Psylla Populations Research Articles

The importance of assessing the population structure and biology of psylla species for pest monitoring and management in pear orchards

The species of pear sucker, also called pear psylla or pear psyllid, which are destructive insects belonging to the genus Cacopsylla (Hemiptera: Psyllidae) cause substantial damage to pear tree plantations. Two consecutive years of research were conducted on the population structure and biological cycle of psylla in a small, elderly, and unmaintained pear orchard in northern Romania. Of the two identified species (C. pyri L. and C. pyricola Forster), C. pyri dominated the psylla population with a percentage of 77.8-80.1%. Adults of both species emerge from hibernation in the first part of March and produce three generations per year. First-generation adults emerge in the first decade of June, the second generation in the last decade of July, and the third generation in the first decade of September as they enter the hibernation phase. Larvae of the first generation appear in the second half of April, the second generation at the end of June - the beginning of July, and the third generation in the second decade of August. There have been reports of up to 11 adults and 27 larvae per leaf, 9 larvae per petiole, and 14 larvae per fruit. The number of adults captured on yellow sticky traps exposed on the southern side of the tree crown was significantly higher compared to the northern side. Following the intense attack, the well-known cv. ‘Williams’ was heavily affected, pear trees were badly defoliated, blackened, and aged prematurely. The climatic conditions of the two years did not influence the phenology of the pests, but the importance of monitoring psyllids is widely argued, considering that it remains the key to integrated protection programs in pear orchards.

Integrated Pest Management Programs for Pear Psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae), Using Kaolin Clay and Reflective Plastic Mulch.

Pear psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae), is the most economically important pest of pears grown in Washington State. Standard conventional management programs involve season-long broad-spectrum insecticide sprays. Although the industry uses some tools that are not disruptive to biological control, such as kaolin clay and selective insecticides, they are additions to broad-spectrum insecticides instead of replacements. Conventional sprays suppress pear psylla through the spring and early summer; however, disruption of biological control leads to pear psylla outbreaks near harvest. In 2018 and 2019, we tested two season-long programs that used only selective approaches. The programs began with either kaolin clay or reflective plastic mulch and were followed by identical spray programs using only selective insecticides. Programs were compared with an industry standard conventional program that used numerous broad-spectrum insecticides throughout the season, and a check program with no insecticides for pear psylla. Experiments were conducted using replicated 40-tree plots in a research orchard near Wenatchee, WA with high pear psylla pressure. In both years, selective programs had similar pear psylla densities to the industry standard program and all had lower pear psylla densities and fruit injury than the check. Both selective programs had lower fruit injury than the industry standard in the first year, and similar injury to the industry standard in the second year. Our results suggest kaolin clay and reflective mulch can effectively suppress pear psylla populations and injury in the early season and support season-long selective management programs without the use of broad-spectrum insecticides.

Energetic costs of resistance in the Agonoscena pistaciae Burckhardt & Lauterer, 1989 (Hemiptera: Aphalaridae), against spirotetramat, acetamiprid and hexaflumuron

Abstract: The common pistachio psylla, Agonoscena pistaciae Burckhardt & Lauterer, 1989 (Hemiptera: Aphalaridae), is a key pest found in pistachio orchards in Iran. This pest has a high potential for developing resistance to insecticides due to its short life cycle and high reproductive potential. Intensive application of insecticides leads to excessive selection pressure followed by resistance to synthetic insecticides in some psylla populations. In this research, effects of four concentrations of three extensively used insecticides (spirotetramat, acetamiprid, and hexaflumuron) on energy resources (like sugar, lipid, glycogen, and protein contents), energy consumption, and cellular energy allocation were investigated in resistant and susceptible populations of the common pistachio psylla in the Kerman province of Iran. Energy resource contents in the susceptible population (133 331.2 mj/insect) were significantly more than in the resistant population (96 253.5 mj/insect), whereas energy consumption in the resistant population (38 630.4 mj energy/h/insect) was higher than in the susceptible population (31 276.8 mj energy/h/insect). Additionally, cellular energy allocation in the resistant population (2 400.9 mj energy/h/insect) was higher than in the susceptible population (2 126.13 mj energy/h/insect). Therefore, stress (especially toxicants) causes variations in metabolism, which influences the growth and reproduction of the pest.

Variation in Insecticidal Susceptibility of Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Aphalaridae), and its Coccinellid Predator, Oenopia conglobata L. (Coleoptera: Coccinellidae)

The common pistachio psylla, Agonoscena pistaciae Burckhardt and Lauterer is a key pest throughout all pistachio producing regions of Iran. Pest management depends primarily on the application of chemical insecticides. The lack of compatibility between natural enemies and pesticides is the main concern to ecologists in the integrated management of psylla. The susceptibility of the fifth instar nymphs of A. pistaciae from five populations of the Kerman province and third instar larvae of the lady beetle species, Oenopia conglobata L., were examined against three commonly used insecticides: acetamiprid, spirotetramat and hexaflumuron, using the spraying tower method. Probit regression analysis was conducted on mortality data at various insecticide concentrations using the POLO-PLUS program to estimate LC50 values. Resistance ratio data revealed that usage of pesticides has led to resistance in the psylla population of Rafsanjan. The results showed that the Rafsanjan psylla population (with LC50 values of 40.55, 43.65 and 95.10 mg a.i. L-1, for acetamiprid, spirotetramat and hexaflumuron, respectively) was the most resistant and the Anar population (with LC50 values of 11.92, 24.13 and 81.06 mg a.i. L-1 for acetamiprid, spirotetramat and hexaflumuron, respectively) was the most susceptible based on the LC50 ratios of insecticides. The LC50 values of acetamiprid, spirotetramat and hexaflumuron for the coccinellid predator O. conglobata in the Rafsanjan population were estimated to be 8.76, 5218.33 and 2268.81 mg a.i. L-1, respectively. The predator was more susceptible to acetamiprid and more tolerant to spirotetramat and hexaflumuron than the psylla A. pistaciae.

Stability of Cacopsylla pyricola (Hemiptera: Psyllidae) Populations in Pacific Northwest Pear Orchards Managed with Long-Term Mating Disruption for Cydia pomonella (Lepidoptera: Tortricidae).

This study focused on conservation biological control of pear psylla, Cacopsylla pyricola, in the Pacific Northwest, USA. We hypothesized that insecticides applied against the primary insect pest, codling moth Cydia pomonella, negatively impact natural enemies of pear psylla, thus causing outbreaks of this secondary pest. Hence, the objective of this study was to understand how codling moth management influences the abundance of pear psylla and its natural enemy complex in pear orchards managed under long-term codling moth mating disruption programs. We conducted this study within a pear orchard that had previously been under seasonal mating disruption for codling moth for eight years. We replicated two treatments, “natural enemy disrupt” (application of two combination sprays of spinetoram plus chlorantraniliprole timed against first-generation codling moth) and “natural enemy non-disrupt” four times in the orchard. Field sampling of psylla and natural enemies (i.e., lacewings, coccinellids, spiders, Campylomma verbasci, syrphid flies, earwigs) revealed that pear psylla populations remained well below treatment thresholds all season despite the reduced abundance of key pear psylla natural enemies in the natural enemy disrupt plots compared with the non-disrupt treatment. We speculate that pear psylla are difficult to disrupt when pear orchards are under long-term codling moth disruption.

SEASONAL FLUCTUATION OF ASIAN CITRUS PSYLLA POPULATIONS IN THE CITRUS ORCHARDS INFECTED WITH HUANGLONGBING IN SARGODHA, PAKISTAN

A study on seasonal fluctuation in Citrus psylla (Diaphorina citri) (CP) population in citrus orchards infected with Huanglongbing was carried out in relation to environmental factors in six tehsils of Sargodha district. The population of citrus psylla was reached to the peak twice in a year. Young flushes favored the build-up in psylla population. Minimum temperature and rainfall had highly significant correlation with build-up in population of citrus psylla in all the six tehsils of Sargodha. Although, high temperature also favored the high population of citrus psylla in two tehsils. August and mid-March to April were the two times when population of citrus psylla reached to the peak. Therefore, an integrated management strategy can be formulated with this study that will not only help in reducing the HLB incidence but also increase in citrus production.

Biological control in winter: novel evidence for the importance of generalist predators

Summary The role of generalist predators in pest control has been neglected because generalists are not able to track pest populations. Generalist predators are suggested to be important in spring before specialist predators become active. Here, we show that some generalist predators are important even during winter, when the majority of arthropod pests and their enemies are dormant. We quantified the role of winter‐active generalist predators on the suppression of pear psylla during winter using a discrete nonlinear model of an intraguild predation system. To parameterize our model, we conducted a series of experiments on (i) functional responses, (ii) prey preferences and (iii) ontogenetic development and made observations on the population densities of spiders and potential prey. We ran the model for different winter scenarios, that is, for very cold and very warm winters. Synthesis and applications. We found that winter‐active predators considerably suppressed the pear psylla population. Predators exerted a stronger effect in a warmer winter than in a colder one. Orchard growers thus should avoid use of non‐selective pesticides during this period and instead aim to support the community of generalist predators. Our results suggest more attention should be given to encouraging generalist predator populations in other systems, even in periods when crops are not producing.

Geographic homogeneity and high gene flow of the pear psylla, Cacopsylla pyricola (Hemiptera: Psyllidae), detected by mitochondrial COI gene and nuclear ribosomal internal transcribed spacer 2

The pear psylla, Cacopsylla pyricola (Hemiptera: Psyllidae), is a serious insect pest of commercial pear crops. The species, which resides on pear trees throughout its life cycle, is rapidly spreading in some regions of the world. The population genetic structure of the species collected from several pear orchards in Korea was studied to understand the nature of dispersal and field ecology of the species. The 658-bp region of mitochondrial COI gene and the 716-bp long complete internal transcribed spacer 2 (ITS2) of the nuclear ribosomal DNA were sequenced. Unlike other previously studied insect pests, the COI-based genetic diversity of the pear psylla was extremely low (maximum sequence divergence of 0.15%). This finding allowed us to conclude that the species may have been introduced in Korea relatively recently. ITS2 sequence-based analyses of phylogeny, population differentiation, gene flow, and hierarchical population structure all concordantly suggested that the pear psylla populations in Korea are neither genetically isolated nor hampered for gene flow. These genetic data are concordant with the dispersal of an overwintering winterform morph outside the non-pear habitat in the fall.

Effect of host plant makeup through nitrogen fertilization and growth regulators on the pear psylla population

The pear psylla, Cacopsylla bidens (Sulc), is one of the most damaging pests of commercial pear orchards in Israel. However, growers today have only two pesticides left to control the pear psylla, therefore alternative control methods are needed. Our goal was to find ways to control the psylla population through rational use of cultural control methods: manipulating the levels of nitrogen fertilization, and using growth regulators. Our objectives were to determine the impact of nitrogen fertilization level on pear psylla populations, the impact of application of plant growth regulators (clormequat chloride and prohexadion-calcium) on psylla populations, and whether there is an interaction between the two factors in a semi-field-scale and in field-scale experiments. Higher oviposition and nymph development rates were found in trees that had higher leaf-nitrogen contents. Lower oviposition, nymph survival, and nymph development rates were found in trees that were treated with growth regulators. The suppress...

Relative attractiveness of colour traps to pear psylla in relation to seasonal changes in pear phenology

AbstractMonitoring of pear psylla (Cacopsylla pyricola (Förster), Hemiptera: Psyllidae) prior to spring bud break could aid in predicting the size of subsequent spring populations and lead to improved proactive management decisions. Yellow traps are commonly used to monitor hemipteran pests including pear psylla, but very little is known regarding seasonal changes in attractiveness of yellow traps or relative attractiveness of colours other than yellow. This study presents seasonal colour-trap preferences of pear psyllas based on pear (Pyrus communis L., Rosaceae) phenological stages in the mid-Atlantic region of the United States of America. Black, blue, brown, clear (colourless), green, orange, red, white, and yellow traps were assayed against wild adult psylla populations over a 2-year period. Pear psyllas had a strong preference for yellow and orange when green leaves were present; however, we found no statistically significant difference between traps of different colours prior to spring bud break. Significantly more female psyllas were caught overall, but there was no gender-based colour bias. None of our colour traps caught significantly fewer psyllas than did clear (background hue) traps, suggesting that no traps were repellent.

Bottom-up and top-down control of pear psylla ( Cacopsylla pyricola): Fertilization, plant quality, and the efficacy of the predator Anthocoris nemoralis

Herbivore population dynamics are governed both by bottom-up (plant-mediated) and by top-down (natural enemy-mediated) processes, with the potential for interaction between them. Pear psylla ( Cacopsylla pyricola Foërster) is a phytophagous pest in pear orchards. Pear psylla is commonly attacked by several different natural enemies, but it may escape control, especially if fertilizer additions and new shoot production are not carefully managed. We tested the hypothesis that plant quality mediates the efficacy of an important natural enemy of pear psylla, Anthocoris nemoralis. One year-old caged Bartlett pear trees were fertilized at either low (5 mM N) or high (20 mM N) levels of nitrogen, then either psylla or psylla and Anthocoris were added to each tree. We measured plant growth, psylla population size, and Anthocoris establishment to determine effects of fertilizer and predation on psylla population dynamics. Trees receiving more N were taller, had longer total branches, a greater total number of leaves, and higher leaf nitrogen content. Psylla populations were also larger in the high N treatment. Anthocoris establishment and reproduction was positively related to the density of psylla at the time predators were added. And although psylla densities were, over-all, lower on trees where Anthocoris was present, the level to which Anthocoris suppressed psylla was not significantly affected by fertilizer level. These results indicate that the efficacy of this predator is not strongly mediated by plant quality, at least at the local (i.e. tree) scale. Minimizing fertilizer additions to the minimum level required for proper fruit set is likely to be an important feature of successful pear psylla biocontrol programs.

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.

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.

Genetic structure and dispersal of pear psylla (Cacopsylla pyri L.) populations

The electrophoretic analysis of eight polymorphic enzyme loci in one Italian and 14 French psylla populations showed no significant differences between the genotype frequencies and the Hardy-Weinberg equilibrium. Gene differentiation was low (Fst = 0.0111) and gene flow was high (Nm = 22.3). Populations from western France presented higher gene differentiation than those from eastern France. Separately studying two genes coding for esterases revealed a high level of structuring. Each locus was independent and characterized by a null allele and an expressed allele with the same mobility. The geographical distribution of each locus and the existence of confluence zones suggest that the exchanges between sub-populations preferentially occur via the north and the south of the Massif Central. The possible involvement of esterase genes in resistance to insecticides is discussed in relation with their known role of detoxification.

Intraspecific Variation in Pear Psylla (Psyllidae: Homoptera) Nymphal Survival and Development on Resistant and Susceptible Pear

Five pear psylla, Cacopsylla pyricola Foerster, isolates from geographically distinct regions of the United States were examined on 6 pear cultivars to determine the extent of intraspecific variation in certain biological parameters, and if host resistance-breaking isolates existed. Newborn nymphs from isolates originating from Michigan, New York, Oregon, Washington, and West Virginia were transferred onto susceptible 'Bartlett' and resistant 'Krupen Burnusus', NY10352, 'Obican Vedenac', 'Mednik', and 'Zelinka' pear. Adult body weights, nymphal survival, and the age structure of the psylla populations were recorded over a 29-d period on each cultivar. Survival and age structure were significantly influenced by cultivar. Lack of significant differences among psylla isolates, and in the strain-by-cultivar interaction suggested that there were no host-dependent differences in survival or development. All of the resistant cultivars, except Obican Vodenac, exhibited moderate to high levels of antibiosis. Obican Vodenac was previously considered resistant, but it was found to be as susceptible as Bartlett to the psylla isolates. The age structures of the psylla isolates were composed mainly of earlier instars on resistant cultivars, although some individuals developed normally to adult-hood as if they were on a susceptible host. The vigorous and healthy condition of some adults that were reared from resistant cultivars implies that pear psylla may have the potential to adapt significantly to host resistance. A population age structure index was developed to characterize the degree of antibiosis in pear cultivars. The index significantly correlated with nymphal survival, indicating that these parameters are related. The formula for calculating population age structure index is presented in detail.

Ovipositional Preference of Pear Psylla (Homoptera: Psyllidae) for Resistant and Susceptible Pear

Ovipositional preference of pear psylla, Cacopsylla pyricola Foerster, for selected Pyrus genotypes known to differ in nymphal feeding antixenosis was quantified in the field and greenhouse during the dormant-bud, green-tip, and fully expanded-leaf stages of bud phenology. Definite ovipositional preferences were displayed by pear psylla. Ovipositional antixenosis was particularly evident in Pyres communis L. and P. communis L. × P. ussuriensis Maxim. hybrids that were also known to have nymphal feeding antixenosis during the fully expanded-leaf stage. Although ovipositional and nymphal feeding antixenosis did show significant correlation, there were exceptions that suggest these two pear traits are independent. In greenhouse and field studies, we found that ovipositional antixenosis varied with bud phenology within pear genotypes, which indicated that ovipositional cues differed. However, several P. communis and P. communis × P. ussuriensis genotypes exhibited ovipositional antixenosis during all stages of bud phenology. Results of greenhouse ovipositional studies were similar to those observed for these pear genotypes in the field. Our greenhouse technique offers a rapid means of evaluating ovipositional antixenosis in pear genotypes compared with field studies, which are hampered by variable pear psylla populations, time, and space requirements.

Side effects of diflubenzuron on a pear psylla predator:Forficula auricularia

A series of laboratory, semi-field and field tests showed the high toxicity of diflubenzuron toForficula auricularia L. nymphs, at concentrations of 15 and 20 g a.i./hl registered in various European countries and the United States to controlCydia pomonella L. Diflubenzuron proved more selective using the 10 g/hl concentration registered in France, but several sublethal effects have been observed: morphological abnormalities, reduced weight increase and mobility. Unexpectedly for a chitin-deposit inhibitor, intake was reduced, which became apparent from the beginning of exposure to the insecticide, before the onset of the moulting process. In the semi-field tests, and despite diflubenzuron's slowing down effect on psylla nymphs, the earwig's reduced predatory activity due to the product resulted in greater growth of the psylla populations than without treatment. The field-test confirmed the efficacy ofF. auricularia as a psylla predator, and the relative selectivity of diflubenzuron at the lowest concentration.

Interactions between citrus psylla,Trioza erytreae (Hem. Triozidae), and spiders in an unsprayed citrus orchard in the transvaal lowveld

During a two year survey, a total of 3,054 spiders represented by 21 families were sampled in an unsprayed citrus orchard in the Transvaal Lowveld. Numerically the Salticidae was the dominant family (34.4%) followed by the Theridiidae (21.9%), Thomisidae (11.9%), Araneidae (7.9%), Clubionidae (7.0%) and the Tetragnathidae (3.7%). Eighteen species of spiders were observed to prey on citrus psylla,Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), while six species trap nymphs and adults under their retreats and webs. There were significant positive correlations between the weekly psylla populations and the weekly populations of web-building spiders and wandering spiders present one to four weeks later but no significant correlation between the weekly spider populations and the weekly psylla populations present one to five weeks later. This seems to indicate that while spiders are unable to keep citrus psylla populations at acceptable low levels, they may contribute in reducing their numbers.

Evaluating the Effectiveness of Ants as Biological Control Agents of Pear Phyla (Homoptera: Psyllidae)

Ant exclusion barriers were constructed in two Chelan County, Wash., pear orchards to prevent ants from foraging in pear tree canopies. Orchard 1 had a naturally occurring high density of Formica neoclara (Emery), a predatory ant. Ants were introduced into Orchard 2 in August 1987. Exclusion studies were carried out in Orchard 1 during 1987-1989 and in Orchard 2 during 1988-1989. Each year, adult and immature pear psylla population densities in selected trees were estimated by beating tray and leaf sampling. During most years, adult and immature pear psylla, Cacopsylla pyricola (Foerster), population densities were significantly higher in ant-excluded trees. In Orchard 2, densities of immature psylla were significantly higher before ant introduction than after introduction on trees without exclusion barriers. Psylla densities did not differ from postant introduction densities in ant-excluded trees. This study showed that predatory ants can significantly reduce pear psylla population densities.

Population studies of the citrus psylla,Trioza erytreae: Factors influencing population size

An attempt was made to correlate population fluctuations of an isolated population of the citrus psylla,Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), with both the availability of young developing leaves and the saturation deficit index. Citrus psylla population dynamics seems to be governed by more than these two factors. There were significant positive correlations among egg, nymph and adult numbers. Increases in the minimum temperature and minimum relative humidity were followed by increases in the numbers of adults, eggs and nymphs. Seedlings of four citrus cultivars which seem to be less attractive to adult psylla than the other cultivars were identified.