Agricultural intensification has resulted in a simplification of agricultural landscapes by the expansion of agricultural land, enlargement of field size and removal of non-crop habitat. These changes are considered to be an important cause of the rapid decline in farmland biodiversity, with the remaining biodiversity concentrated in field edges and non-crop habitats. The simplification of landscape composition and the decline of biodiversity may affect the functioning of natural pest control because non-crop habitats provide requisites for a broad spectrum of natural enemies, and the exchange of natural enemies between crop and non-crop habitats is likely to be diminished in landscapes dominated by arable cropland. In this review, we test the hypothesis that natural pest control is enhanced in complex patchy landscapes with a high proportion of non-crop habitats as compared to simple large-scale landscapes with little associated non-crop habitat. In 74% and 45% of the studies reviewed, respectively, natural enemy populations were higher and pest pressure lower in complex landscapes versus simple landscapes. Landscape-driven pest suppression may result in lower crop injury, although this has rarely been documented. Enhanced natural enemy activity was associated with herbaceous habitats in 80% of the cases (e.g. fallows, field margins), and somewhat less often with wooded habitats (71%) and landscape patchiness (70%). The similar contributions of these landscape factors suggest that all are equally important in enhancing natural enemy populations. We conclude that diversified landscapes hold most potential for the conservation of biodiversity and sustaining the pest control function.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2006.3530

Sustainable pest regulation in agricultural landscapes: a review on landscape composition, biodiversity and natural pest control

Summary 1. Neonicotinoids are now the most widely used insecticides in the world. They act systemically, travelling through plant tissues and protecting all parts of the crop, and are widely applied as seed dressings. As neurotoxins with high toxicity to most arthropods, they provide effective pest control and have numerous uses in arable farming and horticulture. 2. However, the prophylactic use of broad-spectrum pesticides goes against the long-established principles of integrated pest management (IPM), leading to environmental concerns. 3. It has recently emerged that neonicotinoids can persist and accumulate in soils. They are water soluble and prone to leaching into waterways. Being systemic, they are found in nectar and pollen of treated crops. Reported levels in soils, waterways, field margin plants and floral resources overlap substantially with concentrations that are sufficient to control pests in crops, and commonly exceed the LC50 (the concentration which kills 50% of individuals) for beneficial organisms. Concentrations in nectar and pollen in crops are sufficient to impact substantially on colony reproduction in bumblebees. 4. Although vertebrates are less susceptible than arthropods, consumption of small numbers of dressed seeds offers a route to direct mortality in birds and mammals. 5. Synthesis and applications. Major knowledge gaps remain, but current use of neonicotinoids is likely to be impacting on a broad range of non-target taxa including pollinators and soil and aquatic invertebrates and hence threatens a range of ecosystem services.

/pdf/review-an-overview-of-the-environmental-risks-posed-by-hj0ee8p6bs.pdf

REVIEW: An overview of the environmental risks posed by neonicotinoid insecticides

Since their discovery in the late 1980s, neonicotinoid pesticides have become the most widely used class of insecticides worldwide, with large-scale applications ranging from plant protection (crops, vegetables, fruits), veterinary products, and biocides to invertebrate pest control in fish farming. In this review, we address the phenyl-pyrazole fipronil together with neonicotinoids because of similarities in their toxicity, physicochemical profiles, and presence in the environment. Neonicotinoids and fipronil currently account for approximately one third of the world insecticide market; the annual world production of the archetype neonicotinoid, imidacloprid, was estimated to be ca. 20,000 tonnes active substance in 2010. There were several reasons for the initial success of neonicotinoids and fipronil: (1) there was no known pesticide resistance in target pests, mainly because of their recent development, (2) their physicochemical properties included many advantages over previous generations of insecticides (i.e., organophosphates, carbamates, pyrethroids, etc.), and (3) they shared an assumed reduced operator and consumer risk. Due to their systemic nature, they are taken up by the roots or leaves and translocated to all parts of the plant, which, in turn, makes them effectively toxic to herbivorous insects. The toxicity persists for a variable period of time—depending on the plant, its growth stage, and the amount of pesticide applied. A wide variety of applications are available, including the most common prophylactic non-Good Agricultural Practices (GAP) application by seed coating. As a result of their extensive use and physicochemical properties, these substances can be found in all environmental compartments including soil, water, and air. Neonicotinoids and fipronil operate by disrupting neural transmission in the central nervous system of invertebrates. Neonicotinoids mimic the action of neurotransmitters, while fipronil inhibits neuronal receptors. In doing so, they continuously stimulate neurons leading ultimately to death of target invertebrates. Like virtually all insecticides, they can also have lethal and sublethal impacts on non-target organisms, including insect predators and vertebrates. Furthermore, a range of synergistic effects with other stressors have been documented. Here, we review extensively their metabolic pathways, showing how they form both compound-specific and common metabolites which can themselves be toxic. These may result in prolonged toxicity. Considering their wide commercial expansion, mode of action, the systemic properties in plants, persistence and environmental fate, coupled with limited information about the toxicity profiles of these compounds and their metabolites, neonicotinoids and fipronil may entail significant risks to the environment. A global evaluation of the potential collateral effects of their use is therefore timely. The present paper and subsequent chapters in this review of the global literature explore these risks and show a growing body of evidence that persistent, low concentrations of these insecticides pose serious risks of undesirable environmental impacts.

/pdf/systemic-insecticides-neonicotinoids-and-fipronil-trends-iqykc9qemm.pdf

Systemic insecticides (neonicotinoids and fipronil): trends, uses, mode of action and metabolites

We investigate the procedure of checking for overlap between confidence intervals or standard error intervals to draw conclusions regarding hypotheses about differences between population parameters. Mathematical expressions and algebraic manipulations are given, and computer simulations are performed to assess the usefulness of confidence and standard error intervals in this manner. We make recommendations for their use in situations in which standard tests of hypotheses do not exist. An example is given that tests this methodology for comparing effective dose levels in independent probit regressions, an application that is also pertinent to derivations of LC50s for insect pathogens and of detectability half-lives for prey proteins or DNA sequences in predator gut analysis.

/pdf/overlapping-confidence-intervals-or-standard-error-intervals-15elogakm7.pdf

Overlapping confidence intervals or standard error intervals: what do they mean in terms of statistical significance?

In many situations prey choice by predators in the field cannot be established or quantified using direct observation. The remains of some prey may be visually identified in the guts and faeces of predators but not all predators ingest such hard remains and even those that do consume them may also ingest soft-bodies prey that leave no recognizable remnants. The result is, at best, a biased picture of prey choice. A range of molecular techniques and applications are reviewed that allow prey remains to be identified, often to the species and even stage level. These techniques, all of which are still in use, include enzyme electrophoresis, a range of immunological approaches using polyclonal and monoclonal antibodies to detect protein epitopes, and recently developed polymerase chain reaction (PCR)-based methods for detecting prey DNA. Analyses may be postmortem, on invertebrate and vertebrate predators collected from the field, or noninvasive assays of the remains in regurgitated bird pellets or vertebrate faeces. It was concluded that although monoclonal antibodies are currently the most effective method in use today, PCR-based techniques have proved to be highly effective and versatile in recent laboratory trials and are likely to rapidly displace all other approaches.

Molecular identification of prey in predator diets.

We describe polymerase chain reaction (PCR) primers for gut analysis of aphid predators. The primers amplify aphid mitochondrial COII fragments ranging in size from 77 to 386 bp. Using these primers, we were able to distinguish six species of US Great Plains cereal aphids, including two congeners, Rhopalosiphum maidis (Fitch) and R. padi (L.), and to detect them in extracts of coccinellid and chrysopid predators. We devised a protocol for deriving half-lives of detectability for the DNA of a single aphid consumed by predators maintained under simulated field dietary and temperature conditions. Using this protocol and primers that amplify a 198-bp fragment, we determined statistically different half-lives of detectability for a single R. maidis of 3.95 h in Chrysoperla plorabunda (Fitch) and 8. 78 h in Hippodamia convergens Guerin. The detectability half-life for a 339-bp R. maidis fragment was statistically longer in C. plorabunda but not in H. convergens. The sensitivity of the assay for the 198-bp fragment is 10-7 aphid equivalents. For species-specific predator gut analysis, PCR is superior to monoclonal antibody technology, giving comparable detectability half-lives with lower expense, much shorter development times, and greater certainty of a successful outcome.

Identifying key cereal aphid predators by molecular gut analysis

We used multiple regression modeling to investigate the numerical response by the predatory insects Hippodamia convergens Guerin-Meneville, H. parenthesis (Say), and C. septempunctata L. (Coleoptera: Coccinellidae), Chrysoperla plorabunda (Fitch) (Neuroptera: Chrysopidae), and Nabis americoferus Carayon (Hemiptera: Nabidae) to aphids during 5 yr in three geographically separated alfalfa fields in eastern South Dakota. Regression models for abundance of adults of all species were significant. Regression models for immature H. convergens, H. parenthesis, and C. septempunctata were significant, but regression models for immature C. plorabunda and N. americoferus were not significant. Regression parameters differed among the three fields for most predator species, indicating that the numerical response was dependent on geographical location. To obtain insight into why the numerical response by predators differed among fields we determined how the abundance of predators in alfalfa fields was influenced by the landscape surrounding a field and the vegetation in it. Variables describing the complexity of the landscape surrounding alfalfa fields and the plant community in the fields entered into regression models for predator abundance and explained a greater proportion of the variance in predator abundance than aphid abundance did. We conclude that the structure of the landscape matrix plays an important role in determining the abundance of aphid predators in alfalfa fields, as does the plant community in a field. These effects can sometimes overshadow the direct numerical response by predators to aphids.

https://bioone.org/journals/Environmental-Entomology/volume-31/issue-2/0046-225X-31.2.253/Predator-Abundance-in-Alfalfa-Fields-in-Relation-to-Aphids-Within/10.1603/0046-225X-31.2.253.pdf

Predator Abundance in Alfalfa Fields in Relation to Aphids, Within-Field Vegetation, and Landscape Matrix

The effects of planting date and application rate of imidacloprid for control of Schizaphis graminum Rondani, Rhopalosiphum padi L. (Homoptera: Aphididae), and barley yellow dwarf virus (BYDV) in hard red winter wheat were studied. The first experiment was conducted from 1997 to 1999 at two locations and consisted of three planting dates and four rates of imidacloprid-treated seed. The second experiment was conducted from 2001 to 2002 in Stillwater, OK, and consisted of two varieties of hard red winter wheat seed and four rates of imidacloprid. Aphid densities, occurrence of BYDV, yield components, and final grain yield were measured, and yield differences were used to estimate the economic return obtained from using imidacloprid. In the first study, aphid populations responded to insecticide rate in the early and middle plantings, but the response was reduced in the late planting. Yields increased as insecticide rate increased but did not always result in a positive economic return. In the secon...

Economic Evaluation of the Effects of Planting Date and Application Rate of Imidacloprid for Management of Cereal Aphids and Barley Yellow Dwarf in Winter Wheat

The goal of this research was to describe developmental rates, reproductive rates, and infestation patterns of Aphis craccivora Koch on alfalfa (Medicago sativa L.). All studies were conducted on the susceptible cultivar OK08 using aphids reared from collections made in Oklahoma. To determine thermal requirements for growth of A. craccivora, development from birth to adult was recorded at 7.2, 12.8, 18.3, 23.9, and 29.4 degrees C. The same constant temperature treatments (except for 7.2 degrees C being raised to 8.3 degrees C) were used to assess the influence of temperature on reproductive rates. Within-plant distribution patterns were determined by infesting three stems on each of 24 plants and recording numbers of A. craccivora on leaf blades, petioles, and internodal stems sections at 2-d intervals through 10 d after infestation. Aphid counts were analyzed to determine significant differences among node parts (leaf blades, petioles, and stem sections). The developmental threshold temperature for A. craccivora was calculated to be 7.1 degrees C, and the thermal constant for development from the first instar to reproducing adult was 100 DD ( degrees C). The optimal temperature range for reproduction on alfalfa was 18-24 degrees C, with a mean of 82 nymphs produced per female. From the initial infestation of three apterae per stem, numbers increased to a mean of 510 per stem after 10 d. Plant profiles showed that the greatest numbers of aphids were located in middle and lower portions of the plant canopy. On all sampling dates, the proportion of aphids on internodal stem sections was significantly greater (P < 0.05) than on petioles and leaf blades.

https://bioone.org/journals/environmental-entomology/volume-38/issue-6/022.038.0630/Development-Reproduction-and-Within-Plant-Infestation-Patterns-of-Aphis-craccivora/10.1603/022.038.0630.pdf

Development, Reproduction, and Within-Plant Infestation Patterns of Aphis craccivora (Homoptera: Aphididae) on Alfalfa

We studied the effects of temperature and relative humidity on population growth and development of the psocid Liposcelis brunnea Motschulsky. L. brunnea did not survive at 43% RH, but populations increased from 22.5 to 32.5°C and 55–75% RH. Interestingly, we found population growth was higher at 63% RH than at 75% RH, and the greatest population growth was recorded at 32.5°C and 63% RH. At 35°C, L. brunnea nymphal survivorship was 33%, and populations declined or barely grew. L. brunnea males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 13, 82, and 5%, respectively. Female L. brunnea have three to five instars, and the percentages of females with three, four, and five instars were 18, 78, and 4%, respectively. The life cycle was shorter for males than females. We developed temperature-dependent development equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages and nymphal survivorship. The ability of L. brunnea to multiply rather rapidly at 55% RH may allow it to thrive under conditions of low relative humidity where other Liposcelis species may not. These data give us a better understanding of L. brunnea population dynamics and can be used to help develop effective management strategies for this psocid.

https://bioone.org/journals/Journal-of-Economic-Entomology/volume-103/issue-5/EC10127/Population-Growth-and-Development-of-the-Psocid-Liposcelis-rufa-Psocoptera/10.1603/EC10127.pdf

K. L. Giles

Papers

Identifying key cereal aphid predators by molecular gut analysis

Predator Abundance in Alfalfa Fields in Relation to Aphids, Within-Field Vegetation, and Landscape Matrix

Economic Evaluation of the Effects of Planting Date and Application Rate of Imidacloprid for Management of Cereal Aphids and Barley Yellow Dwarf in Winter Wheat

Development, Reproduction, and Within-Plant Infestation Patterns of Aphis craccivora (Homoptera: Aphididae) on Alfalfa

Population Growth and Development of the Psocid Liposcelis rufa (Psocoptera: Liposcelididae) at Constant Temperatures and Relative Humidities