Organic orchard floor management in peach: effects on arthropods and associated fruit injury in the Intermountain West

Understanding orchard floor management is critical to organic tree-fruit production systems given its impact on weeds, soil fertility, tree health, and crop yield. Several viable options are available to producers for weed management and promotion of organic fertility, including use of turf and broadleaf alleyway covers and living and nonliving tree-row mulches. While these measures can be effective, little is known about how these strategies influence arthropod pests, which cause fruit injury. Here, we assessed 6 organic orchard floor management strategies for their impact on arthropod abundance and diversity in an organic peach production system in northern Utah from 2010 to 2014, using sweep netting and pitfall collections along with observed peach fruit damage. Generally, we found that alleyway and tree-row treatments had no impact on total arthropod diversity, species richness, or community diversity. However, earwig (Forficula auricularia) abundance was significantly impacted by alleyway and tree-row treatments that resulted in increased fruit injury. Trefoil alleyway treatments consistently increased earwig abundance across life-history stages, while mulch or Alyssum (straw) tree-row treatments harbored more earwigs and, as a result, increased earwig fruit injury. Since earwigs are especially prone to damaging young, developing fruits, it is imperative that more work is done to assess earwig abundances and life-history traits. Our results demonstrate that detrimental arthropods are sensitive to orchard floor management and can further inform integrated pest management approaches that complement sustainability goals.

Blue orchard bee (Hymenoptera: Megachilidae) origin and orchard growing region affect female retention at artificial nest sites in cherry orchards

The blue orchard bee, Osmia lignaria Say (Hymenoptera: Megachilidae), is a solitary, cavity-nesting species used for pollinating spring blooming crops. Commercial stocks are sourced from a few locations in the western United States but are sold across the country. However, the existence of local adaptations of these bees is unknown, such as the propensity to nest in nearby provided materials or to disperse broadly beyond release sites. In spring 2019, California- and Utah-sourced blue orchard bees were introduced into cherry orchards in both source and reciprocal states. Nest boxes were placed near (within 78 m) and far (500 m-1 km) from central bee release points. Paint-marked bees were released when floral resources were available. Observations of marked bees at nest boxes were used to evaluate female retention and dispersal pattern. Nesting bee counts in March-blooming California orchards revealed a significant difference in female retention by population source; over twice as many UT bees established nests than did CA bees. Few females were found at far nest sites. In May-blooming Utah orchards, counts of CA and UT bees were similar at near and far nest sites; neither female retention nor dispersal was significantly affected by bee origin. It is concerning that CA females were less likely to be retained in California orchards because the demand for commercial pollination is high for early-blooming California almond and cherry. Our results highlight the need to understand potential consequences of bee origin and their management on pollinator performance and reproduction in target crops.

Efficacy of Kairomone Lures to Attract Parasitoids of Halyomorpha halys

In its native range, Halyomorpha halys (Stål) is suppressed by parasitoids in the genus Trissolcus (Hymenoptera: Scelionidae). Trissolcus native to Utah have demonstrated low parasitism of H. halys, while adventive Trissolcus japonicus (Ashmead) have shown parasitism of up to 20%. Custom rubber septa lures containing stink bug kairomones, n-tridecane (attractant), and (E)-2-decenal (repellent), at 100%, 90%, and 80% levels of attractant (10 mg load rate), were placed adjacent to sentinel H. halys egg masses in northern Utah field trials. Egg masses were evaluated for the presence and intensity (proportion of parasitized eggs) of parasitism. Parasitism by T. japonicus and T. euschisti (Ashmead) was low; however, the 100% lure showed double the parasitism of the control and more than three times that of the 90% and 80%. Two-way choice mesocosm trials in the laboratory evaluated previous lures and a lower load rate of 5 mg-100% attractant treatment. Lures of 10 mg at 100% and 80% were more attractive to T. japonicus than the control, while 5 mg at 100% and 10 mg at 90% showed no significant attraction. Our results support a proof-of-concept of rubber septa as release devices for kairomones to attract T. japonicus and provide a baseline for future field-based studies.

Evaluating invasion risk and population dynamics of the brown marmorated stink bug across the contiguous United States

BACKGROUND

Invasive species threaten the productivity and stability of natural and managed ecosystems. Predicting the spread of invaders, which can aid in early mitigation efforts, is a major challenge, especially in the face of climate change. While ecological niche models are effective tools to assess habitat suitability for invaders, such models have rarely been created for invasive pest species with rapidly expanding ranges. Here, we leveraged a national monitoring effort from 543 sites over 3 years to assess factors mediating the occurrence and abundance of brown marmorated stink bug (BMSB, Halyomorpha halys), an invasive insect pest that has readily established throughout much of the United States.

RESULTS

We used maximum entropy models to estimate the suitable habitat of BMSB under several climate scenarios, and generalized boosted models to assess environmental factors that regulated BMSB abundance. Our models captured BMSB distribution and abundance with high accuracy, and predicted a 70% increase in suitable habitat under future climate scenarios. However, environmental factors that mediated the geographical distribution of BMSB were different from those driving abundance. While BMSB occurrence was most affected by winter precipitation and proximity to populated areas, BMSB abundance was influenced most strongly by evapotranspiration and solar photoperiod.

CONCLUSION

Our results suggest that linking models of establishment (occurrence) and population dynamics (abundance) offers a more effective way to forecast the spread and impact of BMSB and other invasive species than simply occurrence-based models, allowing for targeted mitigation efforts. Implications of distribution shifts under climate change are discussed. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparison of Yellow and Blue Sticky Cards for Detection and Monitoring Parasitoid Wasps of the Invasive Halyomorpha halys (Hemiptera: Pentatomidae)

The invasive Halyomorpha halys (Stål) is a significant agricultural and urban nuisance pest in many parts of the world. In North America, biological control of H. halys by parasitoid wasps in the families Scelionidae and Eupelmidae has shown promise. An effective technique for detection and monitoring native and exotic parasitoids is the deployment of yellow sticky cards; however, yellow cards also attract nontarget arthropods, reducing efficiency and accuracy of parasitoid screening. This study sought to identify an alternative yet effective trapping technique by comparing the number of target parasitoid wasps [Anastatus spp. Motschulsky (Hymenoptera: Eupelmidae), Telenomus spp. Haliday (Hymenoptera: Scelionidae), and Trissolcus spp. Ashmead (Hymenoptera: Scelionidae)] and arthropod bycatch on yellow and blue sticky cards deployed in urban, orchard, and vegetable landscapes in northern Utah from late May to early October in 2019 and 2020. Yellow sticky cards captured 54-72% more target parasitoids than blue cards from June through August in all three landscape types in both years; however, a positive correlation in parasitoid capture indicated blue cards detect target parasitoids, just in fewer numbers. Both card colors detected adventive Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) in initial findings of 2019, and in expanded locations of 2020. Furthermore, blue cards captured 31-48% less Diptera and nontarget Hymenoptera than yellow cards in both years across all three landscapes, translating to reduced card processing time and impacts to beneficial insect populations. Our results suggest that blue vs yellow sticky cards offer an alternative monitoring technique to survey for H. halys parasitoids.

Urban host plant utilisation by the invasive Halyomorpha halys (Stål) (Hemiptera, Pentatomidae) in northern Utah

The invasive and highly polyphagous brown marmorated stink bug, Halyomorpha halys (Stål), is a severe agricultural and urban nuisance pest in North America. Since its initial invasion into Utah in 2012, H. halys has become well established in urban and suburban locations along the western foothills of the Wasatch Front in northern Utah. Bordering the Great Basin Desert, this area is unique from other North American locations with H. halys due to its high elevation (> 1200 m), aridity (30-year mean RH = 53.1%; dew point = -1.9 °C) and extreme temperatures (the 30-year mean minimum and maximum in January and July in Salt Lake City range from -3.1 to 3.6 °C and 20.3 to 32.4 °C, respectively). To document which plant species harbour H. halys, surveys were conducted in 17 urban/suburban sites in four counties during 2017 and 2018. Halyomorpha halys was more abundant in Salt Lake and Utah counties than in the more northern counties of Davis and Weber and was found on 53 plant species, nine of which hosted two or more developmental stages in both years. The majority of hosts were in the families Fabaceae, Rosaceae and Sapindaceae. Northern catalpa, Catalpa speciosa (Warder), was the most consistent host, supporting a majority of H. halys detections in all life stages; thus we identify it as a sentinel host. Twenty-nine species were novel hosts for H. halys in North America; of these, Acer ginnala Maxim, Populus tremuloides Michx., Prunus armeniaca × domestica ‘Flavor King’ and Prunus virginiana ‘Schubert’ were detected with two or more life stages of H. halys in both years. Peak populations of H. halys occurred from mid-June to mid-September. We describe H. halys plant utilisation by life stage and seasonal period to aid future detection and management of this invasive insect in the greater Intermountain West region.

Impact of Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Feeding on Tart Cherry (Rosales: Rosaceae) Quality and Yield in Utah

Brown marmorated stink bug (Halyomorpha halys Stål) is an invasive and economically important agricultural and ornamental insect pest now established in 46 U.S. states. It was first detected in Utah in 2012 and began causing agricultural damage in 2017. Tart cherry (Prunus cerasus Linnaeus) is a major processed agricultural commodity in Utah; yet, its susceptibility to brown marmorated stink bug is unstudied. Limb cages with six brown marmorated stink bug adults, nymphs, or no brown marmorated stink bug were established in a randomized complete block design in a tart cherry orchard to determine feeding impact on different fruit developmental stages. After 1 wk of feeding, half of the fruits in each cage were removed to assess feeding intensity, and the remainder left through maturity to assess marketability and quality. Feeding by adults and nymphs between petal fall and fruit pit hardening, even at feeding pressures as low as 1.7-4.0 feeding sites per fruit, caused 100% abscission of fruits, significantly reducing marketability when compared with the control treatment. For fruits that escaped abscission and matured, few quality differences were detected among treatments, indicating that brown marmorated stink bug feeding caused minimal detectable quality loss to this processed tree fruit crop. We conclude that tart cherries are at risk of abscission with short-term brown marmorated stink bug feeding between petal fall and pit hardening when overwintered adults or F1 nymphs are present in orchards, and suggest that longer-term feeding may be necessary to cause quality and yield reductions after pit hardening.

Surveys in northern Utah for egg parasitoids of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) detect Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae)

The highly polyphagous and invasive brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), has become a significant insect pest in North America since its detection in 1996. It was first documented in northern Utah in 2012 and reports of urban nuisance problems and plant damage have since increased. Biological control is the preferred solution to managing H. halys in North America and other invaded regions due to its alignment with integrated pest management and sustainable practices. Native and non-native biological control agents, namely parasitoid wasps, have been assessed for efficacy. Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is an effective egg parasitoid of H. halys in its native range of southeast Asia and has recently been documented parasitising H. halys eggs in North America and Europe. Field surveys for native and exotic egg parasitoids using wild (in situ) and lab-reared H. halys egg masses were conducted in suburban and agricultural sites in northern Utah from June to September 2017-2019. Seven native wasp species in the families Eupelmidae and Scelionidae were discovered guarding H. halys eggs and adult wasps from five of these species completed emergence. Native species had low mean rates of adult emergence from wild (0.5-3.7%) and lab-reared (0-0.4%) egg masses. In 2019, an adventive population of T. japonicus was discovered for the first time in Utah, emerging from 21 of the 106 wild H. halys egg masses found that year, and none from lab-reared eggs. All T. japonicus emerged from egg masses collected on Catalpa speciosa (Warder). Our results support other studies that have observed biological control of H. halys from T. japonicus and improved parasitoid wasp detection with wild as compared to lab-reared H. halys egg masses.

Season-Long Monitoring of the Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Throughout the United States Using Commercially Available Traps and Lures

Reliable monitoring of the invasive Halyomorpha halys abundance, phenology and geographic distribution is critical for its management. Halyomorpha halys adult and nymphal captures on clear sticky traps and in black pyramid traps were compared in 18 states across the Great Lakes, Mid-Atlantic, Southeast, Pacific Northwest and Western regions of the United States. Traps were baited with commercial lures containing the H. halys pheromone and synergist, and deployed at field sites bordering agricultural or urban locations with H. halys host plants. Nymphal and adult captures in pyramid traps were greater than those on sticky traps, but captures were positively correlated between the two trap types within each region and during the early-, mid- and late season across all sites. Sites were further classified as having a low, moderate or high relative H. halys density and again showed positive correlations between captures for the two trap types for nymphs and adults. Among regions, the greatest adult captures were recorded in the Southeast and Mid-Atlantic on pyramid and sticky traps, respectively, with lowest captures recorded in the West. Nymphal captures, while lower than adult captures, were greatest in the Southeast and lowest in the West. Nymphal and adult captures were, generally, greatest during July-August and September-October, respectively. Trapping data were compared with available phenological models showing comparable population peaks at most locations. Results demonstrated that sticky traps offer a simpler alternative to pyramid traps, but both can be reliable tools to monitor H. halys in different geographical locations with varying population densities throughout the season.

Mating Disruption for Managing Prionus californicus (Coleoptera: Cerambycidae) in Hop and Sweet Cherry

Larvae of Prionus californicus Motschulsky feed on the roots of many woody perennial plants and are economically important pests of hop Humulus lupulus L. (Urticales: Cannabaceae) and sweet cherry Prunus avium (L.) (Magnoliopsida: Rosaceae) in the United States Pacific Northwest and Intermountain West. Adult males are strongly attracted to a volatile sex pheromone, (3R,5S)-3,5-dimethyldodecanoic acid, produced by females. Here, we summarize the results of field experiments evaluating the synthetic pheromone in a blend of all four possible stereoisomers as a means for managing P. californicus in hop yards and sweet cherry orchards by mating disruption (MD). Mean capture of male beetles was lower, in all 3 yr of the study, from plots in commercial hop yards and sweet cherry orchards treated with synthetic P. californicus pheromone than from similar, untreated plots. Although trap catch was lower in sweet cherry, relative differences between trap catches from MD and nonmating disruption plots were similar to that seen in hop yards. The number of P. californicus larvae recovered from plots in hop yards treated for three consecutive growing seasons with synthetic pheromone was lower than in similar plots that were not treated with the pheromone or treated with the soil fumigant ethoprop. Our research demonstrates that deployment of synthetic P. californicus pheromone effectively reduces mate-finding by males, can effectively reduce larvae populations in pheromone-treated hop yards, and thus, has excellent potential for managing P. californicus in hop, sweet cherry, and perhaps in other crops where it or Prionus species are pests.

Predicting the emergence of the codling moth, Cydia pomonella (Lepidoptera: Tortricidae), on a degree-day scale in North America

BACKGROUND

Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is a major pest of apple, pear and walnut production in North America. Management programs are based on preventing larval entry into the fruit or nut and are typically timed by heat-driven models that are synchronized to field populations by first capture of overwintering moths in pheromone traps. Unfortunately, trap capture is affected by a range of environmental parameters as well as by the use of mating disruption, which makes detecting first flight difficult, thus complicating implementation of management programs. The present goal was to evaluate data collected from a broad range of locations across North America to see whether average first spring emergence times could be predicted.

RESULTS

Average emergence time on a degree-day scale from 1 January was predictable using latitude and elevation. Sites at elevations of <400 m fit a simple quadratic equation using latitude, but, when higher elevations were included, a multiple regression using elevation was required.

CONCLUSIONS

The present models can be used to simplify management programs for codling moth in areas where heat-driven models that require extensive trapping to synchronize with emergence are currently used.

Field efficacy of entomopathogenic fungi and nematodes targeting caged last-instar plum curculio (Coleoptera: Curculionidae) in Michigan cherry and apple orchards

The plum curculio (Conotrachelus nenuphar Herbst) is a key pest of pome and stone fruit in eastern North America. We tested the efficacy of five pathogens over the course of three seasons in 10 Michigan apple and cherry orchards, with introductions of larvae to caged pots containing pathogen-treated soil. The nematode Steinernema riobrave was the most effective pathogen in the 2 yr it was tested, but only in soils with the highest sand content (81-88%) and when it was applied 1 h or 5 d after last instars of plum curculio. S. carpocapsae in an organic formulation was less effective, but significantly reduced plum curculio emergence in 1 yr of the study when applied 3 d before C. nenuphar larvae were introduced. Beauveria bassiana was effective in only 1 of the 3 yr it was tested, only in soils with lower sand content, and only when it was introduced within 1 h of plum curculio larvae. Metarhizium anisopliae and Heterorhabditis bacteriophora were ineffective. Michigan orchards may require sprinkler irrigation coupled with precise timing recommendations and oviposition monitoring to enhance entomopathogen application efficacy against soil-dwelling last instars.

Reproductive maturity of cherry fruit fly (Diptera: Tephritidae) in managed and natural habitats

We studied the timing of reproductive maturity of cherry fruit fly, Rhagoletis cingulata (Loew), a key pest of sweet and tart cherries in the eastern United States. To determine when cherry fruit fly females become reproductively mature in managed and natural habitats, we deployed traps in sweet and tart cherry orchards and nearby stands of the ancestral host tree, black cherry. Flies were removed from the traps and females were dissected to determine the presence of fully developed eggs. We found that capture of reproductively mature female flies occurred earlier in orchards that are not sprayed with insecticides than in sprayed orchards or in black cherry tree sites. In addition, the gap between the flights of immature and mature females in unmanaged sweet or tart cherry orchards was shorter than in managed orchards or black cherry tree sites. We also determined fruit color, size, and skin hardness to characterize the progression of fruit maturity. We found that fruit became mature earlier in sweet and tart cherry orchards than in black cherry tree sites. This study indicates that the timing of female reproductive maturity is plastic and varies among cherry fruit fly populations present in distinct habitats. Variation in the timing of reproductive maturity is related to the fruit maturity period of distinct host plant species and to orchard management.

Potential of two entomopathogenic nematodes for suppression of plum curculio (Conotrachelus nenuphar, Coleoptera: Curculionidae) life stages in northern climates

Plum curculio, Conotrachelus nenuphar, is a major pest of pome and stone fruits in North America. We evaluated the potential efficacy of two entomopathogenic nematode species for suppression of plum curculio in northern regions, targeting life stages that reside in soil during spring and summer. A strain of Heterorhabditis bacteriophora isolated from soil infested with plum curculio in northern Utah and a commercially available strain of Steinernema feltiae known to tolerate cool temperatures were tested in the laboratory against three life stages of plum curculio. Bioassays used the southern strain of plum curculio because availability of the northern strain from the field was inadequate. H. bacteriophora was more virulent than S. feltiae to all plum curculio life stages. Adults and pupae were more susceptible than larvae. Temperature bioassays were conducted with a surrogate host: last instars of Galleria mellonella. The two nematodes exhibited different, but overlapping, thermal activity ranges. Both species performed best at 20 degrees C: virulence and reproductive potential was higher; however, H. bacteriophora was superior to S. feltiae at 30 degrees C and vice versa at 10 degrees C. The reproductive potential of H. bacteriophora was > 2.5 times greater than for S. feltiae, and H. bacteriophora required fewer individuals to initiate a successful host infection. S. feltiae was a better fit for temperatures expected in northern climates, but H. bacteriophora was more virulent to plum curculio and produced more infective juveniles that may benefit nematode recycling and continuation and spread of insect suppression in the field.

Effects of physical and nutritional stress conditions during mycelial growth on conidial germination speed, adhesion to host cuticle, and virulence of Metarhizium anisopliae, an entomopathogenic fungus

Growth under stress may influence pathogen virulence and other phenotypic traits. Conidia of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae (isolate ARSEF 2575) were produced under different stress conditions and then examined for influences on in vitro conidial germination speed, adhesion to the insect cuticle, and virulence to an insect host, Tenebrio molitor. Conidia were produced under non-stress conditions [on potato-dextrose agar plus 1gl(-1) yeast extract (PDAY; control)], or under the following stress conditions: osmotic (PDAY+sodium chloride or potassium chloride, 0.6 or 0.8m); oxidative [(PDAY+hydrogen peroxide, 5mm) or UV-A (irradiation of mycelium on PDAY)]; heat shock (heat treatment of mycelium on PDAY at 45 degrees C, 40min); and nutritive [minimal medium (MM) with no carbon source, or on MM plus 3gl(-1) lactose (MML)]. Conidia were most virulent (based on mortality at 3d) and had the fastest germination rates when produced on MML, followed by MM. In addition, conidial adhesion to host cuticle was greatest when the conidia were produced on MML. Media with high osmolarity (0.8m) produced conidia with slightly elevated virulence and faster germination rates than conidia produced on the control medium (PDAY), but this trend did not hold for media with the lower osmolarity, (0.6m). Conidia produced from mycelium irradiated with UV-A while growing on PDAY had somewhat elevated virulence levels similar to that of conidia produced on MM, but their germination rate was not increased. Hydrogen peroxide and heat shock treatments did not alter virulence. These results demonstrate that the germination, adhesion and virulence of M. anisopliae conidia can be strongly influenced by culture conditions (including stresses) during production of the conidia.

Effects of the insecticide phosmet on solitary bee foraging and nesting in orchards of Capitol Reef National Park, Utah

Capitol Reef National Park, in southcentral Utah, contains 22 small orchards planted with antique fruit varieties by Mormon pioneers beginning over a century ago. The orchards continue to be managed in a pick-and-pay program, which includes spraying with phosmet to suppress codling moth (Cydia pomonella L.). The park is also home to a rich diversity of flowering plants, many of which are rare, bee-pollinated, and have populations within 1 km of the orchards. Over 3 yr, we studied the short-term effects of phosmet spraying on bee populations: (1) foraging on plants within the orchard understory and adjacent to it; and (2) nesting in, and at several distances from, the orchards. We recorded a rich bee fauna (47 taxa) in the orchards and on plants nearby. In 2 yr (2002 and 2004), we found no difference in the number of native bee visits to several species of plants flowering in and near to orchards immediately before and 1 d after spraying. Conversely, our nesting studies using the semidomesticated alfalfa leafcutting bee, Megachile rotundata (F.), showed strong significant declines in the number of adult males, nesting females, and progeny production subsequent to spraying at distances up to 160 m from sprayed orchards where the bees were presumably foraging. We showed that M. rotundata is negatively affected by phosmet spraying and suggest that caution should be exercised in its use in areas where bees are apt to forage.

Effects of spinosad, spinosad bait, and chloronicotinyl insecticides on mortality and control of adult and larval western cherry fruit fly (Diptera: Tephritidae)

Effects of spinosad, spinosad bait, and the chloronicotinyl insecticides imidacloprid and thiacloprid on mortality of the adults and larvae of western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), were determined in the laboratory and the field. Spinosad and spinosad bait caused higher adult mortality than imidacloprid, which caused higher mortality than thiacloprid. Only spinosad bait prevented oviposition. All materials were more toxic to adults when ingested than when topically applied. Spinosad bait had the greatest residual toxicity on leaves, killing 100% of adults when aged for 14 d in the field. When materials were sprayed on infested cherries, numbers of live larvae in fruit after 8 d were lower in imidacloprid and thiacloprid than in spinosad and spinosad bait treatments, which did not differ from the control, but all materials reduced larval emergence over 30 d. In the field, spinosad and spinosad bait were as effective in suppressing larval infestations as azinphos-methyl and carbaryl, whereas imidacloprid was effective in most cases and thiacloprid was generally less effective than azinphos-methyl and carbaryl. Overall, results in the laboratory and field show that spinosad and chloronicotinyl insecticides differed significantly in their effectiveness against adults and larvae of R. indifferens but that spinosad, spinosad bait, and imidacloprid seem to be acceptable substitutes for organophosphate and carbamate insecticides for controlling this fruit fly.

Effects of fungicide residues on the survival, fecundity, and predation of the mites Tetranychus urticae (Acari: Tetranychidae) and Galendromus occidentalis (Acari: Phytoseiidae)

Representative fungicides from three or four families used for management of powdery mildew and other diseases in tree fruits were evaluated for their effects on a common spider mite and predator mite species, respectively. A modified Munger cell technique was effective in measuring the response of phytophagous and predaceous mites to fungicide residues on detached leaves in the laboratory. Demethylation-inhibiting (DMI) (imidazole [triflumazole] and triazole [myclobutanil]) and strobilurin (trifloxystrobin) fungicides were not toxic to female Tetranychus urticae Koch and Galendromus occidentalis (Nesbitt), and no sublethal effects were found on fecundity and predation rate after 3-5-d exposure to residues. Benomyl, a benzimidazole fungicide, increased adult mortality and reduced fecundity for both mite species; however, it did not alter the predation rate of G. occidentalis females on T. urticae eggs and larvae. Female G. occidentalis that survived the lethal effects of benomyl and the comparison acaricide pyridaben were unimpaired in predation. Our results for benomyl substantiate those of earlier studies and provide evidence for nontoxic effects of DMI and strobilurin fungicides on mites. We propose that DMI and strobilurin fungicides are a good fit for integrated mite management programs due to conservation of phytoseiid predatory mites.

Multiple Pest Interactions in Soybean: Effects on Heterodera glycines Egg Populations and Crop Yield

Population changes of Heterodera glycines eggs on soybean in small field plots were influenced by the lepidopterous insect pest, Helicoverpa zea; however, few effects on eggs due to the presence of annual weeds were detected. Soybeans defoliated 15-35% by H. zea during August remained green and continued to produce new flowers and pods later into the season than soybeans without H. zea, resulting in higher numbers of H. glycines eggs at harvest on insect-defoliated soybeans. Final H. glycines populations also were influenced by soil population density (Pi) of the nematode at planting. Fecundity of H. glycines was generally greater at the undetected and low Pi than at high Pi levels. Soybean yields were suppressed 12, 22, and 30% by low, moderate, and high H. glycines Pi, respectively. When weed competition and H. zea feeding damage effects were added, yields were suppressed 34, 40, and 57% by the three respective nematode Pi levels. Effects among the three pests on soybean yield were primarily additive.

Development of Heterodera glycines Life Stages as Influenced by Temperature

The effects of temperature on rates of development of Heterodera glycines egg and juvenile stages were examined as a basis for predicting generation times of the nematode on soybean. The relationship of temperature to H. glycines embryonic development between 15 and 30 C was described by a linear model, The calculated basal temperature threshold was 5 C. Thermal optimum for embryogenesis and hatch with low mortality was 24 C. Development proceeded to first-stage juvenile at 10 C and to second-stage juvenile at 15-30 C. Hatch occurred at 20-30 C. At 36 C, development proceeded to the four-cell stage, then the eggs died. The range of diurnal soil temperature fluctuation and accumulated degree-days between 5 and 30 C (DD5/30) had an impact on rate of development of juveniles in soybean roots. From early June to early July, H. glycines required 534 + 24 DD5/30 (4 weeks) to complete a life cycle in the field. During the midseason (July and August), life cycles were completed in 3 weeks and 429 +/- 24 DD5/30 were accumulated. Late in the season (September to November), declining soil temperatures were associated with generation times of 4 weeks and slower rates of development.

Population Density and Spatial Pattern of Heterodera glycines in Relation to Soybean Phenology

Population dynamics of Heterodera glycines (SCN) were influenced by initial nematode population density in soil, soybean root growth pattern, soil type, and environmental conditions in two field experiments. Low initial populations (Pi) of SCN increased more rapidly during the growing season than high Pi and resulted in greater numbers of nematodes at harvest. Egg and juvenile (J2) populations increased within 2-6 weeks after planting when early-season soil temperatures were 20 C and above and were delayed by soil temperatures of 17 C or below in May and early June. Frequencies of occurrence and number of nematodes decreased with increasing depth and distance from center of the soybean row. Spatial pattern of SCN paralleled that of soybean roots. Higher clay content in the subsoil 30-45 cm deep in one field restricted soil penetration by roots, indirectly influencing vertical distribution of SCN. Shoot dry weight was a good indicator of the effect of SCN on seed yield. Root dry weight was poorly correlated with soybean growth and yield. The relationship of yield (seed weight) to Pi was best described by a quadratic equation at one site, but did not fit any regression model tested at the second site.

Nematode trophic structure in conventional and no-tillage agroecosystems

The effect of tillage intensity on nematode community trophic structure and the role of nematodes in the regulation of decomposition rates in agroecosystems were examined. Conventional (CT) and no-tillage (NT) agroecosystems were sampled monthly for 1 year. Tillage affected nematode trophic structure and total abundance. Monthly mean densities of bacterivorous, fungivorous, and total nematodes were greater in CT than in NT plots. In the summer, however, fungivorous and plant parasitic nematodes were more abundant in NT. No difference was detected for omnivore-predator nematodes.