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Theses and Dissertations Theses and Dissertations
1-1-2012
The Biology and Management of Phytophagous Stink Bugs (Pentatomidae) in Mississippi Soybean Production Systems
James Wesley McPherson
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Recommended Citation McPherson, James Wesley, "The Biology and Management of Phytophagous Stink Bugs (Pentatomidae) in Mississippi Soybean Production Systems" (2012). Theses and Dissertations. 4276. https://scholarsjunction.msstate.edu/td/4276
This Graduate Thesis - Open Access is brought to you for free and open access by the Theses and Dissertations at Scholars Junction. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholars Junction. For more information, please contact [email protected]. THE BIOLOGY AND MANAGEMENT OF PHYTOPHAGOUS STINK BUGS
(PENTATOMIDAE) IN MISSISSIPPI SOYBEAN
PRODUCTION SYSTEMS
By
James Wesley McPherson
A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Agricultural Life Sciences in the Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology
Mississippi State, Mississippi
May 2012
THE BIOLOGY AND MANAGEMENT OF PHYTOPHAGOUS STINK BUGS
(PENTATOMIDAE) IN MISSISSIPPI SOYBEAN
PRODUCTION SYSTEMS
By
James Wesley McPherson
Approved:
______Angus L. Catchot, Jr. Clint Allen Associate Extension Professor of Research Entomologist USDA-ARS Entomology (Committee Member) (Director of Thesis)
______Fred R. Musser Scott T. Willard Associate Professor of Entomology Head of Biochemistry, Molecular (Director of Thesis) Biology, Entomology, and Plant Pathology Department
______Donald R. Cook Michael A. Caprio Assistant Research Professor of Professor of Entomology Entomology (Graduate Coordinator) (Committee Member)
______George Hopper Dean, College of Agriculture and Life Sciences
Name: James Wesley McPherson
Date of Degree: May 11, 2012
Institution: Mississippi State University
Major Field: Agricultural Life Sciences (Entomology)
Major Professor: Dr. Angus L. Catchot, Jr. and Dr. Fred R. Musser
Title of Study: THE BIOLOGY AND MANAGEMENT OF PHYTOPHAGOUS STINK BUGS (PENTATOMIDAE) IN MISSISSIPPI SOYBEAN PRODUCTION SYSTEMS
Pages in Study: 72
Candidate for Degree of Master of Science
Stink bugs are the most economically important insect pest of soybeans in
Mississippi. This study focused on several aspects of stink bug biology and management.
One study examined the residual activity of certain insecticides. Rain was shown to reduce residual activity and after three days most insecticides provided very little control of stink bugs. Stink bugs complete at least one generation a year on early season hosts before moving into soybeans. A study of these early season hosts found that rice stink bug was more prevalent on grasses than the other hosts sampled. Brown stink bug was found on all hosts, while other species were not found very frequently. A third study to determine the effects of an automatic insecticide on insect populations in soybeans found that yield was not affected, but stink bug populations later in the year were lowered during the 2011 study.
DEDICATION
I would like to dedicate this research to my step dad, Lee Arrington, who introduced me to the world of farming.
ii ACKNOWLEDGEMENTS
Above all else I praise and thank my Lord and Savior, Jesus Christ, for through him all things are possible. I acknowledge my advisors, Dr. Angus Catchot, and Dr. Fred
Musser, for their instruction and support without which I would have been lost. I thank my fellow graduate students who were always there to help when I was in need: Lucas
Owen, Brian Adams, Will Scott, and Ben Von Kanel. I also thank members of my graduate committee: Dr. Don Cook, and Dr. Clint Allen for their input in the planning and execution of this research.
I appreciate the Mississippi Soybean Promotion Board for funding this project. I would also like to thank Kathy Knighten for her work and support with this project. I thank Dung Bao, Teresa Ziegelmann, Kevin Langford, Blake Goldman, Jenny Bibb, John
Randle Wells, Joel Moore, Scott Graham, and Walt Grant for their hard work.
iii TABLE OF CONTENTS
DEDICATION ...... ii
ACKNOWLEDGEMENTS ...... iii
LIST OF TABLES ...... vi
LIST OF FIGURES ...... vii
CHAPTER
I. LITERATURE REVIEW ...... 1
Soybean Production ...... 1 Phytophagous Pentatomids ...... 2 Pest Status ...... 3 Action Thresholds ...... 5 Insecticide Susceptibility ...... 5 Chinavia hilaris (Say) ...... 5 Biology ...... 6 Identification ...... 7 Euschistus servus (Say)...... 8 Biology ...... 8 Identification ...... 9 Nezara viridula (L.) ...... 9 Biology ...... 10 Identification ...... 11 Thyanta spp...... 12 Identification ...... 12 Piezodorus guildinii (Westwood) ...... 13 Biology ...... 13 Identification ...... 14 Summary ...... 15 References Cited ...... 16
iv II. RESIDUAL ACTIVITY OF SELECTED INSECTICIDES AGAINST STINK BUGS ...... 23
Introduction ...... 23 Materials and Methods ...... 24 Results and Discussion ...... 26 References Cited ...... 30
III. EARLY SEASON HOSTS OF STINK BUGS IN MISSISSIPPI ...... 36
Introduction ...... 36 Materials and Methods ...... 38 Results and Discussion ...... 39 References Cited ...... 42
IV. IMPACT OF AUTOMATIC INSECTICIDE APPLICATION ON INSECT DENSITIES IN SOYBEAN ...... 48
Introduction ...... 48 Materials and Methods ...... 50 On-farm trial ...... 50 On-station trial ...... 51 Results ...... 53 On-farm trial ...... 53 On-station trial ...... 55 Discussion ...... 55 References Cited ...... 58
V. SUMMARY ...... 71
v LIST OF TABLES
2.1 Mean percent corrected mortality of green stink bugs after 48 hours for selected insecticides from trial 1 in 2010. 5 cm of rain fell on day 2...... 32
2.2 Mean percent corrected mortality of green stink bugs after 48 hours for selected insecticides from trial 2 in 2010...... 33
2.3 Mean percent corrected mortality of green stink bugs after 48 hours for selected insecticides from trial in 2011...... 34
2.4 Mean percent corrected mortality of brown stink bugs after 48 hours for selected insecticides from trial in 2011...... 35
3.1 Actual number of stink bugs collected during 2010 and 2011...... 44
3.2 Average number of stink bugs per 100 sweeps during 2010 and 2011...... 45
4.1 Average number of insects per 25 sweeps from small plot trial located in Starkville during 2010. Treatments were applied on June 21, 2010...... 68
4.2 Average number of insects per 25 sweeps from small plot trial located in Starkville during 2011. Treatments were applied on August 8, 2011...... 69
4.3 Average number of insects per 25 sweeps from small plot trial located in Stoneville during 2010. Treatments were applied on July 17, 2010...... 70
vi LIST OF FIGURES
3.1 Number of brown stink bugs per 100 sweeps by time of year and host. Columns with the same letter within a time period are not significantly different at α = 0.05. NS = no significant differences (α = 0.05) among hosts within the time period...... 46
3.2 Number of rice stink bugs per 100 sweeps by time of year and host. Columns with the same letter within a time period are not significantly different at α = 0.05. NS = no significant differences (α = 0.05) among hosts within the time period...... 47
4.1 Mean ± SEM number of stink bugs per 100 sweeps by weeks relative to insecticide application for MG IV and V insecticide treated and untreated fields in Sunflower County, MS, during 2011. Week zero represents the week the insecticide/fungicide application was applied. * = Significant difference between treated and untreated at this week (Protected F-test at P = 0.05)...... 59
4.2 Mean number of stink bugs per 100 sweeps by weeks relative to insecticide application for MG IV and V insecticide treated and untreated fields in Sunflower County, MS, during 2011 (from Fig. 4.1). The dotted and dashed lines represent the linear regression lines for untreated and treated from weeks 3 to 7, respectively. The comparison of these two lines showed that they were significantly different (F = 4.51, df = 1,51, P = 0.0382)...... 60
4.3 Mean ± SEM number of loopers per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. There were no significant differences between treatments during any week (Protected F-test at P=0.05)...... 61
4.4 Mean ± SEM number of corn earworms per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. Treatments were not significantly different any week (Protected F-test at P=0.05)...... 62
vii
4.5 Mean ± SEM number of threecornered alfalfa hoppers per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. Treatments were not significantly different any week (Protected F-test at P=0.05)...... 63
4.6 Mean ± SEM number of big-eyed bugs per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. * = significant difference between treated and untreated at this week (Protected F-test at P=0.05)...... 64
4.7 Mean ± SEM number of spiders per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. * = significant difference between treated and untreated at this week (Protected F-test at P=0.05)...... 65
4.8 Mean ± SEM number of lacewings per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. * = significant difference between treated and untreated at this week (Protected F-test at P=0.05)...... 66
4.9 Yield from small plot studies combined during 2008, 2010 and 2011 in Starkville, Stoneville, and Verona, MS for treated and untreated plots. Columns with the same letter are not significantly different (α = 0.05)...... 67
viii CHAPTER I
LITERATURE REVIEW
Soybean Production
In the past four years the United States has planted approximately 30.4 million hectares of soybeans, Glycine max, annually (NASS 2011b). In 2010, 809,000 hectares of soybeans were planted in Mississippi with a value of 846 billion dollars (NASS 2011a).
More hectares of soybeans are planted annually in Mississippi than any other crop.
In Mississippi there are a variety of insect pests that can adversely affect yield and overall productivity of soybeans. The defoliation complex: bean leaf beetle, Cerotoma trifurcata (Forster); blister beetle, Epicauta spp.; grasshopper; soybean looper,
Chrysodeixis includens (Walker); cabbage looper, Trichoplusia ni (Hubner); green cloverworm, Hypen scabra (Fabricius); velvetbean caterpillar, Anticarsia gemmatalis
(Hubner); saltmarsh caterpillar, Estigmene acrea (Drury); beet armyworm, Spodoptera exigua (Hubner); and fall armyworm, Spodoptera frugiperda (J.E. Smith) can cause significant yield loss at high defoliation levels. Threecornered alfalfa hopper, Spissistilus festinus (Say), can be a damaging pest by feeding on stems and petioles. Cutworms are another pest that can cause stand loss by cutting young plants off at the soil surface. Corn
1 earworm, Helicoverpa zea (Boddie), is a very significant pest of soybeans in Mississippi.
This insect feeds directly on the developing fruit, and is considered the second most damaging pest of Mississippi soybeans (Musser and Catchot 2009). Stink bugs are the most damaging pest of Mississippi soybeans (Musser and Catchot 2009) . A complex of stink bug species including green stink bug, Chinavia hilaris (Say); southern green stink bug, Nezara viridula L.; and the brown stink bug, Euschistus servus (Say) are the dominant stink bug pests of soybean in the southern U.S. (Funderburk et al. 1999).
Phytophagous Pentatomids
Pentatomidae is one of the largest families of Heteroptera, comprised mainly of phytophagous species (Froeschner 1988). Pentatomids differ from other members of
Heteroptera in that they have five-segmented antennae and a well developed scutellum.
Within the Pentatomidae only the subfamily Pentatominae contains pest species of major economic importance (McPherson and McPherson 2000c). These insects have scent glands located on the metacoxae that produce a foul odor (Panizzi et al. 2000). Eggs are laid on end generally in a mass, and are held together and to the substrate by an adhesive secretion (Esselbaugh 1946). Stink bugs feed by piercing plant tissue with their stylets and extracting nutrients (McPherson and McPherson 2000c; Panizzi et al. 2000). This feeding damages plant tissues, can cause abortion of fruit, and may transmit pathogens that can damage a variety of crops (Panizzi et al. 2000). Stink bugs have been the most costly insect pest of soybeans in Mississippi from 2004-2009 with annual control costs ranging from 27-49 dollars per hectare (Musser and Catchot 2009; Musser et al. 2010).
2 Pest Status
Stink bugs are key pests in soybean production systems across the southern
United States. The predominant species of stink bugs that infest soybeans are the green stink bug, southern green stink bug, and the brown stink bug. From a survey conducted in
Georgia, McPherson et al. (1993) found that these three species comprised 98% of all stink bugs found in soybeans. Boyd et al. (1994) stated that the southern green stink bug represented the highest proportion of the stink bug complex in Louisiana. Gore et al.
(2006) found that the green stink bug, southern green stink bug, and brown stink bug were the most abundant stink bug species in Mississippi soybeans. Smith et al. (2009) found the southern green stink bug and brown stink bug to be the most common species in Arkansas, and recorded the presence of redbanded stink bug, Piezodorus guildinii
(Westwood), in Arkansas soybean fields during 2006 and 2007. Stink bug populations typically increase in August and reach peak levels in late September and October
(Buschman et al. 1984).
Stink bugs feed by piercing plant tissues with their mandibular and maxillary stylets and removing plant fluids (McPherson and McPherson 2000c). All stages except first instar nymphs feed on plants, but adults and fifth instars cause most of the damage in soybeans (McPherson et al. 1979). Stink bugs may attack all parts of the plant, but feeding is generally limited to fruiting structures (Panizzi 1997). Stink bugs prefer to feed on developing seed pods and the direct feeding and indirect disease transmission reduce yield and seed quality (McPherson and McPherson 2000c). Studies with southern green stink bugs in soybeans have shown that feeding causes yield and quality loss, decreases pod fill and seed weight, delays crop maturity, reduces seed oil content, increases seed
3 protein levels, and reduces germination of harvested seed (McPherson et al. 1979).
Feeding punctures form minute discolored spots on the plants and seed that have been heavily damaged may be shriveled or distorted (Miner 1966). Stink bug damage may reduce the value of soybean seed, and if severe enough, it might have little to no value
(Todd 1976). Stink bug damage can also result in foliar retention, delayed plant maturation, and abnormal plant growth (Panizzi and Slansky 1985). Stink bug feeding during the early reproductive stages can result in the abortion of fruit (McPherson et al.
1994). Stink bug feeding can result in delayed maturity. Delayed maturity can be defined as fields retaining leaves, green stems, and/or green pods long after normal harvest date
(Boethel et al. 2000). Southern green stink bug and brown stink bug have been reported to cause delayed maturity in soybeans (Boethel et al. 2000). Sosa-Gomez and Moscardi
(1995) found that redbanded stink bug caused greater leaf retention than the southern green stink bug and Euschistus heros (F.).
Stink bugs are pests of all major row crops grown in Misssissippi, including soybean, corn, cotton, rice, and wheat. Stink bugs damage young corn by feeding on the developing plant distorting the whorl. This can kill the plant or delay it and cause tillering which ultimately reduces yield. Stink bugs also feed on the developing ears which damage the developing kernals and causes cow horned ears. Rice and wheat are damaged by stink bugs from direct feeding on the developing kernels reducing both yield and quality (Barbour et al. 1990). Stink bugs damage cotton by feeding on the developing bolls, resulting in bolls not opening properly (hard lock) and can possibly lead to boll rot
(Greene et al. 1999; Greene et al. 2001).
4 Action Thresholds
Miner (1966) developed an action threshold to initiate insecticide applications when stink bug levels reach one insect per row foot. The action threshold for southern green, green, and brown stink bugs is 9/25 sweeps or 1/row foot in Louisiana, Texas,
Mississippi, and Arkansas (Gouge et al. 1999; Lorenz et al. 2006; Baldwin et al. 2009;
Catchot 2010). The threshold for redbanded stink bug in Louisiana and Mississippi is
6/25 sweeps (Baldwin et al. 2009; Catchot 2010).
Insecticide Susceptibility
Based on results from an adult vial test for stink bugs in Arkansas and
Mississippi, brown stink bug is significantly less susceptible to pyrethroids than southern green and green stink bugs (Snodgrass et al. 2005). Work in Louisiana showed similar results with southern green stink bug being significantly more susceptible to pyrethroids than brown stink bug (Willrich et al. 2003). There does not seem to be any differences in insecticide susceptibility between southern green stink bug and green stink bug
(Snodgrass et al. 2005).
Temple et al. (2009) determined from insecticide efficacy trials that southern green stink bug were more susceptible to both pyrethroid and organophosphate insecticides than redbanded stink bug.
Chinavia hilaris (Say)
The green stink bug, as it is commonly referred, is widely distributed throughout the United States (McPherson 1982). It is highly polyphagous, but in the southern United
5 States it can be a major pest of soybean (Miner 1966; McPherson et al. 1994). Green stink bug was the dominant stink bug species in Mississippi soybeans during the 2010 and 2011 growing seasons (personal obs.).
Biology
In its northern range the green stink bug is univoltine (Javahery 1990), but in the southern states it is bivoltine (Jones and Sullivan 1982). In the southern states the first generation apparently occurs on wild hosts and the second on soybean (Miner 1966;
Jones and Sullivan 1982). Green stink bug needs host plants with overlapping periods of seed production in order to develop high populations during its annual life cycle
(McPherson and McPherson 2000a). Several leguminous woody shrubs and trees are excellent hosts (Jones and Sullivan 1982). As hosts begin seed production they become more suitable, and when cultivated crops fit into the wild host sequence, severe damage can occur (Schoene and Underhill 1933). The second generation of green stink bug occurs on soybeans and is responsible for the majority of the damage to reproductive stage soybean (Miner 1966; Jones and Sullivan 1982). Green stink bug populations are higher in soybean rows bordering wild hosts (Miner 1966). In the southern United States, green stink bug populations in soybeans peak during September and early October (Miner
1966; Jones and Sullivan 1982; Bundy and McPherson 2000a). Both males and females prefer larger mates, and larger females have higher fecundity (Capone 1995). Green stink bug is photoperiod sensitive and remains in reproductive diapause when the photophase is less than eight hours (Wilde 1969). Feeding by green stink bugs on soybeans can significantly reduce seed germination, and fifth instar nymphs are more damaging than
6 other growth stages (Yeargan 1977). The number of feedings per instar increases from the second to the fifth instar with the fifth instar nymphs feeding an average of 31.3 times
(Simmons and Yeargan 1988). Fifth instar nymphs feed a maximum of 6.5 times per day
(Simmons and Yeargan 1988). Three to five days after molting, adult feeding reaches a maximum then decreases to a stable three times per day (Simmons and Yeargan 1988).
Simmons and Yeargan (1988) found feeding duration to be similar for the different instar nymphs and the adults at about one and a half hours at a time. Green stink bugs can reduce soybean yield by reducing seed number (Simmons and Yeargan 1990). However, soybean plants are able to compensate considerably for stink bug damage (Daugherty et al. 1964).
The green stink bug can be found from Quebec and Massachusetts south to
Florida and west to the Pacific coast (Froeschner 1988).
Identification
The adults are green in color and vary from 13 to 19 mm in length (Panizzi et al.
2000). It can be distinguished from southern green by a long ostiolar canal that extends beyond the middle of its supporting plate (McPherson 1982). Egg masses with up to 69 eggs per mass have been observed laid in uniform rows somewhat loosely (Bundy and
McPherson 2000b). The eggs have been described in detail (Bundy and McPherson
2000b). R. M. Decoursey and C. O. Esselbaugh (1962) provided indepth descriptions of the nymphal instars.
7 Euschistus servus (Say)
There are several species of Euschistus that are considered pests of soybean in
North America. E. servus (Say) , E. variolarius (Palisot de Beauvois), E. tristigmus
Dallas, and E. conspersus Uhler are the predominant Euschistus species of economic importance in North America (McPherson and McPherson 2000b). Of the Euschistus spp., Euschistus servus, the brown stink bug, is the most economically important occurring in America north of Mexico (Panizzi et al. 2000). In the southern half of the
United States, E. servus servus is the dominant subspecies (McPherson 1982). Smith et al. (2009) reported that brown stink bug represented 19 percent of the total seasonal abundance of stink bugs in Arkansas soybeans.
Biology
Brown stink bug completes two generations per year in the southern U. S., overwinters as adults, and is highly polyphagous (McPherson and McPherson 2000b). It prefers to overwinter in open fields or edges compared to woodlands (Jones and Sullivan
1981). Peak emergence occurs during the last week of March to the first week of April, but did continue into June in South Carolina (Jones and Sullivan 1981). In some instances it has been reported to be predaceous (McPherson and McPherson 2000b). Egg masses have been reported to have a maximum of 41 (Munyaneza and McPherson 1994) to 55 eggs per mass (Esselbaugh 1946). Egg masses are arranged loosely in a cluster (Bundy and McPherson 2000b). Total developmental period for brown stink bug is approximately
44.3 days (Munyaneza and McPherson 1994). Brown stink bug is capable of transmitting disease causing pathogens associated with soybeans, as well as reducing yield (Daugherty
8 et al. 1964; Russin et al. 1988a; Russin et al. 1988b). Injury from brown stink bug is similar to that of green and southern green stink bugs (McPherson et al. 1979).
Euschistus servus servus ranges throughout the southeastern United States across to California (McPherson 1982).
Identification
All adult Euschistus spp. are brown and species can be hard to distinguish. A dichotomous key is available to identify the different species (McPherson and McPherson
2000f). Euschistus quadrator (Rolston) is identified from the others by the absence of spots in the membranous area of the hemelytra (Esquivel et al. 2009). Euschistus tristigmus (Say) can be distinguished by having large median black spots on the abdominal ventor (Esquivel et al. 2009). Size, color, spiracles, and markings on underside can be used to identify these species (Esquivel et al. 2009).
The eggs and nymphal instars have been described in detail (Munyaneza and
McPherson 1994; Bundy and McPherson 2000b).
Nezara viridula ( L.)
“The southern green stink bug is one of the most important insect pests of agricultural crops in the world” (Jones 1988). In the Southeast, the southern green stink bug is the most damaging of the stink bug complex (McPherson et al. 1993). The southern green stink bug is the pentatomid of greatest economic concern for Mississippi soybeans (Gore et al. 2006). In Arkansas it represented 58 percent of the total stink bug population in soybeans (Smith et al. 2009). Russin et al. (1987) showed that the southern
9 green stink bug represented 61.5 percent of the total stink bug population in soybeans in
Louisiana.
Biology
Southern green stink bug has four generations per year in Louisiana and Florida
(Todd 1989). Adults overwinter in protected sites such as leaf litter, behind bark, and in tree crotches (Jones and Sullivan 1981). Overwintering adults are in reproductive diapause and often have a russet cuticle coloration (Harris et al. 1984). Legume species are the preferred hosts (Todd and Herzog 1980). The average developmental time from oviposition to adult is around 36 days, depending on temperature (Harris and Todd 1980).
Diapausing adults are able to feed during warmer periods of winter (Drake 1920;
Newsome et al. 1980; Todd 1989). Females can move up to 1,000 m per day in search of feeding and oviposition habitat (Todd 1989). Overwintering survivorship can be greatly reduced by low winter temperatures (Kiritani et al. 1966; Jones and Sullivan 1981).
Overwintering survivability is higher for females, larger individuals, and russet colored individuals (Todd 1989). Diapause primarily serves to regulate the lifecycle as it does not increase cold tolerance (Elsey 1993). Southern green stink bug’s ability to survive the winter is one of the major limiting factors affecting populations (Kiritani et al. 1966). The presence of suitable food enhances winter survival (Drake 1920; Newsome et al. 1980).
As temperatures increase in the spring, adults leave overwintering sites to seek food and oviposition sites (Drake 1920; Todd and Herzog 1980; Jones and Sullivan 1981; Jones and Sullivan 1982). Southern green stink bugs prefer to feed on hosts during fruit formation (McPherson and McPherson 2000d). This results in a need for a sequence of
10 suitable host plants for populations to reach maximum levels (Todd and Herzog 1980;
Jones and Sullivan 1982). The third and fourth generations primarily occur on soybean during reproductive stages (Todd and Herzog 1980; McPherson and McPherson 2000d).
Thomas et al. (1974) showed significant reduction in soybean yield only from infestations occurring during early pod development. Todd and Turnipseed (1974) showed southern green stink bugs could reduce yield, greatly increase percent damaged seed, and decrease seed viability when infestations persist throughout the reproductive stages. Southern green stink bug feeding during the R3 through the R5.5 growth stage can also delay soybean maturity (Boethel et al. 2000). Southern green stink bug populations can increase dramatically from R5 through R6 causing severe quality and yield loss
(McPherson et al. 1979). Stink bug damage can also affect the proportions of various fatty acid concentrations in soybean oil (Todd et al. 1973). Chemical control of stink bugs can reduce the amount of seed damaged from southern green stink bug (McPherson et al.
1995).
The southern green stink bug is distributed worldwide inhabiting the warmer regions of the world (Todd 1989). In the United States the southern green stink bug occurs mainly in the south, from the Southeast all the way to California (Todd 1976).
Identification
Adult southern green stink bugs are green and approximately 12 mm long
(Panizzi et al. 2000). Eggs are cream colored and typically laid in tightly packed polygonal clusters glued to the substrate (Todd 1989; Bundy and McPherson 2000b).
11 These egg clusters can have as many as 151 eggs per mass (Bundy and McPherson
2000b). Bundy et al. (2000b) has described the eggs in detail.
Thyanta spp.
Thyanta spp. are polyphagous and feed on a variety of crops including soybean
(McPherson et al. 1993). An appreciable number of Thyanta stink bugs were found in a soybean insect survey in Arkansas (Smith et al. 2009). Thyanta spp. have been found in both cotton and soybeans in Georgia (Bundy and McPherson 2000a). Thyanta spp. have been reported as being the third most common stink bug pest in South Carolina (Jones and Sullivan 1982), and Arkansas (Tugwell et al. 1973). Thyanta custator accera
McAtee, the redshouldered stink bug, is commonly found in soybeans and cotton
(McPherson et al. 1993). In Mississippi it is rarely found in numbers at or exceeding threshold in soybeans, but it is readily found (personal obs.). Redshouldered stink bugs have been recorded overwintering in open fields and wood edges (Jones and Sullivan
1981).
The redshouldered stink bug is distributed from Quebec south to Florida and west to Montana and Utah (Froeschner 1988).
Identification
Egg masses have been recorded having a maximum of 37-72 eggs per cluster loosely arranged in irregular patterns (Esselbaugh 1946; Bundy and McPherson 2000b).
The eggs have been described in detail by Bundy and McPherson (2000b).
12 Piezodorus guildinii (Westwood)
In 2002, an emerging stink bug pest, the redbanded stink bug, Piezodorus guildinii (Westwood), first reached treatable levels in Louisiana soybean fields (Baldwin et al. 2009). In 2007 it was considered the most devastating stink bug pest of soybeans in
Louisiana (Paxton et al. 2007). Preliminary research has shown redbanded stink bugs appear to be more damaging and harder to control than other stink bugs in the complex
(B. R. Leonard, unpublished data).
Biology
In South America, the redbanded stink bug has five generations per year (Panizzi and Slansky 1985). Females lay an average of 15.1 eggs per mass and an average of 31.1 eggs total per female (Panizzi and Smith 1977). The main oviposition site for redbanded stink bug on soybeans is on the pods (Panizzi and Smith 1977). Redbanded stink bug has better longevity and reproductive capacity on some wild hosts such as Indigo spp. than on soybean (Panizzi et al. 2000). First instar nymphs cluster around the egg mass and do not feed (Panizzi and Slansky 1985). The second and third instars are gregarious while the fourth and fifth instars are the principal instars involved in dispersal through soybean fields (Panizzi et al. 1980). Redbanded stink bug adults are more mobile than southern green stink bug adults (Costa and Link 1982).
Studies from Argentina show that the redbanded stink bug is more damaging to soybeans than other South American stink bug species (Vicentini and Jimenez 1977).
Redbanded stink bug is a neotropical pentatomid that can be found from the southern United States to Argentina (Panizzi and Slansky 1985). The redbanded stink bug
13 is among the top stink bug pests of soybean in Brazil (Panizzi and Smith 1977). Since the late 1970’s it has begun to replace the southern green stink bug as the principal stink bug pest of soybeans in portions of Brazil (Turnipseed and Kogan 1976). Since at least the
1960’s redbanded stink bug has been known in the United States, and it has been reported in several states including South Carolina, Florida, Georgia, and New Mexico
(McPherson and McPherson 2000e). In the early 1980’s this pest was a major part of the stink bug complex in Georgia and Florida (Baldwin 2009). However, it is rarely encountered in these states today.
In 2000, small numbers of redbanded stink bugs were reported in Louisiana
(Baldwin 2009). In 2002, it reached treatable levels in Louisiana (Baldwin et al. 2005).
Now, in many areas of Louisiana, after an initial insecticide treatment has been applied, redbanded stink bug is the most common stink bug (Baldwin et al. 2009).
Only in the past few years has redbanded stink bug been found in Mississippi, and generally it has been restricted to the southern delta. In 2009, redbanded stink bug was the primary cause for an increase in number of insecticide applications for stink bugs on soybean acres in Mississippi (Musser et al. 2010).
Identification
Adult redbanded stink bugs can be described as light green to yellowish in color, with a yellowish, reddish, or brownish band at the base of scutellum (Fraga and Ochoa
1972). It can also be distinguished by having a long ventral abdominal spine that reaches the mesothoracic coxae and nearly the proboscis (Greene et al. 2006). Eggs are light to reddish brown with black spines and are laid in rows of two in alternating positions
14 (Bundy and McPherson 2000b). The nymphs for the first to fifth instars are described as
1.30, 2.25, 2.58, 4.60, and 7.87 mm long, respectively (Greene et al. 2006).
Summary
Stink bugs are the principal pests of Mississippi soybeans. Management of this stink bug complex is vital to maximize soybean production and profitability. A better understanding of the stink bug complex is crucial in order to accomplish this. Knowledge of stink bug life cycles, seasonal life history, ability to damage soybeans, ecology, and management tactics play a part in the management decisions for producers.
15 References Cited
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17
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18 McPherson, J. E. and R. M. McPherson. 2000a. Acrosternum hilare (Say). In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, FL. 129- 139.
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19
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22 CHAPTER II
RESIDUAL ACTIVITY OF SELECTED INSECTICIDES AGAINST STINK BUGS
Introduction
Stink bugs are major pests of soybeans in Mississippi. Soybeans can be damaged by stink bugs from R3 through R7, which is a period of about 50 days (Thomas et al.
1974; McPherson et al. 1979; Koger 2009; Musser et al. 2011). Insecticides are the most used management practice once stink bug populations have reached economically damaging levels in soybeans. Of Mississippi’s 800,000 ha of soybeans planted during
2009, approximately 75 % were scouted by a crop consultant, generally on a weekly interval (Musser et al. 2010). Stink bugs are mobile insects and are able to reinfest fields after an insecticide application. Some insecticides provide longer residual control than others (Way and Wallace 1990), so for management of mobile insects like stink bugs, the length of residual control can have economic implications. This can impact the perceived level of control from a product when the consultant returns to the field a week or two after the application was made.
In Mississippi, the recommended insecticides for controlling stink bugs in soybeans include the organophosphates; acephate and methyl parathion, and the pyrethroids; beta-cyfluthrin, bifenthrin, esfenvalerate, gamma-cyhalothrin, lambda- cyhalothrin, and zeta-cypermethrin (Catchot 2010). The toxicity and LC50 values for
23 many of the organophosphate and pyrethroid insecticides against stink bugs were determined by Snodgrass et al. (2005). Numerous studies have reported the efficacy of insecticides for controlling stink bugs (Smith and Catchot 2008; Smith and A. L. Catchot
2009).
Without rain, the half-life of carbamates is 2.4 days, organophosphates is 3.0 days, and pyrethroids is 5.3 days (Boyd and Boethel 1998). It has been shown that rainfall can reduce the efficacy of foliar applied insecticides (Willis et al. 1992).
The duration of effective residual activity of insecticides against stink bugs in soybeans is currently unknown. This study was done to determine how long selected insecticides provide control of green (Chinavia hilaris) and brown (Euschistus servus) stink bugs when applied at recommended rates in soybeans.
Materials and Methods
Three studies were conducted during 2010 and 2011 at Starkville, MS. In all trials, insecticides were applied to soybeans during reproductive growth stages on the R.
R. Foil Plant Science Research Center, and assays were conducted in the basement of the
Clay Lyle Entomology building on the Mississippi State University campus. For both trials during 2010, green stink bugs were collected using sweep nets from an unsprayed soybean field in Grenada County, MS. During 2011, both green and brown stink bugs were collected from unsprayed soybean fields in Sunflower County. Stink bugs were kept in plastic boxes with mesh lids in an insect rearing room at 27°C and 60% RH for up to four days until used in the assay. The boxes contained shredded paper to increase surface area in the box and soybean pods were added as food and moisture source.
24 The insecticides and rates used were the same for all trials based on those suggested by the Mississippi State University Extension Service (Catchot 2010).
Thiamethoxam, which is not labeled in soybeans, was included in order to evaluate each of the components of Endigo ZC®, which is labeled in soybeans. Seven different insecticide treatments were tested plus an untreated control. The treatments were: unsprayed check; bifenthrin (Brigade® 2EC, FMC Corporation, Philadelphia, PA) at
0.112 kg ai/ha; lambda-cyhalothrin (Karate Z® 2.08CS, Syngenta Corporation,
Wilmington, DE) at 0.0336 kg ai/ha; acephate (Orthene® 90S, AMVAC Chemical
Corporation, Axis, AL) at 0.84 kg ai/ha; thiamethoxam (Centric® 40WG, Syngenta
Corporation, Wilmington, DE) at 0.056 kg ai/ha; thiamethoxam + lambda-cyhalothrin
(Endigo ZC®, Syngenta Corporation, Wilmington, DE) at 315 mL form/ha; methyl parathion (Methyl® 4EC, Cheminova, Durham, NC) at 1.12 kg ai/ha; and acephate + bifenthrin (Orthene® 90S + Brigade® 2EC) at 0.84 kg ai/ha + 0.112 kg ai/ha. The treatments were applied using a Mudmaster® (Bowman Manufacturing, Newport, AR) sprayer with TX6 hollow cone tips applying 93.5 L/ha. Plots were 4 rows wide by 23 m long with 4 border rows between plots. Spray dates were as follows: 2010, trial 1,
September 7; trial 2, September 14; and 2011, August 16.
At 1 hour, 1, 3, 5, 7, and 10 days after application, 10 leaves from 3 rows (all trials) and 10 pods from 3 rows (2010 only) were collected from each plot. Leaves and pods were collected from the second node down from the terminal of the plant. One leaf,
(and pod in 2010), and one adult stink bug were placed in a 10 cm diameter petri dish.
During 2010, a 2% water agar solution was put into each petri dish as a moisture source, but this was determined to be unnecessary and was not included in 2011. Because there
25 was little mortality for any treatments after 5 days during 2010, leaves were collected at 1 hour, and 1, 2, 3, 4, and 5 days after application during 2011. Mortality was determined after 24 and 48 hours of exposure. Stink bugs were considered dead if no coordinated movement was observed within five seconds of being prodded. A treatment was no longer tested after it failed to increase mortality compared to the untreated control.
Insecticide treatment data were corrected for natural mortality using Abbott’s correction for natural mortality (Abbott 1925). Corrected data were analyzed as a completely randomized design in SAS using Proc GLM at a 0.05 level of significance.
Results and Discussion
Corrected mortality ranged from 0 to 100% over all three trials. Since control mortality never exceeded 20%, insecticide treatment mortality was corrected for natural mortality (Abbott 1925) and control data are not reported.
2010. Two days after insecticide application, a 5 cm rainfall event occurred. Table
2.1 shows the residual efficacy of the insecticide treatments against green stink bug adults up to five days after application. Mortality was significantly reduced from 1 day (before rainfall) to 3 days after application (after rainfall) (t =5.29 ; df =1 ; P <0.0001). Three days after insecticide application, acephate + bifenthrin was providing the most control, causing 42.7 % mortality (F = 16.8; df = 6, 14; P <0.0001).
Table 2.2 shows the efficacy data from the second trial during 2010. There was no rain throughout the course of this trial. Insecticide efficacy declined over time (F= 10.82; df =5, 84; P <0.0001). There were no significant differences in mortality rates from 1 day to 3 days in the absence of rain (t= 1.58; df = 1; P = 0.1168). By comparing the data from
26 trials one and two, which were sprayed just one week apart, rain appears to have reduced the residual activity of the insecticides. Acephate + bifenthrin was significantly better than acephate, thiamethoxam, and methyl parathion 3 days after application (t = 3.75; df
= 1; P = 0.0021). Table 2.2 shows that even in the absence of rain, none of the insecticides caused more than 50% mortality five days after application.
2011. Tables 2.3 and 2.4 display the residual toxicity data for green and brown stink bugs, respectively. Against brown stink bugs, acephate and acephate + bifenthrin caused significantly higher mortality 2 days after application (t = 11.18; df = 1; P <
0.0001), and 3 days after application (t = 8.67; df = 1; P < 0.0001). The treatments containing acephate provided the highest efficacy against brown stink bugs from 2 days on, and were the only treatments that provided more than 40% control 2 days after application. These were twice as efficacious as all the other treatments two days after application. At 5 days after application the acephate and the acephate + bifenthrin treatments were still providing 83 and 92 percent mortality of brown stink bugs, respectively. After 5 days, brown stink bug mortality in the acephate treatment was not significantly different from mortality at 1 hour after application (t = 1.14; df = 1; P =
0.2856). Thiamethoxam caused the least mortality on brown stink bugs of all the insecticides tested. One hour after application, it only resulted in 28% mortality.
Overall, efficacy of the insecticides declined over time, with the exception of acephate against brown stink bugs in the 2011 trial. In 2010, acephate did not control stink bugs as well as expected based on field efficacy data (Smith and A. L. Catchot
2009). In 2011, water agar was not used in the petri dishes, and acephate provided levels of control more consistent with field efficacy. Three days after application, treatments
27 containing a pyrethroid insecticide, namely acephate + bifenthrin, lambda-cyhalothrin + thiamethoxam, and lambda-cyhalothrin, resulted in greater mortality of green stink bug in the absence of rainfall than the other insecticides. After three days, none of the treatments resulted in > 50 percent mortality of green stink bug. Brown stink bugs tended to be more susceptible to acephate than green stink bugs. Green stink bugs tended to be more susceptible to the pyrethroids and thiamethoxam than the brown stink bugs.
The lack of residual activity for methyl parathion has been previously documented (Way and Wallace 1990). Way and Wallace (1990) also showed that acephate provided 40 percent control of rice stink bug nine days after application. Based on our observed high level of control 5 days after application, acephate control of brown stink bug may be this long as well.
Our finding that rainfall reduces the residual activity of insecticides on stink bugs is consistent with research done by Hulbert et al. (2011), showing that simulated rainfall decreases the activity of some insecticides.
More research is needed to further explore the residual activity of insecticides against stink bugs. The residual activity against stink bug nymphs should also be studied.
Large densities of stink bugs are often primarily composed of nymphs (Smith et al. 2009) and the susceptibility of nymphs can be different from adults. This was not done in the current study because nymphs were not abundant enough to conduct the assays.
There are many abiotic factors that could affect the residual efficacy of insecticides. As seen in this study, a major rainfall event reduced residual efficacy. What is unknown is how this varies with different amounts of rain, the time of the rain in relation to the application, and the rate at which the rain fell. Sunlight quantity and
28 quality may affect residual activity. Temperature, relative humidity, crop type, application coverage, and wind could potentially all be factors that affect the residual efficacy of insecticides for stink bugs.
Hood et al. (2009) showed all foliar insecticides tested reduced stink bug field populations 8 days after application. Rather than assuming the insecticides are still providing control at this time, our data would suggest that the insecticides initially killed a large proportion of the population, and the observed reduction was likely due to limited reinfestation.
In conclusion, all of the insecticides tested resulted in very little mortality of green stink bug after 4 days. Acephate provided residual mortality of brown stink bugs through five days, and may have had longer residual control. This was longer than any of the other insecticides tested. A rainfall event can lower the amount of residual activity of all insecticides against stink bugs.
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Boyd, M. L. and D. J. Boethel. 1998. Residual toxicity of selected insecticides to heteropteran predaceous species (Heteroptera: Lygaeidae, Nabidae, Pentatomidae) on soybean. Environ. Entomol. 27: 154-160.
Catchot, A. L., Jr. 2010. Insect control guide for agronomic crops 2010. http://msucares.com/pubs/publications/p2471.pdf.
Hood, C. D., J. F. Smith, and J. A. L. Catchot. 2009. Efficacy of foliar insecticides against green stink bug and southern green stink bug in soybean (test 2), 2008. Arthropod Manag. Tests F62.
Hulbert, D., R. Isaacs, C. Vandervoort, and J. C. Wise. 2011. Rainfastness and residual activity of insecticides to control Japanese beetle (Coleoptera: Scarabaeidae) in grapes. J. Econ. Entomol. 104: 1656-1664.
Koger, T. 2009. Guide to soybean growth stages. http://msucares.com/pubs/publications/p2588.pdf.
McPherson, R. M., L. D. Newsom, and B. F. Farthing. 1979. Evaluation of four stink bug species from three genera affecting soybean yield and quality in Louisiana. J. Econ. Entomol. 72: 188-194.
Musser, F. R., A. L. Catchot, B. K. Gibson, and K. S. Knighten. 2011. Economic injury levels for southern green stink bugs (Hemiptera: Pentatomidae) in R7 growth stage beans. Crop Protection 30: 63-69.
Musser, F. R., G. M. Lorenz, S. D. Stewart, and A. L. Catchot, Jr. . 2010. 2009 soybean insect losses for Mississippi, Tennessee, and Arkansas. Midsouth Entomol. 3: 48-54.
Smith, J. F. and J. A. L. Catchot. 2009. Efficacy of foliar insecticides against green stink bug and southern green stink bug in soybean (test 1), 2008. Arthropod Manag. Tests 34.
Smith, J. F. and A. L. Catchot. 2008. Efficacy of foliar insecticides against southern green stink bug, threecornered alfalfa hopper, bean leaf beetle and soybean looper on soybean, 2007. Arthropod Manag. Tests 33: F63.
Smith, J. F., R. G. Luttrell, and J. K. Greene. 2009. Seasonal abundance, species composition, and population dynamics of stink bugs in production fields of early and late soybean in south Arkansas. J. Econ. Entomol. 102: 229-236.
30 Snodgrass, G. L., J. J. Adamczyk, Jr., and J. Gore. 2005. Toxicity of insecticides in a glass-vial bioassay to adult brown, green, and southern green stink bugs (Heteroptera: Pentatomidae). J. Econ. Entomol. 98: 177-181.
Thomas, G. D., C. M. Ignoffo, C. E. Morgan, and W. A. Dickerson. 1974. Southern green stink bug: influence on yield and quality of soybeans. J. Econ. Entomol. 67: 501-503.
Way, M. O. and R. G. Wallace. 1990. Residual activity of selected insecticides for control of rice stink bug (Hemiptera: Pentatomidae). J. Econ. Entomol. 83: 591-595.
Willis, G. H., L. L. McDowell, S. Smith, and L. M. Southwick. 1992. Foliar washoff of oil-applied malathion and permethrin as a functions of time after application. J. Agric. Food Chem. 40: 1086-1089.
31
Table 2.1 Mean percent corrected mortality of green stink bugs after 48 hours for selected insecticides from trial 1 in 2010. 5 cm of rain fell on day 2.
Time After Application
P Chemical 1 Hour 1 Day 3 Days 5 Days F value (df) value acephate 53.4 ± 9.5 C,a 11.7 ± 14.5 C,b 0.0 ± 3.6 B,b NT . . 8.44 (2,6) 0.0180 acephate + bifenthrin 100.0 ± 0.0 A,a 88.0 ± 0.0 A,b 42.7 ± 3.6 A,c 3.5 ± 3.5 d 316.17 (3,8) <.0001 bifenthrin 92.8 ± 7.2 AB,a 59.8 ± 10.6 B,b 3.2 ± 6.2 B,c NT . . 30.37 (2,6) 0.0007 methyl parathion 92.8 ± 3.6 AB,a 0.0 ± 8.0 C,b 0.0 ± 3.6 B,b NT . . 113.78 (2,6) <.0001 thiamethoxam 53.4 ± 7.2 C,a 51.8 ± 0.0 B,a 0.0 ± 3.6 B,b NT . . 43.71 (2,6) 0.0003 λ-cyhalothrin 53.4 ± 12.9 C,a 71.9 ± 4.0 AB,a 0.0 ± 3.6 B,b NT . . 21.56 (2,6) 0.0018 λ-cyhalothrin + 71.3 ± 3.6 BC,a 63.9 ± 12.1 AB,a 0.0 ± 3.6 B,b NT . . 27.27 (2,6) 0.0010 thiamethoxam Overall 73.9 ± 5.0 a 47.8 ± 7.9 b 5.3 ± 3.7 c 32 F value (df) 8.07 (6,14) 16.06 (6,14) 16.8 (6,14)
P value 0.0007 <.0001 <.0001
Means followed by the same letter are not significantly different at P ≤ 0.05. Capital letters represent comparisons among treatments within a time interval, and lowercase letters represent comparisons among time intervals within a treatment. NT: not tested. When corrected mortality < 0, data are reported as 0.
Table 2.2 Mean percent corrected mortality of green stink bugs after 48 hours for selected insecticides from trial 2 in 2010.
Time After Application
F value P Chemical 1 Hour 1 Day 3 Days 5 Days 7 Days 10 Days (df) value 1.26 acephate 14.0 ± 6.2 C,ns 4.2 ± 0.0 C,ns 24.4 ± 9.1 BC,ns 24.4 ± 12.4 NS,ns 10.7 ± 3.5 B,ns NT . . 0.3488 (4,10) acephate + ± 20.75 100 ± 0.0 A,a 83.3 ± 0.0 A,ab 62.2 ± 9.1 A,bc 45.0 ± 9.1 NS,cd 38.1 A,d 10.4 ± 3.6 e <.0001 bifenthrin 10.3 (5,12) bifenthrin 96.4 ± 3.6 A,a 79.2 ± 8.3 A,ab 55.3 ± 17.2 AB,b 17.5 ± 10.3 NS,c NT . . NT . . 9.67 (2,6) 0.0049 33.67 methyl parathion 100 ± 0.0 A,a 45.8 ± 11.0 B,b 14.1 ± 6.9 C,c NT . . NT . . NT . . 0.0005 (2,6) thiamethoxam 60.6 ± 12.9 B,a 12.5 ± 7.2 C,b 14.1 ± 9.1 B,b NT . . NT . . NT . . 7.44 (2,6) 0.0237
λ-cyhalothrin 89.3 ± 0.0 A,a 58.3 ± 23.2 AB,ab 41.6 ± 6.9 ABC,bc 10.7 ± 3.5 NS,c NT . . NT . . 7.26 (3,8) 0.0114 λ-cyhalothrin + 24.92 89.3 ± 0.0 A,a 79.2 ± 4.2 A,a 58.8 ± 10.3 A,b 24.4 ± 6.9 NS,c 17.5 ± 6.0 AB,c NT . . <.0001 thiamethoxam (4,10) Overall 78.5 ± 6.8 a 51.8 ± 7.6 b 38.4 ± 5.5 bc ......
F value (df) 31.85 (6,14) 8.94 (6,14) 4.16 (6,14) 2.06 (4,10) 4 (2,6)
33 P value <.0001 0.0004 0.0131 0.1616 0.0787
Means followed by the same letter are not significantly different at P ≤ 0.05. Capital letters represent comparisons among treatments within a time interval, and lowercase letters represent comparisons among time intervals within a treatment. NT: not tested. NS: overall test was insignificant.
Table 2.3 Mean percent corrected mortality of green stink bugs after 48 hours for selected insecticides from trial in 2011.
Time After Application
F value P Chemical 1 Hour 1 Day 2 Days 3 Days 4 Days (df) value acephate 100.0 ± 0.0 A,ns 80.0 ± 10.0 A,ns 66.7 ± 13.3 A,ns 50.0 ± 10.0 BC,ns NT . . 2.82 (3,4) 0.1708 15.19 acephate + bifenthrin 100.0 ± 0.0 A,a 70.0 ± 10.0 A,b 53.3 ± 6.7 AB,bc 80.0 ± 10.0 A,ab 30.0 ± 10.0 NS,c 0.0027 (4,6) 28.08 bifenthrin 100.0 ± 0.0 A,a 100.0 ± 0.0 A,a 53.3 ± 13.3 AB,b 0.0 ± 0.0 D,c NT . . 0.0006 (3,6) 188.4 methyl parathion 100.0 ± 0.0 A,a 0.0 ± 0.0 B,c 0.0 ± 0.0 C,c 30.0 ± 10.0 C,b NT . . <.0001 (3,6) thiamethoxam 35.5 ± 21.5 B,ns 60.0 ± 8.3 A,ns 26.7 ± 17.6 BC,ns 30.0 ± 10.0 C,ns NT . . 0.39 (3,4) 0.7678
λ-cyhalothrin 35.5 ± 21.5 B,ns 80.0 ± 20.0 A,ns 53.3 ± 6.7 AB,ns 60.0 ± 0.0 AB,ns 10.0 ± 10.0 NS,ns 3.85 (4,6) 0.0697 λ-cyhalothrin + 85.6 ± 14.3 A,ns 86.7 ± 6.7 A,ns 60.0 ± 20.0 AB,ns 60.0 ± 0.0 AB,ns 40.0 ± 0.0 NS,ns 1.98 (4,8) 0.1910 thiamethoxam Overall 83.3 ± 7.1 a 69.6 ± 8.5 a 44.8 ± 6.3 b 41.5 ± 7.0 b . . .
34 F value (df) 7.27 (6,11) 9.02 (6,8) 3.29 (6,14) 11.62 (6,6) 3.5 (2,3)
P value 0.0025 0.0033 0.0309 0.0044 0.1643
Means followed by the same letter are not significantly different at P ≤ 0.05. Capital letters represent comparisons among treatments within a time interval, and lowercase letters represent comparisons among time intervals within a treatment. NT: not tested. NS: overall test was insignificant. When corrected mortality < 0, data are reported as 0.
Table 2.4 Mean percent corrected mortality of brown stink bugs after 48 hours for selected insecticides from trial in 2011.
Time After Application
Chemical 1 Hour 1 Day 2 Days 3 Days 4 Days 5 Days F value (df) P value ± acephate 100.0 ± 0.0 A,ns 100.0 ± 0.0 A,ns 85.7 ± 7.2 A,ns 69.4 ± 7.7 A,ns NT . . 83.3 NS,ns 1.76 (4,9) 0.2200 16.7 ± ± acephate + bifenthrin 100.0 ± 0.0 A,ns 100.0 ± 0.0 A,ns 85.7 ± 7.2 A,ns 61.8 A,ns 91.7 ns 91.7 ± 8.3 NS,ns 2.02 (5,12) 0.1479 20.3 8.3 ± bifenthrin 85.0 AB,a 93.3 ± 6.7 A,a 21.2 ± 7.2 BC,bc 0.0 ± 7.7 B,b NT . . NT . . 26.85 (3,8) 0.0002 14.3 methyl parathion 100.0 ± 6.7 A,a 13.3 ± 6.7 C,b 0.0 ± 7.2 C,bc 0.0 ± 0.0 B,c NT . . NT . . 111.26 (3,8) <.0001 ± thiamethoxam 28.3 C,ns 0.0 ± 0.0 C,ns 0.0 ± 6.7 C,ns 0.4 ± 7.7 B,ns NT . . NT . . 2.54 (3,8) 0.1298 14.3 ± ± λ-cyhalothrin 46.2 BC,a 20.0 BC,ab 14.0 ± 0.0 BC,bc 0.0 ± 7.7 B,c NT . . NT . . 5.92 (3,7) 0.0247 10.8 11.6 λ-cyhalothrin + ± ± ± 57.0 BC,ns 40.0 B,ns 35.5 B,ns 0.0 ± 7.7 B,ns NT . . NT . . 3.69 (3,8) 0.0619 thiamethoxam 21.5 11.6 12.4 Overall 74.0 ± 7.6 a 52.4 ± 9.4 ab 34.5 ± 8.1 bc 13.5 ± 8.1 c ......
F value (df) 5.29 (6,12) 38.33 (6,14) 23.45 (6,14) 12.77 (6,14) . 0.2 (1,4)
35 P value 0.0070 <.0001 <.0001 <.0001 . 0.6779
Means followed by the same letter are not significantly different at P ≤ 0.05. Capital letters represent comparisons among treatments within a time interval, and lowercase letters represent comparisons among time intervals within a treatment. NT: not tested. NS: overall test was insignificant. When corrected mortality < 0, data are reported as 0.
CHAPTER III
EARLY SEASON HOSTS OF STINK BUGS IN MISSISSIPPI
Introduction
Stink bugs are major pests of soybeans and other agronomic crops in Mississippi.
Chemical control is a major method for controlling stink bugs. Agronomic crops are suitable hosts for stink bugs during brief periods throughout the year, so a knowledge of seasonal life history of these pests would permit the development of more sustainable integrated pest management strategies (Jones and Sullivan 1982).
The primary stink bugs of Mississippi are Euschistus spp.; green stink bug,
Chinavia hilaris (Say); southern green stink bug, Nezara viridula L., Thyanta spp.; and rice stink bug, Oebalus pugnax pugnax (Fab.). All these are in the family Pentatomidae which are described as having five-segmented antennae and a well developed scutellum
(McPherson and McPherson 2000c). Euschistus adults are generally brown colored
(McPherson and McPherson 2000b). The green and southern green adults are green colored, and can be distinguished by the green stink bug having brown bands on its antennae, and a long abdominal spine (McPherson and McPherson 2000a). The southern green stink bug has a rounded spine and red bands on the antennae (McPherson and
McPherson 2000d). Thyanta spp. are smaller green colored stink bugs (McPherson and
McPherson 2000f).
36
All stink bug species have five nymphal instars, and overwinter as adults. Stink bugs begin to emerge from their overwintering sites in March (Jones and Sullivan 1981).
In Mississippi, Euschistus spp, and green stink bug complete two generations per year.
Southern green stink bug completes four generations per year, and rice stink bug completes two or three generations per year (McPherson and McPherson 2000e).
Of these major stink bug species mentioned, the rice stink bug is the only one that does not feed on soybean ( Miner 1966). Rice stink bug is a major pest of rice, Oryza sativa (L.) (McPherson and McPherson 2000e). The other species are pests of soybean, with Thyanta spp. generally considered the least important. All stink bugs feed on the developing fruiting structures and seeds. Some species are highly polyphagous, while rice stink bug prefers to feed on grasses (Odglen and Warren 1962; McPherson and
McPherson 2000e).
Soybeans are not attractive to stink bugs until developing seeds are present. This usually occurs during late summer. Previous research has shown that stink bugs feed on wild hosts before moving into crops (Miner 1966). Some wild hosts are more suitable hosts for stink bugs than others (Panizzi 1997). Specific host plant sequences may be required for stink bug pests to develop high populations (Jones and Sullivan 1982).
Cherry and Bennett (2005) reported higher rice stink bug numbers within grassy areas of rice fields compared to clean areas. Mowing grass hosts along ditches causes a rapid increase in the number of rice stink bugs in adjacent rice fields (Douglas 1939).
Vetches, Vicia spp., and clovers, Trifolium spp., are early season hosts of many stink bug species in the southern U. S. (Todd 1989; McPherson et al. 1994). Abundance
37 of crimson clover, Trifolium incarnatum L., in the south Mississippi delta is limited primarily to the bluff along the hills and to the Mississippi river levee. White clover,
Trifolium repens L., is much more abundant and can be found virtually anywhere. Vetch species are very common along roadsides. Wheat, Triticum aestivum L., can be found where it has been planted and abundance varies year to year. Ryegrass, Lolium spp., is becoming more and more prevalent due to the spread of glyphosate resistant Italian ryegrass, Lolium perrene L. ssp. Multiflorum (Lam.) Husnot (Jason Bond, unpublished data).
Control of key spring hosts could be a potential management strategy for stink bugs (Jones and Sullivan 1982). Woodside (1947) studied weed hosts of brown stink bug in peach orchard and recommended mowing to reduce host availability. The wild hosts of stink bugs in Mississippi are currently unknown. This study was developed to determine the early season hosts of stink bugs in the Mississippi delta.
Materials and Methods
This study was conducted in the Mississippi delta, south of U. S. Hwy 82 and north of Natchez during April and May of 2010 and 2011. A standard 38.1 cm (15 in.) sweep net was used to sample wild hosts. Sample locations were based upon accessibility. The number of sweeps taken per location was determined by the abundance of pure plant stands. Mixed plant stands were avoided. The minimum and maximum number of sweeps taken per location was 10 and 200, respectively. Stink bugs feed primarily on developing seed, so flowering plants, especially legumes, were the primary plants that were sampled. Roadsides, field edges, ditch banks, pastures, etc. where
38 potential hosts could be found were sampled. The number of stink bug adults and nymphs collected, number of sweeps taken, and location were recorded.
Plants sampled included the following: pigweed species, Amaranthus spp.; horseweed, Conyza canadensis (L.) Cronq.; wild carrot, Daucus carota L.; ryegrass species, Lolium spp.; cutleaf eveningprimrose, Oenothera laciniata Hill; black-eyed
Susan, Rudbeckia hirta var. pulcherrima Farw.; wheat, Triticum aestivum L.; crimson clover, Trifolium incarnatum L.; red clover, Trifolium pretense L.; white clover,
Trifolium repens L.; and vetches, Vicia spp. Stink bugs collected include green stink bug,
Chinavia hilaris (Say); brown stink bug, Euschistus spp.; southern green stink bug,
Nezara viridula L.; rice stink bug, Oebalus pugnax pugnax (Fab.); redbanded stink bug,
Piezodorus guildinii (Westwood); and Thyanta spp.
For statistical data analysis, only those plant hosts that were sampled with at least
20 sweeps were included. Sample dates were pooled into 15 day increments for each year representing early and late April and early and late May. Year was included in the model as a random factor. Only brown stink bug and rice stink bug were abundant enough to analyze host data. Their abundance on various plant hosts were analyzed using Proc mixed in SAS (SAS Institute 2003), with a 0.05 level of significance.
Results and Discussion
Rice stink bug was the most abundant stink bug species with 302 collected over the course of the two year period (Table 3.1). Euschistus spp. was the second most abundant stink bug type at 148. Of the 22 southern green stink bugs collected over the course of this trial 12 were from Trifolium incarnatum, 7 were from Trifolium repens,
39 and 3 were from Vicia spp. The 4 redbanded stink bugs and the 2 green stink bugs collected were from Trifolium incarnatum. Trifolium incarnatum was sampled more than any other host (2043 sweeps), because of its relative abundance along roadsides. 1515 sweeps were taken from Trifolium repens, 1145 sweeps were taken from Vicia spp., 650 sweeps were taken from Lolium spp., and 430 sweeps were taken from Triticum aestivum.
The average number of stink bugs collected in 100 sweeps of each host is shown in Figure 3.2. The highest densities of stink bugs on spring hosts were: rice stink bug with
21.23 / 100 sweeps on Lolium spp.; Thyanta spp. with 5.11 / 100 sweeps on Trifolium pratense, and Euschistus spp. with 4.31 / 100 sweeps on Lolium spp. Southern green stink bug and redbanded stink bug were caught too infrequently to accurately estimate their density on any host. Green stink bug was only collected from plants in the Fabaceae family.
Late April was the only period when there were significant differences between host plants with respect to the density of brown stink bug (F = 3.45; df = 4,17; P =
0.0307) (Fig. 3.1). More brown stink bugs were collected from Trifolium incarnatum in late April than from Trifolium repens and Vicia spp.(t = 3.56; df = 17; P = 0.002).
Trifolium incarnatum typically matures earlier than Trifolium repens and Vicia spp. and that is why it would have been more attractive during late April (personal observation).
There were no differences in brown stink bug densities between hosts from samples collected during early April (F = 0.23; df = 4,18; P = 0.9156), early May (F = 1.37; df =
4,39; P = 0.2636), and late May (F = 1.74; df = 3,8; P = 0.2355). Since brown stink bug
40 seems to have a very broad host range, limiting access or development on any host will not likely have much impact on overall brown stink bug population dynamics.
During late April and early May, more rice stink bugs were found on Lolium spp. than the other hosts sampled (t = 8.81; df = 17; P <0.0001)(t = 5.49; df = 39; P <0.0001)
(Fig. 3.2). In late April, wheat had significantly more rice stink bugs than Trifolium incarnatum, Trifolium repens, and Vicia spp (t = 11.98; df = 17; P <0.0001). There were no differences in rice stink bug densities between host plants sampled during early April
(F = 0.50; df = 4,18; P = 0.7338), and late May (F = 0.12; df = 3,8; P = 0.9486). Because
Triticum aestivum and Lolium spp. are important hosts of rice stink bug, eliminating or managing the proximity of these hosts to rice could prove to be beneficial in managing rice stink bug populations.
Green, southern green, redbanded, and Thyanta species tended to be found more often on legume hosts. These results are similar to those found by Hoffman (1935) reporting that legume hosts are preferred by southern green stink bug. Jones and Sullivan
(1982) reported legumes as being the primary breeding hosts for brown stink bug.
Triticum aestivum, Vicia spp., Trifolium incarnatum are important hosts of brown stink bug in South Carolina (Jones and Sullivan 1982). This study shows that these plus
Trifolium repens and Lolium spp. are also important hosts in Mississippi.
41 References Cited
Cherry, R. and A. Bennett. 2005. Effect of weeds on rice stink bug (Hemiptera: Pentatomidae) populations in Florida rice fields. Journal of Entomol. Sci. 40: 378-384.
Douglas, W. A. 1939. Studies of rice stinkbug populations with special reference to local migration. J. Econ. Entomol. 32: 300-303.
Hoffman, W. E. 1935. The food plants of Nezara viridula (L.) (Hemiptera, Pentatomidae). Congr. Entomol. Madrid 6: 8811-8816.
Jones, W. A., Jr. and M. J. Sullivan. 1981. Overwintering habitats, spring emergence patterns, and winter mortality of some South Carolina hemiptera. Environ. Entomol. 10: 409-414.
Jones, W. A. and M. J. Sullivan. 1982. Role of host plants in population dynamics of stink bug pests of soybean, Glycine max in South Carolina. Environ. Entomol. 11: 867- 875.
McPherson, J. E. and R. M. McPherson. 2000a. Acrosternum hilare (Say). In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, FL. 129- 139.
McPherson, J. E. and R. M. McPherson. 2000b. Euschistus spp. In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, Fl. 101- 127.
McPherson, J. E. and R. M. McPherson. 2000c. General introduction to stink bugs. In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, FL. 1-6.
McPherson, J. E. and R. M. McPherson. 2000d. Nezara viridula (L.). In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, FL. 71-99.
McPherson, J. E. and R. M. McPherson. 2000e. Oebalus spp. In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, Fl. 141-158.
McPherson, J. E. and R. M. McPherson. 2000f. Thyanta spp.: general information. In: Stink Bugs of Economic Importance in America North of Mexico. CRC Press, Boca Raton, FL. 181-182.
McPherson, R. M., J. W. Todd, and K. V. Yeargan. 1994. Stink bugs. In: Handbook of Soybean Insect Pests. L. G. Higley and D. J. Boethel, Eds. Entomol. Soc. Amer., Lanham, MD. 87-90.
42 Miner, F. D. 1966. Biology and control of stink bugs on soybeans. Arkansas Agric. Exper. Station Bull. Fayetteville, AR, U. of Arkansas Agric. Exper. Station. 708: 3-40.
Odglen, G. E. and L. O. Warren. 1962. The rice stink bug, Oebalus pugnax F. (sic), in Arkansas. Arkansas Agric. Exp. Stn. Rep. 107: 1-23.
Panizzi, A. R. 1997. Wild hosts of Pentatomids: ecological significance and role in their pest status on crops. Annu. Rev. Entomol. 42: 99.
Todd, J. W. 1989. Ecology and behavior of Nezara viridula. Annu. Rev. Entomol. 34: 273-292.
43
Table 3.1 Actual number of stink bugs collected during 2010 and 2011.
Stink Bug Species Total Stink Host Host Family Sweeps C. hilaris Euschistus spp. N. viridula O. pugnax P. guildinii Thyanta spp. Bugs Amaranthus spp. Amaranthaceae 30 0 0 0 0 0 0 0 C. canadensis Asteraceae 185 0 3 0 16 0 9 28 D. carota Apiaceae 50 0 0 0 6 0 0 6 Lolium spp. Poaceae 650 0 28 0 138 0 1 167 O. laciniata Onagraceae 125 0 4 0 0 0 0 4 R. hirta Asteraceae 145 0 0 0 0 0 1 1 T. aestivum Poaceae 430 0 2 0 42 0 2 46 T. incarnatum Fabaceae 2043 2 55 12 40 4 10 123
44 T. pratense Fabaceae 235 0 3 0 1 0 12 16
T. repens Fabaceae 1515 0 21 7 47 0 9 84 Vicia spp. Fabaceae 1145 0 32 3 12 0 3 50 Totals . 6553 2 148 22 302 4 47 525
Table 3.2 Average number of stink bugs per 100 sweeps during 2010 and 2011.
Stink Bug Species Oebalus Nezara Piezodorus Chinavia Host pugnax Euschistus spp. Thyanta spp. viridula guildinii hilaris Lolium spp. 21.2 4.3 0.2 0.0 0.0 0.0 Triticum aestivum 9.8 0.5 0.5 0.0 0.0 0.0 Trifolium incarnatum 2.0 2.7 0.5 0.6 0.2 0.1 Trifolium pratense 0.4 1.3 5.1 0.0 0.0 0.0 Trifolium repens 3.1 1.4 0.6 0.5 0.0 0.0 Vicia spp. 0.8 2.8 0.3 0.3 0.0 0.0
45
46
Figure 3.1 Number of brown stink bugs per 100 sweeps by time of year and host. Columns with the same letter within a time period are not significantly different at α = 0.05. NS = no significant differences (α = 0.05) among hosts within the time period.
47
Figure 3.2 Number of rice stink bugs per 100 sweeps by time of year and host. Columns with the same letter within a time period are not significantly different at α = 0.05. NS = no significant differences (α = 0.05) among hosts within the time period.
CHAPTER IV
IMPACT OF AUTOMATIC INSECTICIDE APPLICATION ON INSECT DENSITIES
IN SOYBEAN
Introduction
Over the past ten years, soybean production in Mississippi has been increasing while cotton production has decreased (NASS 2011). Producers are relying more heavily on soybean production for their farm income. With the increase in soybean acres there has been an increase in the level of management of soybeans (Musser et al. 2010). The use of an automatic fungicide application to soybeans during the R3 growth stage has been widely adopted in Mississippi as a way to increase yield in high input soybeans.
Many producers and consultants have now begun to add an insecticide, often a pyrethroid, to the spray tank during R3 fungicide applications, even with very low insect densities.
There are typically many different insect pest species in soybean fields at the time of an R3 fungicide application. In Mississippi, the commonly observed insect pests at this time would be green stink bug Chinavia hilaris (Say ) , brown stink bug, Euschistus servus (Say), southern green stink bug Nezara viridula ( L.), threecornered alfalfa hopper,
Spissistilus festinus (Say); bean leaf beetle, Cerotoma trifurcata (Forster); grape colaspis,
Colaspis brunnea (Fabricius); spotted cucumber beetle, Diabrotica undecimpunctata
48 (Barber); tarnished plant bug, Lygus lineolaris (Palisot de Beauvois); green clover-worm,
Hypena scabra (Fabricius); armyworm, Spodoptera spp.; soybean looper, Chrysodeixis includens (Walker); corn earworm, Helicoverpa zea (Boddie); alfalfa caterpillar, Colias eurytheme (Boisduval); velvetbean caterpillar, Anticarsia gemmatalis (Hubner); saltmarsh caterpillar, Estigmene acrea (Drury); grasshopper species, burrower bug,
Pangaeus bilineatus (Say); dectes stem borer, Dectes texanus (LeConte); corn flea beetle,
Chaetocnema pulicaria (Horn); soybean nodule fly, Rivellia quadrifasciata (Macquart); chinch bug, Blissus spp.; and potato leafhopper, Empoasca fabae (Harris) (personal obs)(Boyd et al. 1997; Baur et al. 2000).
There are also many different species of beneficial insects in soybeans at R3.
They include lady beetles (Coccinellidae); spined soldier bug, Podisus maculiventris
(Say); assassin bugs (Reduviidae); minute pirate bug, Orius tristicolor (White); spiders, syrphid flies (Syrphidae); ants (Formicidae); damsel bugs, Nabis spp.; green lacewings
(Chrysopidae); and brown lacewings (Hemerobiidae)(Boyd et al. 1997; Baur et al. 2000).
Big-eyed bugs, damsel bugs, and spiders are the dominant beneficial arthropods in soybeans in Louisiana (Boyd et al. 1997).
The effects of this automatic insecticide application have not been studied. There are several potential benefits and risks associated with automatic insecticide applications.
By removing the wide array of pests at sub-threshold densities, there is the potential for reducing damage from these pests and increasing yield. It could also prevent the late season buildup of some pest populations, therefore reducing the need for late season insecticide applications for pests such as stink bugs. These benefits could result in increased yields, decreased costs, and/or improved profitability. Non-selective
49 insecticides like pyrethroids have been known to hurt beneficial insect populations
(Pietrantonio and Benedict 1999). Some of the risks include removal of beneficial predators and parasitoids which can lead to outbreaks of some insect pests (Gratwick
1957; Croft 1990). This could result in the need for more insecticide applications than would have been required if the first insecticide application had not been made, resulting in reductions in yield and/or profitability. Increased frequency of insecticide applications also increases the rate of insecticide resistance by selecting for the resistant insects. Trials were set up to determine how an automatic insecticide application applied at the R3/R4 soybean growth stage affects insect populations and soybean yield.
Materials and Methods
On-farm trial
This trial was conducted in Sunflower County, MS in the Mississippi Delta in
2011. Eight production fields, four maturity group IV fields and four maturity group V fields were used. All fields were irrigated. One of the group IV fields was planted to
Asgrow® 4605, and the other group IV four fields were planted to Asgrow® DK 4866.
All of the group V fields were planted to Hornbeck® 5529 soybeans. All fields were treated with 293 ml of azoxystrobin (Quadris® F, Syngenta Corporation, Wilmington,
DE) fungicide per hectare at the R3/R4 growth stage and half of each field had 312 ml of bifenthrin (Brigade® 2EC, FMC Corporation, Philadelphia, PA) insecticide per hectare added in with the fungicide. Insect populations were monitored weekly from R2 (before treatments were applied) through R7 by taking 100 sweeps per field with a standard 38.1
50 cm (15 in.) sweep net. All pest and beneficial insects that could be readily identified were recorded.
There were no observable differences in insect densities between maturity group
IV and group V varieties, therefore the data were pooled. All insect data were analyzed using least significant means in Proc Mixed in SAS at the 0.05 level of significance.
Insect counts at each week were analyzed independently from other weeks. Where there were consistent trends over consecutive weeks, data from these weeks were analyzed as a linear regression to determine if these longer term differences were significant.
On-station trial
Starkville small plots during 2010/2011: An insecticide / fungicide trial was conducted to evaluate the effects of automatic applications in a small plot study. This was conducted at R. R. Foil Research Center in Starkville, Mississippi during the 2010 and
2011 growing seasons. Pioneer 94B73 soybeans were planted on 6 May 2010 and 20 Jun
2011 in 3.9 m (4 rows) wide by 12.2 m long plots replicated four times, and arranged in a randomized complete block design. Pesticide applications were made on 21 Jun 2010 and
8 Aug 2011during the R3 growth stage with a Mudmaster sprayer (Bowman
Manufacturing, Newport, AR) equipped with eight TX6 hollow cone tips (Teejet
Technologies, Wheaton, IL) applying 93.75 L/ha. All treatments received azoxystrobin fungicide at 73 g ai/ha. The treatments were as follows: untreated- no insecticide added to the fungicide, and treated- bifenthrin insecticide (91 g ai/ha) tank mixed with the fungicide. Each plot was sampled weekly from R2 through R7 by making 25 sweeps on one of the middle rows of the plot. All recognized soybean pests that were collected were
51 recorded. The center 2 rows of each plot were harvested using a Massey Ferguson plot combine on 26 Aug 2010 and 17 Oct 2011. Harvested yields were corrected to 13% moisture.
Verona small plots during 2008: Similar insecticide / fungicide trials were conducted at Verona, Mississippi at the Northeast Mississippi Branch Experiment
Station. Progeny 4706 soybean seed were planted on a Catalpa silty clay loam soil on 24
Apr 2008. Plot size was 4.06 m (4 rows) wide by 15.24 m long replicated four times. All treatments received azoxystrobin fungicide at 73 g ai/ha. The treatments were as follows: untreated- no insecticide added to the fungicide, and treated- lambda-cyhalothrin
(Karate®, Syngenta Corporation, Wilmington, DE) insecticide at 0.035 kg/ha added to the fungicide. Treatments were replicated four times in a randomized complete block design. Treatments were applied to separate plots during the R3 growth stages on 27 Jun.
Treatments were applied with a backpack sprayer and CO2 charged spray system calibrated to deliver 93.5 L/ha through Teejet 80015 flat fan nozzles (2/row). Plots were mechanically harvested using a small plot combine harvester on 20 Oct. Yields were corrected to 13% moisture content.
Stoneville small plots during 2010/2011: Two similar insecticide / fungicide trials were conducted in Stoneville, Mississippi at the Delta Research and Extension Center during 2010 and 2011. As grow 4605 soybean seeds were planted 30 Apr 2010, and 17
May 2011. Plot size was 4.06 m wide by 19.8 m long. Treatments were replicated four times in a randomized complete block design. All treatments received azoxystrobin fungicide at 73 g ai/ha. The treatments were as follows: untreated- no insecticide added to the fungicide, and treated- bifenthrin insecticide at 91 g ai/ha added to the fungicide.
52 Treatments were applied to separate plots during the R3 growth stages on 8 July 2010 and 21 July 2011. Treatments were applied with a high clearance sprayer and compressed air charged spray system calibrated to deliver 93.75 L/ha through TX 10 hollow cone tips
(Teejet Technologies, Wheaton, IL) (2/row). The two center rows of each plot were sampled with a 38.1 cm diameter sweep net one day prior to treatment. During 2010, they were also sampled 2 days after application. A sample of 25 sweeps per row per plot was collected. Plots were mechanically harvested using a small plot combine harvester on 22
Sep 2010 and 4 Oct 2011. Yields were corrected to 13% moisture content.
Yield data from all insecticide / fungicide trials were analyzed together in SAS using Proc Mixed at a 0.05 level of significance. Location and year were treated as random variables.
Results
On-farm trial
Over the course of this experiment, 42 different insect species were collected, identified, and recorded. All figures presented are combined data from all group IV and group V fields. All insect numbers are based on total number of adults and nymphs.
Stink bugs were the only pest that was significantly affected by the R3 insecticide application. Stink bug densities were lower in the insecticide treated fields compared to the untreated fields four (F = 18.77; df = 1,5; P = 0.0075), and six (F = 9.40; df = 1,7; P =
0.0182) weeks after insecticide application (Figure 4.1). This delayed effect was probably due to a reduction of the previous generation of stink bugs at the time of the insecticide
53 application. The dominant stink bug species collected were green and brown stink bugs.
These stink bug species tend to be less mobile than southern green stink bug when suitable host plants are available (Angus Catchot, personal observation). Therefore, the
R3 insecticide application reduced stink bug densities beyond the residual activity of the insecticide. Linear regression analysis of the stink bug data shows that there was a significant difference in the slope of the treated and untreated lines (F = 20.61; df = 1, 45;
P = 0.0007) from week 3 to week 7 (Figure 4.2), indicating that populations in the treated fields were building at a slower rate than those in untreated fields.
There were no significant differences in looper or corn earworm populations during any week (F = 0.01; df = 1,45; P = 0.9101) (F = 2.40; df = 1,35; P =
0.1301)(Figure 4.3 and 4.4). There were no significant differences between treated and untreated fields with respect to the number of threecornered alfalfa hoppers (F = 0.18; df
= 1, 45; P = 0.6773), but large numerical differences occurred one, two, and three weeks after application where the treated fields had lower densities (Figure 4.5).
Of the beneficial insects observed, there were no consistent significant differences between treated and untreated fields. Big-eyed bugs were numerically lower where insecticides had been applied from 1 to 5 weeks after application, but only at 3 weeks was the difference statistically significant (F = 6.66; df = 1,6; P = 0.0418 ) (Figure 4.6).
One week after treatment there were significantly fewer spiders in the treated fields compared to the untreated fields (F = 60.03; df = 1,9; P < 0.0001) (Figure 4.7). No other significant differences were observed with respect to spiders. The number of lacewings was not affected by the insecticide application as shown in Figure 4.8 (F = 1.77; df =
1,45; P = 0.1522).
54 Population densities of all insect pests were relatively low with the exception of threecornered alfalfa hoppers, but insecticides were never applied for threecornered alfalfa hoppers because populations never exceeded recommended thresholds (Catchot
2011). Two of the fields (both treatments) were treated for corn earworm with an application of flubendiamide (Belt® SC, Bayer Crop Science, Research Triangle Park,
NC) insecticide at 146 ml per ha on July 23, so the corn earworm and looper data from these fields are not included in the data presented.
On-station trial
Insect densities in these trials never approached economic thresholds (Tables 4.1 through 4.3). Across all of the on-station trials, the highest stink bug density recorded was 33% of the economic threshold. The highest bean leaf beetle density only reached
32% of the economic threshold in these trials. Threecornered alfalfa hopper populations only exceeded 32% of the economic threshold one time and there it never exceeded the threshold. There were no significant differences observed between treatments for yield
(Figure 4.9). The average yield from the treated and untreated plots was 2928 ± 265 kg/ha and 3010 ± 232 kg/ha, respectively.
Discussion
The insect densities were similar for both the on-station trials and the on-farm trial. Due to equipment malfunction and lack of farmer cooperation, yield could not be collected from the on-farm trials, so it is not known if there was a yield response.
However, based on the lack of yield response in the small plot trials and the minimal
55 insect density changes in the on-farm trials, no yield response would be expected.
Therefore, an automatic insecticide application at the time of the fungicide application is not recommended. Even the least expensive insecticide costs about $8/ha and there was no yield increase (Fig. 4.9), so net income was reduced by adding the insecticide. This recommendation is only in the absence of insects approaching an economic threshold. In situations where insect densities are near or above the economic threshold at the time of fungicide application, it is recommended to add the insecticide to the fungicide and save a trip across the field. If long residual insecticides were available and future pest densities could be more accurately predicted, then there would be more situations where the addition of an insecticide at the time of fungicide application could potentially be justified. Some negative impacts on beneficial insects were observed in these trials, but these impacts did not persist, nor did they lead to increased pest densities. With currently available short residual insecticides, preventative insecticide applications provide no benefit and should be avoided.
The significant reduction of stink bug densities 3-7 weeks after insecticide application was unexpected. It is unknown whether this would have been observed at more economically important densities. The stink bugs during 2011 were predominantly green and brown stink bugs, which only have 2 generations per year. When stink bugs are numerous in Mississippi, southern green stink bug, which has 3-4 generations per year, is typically the dominant species in the complex. Further research still needs to explore the potential impact of R3 insecticide applications on stink bug densities when stink bugs are more numerous and when southern green stink bug comprises a major portion of the complex.
56 References Cited
Baur, M. E., D. J. Boethel, M. L. Boyd, G. R. Bowers, M. O. Way, L. G. Heatherly, J. Rabb, and L. Ashlock. 2000. Arthropod populations in early soybean production systems in the mid-south. Environ. Entomol. 29: 312-328.
Boyd, M. L., D. J. Boethal, B. R. Leonard, R. J. Habetz, L. P. Brown, and W. B. Hallmark. 1997. Seasonal abundance of arthropod populations on selected soybean varieties grown in early season production systems in Louisiana. LSU Agricultural Experiment Station 860: 1-27.
Croft, B. A. 1990. Arthropod Biological Control Agents and Pesticides. New York, NY, John Wiley.
Gratwick, M. 1957. The contamination of insects of diferent species exposed to dust deposits. Bull. Entomol. Res. 48: 741-753.
Musser, F. R., G. M. Lorenz, S. D. Stewart, and A. L. Catchot, Jr. . 2010. 2009 soybean insect losses for Mississippi, Tennessee, and Arkansas. Midsouth Entomol. 3: 48-54.
NASS. 2011. 2010 state agriculture overview. National Agricultural Statistics Service. http://www.nass.usda.gov/Statistics_by_State/Ag_Overview/AgOverview_MS.pdf.
Pietrantonio, P. V. and J. H. Benedict. 1999. Effect of new cotton insecticide chemistries, tebufenozide, spinosad, and chlorfenapyr, on Orius isidious and two Cotesia species. Southwestern Entomologist 24: 21-29.
57
58
Figure 4.1 Mean ± SEM number of stink bugs per 100 sweeps by weeks relative to insecticide application for MG IV and V insecticide treated and untreated fields in Sunflower County, MS, during 2011. Week zero represents the week the insecticide/fungicide application was applied. * = Significant difference between treated and untreated at this week (Protected F-test at P = 0.05).
59
Figure 4.2 Mean number of stink bugs per 100 sweeps by weeks relative to insecticide application for MG IV and V insecticide treated and untreated fields in Sunflower County, MS, during 2011 (from Fig. 4.1). The dotted and dashed lines represent the linear regression lines for untreated and treated from weeks 3 to 7, respectively. The comparison of these two lines showed that they were significantly different (F = 4.51, df = 1,51, P = 0.0382).
60
Figure 4.3 Mean ± SEM number of loopers per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. There were no significant differences between treatments during any week (Protected F-test at P=0.05).
61
Figure 4.4 Mean ± SEM number of corn earworms per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. Treatments were not significantly different any week (Protected F-test at P=0.05).
62
Figure 4.5 Mean ± SEM number of threecornered alfalfa hoppers per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. Treatments were not significantly different any week (Protected F-test at P=0.05).
63
Figure 4.6 Mean ± SEM number of big-eyed bugs per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. * = significant difference between treated and untreated at this week (Protected F-test at P=0.05).
64
Figure 4.7 Mean ± SEM number of spiders per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. * = significant difference between treated and untreated at this week (Protected F-test at P=0.05).
65
Figure 4.8 Mean ± SEM number of lacewings per 100 sweeps by weeks relative to insecticide application for all insecticide and untreated fields. Week zero represents the week the insecticide/fungicide application was applied. * = significant difference between treated and untreated at this week (Protected F-test at P=0.05).
66
Figure 4.9 Yield from small plot studies combined during 2008, 2010 and 2011 in Starkville, Stoneville, and Verona, MS for treated and untreated plots. Columns with the same letter are not significantly different ( α = 0.05).
Table 4.1 Average number of insects per 25 sweeps from small plot trial located in Starkville during 2010. Treatments were applied on June 21, 2010.
Insect Numbers per 25 Sweeps SB BLB TCAH Date Treatment # / 25 sweeps % ET # / 25 sweeps % ET # / 25 sweeps % ET 9-Jun Untreated 0.5 ± 0.5 6% 0.8 ± 0.8 2% 1.0 ± 0.6 4% Insecticide 0.3 ± 0.3 3% 0.0 ± 0.0 0% 0.8 ± 0.5 3% 14-Jun Untreated 0.5 ± 0.3 6% 4.0 ± 1.1 8% 1.3 ± 0.3 5% Insecticide 0.5 ± 0.3 6% 5.3 ± 0.9 11% 3.3 ± 0.6 13% 21-Jun Untreated 0.5 ± 0.5 6% 8.8 ± 1.5 18% 2.3 ± 0.5 9% Insecticide 0.8 ± 0.3 8% 9.8 ± 2.9 20% 1.8 ± 0.9 7% 12-Jul Untreated 0.3 ± 0.3 3% 3.3 ± 1.4 7% 0.5 ± 0.5 2%
67 Insecticide 0.0 ± 0.0 0% 5.3 ± 1.3 11% 0.0 ± 0.0 0% 21-Jul Untreated 0.0 ± 0.0 0% 7.8 ± 0.5 16% 0.5 ± 0.5 2% Insecticide 0.5 ± 0.5 6% 3.0 ± 0.4 6% 1.5 ± 0.6 6% 29-Jul Untreated 1.5 ± 0.3 17% 5.0 ± 1.7 10% 0.5 ± 0.3 2% Insecticide 0.3 ± 0.3 3% 2.5 ± 0.9 5% 0.0 ± 0.0 0% SB= stink bug, BLB= bean leaf beetle, TCAH= threecornered alfalfa hopper, %ET= percent of economic threshold (Mississippi State Extension Service 2011)
Table 4.2 Average number of insects per 25 sweeps from small plot trial located in Starkville during 2011. Treatments were applied on August 8, 2011.
Insect Numbers per 25 Sweeps SB BLB TCAH CEW Looper % % % % % Date Treatment # / 25 sweeps ET # / 25 sweeps ET # / 25 sweeps ET # / 25 sweeps ET # / 25 sweeps ET 8-Aug Untreated 0.0 ± 0.0 0% 0.0 ± 0.0 0% 7.8 ± 1.6 31% 0.5 ± 0.5 6% 0.0 ± 0.0 0% Insecticide 0.0 ± 0.0 0% 0.0 ± 0.0 0% 7.8 ± 1.9 31% 0.0 ± 0.0 0% 0.3 ± 0.3 1% 17-Aug Untreated 0.0 ± 0.0 0% 0.0 ± 0.0 0% 12.8 ± 2.5 51% 1.0 ± 0.7 11% 0.8 ± 0.5 4% Insecticide 0.3 ± 0.3 3% 0.0 ± 0.0 0% 11.5 ± 2.6 46% 0.3 ± 0.3 3% 0.8 ± 0.5 4% 23-Aug Untreated 0.8 ± 0.5 8% 0.0 ± 0.0 0% 13.8 ± 4.3 55% 0.5 ± 0.3 6% 1.5 ± 0.3 8% Insecticide 0.3 ± 0.3 3% 0.0 ± 0.0 0% 15.5 ± 5.1 62% 0.0 ± 0.0 0% 2.0 ± 1.7 11% 31-Aug Untreated 0.5 ± 0.5 6% 0.0 ± 0.0 0% 18.5 ± 2.1 74% 0.3 ± 0.3 3% 5.5 ± 2.3 29% 68
Insecticide 0.3 ± 0.3 3% 0.0 ± 0.0 0% 6.5 ± 1.5 26% 0.0 ± 0.0 0% 3.3 ± 0.9 17% 13-Sep Untreated 1.3 ± 0.6 14% 0.0 ± 0.0 0% 17.0 ± 3.3 68% 0.0 ± 0.0 0% 2.0 ± 0.8 11% Insecticide 0.3 ± 0.3 3% 0.0 ± 0.0 0% 11.5 ± 2.3 46% 0.0 ± 0.0 0% 2.3 ± 0.6 12% SB= stink bug, BLB= bean leaf beetle, TCAH= threecornered alfalfa hopper, %ET= percent of economic threshold (Mississippi State Extension Service 2011)
Table 4.3 Average number of insects per 25 sweeps from small plot trial located in Stoneville during 2010. Treatments were applied on July 17, 2010.
Insect Numbers per 25 Sweeps SB BLB TCAH CEW Date Treatment # / 25 sweeps % ET # / 25 sweeps % ET # / 25 sweeps % ET # / 25 sweeps % ET 16-Jul Untreated 0.0 ± 0.0 0% 9.5 ± 1.2 19% 0.8 ± 0.5 3% 0.0 ± 0.0 0% Insecticide 0.3 ± 0.3 3% 8.5 ± 1.9 17% 1.8 ± 0.3 7% 0.0 ± 0.0 0% 19-Jul Untreated 0.5 ± 0.3 6% 2.3 ± 1.1 5% 0.5 ± 0.3 2% 0.0 ± 0.0 0% Insecticide 0.3 ± 0.3 3% 2.5 ± 1.3 5% 1.0 ± 0.4 4% 0.0 ± 0.0 0% SB= stink bug, BLB= bean leaf beetle, TCAH= threecornered alfalfa hopper, %ET= percent of economic threshold (Mississippi State Extension Service 2011)
69
CHAPTER V
SUMMARY
When stink bug densities return to levels commonly encountered prior to 2010, stink bug management will be crucial for optimizing soybean production in Mississippi.
Insecticides only provide about 3 days residual control of green stink bug. If rainfall occurs after insecticide application, the amount of residual control is further reduced.
Acephate provides better residual control against brown stink bug than other labeled insecticides, up to at least five days after application in the absence of rain.
Stink bugs can be found on a variety of host plants in the spring. Ryegrass and wheat are important early season hosts for rice stink bug. Due to low densities during
2010 and 2011, early season host preferences for the other stink bug species are still not known. Controlling certain wild hosts, such as ryegrass, could potentially help reduce stink bug populations in soybeans later in the year, but this would need to be tested with higher stink bug densities before recommending this as a practical management strategy.
Under low pressure, automatic insecticide applications at R3 seemed to lower late season stink bug populations. This automatic application did not consistently affect the populations of other pest or beneficial species. Automatic insecticide application did not increase yield, and therefore provided no economic benefit to the producer. Soybean
71 fields should be properly scouted and insecticide applications made as needed to manage economically threatening insect densities.
72