Search

The Russian wheat aphid (RWA, Diuraphis noxiaKurdjumov) is a global pest of wheat (Triticum aestivumL.) that became a significant problem to wheat and barley (Hordeum vulgareL.) in the United States soon after it was detected in 1986. Russian wheat aphid‐resistant wheat varieties expressing the Dn4gene were effective in managing the first biotype, RWA1, from 1995–2003 until a new biotype, RWA2, overcame this resistance in 2003. Currently, only three genes are useful in developing RWA2 resistance in wheat. A new gene, Dn10, was recently discovered that is resistant to RWA2. This study characterized the effects that RWA1 and RWA2 had on the damage (leaf chlorosis and leaf roll) and growth components (plant height and leaf number) of plants expressing RWA resistance genes Dn4, Dn7, Dn10, Dn2401, Dn626580, and Dn2414and the susceptible ‘Yuma’ 22 d after infestation. All plant genotypes that were RWA resistant expressed strong resistance to leaf chlorosis and leaf roll after RWA1 feeding. Results were similar for RWA2 except for the Dn4genotype, which was equally susceptible as Yuma. Plant height was reduced by 50% for susceptible Yuma and Dn626580by RWA1 and RWA2 feeding. Plant height and leaf reduction from RWA2 feeding on the susceptible Dn4genotype were also reduced by 50%, whereas Dn7, Dn10, and Dn2414reductions were <23%. Dn10exhibited strong resistance to RWA1 and RWA2 feeding damage comparable with Dn7and Dn2414and showed less reduction in plant height than Dn2401and Dn626580, which makes it a potentially valuable gene for wheat breeding programs.

Russian wheat aphid (Diuraphis noxiaKurdjumov [RWA]) is one of the most invasive and detrimental pests, and host plant resistance is the most efficient approach to manage RWA. Wheat (Triticum aestivumL.) accessions resistant to RWA biotype 1 (RWA1) and biotype 2 (RWA2) were previously identified by screening wheat accessions available at the USDA‐ARS National Small Grains Collection. However, RWA biotypic variation necessitates a continuous search for sources of resistance to new RWA biotypes. The objective of this study was to identify wheat accessions resistant to all major RWA biotypes in the United States. A set of 172 RWA‐resistant wheat accessions, mainly Iranian landraces, were evaluated for responses to five predominant U.S. biotypes—RWA1, RWA2, RWA3, RWA6, and RWA8—in controlled environments. Of these, 137 accessions showed homogeneous or heterogeneous resistance to at least one biotype, and 14 of them were resistant or highly resistant to all five biotypes. Another set of 19 accessions were resistant or highly resistant to two to four biotypes. These RWA‐resistant accessions are valuable sources for RWA resistance improvement, and further purification of some accessions and characterization of the underlying RWA resistance genes are imperative for their utilization in wheat breeding.

Russian wheat aphid [RWA, Diuraphis noxia(Mordvilko)] is a serious pest of wheat (Triticum aestivumL.) and barley (Hordeum vulgareL.) that causes heavy yield losses in many countries, and RWA biotype 2 (RWA2) is virulent to most RWA resistance genes. The objective of this study was to characterize a gene for resistance to RWA2 in Iranian landrace PI 682675, a single‐plant selection from PI 624151. F2:3and F3:4families derived from cross PI 682675 × Zhengyou 6 were used to map the resistance gene. PI 682675 carries a dominant resistance gene, Dn10, flanked by simple sequence repeat markers Xgwm437and Xwmc488on chromosome 7DL. Physical mapping indicated that Dn10resides in bin 7DL 0.1 to 0.77, whereas Dn2401and Dn626580that also confer resistance to RWA2 were physically mapped to 7DS. Allelism tests showed that Dn10was located ∼17.4 cM from Dn2401and 22.2 cM from Dn626580. Dn10is a new resistance gene that should be used widely in wheat breeding.

Experiments were performed over 3 years to examine the effect that particle film (PF) treatment had on fruit quality of several apple (Malus xdomestica) cultivars in Washington and West Virginia. In the first study, a highly reflective, white, hydrophilic particle-based kaolin mineral (Surround WP) was applied to 'Empire' apple in May and June, on a season-long basis, or not at all. Red fruit color was increased by both the PF treatments compared with no treatment in all years. In a second study, the PF material was applied, starting at petal fall, every week for 6 weeks and then every 2 weeks until harvest to 'Empire', 'Gala', and 'Fuji' trees in West Virginia and to 'Cameo', 'Fuji', and 'Gala' trees in Washington. In the latter study, cultivar response to season-long applications varied by year and location. 'Empire' consistently had improved red color with season-long applications of PF materials. 'Gala' had greater fruit weight and red color with PF application in 1 of 2 years in West Virginia but not in Washington. 'Fuji' had greater fruit weight and soluble solids content and 'Cameo' had greater soluble solids, higher starch indices, and greater red color in Washington with the PF application. In these studies, application of a PF never reduced the surface red color in apples. A taste panel did not identify quality differences in 'Empire' apples treated with PF vs. the control. Cultivar responses to PF applications were variable due to location and yearly environmental characteristics. While particle film technology has value for insect control and reducing sunburn, it has limited value to enhance fruit color due to the inconsistent response. [ABSTRACT FROM AUTHOR]

Adults of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed to kaolinite-based particle film dusts. When beetles were continuously exposed to the hydrophobic particle film M-96-018 at the rate of 0.1-0.5 mg/cm, all the T. castaneum at 0.1 mg/cm were dead after 3 days, but 40±13.8% of the exposed T. confusum were still alive after 7 days. At higher concentrations, all the T. castaneum were dead after 2 days, but 5-6 days of exposure were needed to kill all T. confusum . In a subsequent test, adults of both species were exposed for 8-72 h to 0.5 mg/cm of the particle film M-96-018, removed, then held without food for 1 week. No T. castaneum survived, while survival of the T. confusum ranged from 0 to 55±17.3%, depending on the exposure interval. In a test conducted at controlled conditions of 40%, 57% and 75% r.h. , 27°C, T. confusum were exposed for 8-72 h to the particle film M-96-018 and a hydrophilic particle film M-97-009 at the rate of 0.5 mg/cm, then removed and held either with or without wheat flour for 1 week. All the T. confusum exposed to the particle film M-97-009 usually survived, while survival of the T. confusum exposed to the particle film M-97-018 after the 1-week holding period increased with increasing relative humidity and with the presence of food. The particle film M-96-018 was effective against both the Tribolium species, and appears to have a potential for use in management programs to control beetles within storage facilities.

Abstract: This paper reviews the research on entomopathogenic fungi in orchard systems and presents research on a mycoinsecticidal approach to an important pest of pear, the pear psylla. The review identifies the host-pathogen relationships that have been examined to date, the microbial formulation and application strategies that have been used, and the results that were obtained. The mycoinsecticides used in the pear psylla research were based on conidia of Beauveria bassiana (ARSEF #2860) and Paecilomyces fumosoroseus (ARSEF #2658). These were formulated into sprayable solutions containing water, 0.1% or 0.5% Ultrafine Sunspray oil (paraffinic oil) in water, or 0.1% acrylic polymer (StressguardTM) in water. Final spray solutions that contained 6 × 106 conidiospores/ml were applied to psylla nymph infested trees at a rate of 5.39 × 1013 conidiospores/ha during the 1993--1995 seasons. In addition, two commercial formulations of B. bassiana, GHA from Mycotech and Naturalis L from Fermone Corp., were mixed in water at the same conidiospore application rates as the other fungal isolates. Single applications of the ARSEF fungal strain/formulation combinations produced psylla nymphal mortalities that ranged from 18.2--37.1%, but the results varied with formulation. Conidia formulated with acrylic polymers in water caused significantly higher mortalities several days earlier than either the water or water and oil combination in 1993. However, no significant differences among pathogen/formulation combinations occurred in 1994 or 1995. The performance of Naturalis L was comparable to the ARSEF fungal strain/formulation combinations with peak nymphal mortalities of 34.1%, while GHA produced a significantly lower peak mortality of only 10.8%. However, because of the low conidiospore concentrations in the Naturalis L formulation, final spray solutions contained nearly 25% of the oil-like carrier. Thus, psylla mortalities may not have been entirely attributed to mycosis. Based on the results from the ARSEF fungal formulations, a mycoinsecticidal approach to pear psylla management could be a useful component in an integrated pest management program for pear.

The genetic sources for host-plant resistance to the greenbug (Schizaphis graminum Rondani) in barley (Hordeum vulgare ssp. spontaneum) are limited in that only two single dominant genes Rsg1 and Rsg2 are available for the complex of greenbug biotypes. We evaluated four new barley lines from the Wild Barley Diversity Collection (WBDC) that previously showed potential for greenbug resistance. Three of those entries, WBDC 53, WBDC 117, WBDC 336, exhibited very dominant sources of resistance to older known biotypes B, C, E, F, H, I, and TX1, which also add to the host-plant differentials used to separate these greenbug biotypes. We also re-evaluated the earlier known set of greenbug biotypes that have been in culture for several years against the known host-plant differentials, and included seven newer greenbug isolates collected from Wyoming to the full complement of small grain differentials. This resulted in the discovery of five new greenbug biotypes, WY10 MC, WY81, WY10 B, WY12 MC, and WY86. Wyoming isolates WY4 A and WY4 B were identical in their phenotypic profile, and should be combined as a single unique greenbug biotype. These barley trials resulted in finding new sources of host-plant resistance, although more research needs to be conducted on what type of resistance was found, and how it can be used. We also document that the Wheatland, Wyoming area serves as a very conducive environment for the development of new greenbug biotypes.

Lygus hesperus Knight (Hemiptera: Miridae) is a key agricultural pest in the western United States. In a recent study, proteins from Pantoea ananatis and Serratia marcescens (Enterobacteriales: Enterobacteriaceae) were identified in diet that was stylet probed and fed on by L. hesperus adults. P. ananatis and S. marcescens are ubiquitous bacteria that infect a wide range of crops. The objective of our study was to determine whether L. hesperus transfer P. ananatis and S. marcescens to food substrates during stylet-probing activities. Sucrose (5%) was spread under parafilm and exposed to adult L. hesperus for 24 h. Diet similarly prepared but not exposed to insects was used for controls. MacConkey agar was inoculated with stylet-probed or control diets and incubated at 25°C. After 24 h, bacterial colonies were observed on agar that was inoculated with stylet-probed diet, but were not observed on agar inoculated with control diet. Isolated bacterial colonies were putatively identified as either Pantoea spp. or S. marcescens using the API 20e identification kit. These results indicate that L. hesperus is capable of vectoring P. ananatis and S. marcescens.

Three Diuraphis species, Diuraphis frequens (Walker), Diuraphis mexicana (McVicar Baker), and Diuraphis tritici (Gillette), were known to exist in the United States before the 1986 appearance of the Russian wheat aphid, Diuraphis noxia Kurdjumov. The Russian wheat aphid soon became a significant pest of wheat although other endemic Diuraphis species were known to infest wheat. Wheat and barley entries resistant and susceptible to Russian wheat aphid biotype 2 were evaluated against all four Diuraphis species to determine their host interrelationships. Leaf chlorosis, leaf roll, leaf number, plant height, and infestation levels were assessed 21 d after the plants were infested by aphids in a no-choice caged environment. D. mexicana was unable to survive on wheat by 21 d after infestation and effects on the plant damage variables were negligible. D. frequens survived at low levels on resistant and susceptible plant entries and had a low impact on plant damage and growth. Russian wheat aphid biotype 2 and D. tritici were damaged most wheat and barley lines except the Russian wheat aphid biotype 2-resistant wheat lines containing genes from Dn7, STARS 2414-11, and CI2401; and resistant barley containing genes from STARS 9577B and 9301B. Russian wheat aphid biotype 2 and D. tritici reduced the growth of resistant plants by 25–50% and susceptible entries by 65–75%. Reductions at this level are typical under no-choice studies but resistant cultivars do not have these reductions under field conditions. The Russian wheat aphid biotype 2 resistant wheat lines would be effective in managing both wheat pest species.

Lygus hesperus Knight (Hemiptera: Miridae) causes economic damage to a wide range of crops in the western United States. While stylet-probing, L. hesperus discharge saliva consisting of lytic enzymes that facilitate extraoral digestion of host tissues. L. hesperus saliva primarily consists of polygalacturonases, a-amylases, and proteases, but salivary constituents other than these enzymes have not been documented. Improved knowledge of L. hesperus salivary proteins could lead to a better understanding of Lygus-host interactions, and aid in the development of crops that are resistant or tolerant to injury caused by Lygus spp. The objective of our study was to use mass spectrometry to identify salivary proteins of L. hesperus adults. Multiple polygalacturonases and proteases were identified from diet that was stylet-probed and fed upon by L. hesperus. Laccase, alkyl hydroperoxide reductase-like protein, glucose dehydrogenase, and xanthine dehydrogenase were identified in stylet-probed diets by using mass spectrometry, and laccase activity was confirmed using a colorimetric assay. This is the first study to identify laccase, glucose dehydrogenase, and xanthine dehydrogenase from L. hesperus saliva; we propose these enzymes target plant-defense compounds. Nearly 100 proteins from the bacterial plant pathogen, Pantoea ananatis and nine proteins from Serratia spp. were identified in stylet-probed diets. These results suggest L. hesperus may vector these plant pathogens. Our study adds to the list of documented L. hesperus salivary proteins, and provides information that will be useful for the further study of L. hesperus saliva and Lygus-microbe interactions.

Aphid (Hemiptera: Aphididae) saliva, when injected into host plants during feeding, causes physiological changes in hosts that facilitate aphid feeding and cause injury to plants. Comparing salivary constituents among aphid species could help identify which salivary products are universally important for general aphid feeding processes, which products are involved with specific host associations, or which products elicit visible injury to hosts. We compared the salivary proteins from five aphid species, namely, Diuraphis noxia (Kurdjumov), D. tritici (Gillette), D. mexicana (Baker), Schizaphis graminum (Rondani), and Acyrthosiphon pisum (Harris). A 132-kDa protein band was detected from the saliva of all five species using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Alkaline phosphatase activity was detected from the saliva of all five species and may have a universal role in the feeding process of aphids. The Diuraphis species cause similar visible injury to grass hosts, and nine electrophoretic bands were unique to the saliva of these three species. S. graminum shares mutual hosts with the Diuraphis species, but visible injury to hosts caused by S. graminum feeding differs from that of Diuraphis feeding. Only two mutual electrophoretic bands were visualized in the saliva of Diuraphis and S. graminum. Ten unique products were detected from the saliva of A. pisum, which feeds on dicotyledonous hosts. Our comparisons of aphid salivary proteins revealed similarities among species which cause similar injury on mutual hosts, fewer similarities among species that cause different injury on mutual hosts, and little similarity among species which feed on unrelated hosts.

The Russian wheat aphid, Diuraphis noxia Kurdjumov, is an introduced species first identified in 1986 into the United States. It has since become a major pest of wheat, Triticum aestivum L., and other small grains in the western United States. Three other Diuraphis species, Diuraphis frequens (Walker), Diuraphis mexicana (McVicar Baker), and Diuraphis tritici (Gillette), were already endemic to the United States before the introduction of D. noxia. The objective of this study was to determine the occurrence and host associations of these four Diuraphis spp. in the Rocky Mountain region that borders the western Great Plains to better understand their distribution and ecological interactions. In addition, a key to these species with photographs of live or fresh preparations of specimens is presented to aid in their identification. D. noxia was the most widely distributed species in the study area spanning the Rocky Mountain areas of Wyoming, New Mexico, Utah, and Colorado. This species was most common in the cereal-producing areas of the Colorado Plateau ecoregion. D. frequens was found to be the predominant species in the Alpine/Aspen Mountain areas of the South Central Rockies and Colorado Rockies ecoregions. The other Diuraphis species were rarely encountered even though their plant hosts occurred in the ecoregions sampled. D. noxia shared common hosts and was found co-infesting grasses with other Diuraphis species. Therefore, the potential exists for D. noxia to impact the other native Diuraphis species.

The Russian wheat aphid, Diruaphis noxia (Kudjumov) (Hemiptera: Aphididae), is globally one of the most devastating pests of bread wheat, Tritium aestivum L., durum wheat, Triticum turgidum L., and barley, Hordeum vulgare L. Several sources of D. noxia resistance have been incorporated in commercial wheat and barley genotypes, but up to eight virulent biotypes, defined based on their ability to damage different wheat and barley genotypes, now occur across the western United States since the first appearance of D. noxia in North America in 1986. Critical to the study of D. noxia and other invasive species is an understanding of the number and origin of invasions that have occurred, as well as the rate or potential of postinvasion adaptation and geographic range expansion. The goal of this study was to determine whether D. noxia biotypes are by-products of a single invasion or multiple invasions into North America. We used the genome-wide technique of amplified fragment length polymorphisms, in combination with 22 collections of D. noxia from around the world, to assess this question, as well as patterns of genetic divergence. We found multiple lines of evidence that there have been at least two D. noxia invasions of different origin into North America, each resulting in subsequent postinvasion diversification that has since yielded multiple biotypes.

Salivary secretions play critical roles in aphid–host plant interactions and are responsible for damage associated with aphid feeding. The objectives of this study were to evaluate aspects of salivation and the salivary constituents of Diuraphis noxia (Hemiptera: Aphididae). Salivary proteins were isolated and compared from three aphid probed diets: pure water, 15% sucrose, or amino acids (100 mM serine, 100 mM methionine, 100 mM aspartic acid, and 15% sucrose). After 6 h, more aphids settled on sucrose diet compared with other diets, but there were no significant differences in the number of stylet sheaths produced per aphid after 24 h. There were differences in the amount of soluble salivary protein (watery saliva), with the greatest amount secreted in sucrose diet, followed by amino acid diet and pure water, respectively. Protein constituents secreted into sucrose and amino acid diets were compared using gel electrophoresis using standardized amounts of protein. More protein bands and bands of greater intensity were visualized from probed sucrose diet compared with probed amino acid diet, indicating qualitative differences. Phosphatase was putatively identified from D. noxia saliva from a major protein band using gel electrophoresis and mass spectrophotometry. Alkaline phosphatase activity was confirmed in sucrose diet using enzymatic assays but was not detected in aphid probed water or amino acid diets. Other peptides in sucrose diet weakly but significantly showed similarities to putative dehydrogenase and RNA helicase expressed sequence tags identified from other aphids. The implications of these findings in aphid salivation and plant–insect interactions are discussed.

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), is a serious wheat, Triticum aestivum L., and barley, Hordeum vulgare L., pest throughout the small grain-producing areas in the western United States. The virulency and classification of recently described Russian wheat aphid biotypes 1–7 (RWA1–7) were clarified using 24 plant differentials. These seven biotypes had been described previously using various methods and test environments; therefore, the purpose of this study was to test them all under uniform environmental conditions. RWA1 was the least virulent of the biotypes tested, with susceptible ratings observed in five plant differentials and intermediate ratings observed in four plant differentials. RWA4, RWA5, RWA6, and RWA7 had intermediate virulence. RWA4, RWA5, and RWA7 share similar responses, with susceptible responses in six plant differentials and intermediate responses in five plant differentials. Small differences within a few plant differentials separate RWA4, RWA5, and RWA7. RWA6 has susceptible responses with only four plant differentials, but 10 plant differentials had intermediate responses. RWA3 was highly virulent, with susceptible responses in 10 plant differentials and intermediate responses in five plant differentials. RWA2 was the most virulent strain tested with susceptible responses to 12 plant differentials and intermediate responses to five plant differentials. This study has demonstrated that RWA1–7 have different combinations of virulence to the plant differentials tested, thereby confirming previous Russian wheat aphid biotype designations.

Wheat, Triticum aestivum L., with Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) resistance based on the Dn4 gene has been important in managing Russian wheat aphid since 1994. Recently, five biotypes (RWA1–RWA5) of this aphid have been described based on their ability to differentially damage RWA resistance genes in wheat. RWA2, RWA4, and RWA5 are of great concern because they can kill wheat with Dn4 resistance. In 2005, 365 Russian wheat aphid clone colonies were made from collections taken from 98 fields of wheat or barley, Hordeum vulgare L., in Oklahoma, Texas, New Mexico, Colorado, Kansas, Nebraska, and Wyoming to determine their biotypic status. The biotype of each clone was determined through its ability to differentially damage two resistant and two susceptible wheat entries in two phases of screening. The first phase determined the damage responses of Russian wheat aphid wheat entries with resistance genes Dn4, Dn7, and susceptible ‘Custer’ to infestations by each clone to identify RWA1 to RWA4. The second phase used the responses of Custer and ‘Yuma’ wheat to identify RWA1 and RWA5. Only two biotypes, RWA1 and RWA2, were identified in this study. The biotype composition across all collection sites was 27.2% RWA1 and 72.8% RWA2. RWA biotype frequency by state indicated that RWA2 was the predominant biotype and composed 73–95% of the biotype complex in Texas, Oklahoma, Colorado, and Wyoming. Our study indicated that RWA2 is widely distributed and that it has rapidly dominated the biotype complex in wheat and barley within its primary range from Texas to Wyoming. Wheat with the Dn4 resistance gene will have little value in managing RWA in the United States, based on the predominance of RWA2.

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has been a major economic pest of small grains in the western United States since its introduction in 1986. Recently, a new Russian wheat aphid biotype was discovered in southeastern Colorado that damaged previously resistant wheat, Triticum aestivum L. Biotype development jeopardizes the durability of plant resistance, which has been a cornerstone for Russian wheat aphid management. Our objective was to assess the relative amount of biotypic diversity among Russian wheat aphid populations collected from cultivated wheat and barley, Hordeum vulgare L. We conducted field surveys from May through June 2002 and August 2003 from seven counties within Texas, Kansas, Nebraska, and Wyoming. Based upon a foliar chlorosis damage rating, three new Russian wheat aphid biotypes were identified, one of which was virulent to all characterized sources of Russian wheat aphid resistance. The future success of Russian wheat aphid resistance breeding programs will depend upon the continual monitoring of extant biotypic diversity and determination of the ecological and genetic factors underlying the development of Russian wheat aphid biotypes.

Particle films with different properties have been developed for arthropod pest control. Two basic film types are hydrophobic and hydrophilic films. The hydrophilic film formulations differ in the amount and kind of spreader-sticker that is incorporated into the kaolin particles. The effects of particle film type (hydrophobic versus hydrophilic) and formulation (Surround versus Surround WP) on the biology and behavior of pear psylla, Cacopsylla pyricola (Foerster), were investigated on pear in a series of laboratory studies. Scanning electron microscopy determined that the number of particles that attached to the front tibia of adult psylla differed by particle formulation but the particle sizes were fairly uniform and ranged from 3.6 to 4.5 μm in diameter. Adults had difficulty grasping particle film-treated leaves, and this effect was influenced by film type and leaf surface. Choice and no-choice tests indicated that adult settling and oviposition were very low, regardless of film type or formulation. Under no-choice conditions, adult mortality was low, in part, because the adults were able to feed through all 3% particle films, but at reduced rates. However, the mortality of adults sprayed with 3% particle film solutions ranged from 22.2 to 62.5% within 72 h after treatment, and mortalities differed most between the hydrophilic formulations. Nymphs born on particle film-treated foliage incurred high mortalities ranging from 58.9 to 82.0% by the time they reached the fifth instar and were affected most by particle film type. Nymphal development was not affected by particle film type or formulation. Egg fertility and nymphal hatch also were unaffected by particle films. These studies determined that there are a number of biological effects particle films have on pear psylla beyond the deterrence of adult settling and oviposition.

The sweetpotato whitefly, Bemisia tabaci (Gennadius), B biotype, presents a unique problem for vegetable growers by serving as a vector of plant viruses and by inducing physiological disorders of leaves and fruit. An action threshold of a single whitefly is necessary because of the threat of disease in many areas and growers rely heavily on a single class of insecticides (neonicotinoids) for whitefly control. Additional control methods are needed to manage this pest in commercial vegetables. Extracts of wild tobacco contain natural sugar esters that have previously been shown effective in controlling many soft-bodied insects. We developed a novel tomato leaf bioassay system to assess a synthetic sugar ester derivative, sucrose octanoate, for insecticidal activity against the eggs, nymphs, and adults of B tabaci. The LC50 values for sucrose octanoate against adults, second instars, and fourth instars of the whitefly were 880, 686, and 1,571 ppm, respectively. The LC50 against whitefly eggs was higher (11,446 ppm) but indicated that some egg mortality occurred at the recommended application rate of 0.8–1.2% (3,200–4,800 ppm [AI]). Toxicity of sugar esters to whitefly eggs has not been reported previously. The tomato leaf bioassay produced reliable and repeatable results for whitefly toxicity studies and predicted that effective nymph and adult whitefly control can be achieved with sucrose octanoate at application rates ≤1% (4,000 ppm [AI]). Field efficacy studies are warranted to determine whether this biorational pesticide has application in commercial tomato production.

We report the toxicological effects of a new biorational, synthetic sucrose octanoate (AVA Chemical Ventures L.L.C., Portsmouth, NH), on brown citrus aphid, Toxoptera citricida (Kirkaldy), nymphs and adults and to its native parasitoid Lysiphlebus testaceipes (Cresson). Sucrose octanoate topically applied was equally toxic to brown citrus aphid adults and nymphs with LC50 and LC90 values ranging from 356 to 514 and 1029 to 1420 ppm, respectively. Mortalities of both stages did not differ significantly over time during the 3–24-h sampling period. Dry residues of sucrose octanoate exhibited similar levels of toxicity to both nymphs and adults. Mortality ranged from 60 to 70% at 6,000 ppm 4 h after exposure. L. testaceipes was not harmed by treatments as high as 4,000 ppm of sucrose octanoate as long as the parasitoid had mummified before treatment. Based on these results, sucrose octanoate would be a useful biorational in citrus integrated pest management programs.

The biology and behavior of pear psylla, Cacopsylla pyricola Foerster, on a transgenic clone of ‘Bartlett’ pear, Pyrus communis L., containing a synthetic antimicrobial gene, D5C1, was compared with that of a nontransgenic parental clone to determine whether there were any nontarget effects. The gene construct also contained the marker gene nptII (aminoglycoside 3′-phosphotransferase II) that encodes for antibiotic resistance to identify transformed plants. The purpose of the original transformation was to enhance pear resistance to the bacterial disease fireblight caused by Erwinia amylovora (Burr.) Winslow et al. The biology and behavior of pear psylla on a transgenic clone were compared with a nontransgenic parental pear clone in short- (≤7-d) and long-term (32-d) studies. Short-term studies indicated pear psylla adults preferred to settle and oviposit, and nymphs fed more and developed slightly faster, on transgenic pear compared with nontransgenic pear. In contrast, a long-term study on psylla colony development showed considerably fewer eggs, nymphs, and adults were produced on transgenic pear. Although adults reared on transgenic pear did not have weight affected, females produced fewer eggs and nymphal hatch was significantly reduced on the transgenic pear clone. Our results suggest that pear psylla biology and behavior are initially enhanced on this transgenic pear clone. However, chronic exposure of psylla populations to transformed pear plants that express the nptII marker and lytic peptide genes had detrimental effects on pear psylla reproductive biology. Field studies would be required to determine the specific effects of each gene on pear psylla biology and behavior and whether these effects would be expressed under natural conditions. The four-fold reduction in psylla population levels that resulted on this disease resistant transgenic pear line would be an added benefit to a pear integrated pest management (IPM) program. Overall, this study demonstrates that genetically altering plants to control one particular organism can have unintentional yet beneficial effects against other nontarget pest organisms in agricultural crops.

The biology and behavior of pear psylla, Cacopsylla pyricola Foerster, on a transgenic clone of ‘Bartlett’ pear, Pyrus communis L., containing a synthetic antimicrobial gene, D5C1, was compared with that of a nontransgenic parental clone to determine whether there were any nontarget effects. The gene construct also contained the marker gene nptII (aminoglycoside 3'-phosphotransferase II) that encodes for antibiotic resistance to identify transformed plants. The purpose of the original transformation was to enhance pear resistance to the bacterial disease fireblight caused by Erwinia amylovora (Burr.) Winslow et al. The biology and behavior of pear psylla on a transgenic clone were compared with a nontransgenic parental pear clone in short- (=7-d) and long-term (32-d) studies. Short-term studies indicated pear psylla adults preferred to settle and oviposit, and nymphs fed more and developed slightly faster, on transgenic pear compared with nontransgenic pear. In contrast, a long-term study on psylla colony development showed considerably fewer eggs, nymphs, and adults were produced on transgenic pear. Although adults reared on transgenic pear did not have weight affected, females produced fewer eggs and nymphal hatch was significantly reduced on the transgenic pear clone. Our results suggest that pear psylla biology and behavior are initially enhanced on this transgenic pear clone. However, chronic exposure of psylla populations to transformed pear plants that express the nptII marker and lytic peptide genes had detrimental effects on pear psylla reproductive biology. Field studies would be required to determine the specific effects of each gene on pear psylla biology and behavior and whether these effects would be expressed under natural conditions. The four-fold reduction in psylla population levels that resulted on this disease resistant transgenic pear line would be an added benefit to a pear integrated pest management (IPM) program. Overall, this study demonstrates that genetically altering plants to control one particular organism can have unintentional yet beneficial effects against other nontarget pest organisms in agricultural crops.

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.

Greenbug, Schizaphis graminum (Rondani), biotypes C, E, and F were inbred, crossbred, and backcrossed with recessive testers under laboratory conditions to determine the inheritance of virulence to resistance in sorghum (Sorghum bicolor [L.] Moench). Each progeny was reared to adult and cloned during its parthenogenesis reproductive phase. Clones were. evaluated on three sorghum entries with greenbug resistance acquired from different germplasm sources. Greenbug virulence to biotype F-resistant 'Piper' was dominantly inherited and governed by a duplicate-dominant gene that was influenced by a third modifier gene. The modifier gene was epistatic to one of the duplicate genes when dominant. Virulence to biotype C- and E-resistant 'Pioneer 8493' with resistance from PI 264453 was also controlled by a duplicate dominant gene-modifier gene, but green bug virulence was recessive. The modifier gene Was also epistatic to one of the duplicate genes when dominant. In contrast, greenbug virulence to biotype C-resistant 'Pioneer 8515' with resistance from SA 7536-1 was recessive and simply inherited. No linkage occurred between the genes governing virulence to these resistant sorghum entries, regardless of biotype. The genes influencing virulence to a particular resistant sorghum, were found to be allelic among the biotypes. Specific greenbug virulence-sorghum resistance interactions followed a gene-for-gene relationship similar to those first reported in plant-pathogen interactions. Our results provide further evidence that genetic recombination during the green bug's sexual cycle can produce the biotypic variation inherent to this aphid.

Insecticidal activity of a sugar ester fraction isolated from leaf trichomes of wild tobacco, Nicotiana gossei Domin, to egg, nymph, and adult stages of pear psylla, Cacopsylla pyricola Foerster, was determined in replicated laboratory bioassays. Aqueous solutions of sugar ester concentrations ranging from 62 to 1,000 ppm (mg/liter) were applied by an ultra-low-volume spray device to petri dishes containing eggs, nymphs, or adults. Data were recorded on nymphal mortality rates 1, 3, 5, and 7 d after treatment, on the percentage of eggs hatched 7 d after treatment, on the mortality rates of eclosed nymphs 3 dafter eclosion (10 d after treatment), and on adult mortality rates 1 d after treatment. Mortality rates did not differ significantly for sugar ester concentrations of 500 and 1,000 ppm, which both produced a mortality rate of ≥94% for nymphs and adults 1 d after treatment. Lethal concentration values for sugar esters to pear psylla nymphs and adults differed significantly 1 d after treatment for the LC50 (90 versus 200 ppm, respectively), but not for the LC90 (300 versus 400 ppm, respectively). Nymphal mortality rates for each sugar ester concentration did not increase over time significantly 1 d after application, which suggests that the sugar ester is a contact insecticide that is active mainly in the liquid state. The percentage of eggs hatched was not affected by any of the sugar ester treatments 7 d after application. In contrast, the mortality rates of newly eclosed nymphs ranged from 18.7 to 67% for sugar ester concentrations of 62- 1,000 ppm. Our data suggest that both nymphs and adults would be equally controlled with sugar ester concentrations high enough to obtain a mortality rate of >90%. These results will be useful in determining the range of sugar ester concentrations for field trials. In addition, an inexpensive ultra-low-volume spray device used in the bioassays is described that is capable of applying microliter amounts of candidate insecticidal materials to target insects.