Thomas R. Unruh

Progress Toward Liquid Formulations of Particle Films for Insect and Disease Control in Pear

Abstract Particle film technology is aimed at controlling both arthropod pests and diseases of plants with a hydrophobic particle barrier primarily composed of kaolin. Field studies were conducted from 1996 to 1998 to compare the efficacy of dust and liquid applications, and hydrophobic and hydrophilic particle films, against key pests of pear. In addition, the effects of particle film applications on pear yield and quality were investigated in 1998. Dust and liquid applications of hydrophobic and hydrophilic particle films obtained high levels of early-season pear psylla control and prevented pear rust mite damage. We also found that prior seasonal applications of particle films in 1997 can carry over into the 1998 season to suppress early season pear psylla oviposition. A major concern in the shift from hydrophobic to hydrophilic particle films was the loss of disease control. We found that a water-repellant particle film was not required to control the fungal disease fabraea leaf spot. Pear yields were nearly doubled by liquid formulations of hydrophobic and hydrophilic particle films. Particle film deposits were measured using a spectrophotometer method we developed. Particle deposition differed among formulations for both leaf age and leaf surface (top or bottom). Yet, the particle formulations performed about the same against insects and fungal diseases, and in how they influenced the horticultural traits. None of the particle film formulations were found to be phytotoxic to pear foliage or fruit during the study period. A shift from hydrophobic to hydrophilic particles makes it possible to more easily formulate and disperse the particles in water so that conventional spray equipment can be used. The multifunctionality and low toxicity of particle films could make them an attractive alternative to conventional pesticides.

Particle Films for Suppression of the Codling Moth (Lepidoptera: Tortricidae) in Apple and Pear Orchards

Abstract Studies were conducted in 1997and 1998 to evaluate the effects of three particle film formulations consisting of kaolin and adjuvants on neonate larvae, ovipositing adult females, and eggs of the codling moth, Cydia pomonella (L.). Neonate larval walking speed, fruit discovery rate, and fruit penetration rate on apple host plants coated with particle films were significantly lower than on host plants without particle films in laboratory assays. Females oviposited less on host plants covered with a particle film residue than on untreated plants in laboratory choice and no-choice tests. Hatch rate of codling moth neonate larvae was unaffected by particle films sprayed on host plants either before or after oviposition. Fruit infestation rates were significantly reduced on particle film-treated trees compared with untreated trees for both first- and second-generation codling moth in field trials in both apple and pear orchards. Particle films appear to be a promising supplemental control approach for codling moth in orchards where moth density is high, and may represent a stand-alone method where moth densities are lower.

Effects of a Kaolin-Based Particle Film on Obliquebanded Leafroller (Lepidoptera: Tortricidae)

Abstract Studies were conducted in 1997 to evaluate the effects of the kaolin-based particle film formulation M96–018 on adults, eggs, and larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris). Particle film treatments significantly reduced female longevity, mating success, and number of egg masses oviposited compared with moths on untreated apple leaves in sleeve-cage and screen-cage tests. No differences in mating success or oviposition were caused by the application rates and coverage density of M96–018 on foliage. Females avoided ovipositing on particle film-treated leaves in choice tests. Larval hatch was not affected by topical application or residual exposure to M96–018. Larval weight gain and pupal weight were significantly reduced and larval mortality increased in no-choice feeding tests with M96–018. In choice tests, larvae preferred to feed on untreated leaf surfaces. The negative effects on larval development and survivorship on M96–018-treated foliage did not differ across a fourfold difference in spray application rate. A significant reduction in the number of infested shoots was found in orchard trials when M96–018 was applied before bud break in late March compared with untreated trees. No reductions in larval densities were found compared with an untreated control following prebloom and postbloom applications.

Tree fruit IPM programs in the western United States: the challenge of enhancing biological control through intensive management.

The seminal work of Stern and his coauthors on integrated control has had a profound and long-lasting effect on the development of IPM programs in western orchard systems. Management systems based solely on pesticides have proven to be unstable, and the success of IPM systems in western orchards has been driven by conservation of natural enemies to control secondary pests, combined with pesticides and mating disruption to suppress the key lepidopteran pests. However, the legislatively mandated changes in pesticide use patterns prompted by the Food Quality Protection Act of 1996 have resulted in an increased instability of pest populations in orchards because of natural enemy destruction. The management system changes have made it necessary to focus efforts on enhancing biological control not only of secondary pests but also of primary lepidopteran pests to help augment new pesticides and mating disruption tactics. The new management programs envisioned will be information extensive as well as time sensitive and will require redesign of educational and outreach programs to be successful. The developing programs will continue to use the core principles of Stern and his co-authors, but go beyond them to incorporate changes in society, technology and information transfer, as needed.

Effects of mowing frequency on densities of natural enemies in three Pacific Northwest pear orchards

Effects of mowing frequency on ground cover composition and on numbers of predators, parasitoids, and select phytophagous arthropods in the ground cover of three reduced‐insecticide pear orchards were determined. Concurrent samples taken in the tree canopy (with beating trays) and in the herbicide strips on the orchard floor (with pitfall traps) tested whether counts of natural enemies in these two habitats were also affected by mowing regime. A reduction in frequency of mowing from two to three times per month (= control) to once per month or once per growing season led to increased cover of grasses, broadleaf plants, and broadleaf plants in flower. Sweep net samples of natural enemies in the ground cover were dominated numerically by spiders (Araneae), parasitic Hymenoptera, and predatory Heteroptera, with lesser numbers of other taxa (Syrphidae, Neuroptera, Coccinellidae). Predators and parasitoids showed substantial increases in numbers associated with decreased mowing frequency. Sweep net counts of aphids, Lygus spp. (Heteroptera: Miridae), and leafhoppers/planthoppers, all potential prey of predators, also increased significantly with decreased mowing frequency. In the pitfall samples, only the European earwig (Forficula auricularia L.) (Dermaptera: Forficulidae) exhibited a change in counts associated with mowing treatment; numbers of earwigs in pitfall traps declined as mowing frequency decreased. For the beat tray samples, mean tray counts for most natural enemy taxa were higher in the less frequently mowed plots, but significantly (P < 0.05) so only for two taxa: spiders and a predatory mirid, Deraeocoris brevis (Uhler) (Heteroptera: Miridae). It remains to be determined whether biological control of pests in the tree canopy can be enhanced by manipulating mowing frequency. Questions raised by this study include whether there is extensive movement by natural enemies between the ground cover and tree canopy, and whether plot size affects the likelihood of showing that mowing frequency influences predator densities in the tree canopy.

Identification of the Larval Aggregation Pheromone of Codling Moth, Cydia pomonella

Mature larvae of the codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae), exit the fruit and seek sites suitable for pupation. Spinning cocoons in such sites, larvae produce a complex, cocoon-derived blend of volatiles recently shown to attract and/or arrest both conspecific larvae and the prepupal parasitoid Mastrus ridibundus Gravenhorst (Hymenoptera: Ichneumonidae). Here we report components of this blend that constitute the pheromone of fifth-instar C. pomonella larvae. Thirty-one two-choice olfactometer experiments showed that a blend of synthetic (E)-2-octenal, (E)-2-nonenal, sulcatone, and geranylacetone, in combination with either 3-carene and/or three saturated aldehydes (octanal, nonanal, decanal), elicited behavioral responses from C. pomonella larvae. In on-tree experiments with corrugated cardboard bands as pupation sites for larvae affixed to tree trunks, and with laboratory-reared larvae released onto such trees, more larvae cocooned in those halves of cardboard bands baited with cocoon-spinning conspecific larvae, or with synthetic pheromone components, than in unbaited control halves of the bands. With the larval aggregation pheromone identified in this study, there might be an opportunity to manipulate C. pomonella larvae in commercial fruit or nut orchards.

DNA Diagnostics to Identify Internal Feeders (Lepidoptera: Tortricidae) of Pome Fruits of Quarantine Importance

A diagnostic polymerase chain reaction (PCR) method is presented for differentiating among the North American internal apple-feeding pests codling moth, Cydia pomonella (L.); oriental fruit moth, Grapholita molesta (Busck); lesser appleworm, Grapholita prunivora (Walsh); and cherry fruitworm, Grapholita packardi Zeller. An approximately 470-bp fragment of mitochondrial cytochrome oxidase subunit I (COI) was sequenced in three to six specimens of each species. Consistent and diagnostic differences were observed among the species in two regions of COI from which forward and reverse primers were designed to amplify a 112-116-bp segment of the gene. The primer sets were used to selectively amplify DNA from specimens of diverse geographic origin for each corresponding target species. Protocols were adapted for conventional and quantitative PCR, the latter being substantially faster. The method was validated as a decision-making tool for quarantine identifications for Mexico by representatives of their phytosanitary agency (Sanidad Vegetal). The method can facilitate identification of intercepted internal feeding Lepidoptera in apple and pear for many other importing nations.

CHAPTER 4 – Molecular Methods in Classical Biological Control

This chapter represents a primer on the nature of genetic variation and the major techniques—isozyme electrophoresis, mitochondrial and nuclear DNA restriction analysis and sequencing, and DNA fingerprinting—employed for measuring the variation in systematic and population studies. It describes how these methods may be used to address key systematic and population genetic questions in biological control. Gel electrophoresis and histochemical localization of enzymes, within the supporting gel matrix, comprise a powerful method for measuring genetic variation within and between animal populations. Multilocus minisatellite DNA fingerprinting is a specialized technique with limited but powerful applications in population biology. Minisatellites are tandemly arranged repeats of sequences, seven to several hundred base pairs in length. Multilocus DNA fingerprinting consists of fragmenting total genomic DNA with restriction enzyme(s), separating the cut DNA by electrophoresis, and identifying a subset of the thousands of bands with genomic probes. Microsatellites consist of moderately repeated tandem copies of simple sequence repeats, flanked by unique sequences. Primer sequences are determined from sequencing candidate microsatellites. Microsatellites are often highly polymorphic, with as many as 20 alleles segregating in natural populations.

Interactions of two idiobiont parasitoids (Hymenoptera: Ichneumonidae) of codling moth (Lepidoptera: Tortricidae) with the entomopathogenic nematode Steinernema carpocapsae (Rhabditida: Steinernematidae)

Simultaneous use of parasitoids and entomopathogenic nematodes for codling moth (CM) control could produce an antagonistic interaction between the two groups resulting in death of the parasitoid larvae. Two ectoparasitic ichneumonid species, Mastrus ridibundus and Liotryphon caudatus, imported for classical biological control of cocooned CM larvae were studied regarding their interactions with Steinernema carpocapsae. Exposure of M. ridibundus and L. caudatus developing larvae to infective juveniles (IJs) of S. carpocapsae (10 IJs/cm2; approximately LC(80-90) for CM larvae) within CM cocoons resulted in 70.7 and 85.2% mortality, respectively. However, diapausing full grown parasitoid larvae were almost completely protected from nematode penetration within their own tightly woven cocoons. M. ridibundus and L. caudatus females were able to detect and avoid ovipositing on nematode-infected cocooned CM moth larvae as early as 12h after treatment of the host with IJs. When given the choice between cardboard substrates containing untreated cocooned CM larvae and those treated with an approximate LC95 of S. carpocapsae IJs (25 IJs/cm2) 12, 24, or 48h earlier, ovipositing parasitoids demonstrated a significant preference for untreated larvae. The ability of these parasitoids to avoid nematode-treated larvae and to seek out and kill cocooned CM larvae that survive nematode treatments enhances the complementarity of entomopathogenic nematodes and M. ridibundus and L. caudatus.

Mastrus ridibundus parasitoids eavesdrop on cocoon-spinning codling moth, Cydia pomonella, larvae

Cocoon-spinning larvae of the codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae) employ a pheromone that attracts or arrests conspecifics seeking pupation sites. Such intraspecific communication signals are important cues for illicit receivers such as parasitoids to exploit. We tested the hypothesis that the prepupal C. pomonella parasitoid Mastrus ridibundus Gravenhorst (Hymenoptera: Ichneumonidae) exploits the larval aggregation pheromone to locate host prepupae. In laboratory olfactometer experiments, female M. ridibundus were attracted to 3-day-old cocoons containing C. pomonella larvae or prepupae. Older cocoons containing C. pomonella pupae, or larvae and prepupae excised from cocoons, were not attractive. In gas chromatographic-electroantennographic detection (GC-EAD) analyses of bioactive Porapak Q extract of cocoon-derived airborne semiochemicals, ten compounds elicited responses from female M. ridibundus antennae. Comparative GC-mass spectrometry of authentic standards and cocoon-volatiles determined that these compounds were 3-carene, myrcene, heptanal, octanal, nonanal, decanal, (E)-2-octenal, (E)-2-nonenal, sulcatone, and geranylacetone. A synthetic 11-component blend consisting of these ten EAD-active compounds plus EAD-inactive (+)-limonene (the most abundant cocoon-derived volatile) was as effective as Porapak Q cocoon extract in attracting both female M. ridibundus and C. pomonella larvae seeking pupation sites. Only three components could be deleted from the 11-component blend without diminishing its attractiveness to M. ridibundus, which underlines the complexity of information received and processed during foraging for hosts. Mastrus ridibundus obviously “eavesdrop” on the pheromonal communication signals of C. pomonella larvae that reliably indicate host presence.