Pear Psylla Research Articles

Reduction of Pear Psylla Damage by the Predatory Bug Anthocoris nemoralis (Heteroptera: Anthocoridae): The Importance of Orchard Colonization Time and Neighboring Vegetation

This 5-year field study was aimed at assessing the importance of predatory arthropods in suppressing pear psylla, Cacopsylla bidens (Sulc), and reducing damage caused by psylla in pear orchards in northern Israel. Correlative data suggest that Anthocoris nemoralis (Fabricius) is the only naturally occurring predator in the system that may reduce pear psylla damage; densities of other predacious taxa in the system (Araneidae, Orius spp., Chrysopidae and Coccinellidae) were not correlated significantly with psylla numbers in the orchards. However, A. nemoralis entered pear orchards at least a month after the beginning of pear psylla activity, apparently too late to prevent fruit damage. Data suggest that A. nemoralis reproduction is lower on both wild and cultivated pears than on Rhamnus, Laurus and Pistacia trees in nearby woods. Furthermore, A. nemoralis populations build up on the wild trees in March, but appear in orchards only in late May. We propose that planting R. alaternus trees near pear orchards could enhance the level of biological control of pear psylla by A. nemoralis. Preliminary results indeed show that pear psylla densities were lower on pear trees grown near Rhamnus alaternus trees than on distant trees.

Oviposition deterrency and deterrent stability of some oily substances against the pear psyllaCacopsylla pyri

Oviposition deterrents have the potential to prevent insect infestations in agroecosystems. In the present study, the level and duration of this behavioral effect was evaluated against pear psylla,Cacopsylla pyri (L.) (Hemiptera: Psyllidae), a serious pest of pears in Turkey. The activity of four oily substances — cotton seed oil, fish-liver oil, neem oil and summer oil — was tested against winterform and summerform females of the pest in laboratory and field experiments, in order to determine their oviposition deterrency and stability as deterrents. In the laboratory assays, the initial (3 days after treatments) deterrency of all test materials was 100%. While decreases in initial deterrency started after 1 week for neem oil and after 2 weeks for cotton seed oil, fish-liver oil and summer oil exhibited 100% deterrent activity against winterforms, but not summerforms during the 3-week test period. The last two also exhibited strong oviposition deterrent activity for both forms ofC. pyri females in field trials. A significant reduction in the total number of eggs laid was observed in the field plots. Data showed that summer oil and fish-liver oil are the most promising oviposition deterrents against pear psylla females.

The Role of Chemical Cues in Host and Mate Location in the Pear Psylla Cacopsylla bidens (Homoptera: Psyllidae)

Chemical communication was shown to play a role in the pear psylla, Cacopsylla bidens. Electrophysiological (EAG) and behavioral responses were investigated in males and females pear psylla . Males were found to be attracted to females, and especially to those on host plants, but not to males, uninfested host plants, or plants infested with conspecific larvae. On the other hand, females were not attracted to males or females but displayed some attraction to host plants. Furthermore, females showed a preference for uninfested pear versus plants infested with conspecific larvae. The antennae of males gave highest electroantenographic response to volatiles from pears infested with females but not males, while females, responded also toward the volatiles of pear alone. These results indicate that females of C. bidens emit sex pheromones that are attractive to the males and suggest that, host volatiles may play a role in host selection by pear psylla females.

Natural enemies of the pear psyllaCacopsylla pyri in treatedvs untreated pear orchards in Antalya, Turkey

Populations of pear psylla,Cacopsylla pyri (L.) (Rhynchota: Psyllidae), and its natural enemies were sampled on pears in Antalya province during the years 2000–2002. Thirty-two species of predators and three species of parasitoids were detected to be associated withC. pyri in Antalya province. The heteropterans (especially anthocorid species) were the most abundant predator group. Among the anthocorids,Anthocoris nemoralis (Fabricius) (Heteroptera: Anthocoridae), whose population was closely related to the dynamics of the pear psylla population, was generally the principal antagonist ofC. pyri. Other species recorded during the study were the miridDeraeocoris spp., the chrysopidChrysoperla carnea L., and many coccinellid species. Although these predators are polyphagous, as are theOrius species, their populations were related to the psylla fluctuations. Among the parasitoid complex belonging to the order Hymenoptera, the encyrtidTrechnites psyllae (Ruschka) was the only primary parasitoid. Two hyperparasites,viz., Syrphophagus mamitus (Walker) andPachyneuron aphidis (Bouche) (Encyrtidae and Pteromalidae, respectively), were detected in the surveys. Also, this study revealed new information concerning the pear psylla parasitoid complex in Turkey. WhileT. psyllae andS. mamitus are new records to Turkish parasitoid fauna,C. pyri is a new host record forP. aphidis. The population development and abundance of pear psylla and its natural enemies, as well as the parasitization rates in treated and untreated pear orchards, are presented here.

Detecting Cacopsylla pyricola (Hemiptera: Psyllidae) in predator guts using COI mitochondrial markers.

Cacopsylla pyricola (Förster) is one of the most important pests of pear in North America, where several native predators have been considered for integrated pest management (IPM) programmes. Two molecular markers of 271 and 188 bp were developed from C. pyricola cytochrome oxidase I (COI) fragments, in order to study the detection of this species in the gut of arthropod predators. Primer sensitivity and the detection period for pear psylla remains in the guts of Anthocoris tomentosus Pericart were determined. The sensitivity threshold was defined at 10-5 dilution of a C. pyricola fifth-instar nymph in all samples. Predator adults were evaluated immediately after ingestion of one to five C. pyricola nymphs (t = 0) and after 2, 4, 6, 8, 16, 24 and 32 h. Detection of the presence of C. pyricola DNA always lasted longer using the shorter fragment and was observed after 32 h of digestion using both markers. The primers amplifying the 188 bp fragment amplified all four psyllid species tested, whereas the primers designed to amplify the 271 bp fragment did so exclusively for C. pyricola and its close relative, Cacopsylla pyri (Linnaeus). Both primers failed to amplify DNA from representative species of the Coccinellidae, Chrysopidae, Hemerobiidae, Anthocoridae, Miridae, Salticidae, Aphididae, Tetranychidae and the Tortricidae, suggesting their suitability for general trophic studies.

Structure-function relationships affecting the insecticidal and miticidal activity of sugar esters.

Synthetic sugar esters are a relatively new class of insecticidal compounds that are produced by reacting sugars with fatty acids. The objective of this research was to determine how systematic alterations in sugar or fatty acid components of sugar ester compounds influenced their insecticidal properties. Sucrose octanoate, sorbitol octanoate, sorbitol decanoate, sorbitol caproate, xylitol octanoate, xylitol decanoate and xylitol dodecanoate were synthesized and evaluated against a range of arthropod pests. Dosage-mortality studies were conducted on pear psylla (Cacopsylla pyricola Foerster) on pear, tobacco aphid (Myzus nicotianae) Blackman and tobacco hornworm (Manduca sexta [Johannson]) on tobacco, and twospotted spider mite (Tetranychus urticae Koch) on apple in laboratory bioassays. These sugar esters were compared with insecticidal soap (M-Pede, Dow AgroSciences L.L.C., San Diego, CA), to determine how toxicologically similar these materials were against the arthropod pests. Substitutions in either the sugar or fatty acid component led to significant changes in the physical properties and insecticidal activity of these compounds. The sugar esters varied in their solubility in water and in emulsion stability, yet, droplet spread upon pear leaves occurred at low concentrations of 80-160 ppm and was strongly correlated with psylla mortalities (R2 = 0.73). Sequentially altering the sugar or fatty acid components from lower to higher numbers of carbon chains, or whether the sugar was a monosaccharide or disaccharide did not follow a predictable relationship to insecticidal activity. Intuitively, changing the hydrophile from sorbitol (C6) to xylitol (C5) would require a decrease in lipophile chain length to maintain hydrophilic-lipophilic balance (HLB) relationships, yet an increase in lipophile chain length was unexpectedly needed for increasing insecticidal activity. Thus, the HLB of these materials did not correlate with pear psylla mortalities. Initial insect bioassays and dosage-mortality data found significant differences among sugar ester compounds' toxicity to the range of arthropod species. Sucrose octanoate high in monoester content had the highest activity against the range of arthropod pests at low concentrations of 1200-2400 ppm. No single chemical structure for the xylitol or sorbitol esters were optimally effective against the range of arthropods we tested and sorbitol octanoate and xylitol decanoate had the highest insecticidal activity of this group. All of the sugar ester materials produced high T. urticae mortalities on apple at very low concentrations of 400 ppm. Overall, most of the sugar esters that were examined had superior insecticidal activity compared with insecticidal soap. Sugar ester chemistry offers a unique opportunity to design an insecticide or miticide specific to certain arthropod pests which would be valuable in crop integrated pest management (IPM) programs. Sucrose esters are currently used as additives in the food industry which makes them especially attractive as safe and effective insecticides.

Resistance of pear psylla (Cacopsylla pyri L.; Hom., Psyllidae) to deltamethrin and synergism with piperonyl butoxide

Abstract: Topical application bioassays, conducted on French populations of Cacopsylla pyri, showed resistance rates to deltamethrin ranging from 31‐fold at the adult stage to 135‐fold at the last larval stage. Synergism studies between deltamethrin and piperonyl butoxide (PBO), applied either topically or by tarsal contact with PBO, showed (i) that the rates of synergism were more than 10‐fold in all the populations and that they could increase to a thousand‐fold in some populations, (ii) that the synergistic effect was present to a similar extent at both the larval and adult stages, (iii) that there was no correlation between the synergistic effect and the resistance rates, and (iv) that no correlation was observed between the dates of collection and the rates of synergism. The results makes it impossible to determine whether resistance to deltamethrin is of genetic origin or results only from the induction of monooxygenases by allelochemical substances present in the food ingested by the species.

Cacopsylla pyri L. (Hom., Psyllidae) and its predators relationship in Italy's Emilia‐Romagna region

Abstract: Sampling techniques for Cacopsylla pyri adults and its predators (Anthocoris nemoralis, Coccinellidae spp. and Chrysopidae spp.) were comparatively studied over autumn–winter 2000 in three pear orchards of Ferrara Province in northern Italy's Emilia‐Romagna Region. Bating tray (or frappage), yellow sticky traps and corrugated cardboard traps were employed for insect monitoring while water pan traps were used for the phenological timing of leaf fall. The beating tray provided a more representative sampling method to evaluate the population dynamics and density of C. pyri and its predators than the yellow sticky traps; the corrugated cardboard proved a reliable tool to assess the predator population dynamic in overwintering refuges. Along with climate (temperature) and plant physiological (leaf fall) data, the results reported provide useful information for the scheduling of winter treatments, also in case to control the spread of the mycoplasma‐like organism (pear decline) in spring.

FACTORS INFLUENCING THE CHANGES IN POPULATION STATE OF PEAR SUCKERS (CACOPSYLLA SP.) IN POLAND

In a pear orchard in Central Poland, the occurrence of three species of pear psylla, Cacopsylla pyri, C. Pyrisuga, and C. Pyricola was ascertained between 1995 and 2000. C. pyri was the most numerous. A high reduction in numbers of this pest was observed in winter (80.6-97.5%) and due to the activity of beneficials (above 90%), mainly Anthocoris nemorum, Orius minutus, Chrysopa carnea, Forficula auricularia, Coccinellidae, Araneae and parasitoids. Applying insecticides fenitrothion, deltamethrin and alfa-cypermethrin caused a drastic increase of the numbers of C. pyri.

PEAR PRODUCTION AND UTILIZATION IN NORTH AMERICA

North America grows about 955,000 tonnes (t) of pears on about 34,000 ha. About 50% of pear production is Bartlett, of which 67% is processed and the rest sold fresh. 'Anjou' is the principal market cultivar with about 11.3 million 20 kg boxes, of which more than 35% is exported. 'Bosc' has about 3.4 million 20 kg boxes. 'Red Anjou', presently with 600,000 boxes, has the greatest planting increase. The three USA Pacific States have about 92% of North American production. Planting and production trends are downward in Canada, California, and Southern Oregon, flat in Mexico and Northern Oregon and slightly downward in the balance of USA except Washington State. Extensive pear plantings in Washington State a few years ago relate to a continued production increase. Storage diseases and maladies are major concerns along with orchard pest control, focused on pear psylla. A dwarfing precocious rootstock is highly desired. Pre-conditioning to reduce time from purchase to edibility is a major issue. Quarantine protocols for export and import are of concern as are fresh Southern Hemisphere imports beginning in late winter. Consolidation of wholesale buying power is ominous. Pears are suffering from lack of profitability in North America.

Frequency and Seasonal Distribution of Pear Psylla Infected with the Pear Decline Phytoplasma in California Pear Orchards

ABSTRACT Pear decline (PD) is an important disease of Pyrus communis fruiting cultivars in Europe, Asia, and the Americas. PD is caused by a phloem-limited phytoplasma that, in California, is transmitted from diseased to healthy trees by pear psylla, Cacopsylla pyricola. The percentage of phytoplasma-infected pear psylla has never been assessed in the United States in field-collected insects. Pear psylla were collected monthly from PD-infected trees from three orchards in northern California. Individual psylla were tested for the presence of PD phytoplasma, using both a quantitative DNA hybridization and PD phytoplasma-specific polymerase chain reaction (PCR) assays. The percentage of infected psylla ranged from 0 to 45% depending on the orchard, the month and year collected, and the method of detection. The PD phytoplasma was detected in both the winterform and summerform pear psylla. Significantly more infected psylla were detected with PCR than with DNA hybridization analysis in two of the three orchards. The number of PD phytoplasma per pear psylla was estimated to range from 1 x 10(6) to 8.2 x 10(7). The percentage of PD-infected pear psylla found in the three northern California pear orchards suggests that both winterform and summerform pear psylla could be important in the transmission of PD.

Natural variation in baseline data: when do we call a new sample 'resistant'?

Mortality of pear psylla to amitraz was studied by means of bioassays. Variation between samples, temporal variation within the season in one orchard and spatial variation between Swiss regions were considered. Variation between samples was large enough to produce different Probit functions and LC50 values. Temporal and spatial variations were too small to indicate resistance. Prediction intervals of the pooled functions using bootstrapping were calculated to determine if future samples come from a population with decreased sensitivity. Probabilistic criteria on the population level were proposed for resistance.

Pear transformed with a lytic peptide gene for disease control affects nontarget organism, pear psylla (Homoptera: Psyllidae).

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- (< or = 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.

Identification of Phytoplasma Taxa and Insect Vectors of Peach Yellow Leaf Roll Disease in California.

Two peach diseases in California, western X-disease (WX) and peach yellow leaf roll (PYLR) are caused by two genetically distinct phytoplasmas. Based on symptoms alone, WX and PYLR cannot be reliably distinguished. The objectives of this study were to determine which phytoplasma was causing PYLR disease in peach orchards planted near pear orchards and which phytoplasmas were present in potential insect vectors captured in both peach and pear orchards. Leafhoppers and pear psylla were collected from yellow sticky traps placed in three pear orchards and four peach orchards located in the Sacramento Valley from 1994 to 1996. DNA was extracted from potential vectors and suspect diseased trees, and analyzed for the presence of the WX and PYLR phytoplasmas using strain-specific DNA hybridization or polymerase chain reaction (PCR) assays. The most abundant phytoplasma detected in diseased peach trees was the PYLR phytoplasma. In 1994 and 1995, 10 to 25% of groups of pear psylla tested positive for the PYLR phytoplasma, while no psylla groups tested positive for the WX phytoplasma. Only one captured leafhopper tested positive for the WX phytoplasma. These results indicate the pear psylla is the primary vector of PYLR in northern California.

An extended laboratory method maximizing plant contact time to study the side‐effects of pesticides on plant‐dwelling predators

An extended laboratory method was developed to study the side‐effects of pesticides on plant‐dwelling, walking beneficial insects such as anthocorids, coccinellids and chrysopids. By using a glass funnel with a slippery surface, larvae of Anthocoris nemoralis, a natural enemy of pear psylla, stayed mainly on the treated plant surface and access to untreated surfaces was discouraged. The optimal ventilation produced a favourable environment and low mortality in the control. Tests with seven insecticides on the anthocorid larvae produced consistent toxicity results.

THE 'LIFE CYCLE' OF PEAR DECLINE PHYTOPLASMA IN THE VECTOR CACOPSYLLA PYRI

The ‘life cycle’ of pear decline phytoplasma in the vector Cacopsylla pyri has been studied. For two consecutive years, groups of insects caught monthly from March to October were used for transmission trials. The psylla was equally infective throughout the experimental period. In the second year, insects were fed on dormant plants from November to March and regularly tested. Retention of infectivity of the pear decline phytoplasma in the vector lasted through the winter. The overwintering adults of C. pyri did not transmit the phytoplasmas to plants in dormancy, but they did, without any previous recharge feeding, after bud break in the spring. Control of the overwintering adults of C. pyri appears to be of fundamental importance for preventing the spread of pear decline.

Genetic analysis of resistance to azinphosmethyl in the pear psylla Cacopsylla pyri

AbstractLaboratory selection with azinphosmethyl had little effect on the chemical resistance in Cacopsylla pyri strains, in comparison to the original wild populations. The resistance ratio relative to a susceptible strain varied from 10‐ to 40‐fold depending on the generation studied. Crosses between two resistant strains and the susceptible strain show resistance to be autosomally inherited and semi‐dominant in expression. Backcrosses between F1 and the susceptible strain were unable to distinguish unabigously between monogenic and polygenic inheritance. In the majority of experiments, however, the overall dose‐response relationship for backcross progeny was consistent with a single gene hypothesis. Additional bioassays showed azinphosmethyl‐resistant strain to cross‐resistant monocrotophos and phosmet, but not carbamates, pyrethroids, amitraz or the organophosphates chlorpyrifos and mevinphos.

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

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.

Biocontrol of Pests of Apples and Pears in Northern and Central Europe - 3. Predators

Predators of apple and pear pests in northern and central Europe and their use as biological control agents are reviewed. Many natural enemy species are specialized feeders and are able to respond to the population dynamics of particular pest species. The most oustandingly successful example of this is the use of phytoseiid mites, particularly Typhlodromus pyri , against phytophagous pest mites in apple. This mite management strategy is now widespread throughout European apple growing regions. Another example is the use of Anthocoris nemoralis against pear psyllids, Cacopsylla pyricola and C. pyri . Several groups of naturally occurring polyphagous predators, such as chrysopids, coccinellids, syrphids and spiders, also prey on a number of pest species in orchards, contributing generally to the reduction in pest populations. However, they are unlikely alone to prevent pest damage fully and reliably. In seeking biological control opportunities for a particular pest, these polyphagous natural enemies are unlikely to be a high priority. An exception, due to its abundance in orchards, is the common earwig, Forficula auricularia , although this predator may also cause some fruit injury. Another option to consider when reviewing possibilities for biological control in orchards is the introduction of biological control agents. The success rate of this approach, using arthropod predators to control pests of field crops, has been generally poor. Furthermore, mass production methods for predators are likely to be difficult and very costly. The biological supplies industry is constantly seeking culture techniques, largely for arthropod biological control agents of pests of protected crops. It is possible that some future advance may be relevant to orchards, though currently available predators do not appear promising. A careful economic appraisal of the feasibility of use of any potential biological control agent would be prudent before embarking on research.

EVALUATION OF ICE-NUCLEATING MICROORGANISMS FOR REDUCING THE SUPERCOOLING CAPACITY AND COLD-HARDINESS OF CACOPSYLLA PYRICOLA (HEMIPTERA: PSYLLIDAE)

AbstractIn laboratory studies, suspensions of killed and live ice-nucleating microorganisms were used to decrease the supercooling capacity of the winter form of pear psylla, Cacopsylla pyricola (Foerster) (Hemiptera: Psyllidae). Dry, untreated adults supercooled extensively before they froze at −22.7 °C. Application of 1000 ppm of a preparation of the killed ice-nucleating bacterium, Pseudomonas syringae Van Hall 1902 (Pseudomonadaceae), significantly decreased the adults’ supercooling capacity causing some individuals to freeze at temperatures as high as −3.9 °C. Topical application of several live microorganisms also reduced the supercooling capacity of adults significantly; Pseudomonas putida (Trevisan 1989) was the most effective, causing more than 80% of C. pyricola adults to freeze at −15 °C or higher. Furthermore, the temperature of crystallization of adults treated with P. putida remained significantly higher than controls for at least lid post-treatment. Application of ice-nucleating microorganisms also reduced the capacity of adults to survive short-term exposure to high subzero temperatures comparable to a mild frost. Realization of this approach for biological control of pear psylla will require the development of methods for the delivery of microorganisms to overwintering adults under field conditions.