

2011*

89.8 ± 7.1 A

59.3 ± 13.6 C

28.2 ± 10.5 D

79.8 ± 9.7 AB

68.9 ± 17.7 BC

of seed)

Percentage ofPercentage mortality of

Treatment

Means are significantly different, p < 0.001, ANOVA. Mean values p 0.001, ANOVA. significantly Mean < different, are Means

Rate in g AI 100 kg in g AI Rate

Table 7.1. Table replicated collected in two were Bioassays larvae with seeds. wheat treated insecticide control untreated 39.0 g thiamethoxam 1.0 g fipronil 39.0 g + thiamethoxam 1.0 g fipronil 5.0 g fipronil 39.0 g + thiamethoxam 5.0 g fipronil a b Tukey’s p < 0.05. test different, significantly

174

nistic

Effect

Additive Additive

Antago Antagonistic

6.4

0.97 1.08

6.26

L. californicus

8.9

68.0 ± 4.5 87.4 ± 2.5 76.6 ± 4.2 87.7 ± 8.1 64.0 ± 77.2 ± 6.8

Mortality

64.0 ± 11.4 68.0 ± 16.4

2011 2012

Effect

Additive Additive Additive

Antagonistic

2.98 0.59 1.98

11.71

H. bicolor

1 of seed. wheat

93.0 ± 8.9 86.0 ± 7.4 87.2 ± 8.5

Mortality

70.0 ± 15.8 60.0 ± 14.1 70.0 ± 20.0 80.0 ± 15.8 93.6 ± 12.4

rved

Expected Expected Expected Expected

Obse Observed Observed Observed

Measurement

comparison that exceeds 3.841, with df = 1 and α = 0.05, is considered synergistic is 0.05, is 1 and or = otherwise 3.841, withα antagonistic, df = considered comparison that exceeds

Laboratory mortality (mean ± SE) of two species of combinations mortality of with two ± SE) of two the interaction Laboratory doses wireworms and (mean species

square square

Treatment

Observed = efficacy of both control agents applied at the same time. Expected = sum of efficacy of each agent of sumcontrol of Expected = each applied time. efficacy of same the efficacy agents at = both control Observed

Treatment doses are in are doses AI 100 kg grams Treatment A chi

Table 7.2. Table 30 DAT at thiamethoxam in 2011 and 2012. and insecticides of fipronil + thiamethoxam 1 gr fipronil + thiamethoxam 5 gr fipronil + thiamethoxam 1 gr fipronil + thiamethoxam 5 gr fipronil a b separately. applied c additive. considered

175

Table 7.3. Probit for mortality of L. californicus with wheat seed treated with fipronil.

Dosesa n Percentage Mortality

Observed Expected 0 50 6 5.459 0.005 50 18 31.150 0.05 50 60 46.410 0.5 50 70 62.822 1.0 50 76 77.421 25 50 78 85.388 50 50 90 88.162 Probit results: Slope 0.4247 ± 0.0940 X2 20.41 Prob > X2 0.0001 a Doses in g AI 100 kg-1 of seed

Table 7.4. Percentage of mortality of H. bicolor and L. californicus and wheat seedlings 30 DAT in greenhouse bioassays with different doses of fipronil applied as seed treatments. Untreated check that was not infested with insects was included as a control for seedling mortality. H. bicolor L. californicus Fipronila Seedling Wireworm Seedling Wireworm

Mortality (%)b Mortality (%) Mortality (%) Mortality (%)

0c 6.0 ± 9.66 B -- 2.0 ± 6.34 B --

0 32.0 ± 14.14 A 4.0 ± 8.43 C 48.0 ± 10.33 A 10.0 ± 10.54 C

1.0 2.0 ± 6.32 B 48.0 ± 9.18 B 8.0 ± 10.36 B 28.0 ± 12.73 B

5.0 2.0 ± 6.32 B 91.5 ± 14.53 A 2.0 ± 6.34 B 90.5 ± 17.07 A

10.0 2.0 ± 6.32 B 100.0 ± 0.0 A 8.0 ± 10.36 B 88.5 ± 12.25 A a Rate in g AI 100 kg-1 of seed b Means are significantly different, p<0.001, ANOVA. Mean values followed by different letters are significantly different, Tukey’s test p < 0.05. c Control without insects.

176

1.0 ± 1.4B 1.0 ± 1.4B

6.0 ± 1.4A 7.5 ± 6.5A

All species

2.5 ± 3.1AB

Mean Mean

Jun

0 1 0 0 0

5 4 4

24 22

(total no.) (total

6 4 8 0 0

Wireworm species Wireworm

.0 ± 2.2

2.8 ± 2.8 2.0 ± 1.4 3 1.3 ± 1.0 1.3 ± 1.9

combined

All species

Mean Mean

1 1 2 2 1

May

6 9 2 3

(total no.) (total

0 1 1 2 1

Wireworm species Wireworm

01, ANOVA. Mean values followed by different letters are values letters significantly followed Mean by different 01, ANOVA.

rms collected from treatment plots in 2012 and identified to species, and the average the average plots to species, and in identified from 2012 and treatment rms collected

5 5

15 15 39 15 15 39

Rate

1 of seed

+ +

Total number number Total of wirewo

a a a a

Treatment

thoxam + thoxam +

Table 7.5. Table in 2011, and in 2012 seed wheat plots all were plot was treated with wireworms planted of all Each number combined. untreated with seed. overplanted control Untreated Fungicide Fungicide Thiamethoxam Fungicide Fipronil Fungicide Thiame Fipronil 1.93% 7.73%, Difenoconazole Mefenoxam a 100 kg in g AI b Rate mellilus. Am, Aeolus Limonius Hb, Hypnoidus bicolor; californicus; Lc, c p<0.0 significantly are different, d Means Tukey’s p test 0.05. < different,

177

Grain

density

lb/bushel

61.0 ± 0.3 60.2 ± 0.1 61.0 ± 0.7 61.6 ± 0.6 61.5 ± 0.8

0.8

Yield

37.2 ± 5.9 49.3 ± 6.2

28.1 ± 10.9 37.4 ± 10.7 38.4 ± 1

bushels/acre

2012

(1 m row) (1 m

95.0 ± 21.6

Dry Weight Dry

136.3 ± 46.7 141.8 ± 29.6 148.3 ± 14.0 151.0 ± 25.6

2012

14.0 ± 10.8C

41.8 ± 11.0A

24.5 ± 8.3BC

36.5 ± 3.5AB

24.3 ± 15.6BC

2012

6.4 ± 5.2B

16.3 ± 5.4B 1

29.8 ± 4.2A 26.7 ± 1.8A 27.3 ± 4.7A

Stand Density

(number of plants per 1 m row) 1 m of plants(number per

40.0 ± 9.4A 41.1 ± 4.1A

22.0 ± 5.6C

29.4 ± 5.6BC

37.4 ± 3.0AB

6/5/2012

5 5

15 15 39 15 15 39

1 of seed

Rate

+ + +

Stand density, dry weight, yield and grain yield and field weight, Stand dry plots density in in 2011. density, planted treated

a a a a

icide

Treatment

Rate in g AI 100 kg in g AI Rate

Difenoconazole 7.73%, Mefenoxam 1.93% 7.73%, Mefenoxam Difenoconazole values p letters different, significantly followedare by different 0.001, ANOVA. significantly Mean < different, are Means

Table 7.6. Table control Untreated Fungicide Fungicide Thiamethoxam Fungicide Fipronil Fung + Thiamethoxam Fipronil a b c p < 0.05. test Tukey’s

178

± 1.0

Grain

density

lb/bushel

59.2 ± 0.8 59.7 ± 1.2 59.1 ± 1.3 60.0 ± 1.1 60.0

Yield

(bs/acre)

38.5 ± 8.5 46.2 ± 3.5 50.9 ± 4.5 52.4 ± 4.0 52.0 ± 11.9

2012

(1 m row) (1 m

Dry Weight Dry

07 301.7 ± 61.9 266.4 ± 27.5 279.1 ± 27.4 247.3 ± 19.3 269.9 ± 57

2012

07 40.5 ± 9.5 56.3 ± 19.5 50.8 ± 14.2 55.5 ± 7.6 54.0 ± 18.7

2012

06 39.6 ± 9.1 39.4 ± 10.1 39.4 ± 7.6 34.3 ± 6.7 35.5 ± 9.3

Stand Density

4.7

(number of plants per 1 m row) 1 m of plants(number per

6/5/2012 53.0 ± 10.3 47.5 ± 4.3 51.5 ± 3.9 56.7 ± 15.3 42.1 ±

5 5

15 15 39 15 15 39

of seed

Rate

+ + +

Stand density, dry weight, yield and grain density in treated field plots over planted with untreated wheat wheat grain yield and untreated with field weight, Stand dry plots planted density in density, over treated

a a a a

Treatment

Rate in g AI 100 kg in g AI Rate

Difenoconazole 7.73%, Mefenoxam 1.93% 7.73%, Mefenoxam Difenoconazole

Table 7.7. Table in 2012. seed control Untreated Fungicide Fungicide Thiamethoxam Fungicide Fipronil Fungicide + Thiamethoxam Fipronil a b

179

References

1. Comstock JH and Slingerland M V. Wireworms. Bull. 33. Cornell University Agricultural Experiment Station. Geneva, NY (1891).

2. EPPO Bulletin. Limonius californicus. EPPO Bulletin 35(3): 377-379 (2005).

3. Furlan L. The biology of Agriotes ustulatus Schaller (Col., Elateridae). II. Larval development, pupation, whole cycle description and practical implications. J Applied Entomology-Zeitschrift Fur Angewandte Entomologie. 122: 71-78 (1998).

4. Furlan L. The biology of Agriotes sordidus Illiger (Col., Elateridae). J Appl Entomol 128(9-10): 696-706 (2004).

5. Strickland EH. Life cycle and food requirements of the Northern Grain Wireworm, Ludius aereipennis destructor Brown. J Econo Entomol 32(2): 322-329 (1939).

6. Pedigo LP. Entomology and Pest Management. MacMillan, New York & Collier Macmillan, London. 646 pp (1989).

7. Lange, WH Jr, Leach D, and Carlson EC. Lindane for Wireworm Control - wireworms affecting certain vegetable and field crops controlled with lindane seed treatment. California agriculture, January (1950).

8. Toba HH, O'Keeffe LE, Pike KS, Perkins EA and Miller JC. Lindane seed treatment for control of wireworms (Coleoptera: Elateridae) on wheat in the Pacific Northwest. Crop Protection 4: 372-380 (1985).

9. Vernon RS, Van Herk WG, Tolman J, Saavedra HO, Clodius M and Gage B. Transitional sublethal and lethal effects of insecticides after dermal exposures to five economic species of wireworms (Coleoptera: Elateridae). J Econo Entomol 101: 365-374 (2008).

10. Vernon RS, Van Herk WG, Clodius M, and Harding C. Wireworm management I: stand protection versus wireworm mortality with wheat seed treatments. J Econo Entomol 102: 2126–2136 (2009).

11. Van Herk WG and Vernon RS. Morbidity and recovery of the Pacific Coast wireworm, Limonius canus, following contact with tefluthrin-treated wheat seeds. Entomologia Experimentalis et Applicata 125(2): 111-117 (2007).

180

12. Venon RS, Van Herk WG, Clodius M, and Harding C. Crop protection and mortality of Agriotes obscurus wireworms with blended insecticidal wheat seed treatments. J Pest Sci. 86:137-150 (2013).

13. Van Herk WG, Vernon RS, Clodius M, Harding C, and Tolman HJ. Mortality of five wireworm species (Coleoptera: Elateridae), following topical application of clothianidin and chlorpyrifos. J Entomological Society of British Columbia, 104: 55-63 (2007).

14. Abbott WS. A method for computing the effectiveness of an insecticide. J Econo Entomol 18: 265-267 (1925).

15. Koppenhöfer AM, and Kaya HK. Synergism of imidacloprid and an entomopathogenic nematode: a novel approach to white grub (Coleoptera: Scarabaeidae) control in turfgrass. J Econo Entomol 91: 618–623 (1998).

16. Koppenhöfer AM, Brown I, Gaugler R, Grewal PS, Kaya HK and Klein MG. Synergism of entomopathogenic nematodes and imidacloprid against white grubs: greenhouse and field evaluation. Biol Control 19: 245–251 (2000).

17. Morales-Rodriguez A and Peck DC. Synergies between biological and neonicotinoid insecticides for the curative control of the white grubs Amphimallon majale and Popillia japonica. Biol Control 51: 169-180 (2009).

18. SAS Institute. PROC user's manual, version 6th ed. SAS Institute, Cary, NC. (2002- 2010)

19. Al Dhafer, H. M. 2009 Revision of the north American species of Limonius (Coleoptera: Elateridae). Transactions of the American Entomological Society, 135, 209- 352.

20. Johnson, P. J. 2009. Classification of the Nearctic genera of Elateridae. www.sdstate.edu/ps/Severin-McDaniel/project-elater/canada- contintentalus/loader.cfm?csModule=security/getfile&PageID=688179

21. Bousquet, Y. (Ed.). 1991. Checklist of beetles of Canada and Alaska. Agriculture Canada Publication 1861/E, Ottawa, ON.

22. Furlan L. Study on the efficacy of imidacloprid and fipronil used as seed dressing in controlling wireworms (Beta vulgaris L. - Emilia-Romagna – Veneto). Italian Phytopathological Society. Biennial Meeting, Baselga di Pine, Trento (Italy), 7-11 Apr (2002).

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23. Van Herk WG, Vernon RS, Tolman HJ and Ortiz Saavedra H. Mortality of wireworm Agriotes obscurus (Coleoptera: Elateridae), after topical application of various insecticides. J. Econ. Entomol. 101 (2): 375-383 (2008).

24. Ansari M, Evans AM, and Butt, TM. Identification of pathogenic strains of entomopathogenic nematodes and fungi for wireworm control. Crop Protection 28, 269- 272 (2009).

25. Jossi W, Schweizer C and Keller S. Click-beetle species and biological control of wireworms. Agrarforschung 15: 76-81 (2008).

182

CHAPTER EIGHT

EFFECTS OF CULTURAL PRACTICES ON WIREWORM POPULATIONS AND DAMAGE IN CEREAL FIELDS

Contribution of Authors and Co-Authors

Manuscript in Chapter 8

Author: Anuar Morales-Rodriguez

Contributions: Conceived and implement the study design the data collection and analysis. Collected and analyzed data. Wrote the manuscript.

Co-Author: David Wichman.

Contributions: Conceived and implemented field treatment for 20 years, comments to the manuscript.

Co-Author: Kevin W. Wanner

Contributions: Provided feedback in the study design, data analysis and comments to the manuscript.

183

Manuscript Information Page

Anuar Morales-Rodriguez, David Wichman, Kevin W. Wanner Crop Sciences Status of Manuscript: X Prepared for submission to a peer-reviewed journal ___ Officially submitted to a peer-review journal ___ Accepted by a peer-reviewed journal ___ Published in a peer-reviewed journal

Published by Crop Science Society of America.

184

Abstract

Wireworms appear to be an increasing threat to the sustainable production of small grains, potatoes, and other crops since the de-registration of lindane, an effective and inexpensive insecticide seed treatment. Producers also believe that soil tillage practices, crop rotation and crop systems can affect wireworm populations. Higher wireworm densities may be associated with conservation tillage, continuous cropping and specific crops such as potatoes and grasses. For more than 20 years the Montana State

University Central Agricultural Research Station near Moccasin Montana has maintained a series of plots under the same regimen of till and no till conditions in combination with continuous and alternating fallow cropping systems. In this study we evaluated wireworm populations and crop damage in these plots over three years to gain insights into the potential effect of cropping practices on wireworm populations. Wireworm populations were higher in continuously cropped plots compared to plots with an alternating fallow rotation. No differences in wireworm numbers were detected as a result of plot tillage.

Additionally we evaluated the effect of seeding density on crop damage at three locations with heavy, medium or light wireworm pressure. Surprisingly, increasing seeding density did not show any apparent benefits to plant stand density or yield.

185

Introduction

Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are the most significant soil-dwelling pests of a wide variety of field crops worldwide (Comstock and

Slingerland, 1891; Toba and Turner, 1983; Seal et al., 1992; Kohno and Miyai, 1993;

Parker and Howard, 2001). Larvae of some species of Elateridae are rhizophagous and are important agricultural pests; larvae of other species are predaceous, often living in soil, subcortical habitats, or rotten logs (Johnson, 2002).

However, little is known about the biology of most species. Wireworms appear to be an increasing threat to the sustainable production of small grains, potatoes, and other crops grown in rotation since the de-registration of lindane, an effective and inexpensive insecticide seed treatment. Although new insecticides have been registered as seed treatments, their efficacy is not satisfactory (Van Herk and Vernon, 2007; Vernon et al.,

2008; 2009) and new IPM tools are required to manage wireworm populations. Before its de-registration, lindane effectively controlled wireworm damage to grains for more than

50 years at low cost (Toba and Turner, 1983). During this period, little wireworm research was conducted and this deficit is reflected in the low number of publications between 1960 and 2010. The peak observed in 1960 includes papers describing the use of first generation insecticides developed in the 1950s. More recently the number of wireworm publications has increased, reflecting their changing pest status.

The first cornerstone of IPM, pest identification, remains largely unresolved for the Elateridae, particularly for the larval stage (Pedigo, 1989; Norris et al., 2003). The

186 effectiveness of many IPM tactics is specific to a set of related species (Morales et al.,

2009).

Click beetles are a large group with about 10,000 described species in 400 different genera worldwide (Johnson, 2002). In North America (not include Mexico), 921 species in 99 genera have been reported by Johnson (2009), and similar numbers (965 species in 91 genera) are reported by Marske and Ivie (2003), ranking elaterids as the seventh-most species rich family in North America. However, the larvae are described in less than 10% of the North American species and of those 95% are of described from a single larval instar (Becker and Dogger, 1991).

A total of 369 species and subspecies have been reported from Canada and Alaska

(Bousquet, 1991), 30 of which are reported as economically important in Canada

(Benefer et al., 2012b). In Montana, 164 species of click beetles in 43 genera have been identified of which 23 are potential crop pests in small grains (Seibert, 1993). However, most of these listed species can only be identified using adult males, and their actual distribution and abundance in cropland remains largely unknown; thus, there is a potential for significant under-estimation of the diversity of wireworm species infesting cropland in Montana. In the Pacific Northwest (PNW) region of North America, the most economically important wireworm species reported belong to six genera, Aeolus,

Agriotes, Ctenicera, Dalopius, Limonius, and Melanotus. In 2008, the five most important species reported in the PNW belonged to two genera, Limonius and Ctenicera

(= Selatosomus), with L. canus, L. californicus, L. infuscatus, L. subauratus LeC., reported on irrigated land and C. pruinina (= S. pruininus) on dry land (Andrews et al.,

187

2008). In central Montana, Athous spp. historically were thought to be the most important crop pests overall (Hastings and Cowen, 1954) although L. canus was the main pest in irrigated areas (Mail, 1932). In 1981, a complex of A. mellillus, C. glauca (=

Hadromorphus glaucus) and C. destructor (= S. aeripennis) was reported from wheat fields in north central Montana (Morrill, 1983). In a 2011-2013 survey, six species were identified in cereal fields in Montana: Aeolus mellillus, Hypnoidus bicolor, Limonius californicus, L. infuscatus and S. aeripennis (Morales – Rodriguez et al., in press).

Due to the broad feeding habits and long life cycles of wireworms, crop or fallow rotations have not proved to be a reliable management tactic (Comstock and Slingerland

1891; Vernon et al. 2009). Cultural practices to improve soil conditions (e.g., no-till production), and to increase profits with higher yields (e.g., irrigation) and continuous cropping have been evaluated for their effects on wireworm populations, with mixed results (Bryson, 1930; Hawkins, 1936; Stapley et al., 1947; Belcher 1989; Willis et al.,

2010). Increasing the seeding density, employing tillage, and delayed planting are the most commonly used cultural practices adopted by wheat and barley producers. At lower seed densities the crops are known to suffer higher damage (Bryson, 1930), and farmers often plant extra seed to adjust for anticipated damage. Tillage has been shown in some cases to reduce wireworm numbers either by mechanical damage or exposure to predation (Seal et al., 1992; Willis et al., 2010). Late-planting shrinks the window of time during which the vulnerable seeds and small seedlings are exposed to wireworm feeding, and may significantly reduce stand damage. Bryson (1930) reported a higher incidence of injured corn plants sown early in April compared with those planted in late May. Other

188 cultural practices include trap crops, physical barriers and light traps to capture adults and in the past. Soil compaction was recommended in the past (Comstock and Slingerland,

1891), but this approach is not compatible with today’s farming practices. Little research has evaluated cultural practices on wireworm populations (Baumler, 2008; Cherry and

Hall, 1986; Vernon et al., 2000 and 2003; Vernon and van Herk, 2013).

In this study a preliminary evaluation of the effect of three different cultural practices on wireworm populations in Montana’s creal crops are povided; the effect of tillage practices, cropping systems and seed density.

Methodology

The Montana State University Central Agricultural Research Station (CARC) near Moccasin, Montana has maintained plots under the same regimen of till and no till conditions in combination with continuous and alternating fallow cropping systems. We made use of this long-term cropping history to assess the effects of tillage and continuous cropping on wireworm populations.

Tillage Effect

Since 1994 the CARC has maintained a split plot design experiment to evaluate the effects of tillage on cereal production. Five plots each measuring 46 m wide and 150 m long (0.7 ha) were split lengthwise, one side receiving tillage and the other side maintained using no till practices. The tilled half received one or two operations of sweep tillage. The shovels were set to a 50 degree angle on 30.5 cm centers. A spoke-angled rolling harrow was attached to the sweeps tool bar. This rolling harrow reduces straw

189 breakage and burial and slows straw decomposition. During the spring season, an application of glyphosate was commonly used to control downy brome (Bromus tectorum

L.). The plots were planted each year with a cereal crop using an experimental plot drill and a general seeding density of 60 seeds m-1 and 30 cm row spacing and maintained under dryland conditions. After maturing the grain was harvested from each plot using a plot combine. During 2011 the plots were planted with spring wheat (var. Choteau), barley (var. Hockett) in 2012 and winter wheat (var. Genou) during 2013.

Five stocking traps spaced approximately 20 m apart were placed along the longitudinal center of each split plot to sample wireworms on three different dates during crop establishment in 2011 - 2013. Detailed methodology of stocking trap deployment and wireworm identification is reported in Chapter 3. Stand density was recorded on two different dates during crop establishment as the number of plants per 1 m row (three subsamples within each split plot) and biomass as the dry weight of foliage from a destructively sampled 1 m row (three subsamples within each split plot). After harvesting the grain was cleaned and the seed density measured as described in Chapter 3.

Tillage and Croping System Effect

At a second location on the CARC four experimental plots have been maintained with consistent cultural practices since 1994. These plots have been planted with cereal, pulse and oilseed crops. Plot 1 is 2.8 ha in size and has been tilled each year and continuously planted. Depending on the amount of residue and the soil tilth, one or two sweep tillage passes with angled rolling harrow operations was completed. During the spring of 2011 the plot was planted with spring wheat (var. Yellowstone), barley (var.

190

Hockett) in 2012 and spring wheat (var. Yellostone) during 2013. Plot 2 is 4.9 ha and has been tilled each year but planted with a crop only during alternating years with a fallow rotation. During 2011 and 2013 this plot was fallow and in 2012 it was planted with spring wheat (var. Yellowstone). Plot 3 is 4.5 ha and was maintained using no-till practices and continuously planted. During 2011 the plot was planted with spring wheat

(var. Yellowstone), barley (var. Hockett) in 2012 and spring wheat (var. Yellowstone) during 2013. Plot 4 is 2.8 ha and was maintained using no-till practices but planted with a crop only during alternating years with a fallow rotation. During 2011 the plot was planted with spring wheat (var. Yellowstone), left fallow in 2012, and planted with spring wheat (var. Genou) in 2013.

All four plots were maintained under dryland conditions using common farming practices. Weeds were commonly managed with applications of herbicide. While planted with cereal crops weeds were commonly controlled with 2, 4-D LV6 (Base Camp® LV6,

Wilbur-Ellis Company, Fresno, CA) or bromoxynil (Vendetta® Wilbur-Ellis Company,

Fresno, CA) + MCPA (MCPA Ester, Wilbur-Ellis Company, Fresno, CA). A fall or early spring pre-plant application of glyphosate (Round up and RT 3®, Monsanto Company, St

Louis, MO and Gly Star® Plus, Agri Start by Albaugh, Inc Ankeny, IA) was frequently used to control downy brome. When seeded to an oilseed or peas, pendimethalin (Prowl

H20 BASF Corporation, Research Triangle Park, NC) was applied as a pre-emergent herbicide.

A NPKS fertilizer blend of 10-10-10-05 was sown in with seed of all crops. In continuously cropped plots winter wheat received 80 lbs. topdressed N, spring wheat

191 received 90 lbs. N, and barley received 60 lbs N. Oilseeds received 60 lbs. N. For peas, no supplemental N was provided.

Cultural practices in this experiment were not replicated. The four plots were divided into four even subplots that were used as replicates to analyze for plot differences in the variables measured. The number of wireworms, stand density, biomass, yield and seed density were assessed within each subplot as described for the previous experiment.

During 2013 only, soil density was measured in four different places within each subplot using a FIELD SCOUT SC900 soil penetrometer (Spectrum Technologies, Inc. Chicago,

IL) at 11 weeks after planting.

Seeding Density

During 2013 five different seeding densities of wheat and barley were evaluated at three locations: Conrad, Fort Ellis and Kalispell, MT. Untreated spring wheat

(AP604CL, developed by Agri-ProSyngenta and sold by Barber Seed Service Inc.

Denton, MT) and barley (variety Conrad, developed by Busch Agricultural Resources

Inc. and sold by Northern Seed LLC, Conrad, MT) were planted in plots measuring 3.7 m x 1.2 m, with 0.3 and 0.5 m separating repetitions and plots, respectively. The plots were seeded on April 26, 2013 in Kalispell, MT, April 28, 2013 in Conrad, MT and on May 18 in Fort Ellis, MT. All fields were planted with an experimental plot drill (composed of a custom 4 row seeder with 4 cones) at 30 cm spacing. Five seed density treatments were planted in a randomized complete block design: 60, 90, 120, 150 and 180 seeds per 0.91 m-1 of row. Each treatment was replicated five times.

192

Plant density (number of plants per 0.91 m-1) was recorded 4 and 11 weeks after planting from the center rows of each plot to avoid edge effects. A destructive 0.91 m row section was sampled from the center rows of each plot to record dry weight (plants dried in an oven for 10 days) 10 weeks after planting. After maturing the grain was harvested from each plot or subplot using a Hege 140 plot combine (Hege Maschinen

GmbH Hohebuch 5 D-74638, Waldenburg). The grain was cleaned using an ASC-3 seed cleaner (Agriculex Inc., Guelph, Ontario, Canada), weighed, and the density evaluated using a filling Hopper and stand with a pint cup (SEEDBURO Equipment Company, Des

Plaines, IL). Wireworm populations were assessed using stocking traps deployed across the experimental plot two weeks before planting and around the perimeter of the experiments after planting. Traps were stored in a walk-in cooler at 4˚C until they were sorted for wireworms using a series of Berlese funnels. Collected larvae were preserved in 95% alcohol for identification.

Data Analysis

A t-test was used to compare the effects of tillage on the wireworm population from pooled stockings, plant stand density at the two dates of evaluation, dry weight, yield and seed bulk density (tillage effect experiment). An analysis of variance was performed to test for the effect of plot on the wireworm population from pooled stockings, plant stand density at the two dates of evaluation, dry weight, yield and seed bulk density (tillage and crop system effect experiment). Differences between means were analyzed using Tukey’s test (P=0.05). Regression analysis was used to determine the relation of seeding density with the plant stand density at the two dates of evaluation,

193 dry weight, yield and seed density. Statically analyses were completed using SAS 9.3 software (2002-2010 SAS Institute Inc., Cary, NC, USA) and/or JMP®, Version 10.0.2 software (2012 SAS Institute Inc., Cary, NC.).

Results

Tillage Effect

During 2011 104 wireworms were collected from all experimental plots, representing six different species: 10 L. californicus (9.6%), 48 H. bicolor (46.2%), 43 A. mellillus (41.3%), 2 L. infuscatus (1.9%) and 1 S. aeripennis (1.0%). No effect of tillage on the total number of wireworms trapped was detected (t (5) = 0.519, Prob > |t| = 0.624)

(Table 8.1). Similarly, no differences were detected in plant density (t (28) = 0.017, Prob >

|t| = 0.985 and (t (28) = 0.248, Prob > |t| = 0.806 for first and second assessment dates, respectively), plant biomass (t (28) = -2.842, Prob > |t| = 0.088), yield (t (28) = 1.408, Prob

> |t| = 0.170) or seed density (t (28) = 0.194, Prob > |t| = 0.243) (Table 8.1).

In 2012 63 wireworms were collected from all plots representing three species: 17

L. californicus (27.0%), 13 H. bicolor (20.6%) and 33 A. mellillus (52.4%). Tillage did not have a significant effect on the total number of wireworms trapped (t (7) = -0.472,

Prob > |t| = 0.651), plant density (t (25) = -0.225, Prob > |t| = 0.233 and (t (27) = 0.021, Prob

> |t| = 0.983 for first and second assessment dates, respectively), yield (t (28) = 1.408, Prob

> |t| = 0.170) or plant biomass (t (23) = -0.158, Prob > |t| = 0.876). Yield data was not collected in 2012 (Table 8.1).

194

In 2013 111 wireworms representing three different species were collected from traps in all plots: 6 L. californicus (5.4%), 40 H. bicolor (36.0%) and 65 A. mellillus

(58.6%). Tillage did not have a significant effect on the total number of wireworms trapped (t (5) = -1.199, Prob > |t| = 0.286), plant density (t (31) = -0.770, Prob > |t| = 0.087 and (t (28) = 0.0, Prob > |t| = 1.000 for first and second assessment dates, respectively), dry weight (t (24) = -0.433, Prob > |t| = 0.668), yield (t (24) = -0.859, Prob > |t| = 0.3984) or seed density (t (27) = -0.094, Prob > |t| = 0.9253) (Table 8.1).

Tillage and Crop System Effect

During 2011 99 wireworms were collected from the four plots representing six species: 34 L. californicus (35.4%), 21 H. bicolor (21.9%), 37 A. mellillus (38.5%), 1 L. infuscatus (1.0%) and 2 S. aeripennis (2.1%). There was a significant effect of plot (F3, 15

= 3.55, P = 0.047) on the number of wireworms collected. Significantly more wireworms were collected in the tilled and continuously cropped plot (n = 43) compared to both plots with an alternating fallow rotation (n = 13 and 9, fallow/no till and fallow/till, respectively). After pooling the data no difference between plots receiving till vs no till practices was detected (t(12) = 0.375, Prob > |t| = 0.714) in the total number of wireworms but there was a significant difference between plots continuously planted with a crop vs rotated with fallow (t(7) = -3.186, Prob > |t| = 0.014) (Table 8.2). Fewer wireworms were collected from plots in a fallow rotation compared to continuously cropped plots.

However, no differences in plant density (F 2, 33 = 0.783; P = 0.465 and F2, 33 = 0.434; P =

0.651, respectively for each date) or plant biomass (F2, 33= 1.759; P = 0.188) were

195 observed between the plots. Significant differences among plots were detected for yield

(F2, 33 = 42.34; P < 0.0001). Higher yield was observed in the no till and continuously cropped plot (3853.7 kg ha-1) and the tilled and fallow plot (3752.8 kg ha-1) compared to the tilled and continuously cropped plot (1560.3 kg ha-1).

In 2012 98 wireworms were collected from the four plots: 25 L. californicus

(25.5%), 28 H. bicolor (28.6%), 39 A. mellillus (39.8%), 4 L. infuscatus (4.1%) and 2 S. aeripennis (2.0%). A significant effect of plot (F3, 15 = 4.63; P = 0.023) on the number of wireworms collected was detected. Significantly more wireworms were collected in the continuously cropped plots (n =39 and 27, till and no till) compared to the tilled and fallow rotation plot (n = 7). After pooling data there was no difference between tilled and no till plots (46 and 48 total wireworms respectively) but continuously cropped plots had more wireworms compared to fallow rotation (66 and 32 wireworms, respectively; t(14) =

-2.429, Prob > |t| = 0.029). No differences in plant density or biomass was detected between plots (Table 8.2). Yield data was not collected in 2012.

During 2013 60 wireworms were collected from the four plots: L. californicus

(1.7%), 7 L. infuscatus (11.7%), 8 H. bicolor (13.3%), 39 A. mellillus (65.0%), 1

Dalopius sp. (1.7%) and 4 S. aeripennis (6.7%). A significant effect of plot on the wireworm population was detected (F3, 15 = 5.22; P = 0.015). More wireworms were collected from the continuously cropped no till plot (35.0%) and the fallow rotation no tilled plot (31.7%) compared to the fallow rotation and tilled plot (11.6%) (Table 8.2).

Pooling the data yields a difference in the number of wireworms collected from tilled vs

196 no till plots (20 and 40 total wireworms, respectively, t(12) = -3.535, Prob > |t| = 0.004) but not between continuously cropped and fallow rotation plots (34 and 26 wireworms, respectively, t(14) = -1.069, Prob > |t| = 0.303). No difference in plant density, biomass or yield was detected between plots (Table 8.2).

The penetrometer data collected in 2013 shows differences in soil compaction between the four plots (Figure 8.1). Using the scale proposed by Murdock et al (1995), cited by Duiker (2014), the percentage of points having a cone index > 300 PSI in the top

37.5 cm can be considered a measure of soil compaction. The no-till and fallow plot had the fewest points exceeding this threshold (31.0%) followed by the tilled and continuously cropped (52.9%) and tilled and fallow rotation (57.9%) plots, respectively.

The no till and continuously cropped plot exhibited the highest compaction (73.0%). We did not found any correlation between soil compaction and wireworm population.

Seeding Density

The three sites selected for seeding density trials varied in wireworm pressure. A heavy wireworm population was observed at the Kalispell site; an average of 10.5 wireworms per stocking trap was collected prior to planting (90.7% L. californicus and

9.3% L. infuscatus). After planting an average of 12.3 wireworms per stocking (89.2% L. californicus and 10.8% L. infuscatus) was collected from the buffer bordering the experimental plot (n = 30 traps). At the Conrad site wireworm populations were moderate, averaging 3.3 per trap prior to planting (40.3% H. bicolor, 33.5% A. mellillus and 26.2 % L. californicus). After planting, an average of 3.6 wireworms per trap was collected from the buffer bordering the experimental plot (41.1% H. bicolor, 39.5% A.

197 mellillus and 19.4 % L. californicus). At Fort Ellis the populations were low, averaging only 0.7 wireworms per trap prior to planting (80.1% L. californicus and 19.9% L. infuscatus). After planting, an average of 0.6 wireworms per trap was collected from the buffer bordering the experimental plot (82.1% L. californicus and 17.9% L. infuscatus).

For both wheat and barley, a general trend of reduced stand densities with increasing seeding density was observed, but the differences were not statistically significant (Tables 3 and 4). Significant difference in yield between the different seeding densities was not detected, and in general, the yield at lower seeding densities was surprisingly good. Plant density expressed as a percentage of seeding density four weeks after planting formed a negative linear relationship (Figures 8.2 and 8.3). At Kalispell with a heavy wireworm infestation the % barley plants relative to seeding density =

2 83.241 - 0.974 barley seeds, R (23) = 0.40 and the % wheat plants relative to seeding

2 density = 68.1 - 0.802 wheat seeds, R (23) = 0.22 (Figures 8.2 and 8.3). In Conrad with medium wireworm pressure the % barley plants relative to seeding density = 61.007 -

2 0.358 barley seeds, R (22) = 0.11 and % wheat plants relative to seeding density = 73.3 -

2 0.4214 wheat seeds, R (23) = 0.05 (Figures 8.4 and 8.5). In Fort Ellis with low wireworm pressure the % barley plants relative to seeding density = 123.19 -1.622 barley seed,

2 R (23) = 0.69 and % wheat plants relative to seeding density = 122.08 -1.5736 wheat

2 seeds, R (23) = 0.71 (Figures 8.6 and 8.7). For the second stand count at 10 weeks after seeding the percentage of plants observed relative to seeding density was similar (Tables

8.3 and 8.4). The percentage of plants could be predicted with the formulas: Kalispell %

2 barley plants = 56.737 -0.627 barley seed, R (24) = 0.18 and % wheat plants = 54.744 –

198

2 0.5565 wheat seeds, R (24) = 0.11 (Figures 8.2 and 8.3); in Conrad % barley plants =

2 93.816 -0.5506 barley seed, R (24) = 0.11 and % wheat plants = 97.764 -0.4666 wheat

2 seeds, R (24) = 0.09 (Figures 8.4 and 8.5); and in Fort Ellis % barley plants = 84.984 -

2 2 0.398 barley seed, R (24) = 0.14 and % wheat plants = 86.864 -0.1998 wheat seeds, R (24)

= 0.03 (Figures 8.6 and 8.7). In all cases the slope of the line was < 1 indicating an inverse relationship between the proportion of plants to seeding density and the number of seeds planted.

Discussion

In the 1880s Comstock and Slingerland (1891) recognized the difficulties of managing wireworms with cultural practices. However, cultural practices are an important component of IPM programs and some recommendations continue although little quantitative research has been published. For example, increasing the seeding density of cereal crops by 10-30% is a common recommendation for commercial fields infested by wireworms. One producer in Pondera County plants untreated wheat seed but doubles the seeding rate to compensate for wireworm feeding, and claims to achieve better yields with this practice. Successive passes by commercial cereal planters with a 30 foot width often overlap by a few inches. These doubly seeded areas are often visible as a green strip of plants within an area of thin crop stand made patchy from wireworm feeding. Tillage can be beneficial if it disrupts the life cycle of an insect pest and exposes it to predators and the elements. In addition tillage operations modify soil texture,

199 temperature, and moisture, and may affect the behavior and survival of soil insects

(Gaylor, 1989). Insects that overwinter in the soil or in the crop residues and become active early in the growing season might be more susceptible to tillage (McGuire, 2002).

“Common knowledge” suggests that continuous cereal cropping increases wireworm populations and soil tillage might reduce their populations. In this study we utilized the existence of long term experimental plots maintained with different cultural practices, and a seeding density trial, to gain preliminary quantitative insights into the effects of cultural practices on wireworms infesting Montana’s cropland.

A replicated experiment to assess the effects of tillage compared to no till practices at the MSU CARC has been maintained for 20 years. Wireworms were sampled from these plots for three consecutive years and no significant difference in the average total numbers was detected due to tillage. In 2011 and 2013 the total wireworms collected in tilled plots was slightly higher than in no-till plots. Crop establishment and yield measured as average stand density, plant biomass and grain yield were all quite consistent between the tilled and no tilled plots, and no significant differences were detected. A second non-replicated experiment at CARC compared two cultural variables, tillage and continuous cropping. Wireworms were subsampled from these four plots for three consecutive years. Populations in the two plots that received tillage were not significantly different from the two no till plots with one exception; the alternating fallow plot that was not tilled had significantly more wireworms compared to the no till plot in 2013 only

(Table 8.2). Collectively this data does not support an effect of 20 years of tillage practice on the wireworm populations at this site.

200

Published results that examine the ability of tillage to reduce wireworm populations are mixed. In corn fields in Missouri, Belcher et al. (2011) suggests that tillage practices do not appear to be closely related to potential economic infestation.

However, other studies find a significant difference in favor of conventional systems.

Seal et al. (1992) notes a reduction of the wireworm population in sweetpotato fields after they were plowed three times. Stapley et al. (1946) demonstrated a reduction of the wireworm population after plowing only once if the cultivation was performed before

July. In the north central states black cutworm damage was reduced to 1% in tilled fields compared to 15% damage in no till fields (Musick and Petty, 1974). In reduced tillage systems, the lack of mechanical disturbance of the soil fails to expose white grubs to parasites and predators, compared to conventional tillage, leading to increased pest population (Gregory and Musick, 1976). A similar effect of reduced tillage was noted for

Diabrotica longicornis Say and D. virgifera LeConte in continuously cropped corn fields where no till plots had four times more eggs compared to the conventional system

(Musick and Petty, 1974). Shrestha and Parajulee (2010) observed significantly higher abundance of ground beetles in conservation tillage plots than in conventional plots.

Organic producers are recommended to avoid no-till practices in favor of deep disc- cultivation to reduce damage from wireworms and black cutworms (Van Duyn, 2005).

Published literature supports the ability of tillage to reduce the population of soil insect pests, including wireworms in some cases. The lack of an effect of tillage on wireworm populations at the CARC is likely due to two factors: the diversity of wireworm species and their associated biology and ecology, and, the diversity of tillage

201 practices. The two experimental fields at CARC were infested with six wireworm species during 2011 – 2013, predominantly H. bicolor (22 – 46% of the total), A. mellillus (38 –

65%) and L. californicus (2 – 35%). These are not the same species that infest sweetpotato and corn crops grown in other regions (Belcher et al. 2011; Seal et al. 1992).

Differences in pest biology and ecology, such as seasonal movement in the soil, larval life span and timing and location of pupation all likely affect efficacy of tillage. Tillage systems vary in the amount of soil disruption they cause. Wireworm larvae can found in the top 60 cm of the soil surface, and pupal cells are found 7.5 – 10 cm deep during

August and September (Comstock and Slingerland, 1891). Deep tillage timed to coincide with larval activity near the soil surface and pupation in the fall are likely to be more effective, but modern practices favor cultivation that is less disruptive to the soil.

The second non-replicated experiment at CARC compared continuous cropping in addition to tillage. In several cases the continuously cropped plots had significantly more wireworms compared to the alternating fallow plots (Table 8.2). When the data was further pooled (ignoring tillage as a factor) continuously cropped plots had significantly more wireworms compared to alternating fallow plots in 2011 and 2012, but not in 2013.

Seal et al. (1992) records fewer wireworms in fallow fields compared to fields continuously planted with sweetpotato, peanut or corn crops. Stapley et al. (1946) reported a marked decline in wireworm populations the year following fallow. The authors hypothesized that the mortality or lack of wireworm catches in fallow plots is a consequence of several factors: the reduction of available food during a period of maximum activity and higher mortality of eggs and larvae caused by hotter and dryer soil

202 conditions near the surface because of the lack of canopy cover. Our plots were primarily infested by two short life cycle species, H. bicolor and A. mellillus, and one long life cycle species, L. californicus. Aeolus mellillus and H. bicolor have 1 – 2 years life cycles

(Jewett, 1940) while L. californicus can require as many as 7 years to complete its life cycle. During the fallow years plots at the CARC were keep free of vegetation using herbicides and tilling, depriving wireworms of a herbivorous diet for as long as 14 – 20 months. Depending on their feeding habits, this may extend the time required to complete their life cycle, and species with short life cycles may be more vulnerable. Another possible explanation for reduced wireworm populations in fallow fields is lack of oviposition by the female beetles. Some species of click beetles prefer oviposit close to plants in damp soils (Miles, 1939). Our results support observations that continuously cropped and irrigated cereal fields in Montana are at higher risk for economic infestations of wireworms. However, this hypothesis needs to be tested with replicated experiments that also account for the species of wireworm infesting the field and the dispersal and oviposition behavior of the female beetles.

Wireworms are thought to avoid compact soil, presumably because it is more difficult to crawl through. Within an infested field, the compacted tracks from equipment are often visible as green strips of crop bordered by thin patchy stands damaged by wireworms. Comstock and Slingerland (1891) suggested compacting the soil as a cultural practice to reduce crop damage from wireworms. Burrowing organisms such as earthworms, termites, ants, and beetles can suffer negative effects from soil compaction.

In Australia, for example, earthworms decreased from 166,000 to 8,000 per acre due to

203 severe compaction of wet soil while compaction of dry soil did not have a negative effect on macrofauna (Duiker, 2014). Interestingly, our results found the no till and alternating fallow plot to be the least compacted, and wireworm populations in this plot were not significantly different from the continuously cropped plots in 2012 and 2013. Soil compaction, however, is not practical or consistent with modern agricultural practice.

Increasing the density of cereal seeds is a common practice by producers to mitigate stand thinning and yield loss damage caused by wireworms. It is thought to offset seeds consumed by the wireworms. Bryson (1930) found that the percentage of damaged corn plants increased as the seeding density decreased. The three experimental sites provided a gradient of wireworm pressure: Kalispell, very high; Conrad, moderate; and Bozeman, low. At each of these sites untreated spring wheat and barley seed was planted at five different rates: 60, 90, 120, 150 and 180 seeds 0.91 m-1 (20, 30, 40, 50 and

60 seeds per row foot). Bozeman was a dry land site with low numbers of wireworms, and the stand density measured as a % of seeding density was close to 100% at the first assessment date for both spring wheat and barley (Table 8.3). As the seeding rate increased, the % of spring wheat and barley plants at the Bozeman site decreased, in the absence of wireworm pressure. These results can be explained by plant competition for resources such as water and nutrients. In dry land cereal fields in Montana 60 seeds m-1 with a 0.30 m row spacing is a common seeding density. As the seeding rate increases competition for resources increases, and seedling mortality rates (proportional to seeding density) increases. This effect of plant competition results in a general negative relationship between seeding density and the plant density expressed as a proportion of

204 seeding density (Figures 8.2 – 8.7). The Kalispell site (irrigated) was heavily infested with wireworms, yielding some of the highest trap counts relative to a state-wide survey of Montana’s cropland (reported in Chapter 5). Here, a different relationship between seeding density, and the plant density expressed as a proportion of seeding density, was expected. The destruction of seeds planted a lower densities was expected to result in significantly lower proportions, that would increase as seeding density increased, an offset of the seeds consumed by wireworms. Stand density as a proportion of seeding density was lower at the Kalispell site, compared to the Bozeman site, a result of the higher wireworm pressure. However, this proportion did not increase with seeding density as expected, rather, it continued to decrease, as it did at the Bozeman site where wireworm pressure was negligible. At the Conrad site (irrigated) with moderate wireworm pressure, the results were intermediate compared to the Bozeman and Kalispell sites. These results suggest a complex relationship between seeding density, seedling mortality caused by wireworms, crop type and wireworm feeding behavior.

At the heavily infested Kalispell site, the proportion of wheat seedlings to seeding density decreased from 60.7% at 60 seeds m-1 to 32.9% at 90 seeds m-1, at the first assessment date. In other words, there was an average of 12 wheat seedlings for every 20 seeds planted, and only 10 for every 30 seeds planted. No offset was observed. Thirty seeds per foot is a standard seeding density for irrigated cereal fields in Montana. These results suggest that wireworm feeding behavior and damage is not linearly correlated to seeding density. Two hypotheses may explain this unexpected result. First, wireworms are attracted to CO2 produced by germinating seeds, and higher seeding densities may

205 attract more wireworms. Second, searching and foraging behavior may be more efficient at higher seeding densities; after feeding on a seed, wireworms may be more likely to encounter a second seed to feed on when seed densities are higher. As the seeding density increases further, it is difficult to separate the effects of plant competition from wireworm damage. Similar results have been reported for wheat stem sawfly (Cephus cintus Norton,

1872) that damages wheat plants when the stem mining larvae cut notches at the base of the stem. A higher percentage of stem cutting was observed in plots seeded with 500 seeds m-2 compared to plots with 100 m-2 but no differences were observed in yield

(Beres et al., 2012). In this case an increased efficiency in oviposition as a result of plant density is implied. However, in a previous study, Beres et al. (2011) observed a lower cutting percentage at higher seeding rates, suggesting the relationship between crop damage and plant density may be more complex. The decrease in plant density as a function of seeding density, between the 20 and 30 seeds per foot rates, was not as pronounced for barley as compared to wheat. Results presented in Chapter 6 demonstrated that barley seeds/seedlings are not inured as much by wireworm feeding as wheat seedlings are.

Producers commonly increase seeding rates in commercial cereal fields infested with wireworms. Seed costs can average 5.1% of the total cost of cereal production in the

Northern Great Plains region (Ali and Vocke, 2002; USDA, Economic Research Service

2014). Our results suggest that increasing seeding rates may not result in increased profits and any increase in the price of the seed going to be reflected in the profit specially when the price of the grain is low. At all three sites there was no clear trend of increasing plant

206 biomass or increasing yield with increasing seeding density. This study provides some preliminary insights into the effects of cultural practices on wireworm densities and damage. It also illustrates the complexities of these relationships and the need for future quantitative research.

Acknowledgements

We thank Frank Etzler, Meghan McGauley, Hannah Johnson, Laura Morales,

Sally Dahlhausen and Joe Vavrovsky for their help in conducting this work. This study was supported in part by funds from the Montana Wheat and Barley Committee, Montana

Seed Potato Producers Association and USDA Crops at Risk Grant 2010-51100-21547.

207

)

Density Density

(lb bu

58.7 ± 2.3 59.7 ± 2.3 57.0 ± 1.2 57.1 ± 1.3

Seed BulkSeed

No Harvest No Harvest

)

Yield

30.4 ± 7.9 34.5 ± 8.1 43.0 ± 8.7 40.7 ± 5.8

(bu acre

No Harvest No Harvest

)

± 37.3

(g 0.91m

Dry Weight Dry

251.7 ± 72.9 251.7 ± 72.9 148.2 150.0 ± 22.5 149.8 ± 22.9 145.0 ± 36.1

)

Second

0.91m

37.3 ± 7.9 29.2 ± 9.2 29.1 ± 0.0 28.3 ± 8.3 28.3 ± 9.3

36.7 ± 13.5

Assessment(

)

First First

(0.91m

26.1 ± 6.0 23.7 ± 4.3 31.7 ± 4.6 35.2 ± 7.6

45.5 ± 20.7 45.3 ± 20.2

Assessment

in Moccasin, MT.

± 15.9

8.4 ± 6.5 5.8 ± 2.6 6.8 ± 3.9 9.2 ± 2.2

13.0 ± 6.7

12.4

Wireworms

Treatment Till No Till Till No Till Till No Till

. Wireworms, stand counts, dry weights and seed densities (mean ± SD) by soil till system and year year and densities (mean andweights dry seed by soil stand± SD) till counts, . Wireworms, system

Table 8.1 Table tillage different two practices under Year 2011 2012 2013

208

)

59.2 ± 1.9 59.1 ± 1.2 61.4 ± 0.5 57.7 ± 1.1 57.7 ± 1.1 57.7 ± 0.6

Fallow Fallow Fallow

Density Density

(lb bu

Seed BulkSeed

No Harvest No Harvest No Harvest

)

ear under four ear

Yield

23.2 ± 7.9 55.8 ± 8.3 46.0 ± 7.8 46.0 ± 7.8

Fallow Fallow Fallow

57.3 ± 13.5 52.1 ± 11.7

(bu acre

No Harvest No Harvest No Harvest

)

Fallow Fallow Fallow

(g 0.91m

215.5 ± 44.2 239.4 ± 55.9 196.3 ± 66.9 133.7 ± 26.5 135.8 ± 28.7 162.5 ± 35.5 162.5 ± 26.5 133.7 ± 28.7 135.8 ± 29.5

Dry Weight Dry

)

31.8 ± 6.8 29.5 ± 9.1 31.6 ± 6.7 31.8 ± 6.8 29.5 ± 9.1 35.8 ± 7.0

Fallow Fallow Fallow

Second

38.4 ± 14.3 43.7 ± 16.8 39.7 ± 11.7

(0.91m

Assessment Assessment

)

First First

38.0 ± 8.4 38.1 ± 8.7 22.3 ± 3.1 27.0 ± 5.2 42.1 ± 5.3 39.7 ± 6.3

Fallow Fallow Fallow

43.5 ± 13.7 41.7 ± 11.4 38.8 ± 10.8

(0.91m

Assessment

2.25 ± 0.5 B 3.25 ± 1.3 B 1.75 ± 0.9 B 1.75 ± 0.5 B

9.75 ± 3.7 A 6.75 ± 2.2 A 5.25 ± 1.9 A 4.75 ± 1.7 A

10.75 ± 6.8 A

7.75 ± 4.8 AB 6.25 ± 4.3 AB 3.25 ± 1.0 AB

Wireworms

Tillage Till No Till Till No Till Till No Till Till No Till Till No Till Till No Till

Treatment

Cropping

Wireworms, stand counts, dry weights and seed densities (mean ± SD) by soil till system and y and densities (mean andweights dry seed by soil stand± SD) till counts, Wireworms, system

Continuous Continuous Fallow Fallow Continuous Continuous Fallow Fallow Continuous Continuous Fallow Fallow

Table 8.2. Table in Moccasin, MT. crop and system practices treatments of tillage different Year 2011 2012 2013

209

Table 8.3. Barley seeding density trial results. Plant density expressed as a % of the seeding density at two assessment dates, plant biomass measured as dry weight, yield and seed density (mean ± SD) at three different locations in Montana. Location First Second Dry Seed Bulk Yield Assessment Assessment Weight Density (kg ha-1)a (%) (%) (g 0.91m-1) (kg cu m-1)b Bozeman

60 96.3 ± 3.2 87.0 ± 22.2 234.9 ± 10.9 2757.5 ± 618.8 593.0 ± 7.5

90 76.9 ± 23.3 61.1± 7.5 242.1 ± 27.6 2468.3 ± 652.4 571.8 ± 12.5

120 46.2 ± 14.0 70.5 ± 10.5 264.2 ± 26.7 1896.6 ± 1042.4 574.3 ± 8.7

150 36.9 ± 15.5 58.0 ± 7.5 233.8 ± 23.9 30.33.2 ± 464.1 609.2 ± 49.9

180 35.2 ± 10.1 68.7 ± 7.0 286.8 ± 11.9 2670.0 ± 625.5 581.7 ± 6.2

Conrad

60 52.2 ± 23.0 80.3 ± 35.5 270.4 ± 45.5 4842.4 ± 470.3 655.4 ± 8.7

90 51.4 ± 15.2 79.1 ± 25.4 298.8 ± 46.5 4748.2 ± 1096.3 627.9 ± 1.2

120 45.3 ± 7.7 69.6 ± 11.9 298.5 ± 89.1 4553.2 ± 1197.1 639.2 ± 8.7

150 48.3 ± 6.2 74.3 ± 9.6 355.8 ± 87.7 5730.2 ± 1405.6 687.9 ± 61.2

180 35.9 ± 16.2 55.2 ± 29.5 366.3 ± 44.3 5346.8 ± 793.6 641.7 ± 5.0

Kalispell

60 63.3 ± 13.9 39.3 ± 16.4 225.4 ± 50.8 No Harvest No Harvest

90 58.4 ± 18.2 38.7 ± 27.0 270.1 ± 17.6 No Harvest No Harvest

120 44.0 ± 30.2 38.0 ± 29.4 192.3 ± 77.5 No Harvest No Harvest

150 32.8 ± 21.5 28.5 ± 19.9 214.6 ± 36.9 No Harvest No Harvest

180 24.8 ± 5.1 15.0 ± 5.9 232.4 ± 84.4 No Harvest No Harvest

Yield in kilograms per hectar b Seed Bulk Density in kilograms per cubic meter

210

Table 8.4. Spring wheat seeding density trial results. Plant density expressed as a % of the seeding density at two assessment dates, plant biomass measured as dry weight, yield and seed density (mean ± SD) at three different locations in Montana. Location First Second Seed Bulk Dry Weight Yield Assessment Assessment Density (g 0.91m-1) (kg ha-1)a (%) (%) (kg cu m-1)b Bozeman

60 97.0 ± 12.4 85.3 ± 26.0 225.3 ± 27.6 3100.5 ± 376.6 651.7 ± 28.7

90 64.7 ± 17.5 75.3± 18.9 242.9 ± 26.7 2770.9 ± 322.8 640.4 ± 43.7

120 61.0 ± 18.3 81.7 ± 14.4 251.8 ± 23.9 2824.7 ± 242.1 654.2 ± 11.2

150 44.7 ± 16.0 78.0 ± 12.9 261.3 ± 11.9 2818.0 ± 349.7 636.7 ± 41.2

180 28.3 ± 6.7 74.0 ± 9.4 266.7 ± 23.1 3134.1 ± 181.6 654.2 ± 6.2

Conrad

60 50.5 ± 21.3 77.7 ± 32.7 309.4 ± 75.3 5750.3± 1029.0 727.8 ± 41.2

90 81.0 ± 39.8 94.7 ± 17.8 356.0 ± 58.2 6866.8 ± 840.7 725.3 ± 67.4

120 50.1 ± 10.1 78.3 ± 15.6 337.8 ± 55.0 6375.8 ± 417.0 749.0 ± 6.2

150 63.7 ± 18.6 86.3 ± 16.7 340.6 ± 115.4 6187.5 ± 1210.6 802.7 ± 8.7

180 38.1 ± 5.3 58.6 ± 8.2 352.7 ± 74.0 7929.4 ± 894.5 764.0 ± 11.2

Kalispell

60 60.7 ± 26.4 51.3 ± 33.8 265.4 ± 28.8 No Harvest No Harvest

90 32.9 ± 22.4 25.6 ± 10.4 203.6 ± 39.6 No Harvest No Harvest

120 35.2 ± 27.2 35.2 ± 26.7 254.3 ± 119.7 No Harvest No Harvest

150 28.7 ± 18.3 28.1 ± 19.0 290.1 ± 115.5 No Harvest No Harvest

180 22.7 ± 19.2 22.2 ± 22.8 198.8 ± 98.5 No Harvest No Harvest a Yield in kilograms per hectar b Seed Bulk Density in kilograms per cubic meter

211

Figure 8.1. Penetration resistance measurement in four fields under different management in Moccasin, Montana. Red line at 300 PSI mark indicate the compaction level of the data above the line.

212

Figure 8.2. Regression percentage of barley plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Kalispell’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits.

213

Figure 8.3. Regression percentage of wheat plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Kalispell’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits.

214

Figure 8.4. Regression percentage of barley plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Conrad’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits.

215

Figure 8.5. Regression percentage of wheat plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Conrad’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits.

216

Figure 8.6. Regression percentage of barley plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Fort Ellis’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits.

217

Figure 8.7. Regression percentage of wheat plants versus number of seed planted per 0.3 m-1 (1 foot) at 4 and 11 weeks after planting in Fort Ellis’s seed density trial. Doted line = 95% Prediction limits; Blue shadow 95% Confident limits.

218

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Baumler, R. E. 2008. Effects of crop rotation on wireworm (Coleoptera: Elateridae) populations in North Carolina sweetpotato fields, M.S. thesis, North Carolina State University, Raleigh.

Becker, E. C. and Dogger, J. R. 1991. Elateridae (Elateroidea) (including Dicronychidae, Lissomidae). Pages 410-417. W. Stehr (ed.) Immature Insects, Vol. 2. Kendall/Hunt Publishing, Dubuque, Iowa.

Benefer, C., van Herk, W., Ellis, J., Blackshaw, R., Vernon, R., M. Knight. 2013. The molecular identification and genetic diversity of economically important wireworm species (Coleoptera: Elateridae) in Canada. J. Pest Sci. 86(1): 19 - 27.

Belcher, D. W. 1989. Influence of cropping Systems on the number of wireworms (Coleoptera: Elateridae) Collected in Baits in Missouri cornfields. J. Kans. Entomol. Soc. 62(4): 590 – 592.

Beres, L. B., Cárcamo, H. A., Yang, R-C., and D. M., Spaner. 2011. Integrating spring wheat sowing density with variety selection to manage wheat stem sawfly. Agron. J. 103(6): 1755- 1764.

Beres, L. B., McKenzie, R. H., Cárcamo, H. A., Dosdall, L. M., Evenden, M. L., Yang, R-C., and D. M., Spaner. 2012. Influence of seeding rate, nitrogen management, and micronutrient blend applications on pith expression in soil-stemmed spring wheat. Crop Sci. 52: 1316 – 1329.

Bousquet, Y. (Ed.). 1991. Checklist of beetles of Canada and Alaska. Agriculture Canada Publication 1861/E, Ottawa, ON. 144 pp.

Bryson, H. R. 1930. A study of field practices as related to wireworm infestations (Elateridae). J. Econ. Entomol. 23: 303-315.

Comstock, J. H. and Slingerland, M. V. 1891. Wireworms. Bull. 33. Cornell University Agric. Exp. Sta. Geneva, NY.

219

Cherry, R. H. and Hall, D. G. 1986. Flight activity of Melanotus communis (Coleoptera: Elateridae) in Florida sugar cane fields. J. Econ. Entomol. 79(3): 626-628.

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Gaylor, M. J. 1989. Direct and indirect effects of conservation tillage on the management of insect pests of cotton. Pages 10-12 in: Proc. Southern Conservation Tillage Conf. Sustainable Agric., 12th. Tallahasee, FL.

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Seibert, C. E. 1993. A faunal survey of the Elateroidea of Montana. Montana State University, Department of Plant Science and Plant Pathology. MSc Thesis. Bozeman, MT. 320 pp.

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222

CHAPTER NINE

GENERAL CONCLUSIONS

Wireworms are an increasing threat to the sustainable production of cereal, potato and other crops grown in rotation in the northwestern USA. They represent a unique and potentially devastating pest complex that may comprise more than 30 different species of click beetles nationally. Historically, wireworms were severe pests with no effective management techniques. John Comstock, one of the first American entomologists, considered wireworms “among the most prominent of the pests that infest field crops”

(Comstock and Slingerland 1891). During the early 20th century wireworms were major pests of most agronomic crops grown throughout the continental US as documented by early agriculturalists. Effective wireworm control was not achieved until the insecticide era that began in the 1950s, that produced inexpensive, potent and persistent broad- spectrum insecticides that were applied to crop seeds and soil (Pedigo 1989; Vernon et al.

2008; Toba et al. 1985; Furlan 2005). Inexpensive and effective insecticides created a low pest status, resulting in little integrated pest management (IPM) research for nearly

40 years. Incredibly, even the most basic elements of integrated pest management (IPM) have not been developed and most producers apply prophylactic insecticidal seed treatments to manage wireworm damage. However, current insecticidal seed treatments do not provide effective control. Results from greenhouse and field studies presented in

Chapter 7 of this thesis demonstrate that thiamethoxam, even at its highest labeled rates,

223 does not cause wireworm mortality, and field infestations can continue to increase. The purpose of this research was to provide a foundation of knowledge for the future management of this pest complex in Montana and the northwestern region.

The first critical step of IPM is to identify the key pest species causing crop damage. The only intensive survey of wireworm fauna in Montana was conducted by

(Seibert 1993), but it focused on the adult beetles that do not cause damage. This current study identified as many as six different pest wireworm species, representing five different genera, infesting and damaging grain fields across Montana. Limonius californicus (Mannerheim, 1843), L. infuscatus Motschulsky, 1859, Hypnoidus bicolor

(Eschscholtz, 1829) and Aeolus mellillus (Saylor, 1836) were identified as the most common species in this study (Chapter 5). Interestingly, the prairie grain wireworm,

Selatosomus aeripennis (Kirby, 1837), was thought to be the most common species damaging wheat and barley in the region, but was found only as a minor species. The geographic distribution of some pest species identified in this study was clearly limited.

These results support the need for, and value of, modern pest surveys to identify key pest species. Future research and resources can now be allocated more effectively, to study the species causing the economic damage to cereal crops in Montana.

Understanding species-specific behavior and ecology is important information required to develop future management tools based on IPM. Greenhouse studies conducted in Chapter 6 confirmed field observations that wheat is more susceptible to wireworm damage compared to barley, valuable information when recommending crop rotation strategies for wireworm management. These studies also suggested that L.

224 californicus larvae could cause more damage to wheat, even when compared to the closely related L. infuscatus, critical information required to establish accurate economic thresholds. A second factor related to crop injury and pest status is the vertical movement and activity of larvae near the soil surface where cereal crop seeds are planted. In general, peak wireworm activity in Montana occurred during May and the first part of June, coinciding with cereal germination and stand development, stages vulnerable to wireworm damage. Limonius californicus appeared to be active at the soil surface earlier than H. bicolor, a species-specific behavior that may be important knowledge when targeting larvae with IPM tactics. Spikes of activity early in the spring when larvae are searching for food after overwintering deeper in the soil may provide an opportune time to deliver attractive insecticidal baits. Cultural practices that prevent or reduce pest damage are an important component of IPM. One of the most common cultural recommendations is to increase cereal-seeding density by 10-30% to offset seeds and seedlings damaged by wireworms. Surprisingly, results from a wheat and barley seeding density trial conducted during a single growing season did not support the effectiveness of this recommendation. This research needs to be repeated, but it illustrates the need for

IPM recommendations based on quantitative data.

Prior to the body of research described in this thesis, published information about wireworms infesting Montana’s cropland was scant. Five years of field, greenhouse and laboratory research, with support from collaborating producers, students and colleagues, has significantly increased the knowledge of pest wireworms in areas critical to the development of future IPM tools. Importantly, we identify L. californicus as a key pest

225 species of crops grown in Montana. Not only is it one of the most common pest species, it is also more commonly found at high numbers and may cause more injury to cereal crops compared to other pest species. However, while some species may be less common based on incidence, they can be the dominat pest species infesting a field and cannot be ignored if future IPM tools are based on their biology and ecology. The efficacy of IPM tactics likely will depend on the species of wireworm infesting the field. Studies conducted as part of this thesis have increased the body of knowledge related to pest wireworms infesting Montana’s cropland, but much more research remains to be conducted.

226

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Western Regional Integrated Pest Management Center. 2003f. Pest management strategic plan: Cantaloupe, honeydew, and mixed melon production in California. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/CAMelon.pdf, 69 pp.

Western Regional Integrated Pest Management Center. 2003g. Tennessee’s strawberry strategic plan meeting, Knoxville TN. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/TNstrawberry.pdf, 52 pp.

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Western Regional Integrated Pest Management Center. 2004c. Pest management strategic plan for Washington state wine grape production. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/WAWineGrapePMSP.pdf, 55 pp.

Western Regional Integrated Pest Management Center. 2004d. Pest management strategic plan for dry bulb storage onions in Colorado, Idaho, Oregon, Utah, and Washington. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/WesternONION.pdf, 76 pp.

Western Regional Integrated Pest Management Center. 2004e. Pest management strategic plan for PNW small grains (wheat and barley). Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/WesternONION.pdf, 90 pp.

Western Regional Integrated Pest Management Center. 2004f. Pest management strategic plan for northern wheat: Hard red spring wheat, amber durum wheat, and hard red winter wheat in ND, SD, MN and NE. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/NorthernWheatPMSP.pdf, 89 pp.

Western Regional Integrated Pest Management Center. 2005a. Pest management strategic plan for processed snap beans in Oregon and Washington. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/ORWA%20SnapBean.pdf, 41 pp.

Western Regional Integrated Pest Management Center. 2005b. Pest management strategic plan for snap beans in Virginia, North Carolina, and Delaware. Accessed on- line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/VA-NC-DEsnapbeanPMSP.pdf, 45 pp.

Western Regional Integrated Pest Management Center. 2005c. A pest management strategic plan for fresh carrot production in California. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/CACarrot.pdf, 51 pp.

Western Regional Integrated Pest Management Center. 2005e. A pest management strategic plan for potato production in California. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/CAPotato.pdf, 56 pp.

Western Regional Integrated Pest Management Center. 2005f. Pest management in the future: A strategic plan for the Wisconsin, Minnesota, Michigan, and North Dakota potato industry. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/MidwestPotatoPMSP.pdf, 75 pp.

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Western Regional Integrated Pest Management Center. 2005g. Midwest pest management strategic plan for processing and jack-o-lantern pumpkins: Illinois, Indian, Iowa and Missouri. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/MidwestPumpkin.pdf, 101 pp.

Western Regional Integrated Pest Management Center. 2005h. Pest management strategic plan for western U.S. sugarbeet production. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/PNWSugarbeet.pdf, 114 pp.

Western Regional Integrated Pest Management Center. 2006a. Sweet corn pest management strategic plan (northeastern states). Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/NE_Sweet_Corn.pdf, 90 pp.

Western Regional Integrated Pest Management Center. 2006b. Pest management strategic plan for Pacific Northwest potato production. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/PNWPotatoPMSP.pdf, 106 pp.

Western Regional Integrated Pest Management Center. 2007a. Pest management strategic plan for pulse crops (chickpeas, lentils, and dry peas) in the United States. Accessed on-line 12/14/2011 athttp://www.ipmcenters.org/pmsp/pdf/USPulseCrops.pdf, 80 pp.

Western Regional Integrated Pest Management Center. 2007b. Texas spinach pest management strategic plan. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/TXspinachPMSP.pdf, 24 pp.

Western Regional Integrated Pest Management Center. 2007c. Pest management strategic plan for tomato in Georgia and South Carolina. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/GA-SC-TomatoPMSP.pdf, 69 pp.

Western Regional Integrated Pest Management Center. 2008a. Pest management strategic plan for pepper in Georgia and South Carolina. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/GA-SCpepperPMSP.pdf, 70 pp.

Western Regional Integrated Pest Management Center. 2008b. Pest management strategic plan for organic potato production in the West. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/CA-CO-ID-OR-WAOrganicPotatoPMSP.pdf, 108 pp.

Western Regional Integrated Pest Management Center. 2008c. Pest management strategic plan for watermelons in Delaware, Maryland, New Jersey, and North Carolina. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/DE-MD-NJ- NCWatermelonPMSP.pdf, 70 pp.

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Western Regional Integrated Pest Management Center. 2011. Pest management strategic plan for blueberries in Oregon and Washington. Accessed on-line 12/14/2011 at http://www.ipmcenters.org/pmsp/pdf/ORWABlueberry.pdf , 88 pp.

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