Asian Citrus Psyllid Populations Research Articles

Analysis and evaluation of China-native citrus and citrus related germplasm on their susceptibility to the infestation by Diaphorina citri Kuwayama (Homotera: Psyllidae)

Huanglongbing (HLB) is the most devastating disease of citrus worldwide and vectored by the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae). The pathogen associated with HLB maintains uncultural in vitro, and there are few effective options against HLB-affected plants. Identification and deployment of ACP- resistance traits of citrus and citrus related germplasm to suppress ACP populations may be a potential management strategy for the management of HLB. In the present study, the susceptibilities of 71 Chinese citrus genotypes to ACP infestation were evaluated and analyzed in a free-choice situation under field conditions by using the method of systematic clustering and dynamic clustering. The results showed that there was significant difference in susceptibility to ACP infestation among the genotypes of citrus. These genotypes can be graded according to the number of psyllids on the trees. Grade I: highly susceptible with a total of 8 genotypes. Grade II: moderately susceptible with a total of 18 genotypes. Grade III: lower susceptibility with a total of 45 genotypes. The 71 genotypes of citrus are used to be classified into 8 groups according to the Chinese classification system “Citrus Varieties in China” (Chinese Citrus Association). There existed significant differences among the 8 groups. Lemons and Pummelos were highly susceptible hosts to ACP, with no significant difference from Murraya panciculata L., which was the most suitable host to ACP. Mandarins, Hybrid citrus, Sweet oranges and Tangerines were moderately susceptible hosts. Kumquat and Sour oranges were lower susceptible hosts. Some genotypes of Kumquat, like Citrus medurenisi var. Variegated Calamondin, Fortunella hindsii var. Chintou, and Sour orange, Citrus aurantium var. Variegated sour orange, had the lowest susceptiblility to ACP infection. Further experiment will be done to confirm the low ACP- susceptibility of genotypes from Kumquat and Sour orange.

The Flicker: A Vehicle-Driven, Mechanical Device for Detecting and Monitoring Adult Asian Citrus Psyllid and Other Arthropods in Citrus

A number of different methods have been used to detect and monitor Asian citrus psyllid (ACP) in citrus including: stem tap samples, yellow sticky traps, vacuum samples, suction traps, sweep net samples, visual searches per unit of time, and samples of flush shoots or pairs of mature leaves (Hall et al. 2012).  Each of these methods has some value in determining the presence and abundance of ACP in citrus, but there are advantages and disadvantages associated with each method and a number of factors may ultimately influence which of these sampling methods to use including cost, the objective of sampling, and the particular circumstances under which sampling is conducted.  However, none of these sampling methods can be used to quickly survey a large block of trees unless relatively few trees are actually examined and/or a large number of scouts is available to do the survey.  Pest & Disease Management, LLC (PDM) recently designed and built a mechanical device for detecting and monitoring ACP populations in citrus (Figure 1). The device (patent pending) is attached to a truck, tractor or all-terrain-vehicle and pulled through a grove.  Vertical baffles attached to metal arms extending from the device are kept in contact with the outer edge of tree canopies while driving along a row.  Adult psyllids are flicked (hence the name ‘flicker’) by these baffles onto large sticky traps positioned horizontally below the baffles.  Depending on the size of trees, from 1 to 4 baffles with traps 2 to 6 feet above ground can be used; there are two horizontal traps associated which each baffle, one ahead of the baffle (front traps) and one behind the baffle (rear traps).  Moving at speeds of 2.5 to 5.0 mph, the Flicker can be used to sample a large number of trees at a fast pace.  We constructed a dataset of numbers of psyllids captured using the Flicker in Florida citrus orchards [n = 235 runs, 0.6 to 2.2 miles of trees per run, average 1.2 miles per run, an average of 3.6 baffles (6.7 sticky traps) per run].  The Flicker caught an average of 4.9 ACP per 1000 ft of trees (=0.8 ACP per trap per 1000 ft of trees); the maximum number of ACP observed among these 235 runs was 177 ACP per 1,000 ft (30 ACP per trap per 1000 ft). Among 154 runs in which at least one ACP was detected, the flicker caught an average of 1.3 ± 0.2 ACP per trap per 1,000 ft of trees (Figure 2).  The number of ACP captured per trap per 1000 ft of trees was statistically the same for front traps (4.7 ± 1.1) and rear traps (4.4 ± 1.1).  Among runs that included all four trap levels, the lowest traps caught significantly fewer ACP than the highest traps (F = 5.1, P = 0.006, 3 df).

Botanicals, selective insecticides, and predators to control Diaphorina citri (Hemiptera: Liviidae) in citrus orchards.

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama vectors pathogens that cause huanglongbing (HLB) or citrus greening devastating and economically important disease present in most citrus growing regions. Young citrus shoots are required for psyllid reproduction and development. During winter citrus trees produce little or no new growth. Overwintering adults reproduce in spring on newly emerging shoots also attractive to other pests and beneficial insects. Botanicals and relatively selective insecticides could help to conserve beneficial insects and reduce pest resistance to insecticides. Sprays of Azadirachtin (Neem), Tropane (Datura), Spirotetramat, Spinetoram, and broad-spectrum Imidacloprid were evaluated to control ACP in spring and summer on 10-year-old "Kinow" Citrus reticulata Blanco trees producing new growth. Psyllid populations were high averaging 5-9 nymphs or adults per sample before treatment application. Nymphs or adults were significantly reduced to 0.5-1.5 per sample in all treatments for 3 weeks, average 61%-83% reduction. No significant reduction in ladybeetles Adalia bipunctata, Aneglei scardoni, Cheilomenes sexmaculata, and Coccinella septempunctata was observed. Syrphids, spiders and green lacewings were reduced in treated trees except with Tropane. Studies are warranted to assess impact of these predators on ACP and interaction with insecticides. Observed reduction in ACP populations may not be enough considering its reproductive potential and role in the spread of HLB. Follow-up sprays may be required to achieve additional suppression using rotations of different insecticides.

Insecticide sprays, natural enemy assemblages and predation on Asian citrus psyllid, Diaphorina citri (Hemiptera: Psyllidae).

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama is considered a key citrus pest due to its role as vector of 'huanglongbing' (HLB) or citrus greening, probably the most economically damaging disease of citrus. Insecticidal control of the vector is still considered a cornerstone of HLB management to prevent infection and to reduce reinoculation of infected trees. The severity of HLB has driven implementation of intensive insecticide programs against ACP with unknown side effects on beneficial arthropod fauna in citrus agroecosystems. We evaluated effects of calendar sprays directed against this pest on natural enemy assemblages and used exclusion to estimate mortality they imposed on ACP populations in citrus groves. Predator exclusion techniques were used on nascent colonies of D. citri in replicated large untreated and sprayed plots of citrus during the four major flushing periods over 2 years. Population of spiders, arboreal ants and ladybeetles were independently assessed. Monthly sprays of recommended insecticides for control of ACP, adversely affected natural enemy populations resulting in reduced predation on ACP immature stages, especially during the critical late winter/early spring flush. Consequently, projected growth rates of the ACP population were greatest where natural enemies had been adversely affected by insecticides. Whereas, this result does not obviate the need for insecticidal control of ACP, it does indicate that even a selective regimen of sprays can impose as yet undetermined costs in terms of reduced biological control of this and probably other citrus pests.

Evaluation of Color and Scent Attractants Used to Trap and Detect Asian Ctirus Psyllid (Hemiptera: Liviidae) in Urban Environments

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a serious pest of citrus due to its ability to vector the putative causal agent of huanglongbing, ‘Candidatus Liberibacter asiaticus'. Populations of Asian citrus psyllid (ACP) can increase in density in urban areas and then move out into adjacent commercial citrus production. Current presence/ absence detection methods for ACP in urban areas rely on the use of yellow sticky traps without a scent lure. This method was selected because of its accepted use in commercial production, however, in urban areas it may not be the most efficient method for trapping ACP. Therefore, we investigated the relative trapping efficiency of 4 different colored traps (2 hues of yellow and 2 hues of green) and the addition of 2 scent lures to yellow sticky traps. The lures were based on the volatiles emitted either from flush growth of Eureka lemon or Mexican lime. The tests were conducted in residential areas in Los Angeles, California in 2011. All of the sites were dooryard sites and trapping was done with homeowner permission. There were no statistically significant differences in trap catch between the yellow and green traps, suggesting that any of the traps tested could be used for ACP detection in an urban environment. There was no correlation between flush density and trap catches. The host plant on which the colored traps were placed did not significantly influence trap catch, although numerically more ACP adults were captured on lemon and lime trees, regardless of trap color. When scent lures were added to yellow sticky traps, no statistically significant differences were found between traps with lures and those without lures, regardless of host plant. Trapping studies for ACP in the urban environment need to be continued using more sample sites to determine if the addition of scent lures based on plant volatiles will increase trap catches.

Metalized polyethylene mulch to repel Asian citrus psyllid, slow spread of huanglongbing and improve growth of new citrus plantings

Greening or huanglongbing (HLB) is a debilitating disease of citrus caused by Candidatus Liberibactor asiaticus and transmitted by the Asian citrus psyllid (ACP), Diaphorina citri. HLB now occurs worldwide in all major citrus growing regions except the Mediterranean and Australia. Management relies principally on insecticidal control of the ACP vector, but is insufficient, even for young trees which are most susceptible to the disease. We tested the ability of metalized polyethylene mulch to repel adult ACP as well as effects on incidence of HLB and early tree growth. Metalized mulch significantly reduced ACP populations and HLB incidence compared to whiteface mulch or bare ground. In addition, metalized mulch, together with the associated drip irrigation and fertigation system, increased soil moisture, reduced weed pressure, and increased tree growth rate. Metalized mulch slows spread of ACP and therefore HLB pressure on young citrus trees. Metalized mulch can thereby augment current control measures for young trees based primarily on systemic insecticides. Additional costs could be compensated for by increased tree growth rate which would shorten time to crop profitability. These advantages make a compelling case for large-scale trials using metalized mulch in young citrus plantings threatened by HLB.

Carbon Dioxide Anesthesia ofTamarixia radiata(Hymenoptera: Eulophidae) Parasitoid ofDiaphorina citri(Hemiptera: Psyllidae)

Tamarixia radiata (Waterston) (Hymenoptera: A T. radiata colony was maintained at Eulophidae), is an arrhenotokous ectoparasite of FDACS-DPI in Gainesville on ACP nymphs the Asian citrus psyllid (ACP) Diaphorina citri using orange jasmine, Murraya paniculata (Kuwayama) (Hemiptera; Psyllidae), vector of (1.) Jack (Sapindales: Rutaceae), as plant host citrus greening disease or huanglongbing (HLB). (Skelley & Hoy 2004). Six newly trimmed The parasitoid is reported to have controlled plants with new growth were held in an acrylic ACP populations to low levels on the islands of 62 cm cubic cage and 600 D. citri adults were Reunion, Guadeloupe and Puerto Rico (Aubert released for 72 h for oviposition a greenhouse & Quilici 1984; Etienne et al. 2001; Pluke et al. under natural sunlight 25 ± 5 °C and 50% ~ 2008). Tamarixia radiata was first imported to 70% RH. Adults were removed and plants held Florida from Taiwan and Vietnam in 1998 and for 10 d until 4th instar nymphs were available, released in 1999-2001 (Hoy & Nguyen 2001). A Plants were moved into another clean cage of survey conducted in 2006-07 determined that T. the same type for 20 days into which 100 T. ra radiata was well distributed in citrus orchards diata were released. Adult progeny were later throughout the state (Qureshi et al. 2009). Howcollected daily until no more emerged, ever, incidence of parasitism was generally low, A gas chamber was constructed consisting of a especially early in the growing season, suggesting vial, 6.50 cm in diam and 12 cm in height (Fish a need for augmenting parasitoid populations at er Scientific, Pittsburg Pennsylvania), provided that critical time as component of an integrated with two 0.50 cm diam holes in the lid into each management program (Qureshi et al. 2007,2009). of which was fitted a 0.5 cm plastic tube inserted Studies of T. radiata biology and current efforts either 1 cm or 11 cm into the chamber for a gas at mass rearing and release of this species might outlet and inlet respectively. Plasticine modeling benefit from an ability inactivate adults by C02 clay (Flair Leisure Products, Cheam Surrey, Eng anesthetization, including separation of emerland) was molded around the openings of the lid gent wasps and psyllids. to prevent leakage. Carbon dioxide (C02) is widely used to anesFlow time of gas at 3.8 kpa (2 psi) needed to thetize insects, but may also cause deleteridisplace all air in the chamber was assessed by ous side effects on biology and behavior. Brooks filling the vial with water and then replacing (1957) found that development rate of German with C02 through the inlet. All the water was dis cockroach, Blattella germanica L. (Blattodea: placed in 10 s. A C02 sensor (K-33 ICB 30% CO, Blattellidae), nymphs decreased 53% when exSensor, C02Meter Inc., Ormond Beach Florida, posed weekly to high C02 concentrations for 3 USA) was used to determine that 3 s of flow time min. Crystal (1967) reported significantly dewere necessary to attain a 30% C02 concentration creased survival rates and fertility of screwworm, confirming the earlier result. The C02 sensor was Cochliomyia homini-vorax (Coquerel) (Diptera: also used to test for leaks by confirming that a Calliphoridae), exposed to 100% C02 for 30 min. given concentration remained constant over sev Sherman (1953) reported that C02 anesthesia of eral min. Mediterranean fruit fly, Ceratitis capitata (WiFive wasps having emerged within 24 h or less edemann) (Diptera: Tephritidae), led to increased were placed in the chamber. The lower % of the mortality. vial was covered with black cloth to induce the This study was undertaken as a first step towasps to walk to the top and thus avoid injury ward using anesthetization for mass rearing by from in rushing gas. Gas was introduced through evaluating the response of T. radiata to C02 exan inlet from a C02 tank at 3.8 kpa for 15s to posure. The objective was to test the effectiveness exchange all the air, and then the 2 tubes closed of C02 anesthetization of T. radiata and to deterwith metal clamps. Wasps were removed after a mine the incidence and severity of side effects of 5 min exposure and observed with the naked eye C02 anesthetization on longevity, parasitism rate using a stop watch to record recovery time (nor and sex ratio. mal movement). Males and females were treated

Characterization of the Relative Abundance of the Citrus Pathogen Ca. Liberibacter Asiaticus in the Microbiome of Its Insect Vector, Diaphorina citri, using High Throughput 16S rRNA Sequencing

The relationship between the causal agent of Huanglongbing (HLB), Ca. Liberibacter asiaticus(Las), and the naturally occurring endosymbiotic community of its insect vector, the Asian citrus psyllid (ACP), Diaphorina citri, was studied. Variation was observed in the titer of Las within an ACP population feeding on the same material. The cause of this disparity is unknown, and has implications for Las transmission and the spread of HLB. This study utilizes culture independent methods to establish the relationship between the ACP’s microbial community and Las acquisition. DNA from 21 psyllids was amplified using universal 16S rRNA primers with Illumina adaptor regions and a sample-specific 7- base identifier. These amplicons were then batch-sequenced on the Illumina platform. The resulting sequences were separated by the identifier, and compared to known sequences in a 16S rRNA database. The microbial communities of each psyllid were compared to determine whether a correlation exists between the ACP’s endosymbionts and level of Las acquisition.ACPs were dominated by the same four bacterialgenera regardless of the abundance of Ca.Liberibacter. A combination of qPCR and Illumina sequencing was used to establish an infection gradient among the sampled ACPs. The Ca. Liberibacter titer within the insect was found to have a strong negative relationship with an endosymbiont residing in the syncytium of the mycetocyte and a positive relationship with Wolbachia. These correlations have implications in the acquisition of Las by the ACP as well as the activities of Las within this vector.

Two Separate Introductions of Asian Citrus Psyllid Populations Found in the American Continents

Abstract A phylogeographic analysis inferred from the partial mitochondrial cytochrome oxidase subunit I gene (433 bp) was performed with 22 populations of Diaphorina citri Kuwayama collected in the Americas and one in the Pacific. Eight populations from four countries in South America, 14 from four countries in North America, and one from Hawaii were analyzed. Twenty-three haplotypes (hp) were identified and they fell into two groups: hp1–8 were identified in South America (group 1) and hp9–23 were identified in North America and Hawaii (group 2). Hp1 and nine were present in the highest frequencies within each population and within their group, 81 and 85% for group 1 and group 2, respectively. A diagnostic nucleotide at position 48 was identified that allowed for the discrimination of the two groups; in addition, no haplotypes were shared between the two groups. An analysis of molecular variance uncovered significant genetic structure (φCT = 0.733; P < 0.001) between the two groups of the Americas. Two haplotype networks (ParsimonySplits and Statistical Parsimony) discriminated the two groups and both networks identified hp1 and nine as the predicted ancestral or founding haplotypes within their respective group. The data suggest that two separate introductions or founding events of D. citri occurred in the Americas, one in South America and one in North America. Furthermore, North America and Hawaii appear to share a similar source of invasion. These data may be important to the development of biological control programs against D. citri in the Americas.

A New Method for Short-Term Rearing of Citrus Psyllids (Hemiptera: Pysllidae) and for Collecting their Honeydew Excretions

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an eco nomically important pest of citrus in the United States, Asia and other parts of the world, as a vec tor of huanglongbing (HLB) or citrus greening, which is considered one of the world's most seri ous diseases of citrus (Gottwald 2010). Addition ally, large populations of ACP can damage plants directly through feeding and excretion activities; ACP feeds on citrus phloem tissues and produces copious amounts of honeydew excretions (Brian sky & Rogers 2007). ACP adults can feed on ma ture citrus leaves, but nymphs must have young tender flush to survive. For biological and patho gen-vector relation studies on ACP (e.g., Wen ninger & Hall 2007; Pelz-Stelinski et al. 2010) rearing of single or small groups of psyllid nymphs or adults on whole citrus plants takes considerable space, time and other resources. Here, we describe a new, simpler method for short-term rearing of ACP using detached mature citrus leaves for adults and detached young ter minal shoots for nymphs (Fig. 1). ACP adults and nymphs were reared singly or in small groups (5-10 per tube) in clear plastic (polypropylene) 50-ml conical centrifuge tubes (3 cm wide and 11.5 cm long; Fisher Scientific, Pitts burg, PA). Young psyllid adults (approximately 1 wk-old) were reared on detached, mature, me dium-size leaves of sweet orange (Citrus sinensis (L.) Osbeck var Ridge Pineapple). Leaf sizes used for adults ranged between 3-4 cm in width and 6-8 cm in length with petioles about 2-3 cm long. The petioles of these leaves were cut diagonally with a sharp razor blade, and each inserted in a small (0.3 or 0.5 mL) microfuge tube filled with water or a piece of moistened cotton wool (Figs. 1A and IE). A piece of Parafilm membrane was wrapped around the top of this tube and the petiole to keep insects from drowning or contact with water. The detached leaf and microfuge tube were then inserted into the rearing tube, and the psyllid adults were added to the latter. The rearing tube was covered with a screw cap that had been finely perforated by a hot needle for ventilation. For better ventilation, how ever, wider holes can be cut in the plastic cap and a piece of fine mesh screen placed under the screw cap to prevent escape of the psyllids. The tubes were kept in an environmental chamber at 25°C and 14 h light per day. The clear plastic wall of the rearing tubes al lowed close observation and photography of the enclosed psyllids during their various activities either by the naked eye or through a stereomicro scope with minimal disturbance (Figs. IB-IE). For example, adults were observed feeding for long periods in their normal feeding posture (Fig. IB) mainly on the midrib or other veins on either side of the detached leaves. They were also observed excreting honeydew droplets regularly (Fig. IE), and occasionally laying eggs (Fig. IB in set), although they normally prefer younger leaves for laying eggs (Brlansky & Rogers 2007). Survival of young adults under the above condi tions on detached mature leaves, that were changed to fresh ones weekly, was 89, 80 and 75% after 2, 3, and 4 weeks, respectively (n = 130 adults). It was later observed, however, that ma ture leaves can stay fresh in the rearing tubes at least for 2 weeks.

Insecticide resistance in field populations of Asian citrus psyllid in Florida

Asian citrus psyllid (ACP), Diaphorina citri, is a major pest of citrus because it vectors the putative causal agent of huanglongbing disease. Insecticides are currently the basis of psyllid management programs, and the number of annual insecticide applications has increased significantly. In this paper, a series of investigations of insecticide resistance among field populations of adult and immature ACP in Florida is described. In 2009, the highest level of resistance for adult ACP, as compared with the laboratory susceptible (LS) population, was found with imidacloprid with an LD(50) resistance ratio (RR(50) ) of 35 in one population. This was followed by chlorpyriphos (RR(50) = 17.9, 13.3, 11.8 and 6.9), thiamethoxam (RR(50) = 15 and 13), malathion (RR(50) = 5.4 and 5.0) and fenpropathrin (RR(50) = 4.8). In 2010, mortality of adults from all five sites sampled was lower than with the LS population at three diagnostic concentrations of each insecticide tested. Among nymph populations, indications of resistance were observed with carbaryl (RR(50) = 2.9), chlorpyriphos (RR(50) = 3.2), imidacloprid (RR(50) = 2.3 and 3.9) and spinetoram (RR(50) = 4.8 and 5.9). General esterase, glutathione S-transferase and monooxygenase levels were also elevated in field-collected adult and nymph ACP as compared with the LS population. The present results suggest that varying levels of insecticide susceptibility exist in ACP populations across the citrus-growing areas of Florida. Increased levels of detoxifying enzymes in these populations may partially explain these differences. The present results indicate that insecticide resistance may become an emerging problem for ACP control if effective resistance management is not practiced.

Efficacy and Uptake of Soil-Applied Imidacloprid in the Control of Asian Citrus Psyllid and a Citrus Leafminer, Two Foliar-Feeding Citrus Pests

The systemic neonicotinoid insecticide imidacloprid, Admire Pro, was applied to 3- and 4-yr-old nonbearing 'Rio Red' grapefruit, Citrus x paradisi Macfad., trees in 2006 and 2007, respectively, to determine its effects in the control of two major citrus pests, the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), and a citrus leafminer Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae). Young flush shoots were randomly collected weekly for 13 and 11 wk in 2006 and 2007, respectively, to determine the infestation levels and densities of immature stages of both Asian citrus psyllid and P. citrella. Additional flush shoot samples were collected in 2007 and titers of imidacloprid in leaf tissue were determined using an enzyme-linked immunosorbent assay. Soil application of imidacloprid significantly reduced the infestation levels and densities of both pests on flush shoots, starting from the second week post application. The effects of the neonicotinoid insecticide were similar in both years. Analysis of imidacloprid concentration in leaf tissue showed a gradual increase during the first 3 wk, and titers remained well above 200 ppb for 11 wk postapplication. Significant positive correlations were obtained between imidacloprid titers in leaf tissue and the percentage of control levels achieved for both pests. A high level of suppression of both P. citrella and Asian citrus psyllid populations on citrus trees was associated with imidacloprid titer in leaf tissue >200 ppb, which was reached 2 wk after soil treatment. Although soil application of imidacloprid did not provide rapid knockdown of Asian citrus psyllid and P. citrella populations, it resulted in chronic residues in leaf tissue and long-term suppression of both pests.

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The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae) vectors a bacterium, ‘Candidatus Liberibacter asiaticus’ (CLas), associated with one of the world's most serious diseases of citrus, huanglongbing (HLB) (also known as citrus greening disease). There is no known cure for this disease, which severely reduces tree productivity and fruit quality and promotes tree decline and death. Most growers apply insecticides to control ACP as a tactic to prevent or reduce the incidence of HLB. Plant resistance to ACP may be a viable tactic for managing ACP and CLas. Resistance to colonization by ACP populations has been reported in the genotype Poncirus trifoliata L., which is cross compatible with citrus. The Citrus Research Center (CRC) in Riverside, California, maintains a large number of accessions of P. trifoliata. We conducted four free-choice experiments with 29 CRC accessions of P. trifoliata and found that ACP deposited fewer eggs on 19 of those accessions compared with susceptible sweet orange, Citrus sinensis (L.) Osbeck. Subsequent infestation densities of nymphs generally reflected reductions in oviposition but there were notable exceptions. Some accessions may be susceptible to oviposition but contain traits that confer antibiosis to nymphs. In no-choice experiments with seedling plants representing eight P. trifoliata accessions, oviposition rates were reduced compared with sweet orange and it appeared that factors associated with mature leaves were involved. In no-choice experiments with adult ACP confined to flush cuttings, large reductions were observed in the number of eggs and nymphs on each of five P. trifoliata accessions compared with sweet orange. Based on these results in conjunction with published reports, accessions were identified that consistently showed resistance to oviposition. However, the level of resistance in these accessions has been variable possibly due to environmental conditions, plant age, proximity of plants to susceptible germplasm, and other factors.