Influence of meteorological factors on the quantitative following relationship between Empoasca onukii Matsuda (Hemiptera: Cicadellidae) and its natural enemies in tea plantations

Our aim was to study the close relationship between the number of Empoasca onukii and its natural enemies in tea plantations to provide a scientific basis for the control of E. onukii. The relationship between the number of E. onukii and its main natural enemies in tea plantations in Hefei, China, were compared by gray relational analysis, and then the relationships between seven meteorological factors and the populations of E. onukii were analyzed by the method of path analysis. The results showed that among the top six natural enemies most closely related to the population of E. onukii, two natural enemies were the same in the three years of study and four natural enemies were the same in any two years of the study, and that the natural enemy species closely related to the population of E. onukii varied greatly among years. The direct effect of monthly average relative humidity was the greatest effect in 2020 and the direct effect of monthly average temperature was the greatest effect in 2021, with both being negative in terms of their effect on the population size of E. onukii. The direct effect of the number of days of rainfall was the greatest effect in both 2021 and 2022, and the indirect effect of monthly sunshine hours through rainfall days was the greatest effect on the population of E. onukii. The highest temperatures in early and mid-August 2022 were higher than in previous years, which had an impact on the growth and development of subsequent E. onukii.     

Feeding behavior of aphids on narrow‐leafed lupin (Lupinus angustifolius) genotypes varying in the content of quinolizidine alkaloids

Since the beginning of breeding narrow‐leafed lupins [Lupinus angustifolius L. (Fabaceae)] with a low alkaloid content, susceptibility to several aphid species has increased. Therefore, the probing and feeding behavior of Aphis fabae Scopoli, Aphis craccivora Koch, Acyrthosiphon pisum (Harris), Myzus persicae (Sulzer), and the well‐adapted Macrosiphum albifrons Essig (all Hemiptera: Aphididae) was studied over 12 h on narrow‐leafed lupin genotypes containing varying amounts and compositions of alkaloids. We used the electrical penetration graph (EPG) technique to obtain information on the influence of alkaloid content and composition on the susceptibility to various aphid species. Results indicated that the total time of probing of A. fabae, A. craccivora, A. pisum, and M. persicae increased with a reduced alkaloid content, whereas the alkaloid content had no influence on M. albifrons. Almost all of the individuals (>93%) conducted sieve element phases on the highly susceptible genotype Bo083521AR (low alkaloid content). A reduced occurrence of phloem phases was observed during the 12‐h recording on the alkaloid‐rich cultivar Azuro, especially for A. pisum (37.5%) and A. fabae (55.0%). Furthermore, aphids feeding on genotypes with low alkaloid content had in most cases significantly longer sieve element phases than when feeding on resistant genotypes (Kalya: low alkaloid content, yet resistant; Azuro: high alkaloid content, resistant), whereas M. albifrons showed the longest phloem phase on the alkaloid‐rich cultivar Azuro. As most significant differences were found in phloem‐related parameters, it is likely that the most important plant factors influencing aphid probing and feeding behavior are localized in the sieve elements. The aphids’ feeding behavior on the cultivar Kalya, with a low alkaloid content but reduced susceptibility, indicates that not only the total alkaloid content influences the feeding behavior but additional plant factors have an impact.     

Volatiles from non‐host aromatic plants repel tea green leafhopper Empoasca vitis

The tea green leafhopper, Empoasca vitis Göthe (Hemiptera: Cicadellidae), is a serious pest of tea crops in China. The effectiveness of five aromatic non‐host plants, Corymbia citriodora (Hook.) (Myrtaceae), Ocimum basilicum L. (Lamiaceae), Lavandula pinnata L. (Lamiaceae), Ruta graveolens L. (Rutaceae), and Rosmarinus officinalis L. (Lamiaceae), was investigated to determine their ability to suppress E. vitis on tea plants. Volatile organic compounds derived from L. pinnata, R. officinalis, and C. citriodora were found to repel leafhoppers and to mask the host's odors. Intercropping L. pinnata and C. citriodora with tea plants significantly reduced the E. vitis population levels in the tea plantation associated with higher population densities of generalist predators. The volatile compounds from the five non‐host plants were collected by headspace absorption under field conditions, and the 10 major components were identified. Qualitative and quantitative differences were found among the five odor profiles. Moreover, the emission dynamics of non‐host volatiles were monitored. Non‐host volatile emissions showed two peak periods, one in the spring and one in the autumn period. These peaks were almost consistent with the population dynamics of E. vitis. Our findings suggested that this newer approach to ecologically based, sustainable pest management implemented via intercropping with non‐host aromatic plants such as L. pinnata and C. citriodora offers a promising alternative to chemical control of the leafhopper population.     

Barley yellow dwarf virus transmission and feeding behaviour of Rhopalosiphum padi on Hordeum bulbosum clones

A Hordeum bulbosum L. (Poaceae) clone A17 was identified, which showed complete resistance to Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV). It was not possible to infect plants of A17 with BYDV‐PAV, ‐MAV, or with CYDV‐RPV by the aphid vectors Rhopalosiphum padi (L.) or Sitobion avenae (Fabricius) (both Hemiptera: Aphididae). Plants of the A17 clone and of the BYDV‐susceptible H. bulbosum clone A21 revealed some resistance to R. padi compared to the susceptible winter barley cultivar Rubina [Hordeum vulgare L. (Poaceae)]. The development time to the imago was longer and the number of nymphs was reduced on both clones compared with cv. Rubina. The probing and feeding behaviour of R. padi on plants of the H. bulbosum clones was studied over 12 h and compared with that on plants of the barley cv. Rubina. Principal component analysis of the results of the feeding behaviour revealed a clear separation of the H. bulbosum genotypes from Rubina. On H. bulbosum the number of penetrations was higher but total feeding time was shorter. Significant differences were mainly found in the phloem feeding parameters for plants of both clones in comparison to Rubina, with the virus resistant A17 clone having the strongest effect and the susceptible A21 clone being intermediate. Most significant differences were found in parameters of the phloem salivation phase. On A17, an average of less than one (0.9) E1 phase per plant was observed (3.3 on A21 and 5.7 on Rubina) and its duration was reduced to less than 1 min (0.9 min) in comparison to 2.4 min on A21 and 5.7 min on Rubina. Also, the phloem feeding (E2) phase was clearly reduced on A17 plants with 0.5 E2 phases per test and a mean duration of 1.1 min in contrast with 2.9 and 3.5 E2 phases per test and 34.1 and 421.3 min for A21 and Rubina, respectively. These results point towards a phloem‐localized factor for aphid resistance in H. bulbosum, i.e., on A17 plants the phloem salivation time is too short for a successful infection by BYDV leading to vector resistance.     

Effects of Rag1 aphid‐resistant soybean on mortality,development, and preference of brown marmorated stink bug

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), poses a new threat to soybean, Glycine max (L.) Merrill (Fabaceae), production in the north central USA. As H. halys continues to spread and increase in abundance in the region, the interaction between H. halys and management tactics deployed for other pests must be determined. Currently, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is the most abundant and damaging insect pest of soybean in the region. Aphid‐resistant soybean, mainly with the Rag1 gene, is commercially available for management of A. glycines. Here, experiments were performed to evaluate the effects of Rag1 aphid‐resistant soybean on the mortality, development, and preference of H. halys. In a no‐choice test, mortality of H. halys reared on Rag1 aphid‐resistant soybean pods was significantly lower than when reared on aphid‐susceptible soybean pods (28 vs. 53%). Development time, adult weight, and proportion females of surviving adults did not differ when reared on Rag1 aphid‐resistant or aphid‐susceptible soybean pods. In choice tests, H. halys exhibited a preference for Rag1 aphid‐resistant over aphid‐susceptible soybean pods after 4 h, but not after 24 h. Halyomorpha halys exhibited no preference when tested with vegetative‐stage or reproductive‐stage soybean plants. The preference by H. halys for Rag1 aphid‐resistant soybean pods and the decreased mortality when reared on these pods suggests that the use of Rag1 aphid‐resistant soybean may favor this emerging pest in the north central USA.     

Species‐specific elicitors induce tea leaf to arrest the endoparasitoid Ascogaster reticulata (Hymenoptera: Braconidae)

Ascogaster reticulata Watanabe (Hymenoptera: Braconidae) is an egg‐larval endoparasitoid of the smaller tea tortrix, Adoxophyes honmai Yasuda. Recent studies have examined tritrophic interactions among Camellia sinensis, A. honmai and A. reticulata, but the effect of non‐host insects on the induction of tea plant that may affect foraging behaviour of A. reticulata remains unclear. In this study, we selected two non‐host insects, Homona magnanima Diakonoff and Ostrinia furnacalis (Guenée), as representative species in our bioassays. Tea leaves were treated with homogenized female reproductive tissues of a non‐host insect in comparison with untreated leaves in a choice test. Residence times of parasitoids on both leaves were recorded. The parasitoids seemed to prefer walking on leaves treated with homogenates of H. magnanima over untreated leaves, but the difference in residence times was not significant. In contrast, its residence time on leaves treated with homogenates of O. furnacalis was significantly shorter than that on untreated leaves. Thus, the induction of tea leaf surface chemicals may differ among moth species, which may produce different types of elicitors. This difference may, in turn, affect the host‐searching behaviour of A. reticulata.     

Stripe Rust Resistance in Roegneria kamoji (Poaceae: Triticeae) and its Genetic Analysis

The Roegneria kamoji accession ZY 1007 was resistant to the mixed predominant races of Puccinia striiformis f.sp. tritici (Pst) in China based on field tests at adult‐plant stage. The seedling resistance evaluation of ZY 1007 showed that it was resistant to stripe rust physiological strains CYR29, CYR33 and PST‐V26, which were the predominant races of Pst in China. The female parent R. kamoji cv. Gansi No.1 (susceptible to Pst) was crossed with ZY 1007 (resistant to Pst). Parents, F₁ and F₂ populations were tested in a field inoculated with the mixed urediniospores. ZY 1007 and all the observed 11 F₁ hybrid plants were resistant, while plants of Gansi No.1 were susceptible. Among the 221 F₂ plants, 168 plants were resistant and 53 were susceptible, and the segregation of resistant and susceptible plants fits 3R:1S ratio (χ² = 0.074, P > 0.75). It confirmed that the resistance of stripe rust in ZY 1007 was controlled by a single dominant gene and temporarily designated as YrK1007.     

Defence‐Related Enzymes in Soybean Resistance to Target Spot

Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), β‐1‐3‐glucanases (GLU), phenylalanine ammonia‐lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin‐thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm² of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDACEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence‐related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot.     

Engineering fire blight resistance into the apple cultivar ‘Gala’ using the FB_MR5 CC‐NBS‐LRR resistance gene of Malus × robusta 5

The fire blight susceptible apple cultivar Malus × domestica Borkh. cv. ‘Gala’ was transformed with the candidate fire blight resistance gene FB_MR5 originating from the crab apple accession Malus × robusta 5 (Mr5). A total of five different transgenic lines were obtained. All transgenic lines were shown to be stably transformed and originate from different transgenic events. The transgenic lines express the FB_MR5 either driven by the constitutive CaMV 35S promoter and the ocs terminator or by its native promoter and terminator sequences. Phenotyping experiments were performed with Mr5‐virulent and Mr5‐avirulent strains of Erwinia amylovora, the causal agent of fire blight. Significantly less disease symptoms were detected on transgenic lines after inoculation with two different Mr5‐avirulent E. amylovora strains, while significantly more shoot necrosis was observed after inoculation with the Mr5‐virulent mutant strain ZYRKD3_1. The results of these experiments demonstrated the ability of a single gene isolated from the native gene pool of apple to protect a susceptible cultivar from fire blight. Furthermore, this gene is confirmed to be the resistance determinant of Mr5 as the transformed lines undergo the same gene‐for‐gene interaction in the host–pathogen relationship Mr5–E. amylovora.     

Non‐host plant essential oil volatiles with potential for a ‘push‐pull’ strategy to control the tea green leafhopper,Empoasca vitis

The tea green leafhopper, Empoasca vitis Göthe (Hemiptera: Cicadellidae), is an economically important pest of tea crops, Camellia sinensis (L.) O. Kuntze (Theaceae), in China. The use of non‐host plant essential oils for manipulation of E. vitis was investigated for potential incorporation into a ‘push‐pull’ control strategy for this pest. The effectiveness of 14 plant essential oils in repelling E. vitis was investigated in laboratory assays. Rosemary oil, geranium oil, lavender oil, cinnamon oil, and basil oil repelled leafhoppers in a Y‐shaped olfactometer. We also compared the efficacy of these five plant essential oils to repel E. vitis in the presence of a host plant volatile‐based leafhopper attractant, (Z)‐3‐hexenyl acetate, in a tea plantation. In the treatment combination, four plates (north, south, east, and west) treated with an essential oil surrounded a central sticky plate treated with (Z)‐3‐hexenyl acetate. Fewer E. vitis were found on the plates treated with rosemary oil (12.5% reduction) than on the four water‐sprayed control treatment plates surrounding a central plate with (Z)‐3‐hexenyl acetate. We compared the distribution of E. vitis on the plates, and the relative numbers of E. vitis on each plate were compared with similar plates in the control treatment. When four plates treated with rosemary oil surrounded a central (Z)‐3‐hexenyl acetate‐treated plate, the distribution of E. vitis on the different plates changed significantly compared with that of the control. Relatively fewer E. vitis were found on the east (13.0% reduction) rosemary oil‐treated plates and more E. vitis (11.3% increase) were found on the central attractant‐treated plate. Our findings indicate that rosemary oil is a promising leafhopper repellent that should be tested further in a ‘push‐pull’ strategy for control of E. vitis.     

Biocontrol potential of phylloplane bacterium Ochrobactrum anthropi BMO‐111 against blister blight disease of tea

Aims

The present study was carried out to screen the phylloplane bacteria from tea for antagonism against grey blight caused by Pestalotiopsis theae and blister bight caused by Exobasidium vexans and to further evaluate the efficient isolates for disease control potential under field condition.

Methods and Results

A total of 316 morphologically different phylloplane bacteria were isolated. Among the antagonists, the isolates designated as BMO‐075, BMO‐111 and BMO‐147 exhibited maximum inhibitory activity against both the pathogens under in vitro conditions and hence were selected for further evaluation under microplot field trial. Foliar application of 36‐h‐old culture of BMO‐111 (1 × 10⁸ colony‐forming units ml^?1) significantly reduced the blister blight disease incidence than the other isolates. The culture of BMO‐111 as well as its culture filtrate effectively inhibited the mycelial growth of various fungal plant pathogens. The isolate BMO‐111 was identified as Ochrobactrum anthropi based on the morphological and 16S rDNA sequence analyses.

Conclusions

It could be concluded that the biocontrol agent O. anthropi BMO‐111 was effective against blister blight disease of tea.

Significance and Impact of the Study

Further study is required to demonstrate the mechanism of its action and formulation for the biocontrol potential against blister blight disease of tea.     

Feeding behavior and performance of Nasonovia ribisnigri on grafts,detached leaves,and leaf disks of resistant and susceptible lettuce

Aphids are dependent on the phloem sap of plants as their only source of nutrients. Host‐plant resistance in lettuce, Lactuca sativa L. (Asteraceae), mediated by the Nr gene is used to control the lettuce aphid Nasonovia ribisnigri (Mosely) (Hemiptera: Aphididae). The resistance is located in the phloem; however, the exact mechanism of resistance is unknown. In this study, we investigated whether the resistance factor (or factors) is synthesized in the root or in the shoot. The feeding behavior and performance of avirulent N. ribisnigri were studied on grafts of resistant and susceptible lettuce. In addition, the persistence of resistance in excised lettuce tissue was measured, by studying the feeding behavior and performance of N. ribisnigri on detached leaves and leaf disks of resistant lettuce. It appears that the resistance factor encoded by the Nr gene is produced in the shoots: aphid feeding was reduced on resistant shoots grafted on susceptible roots, whereas aphids were able to feed on grafts of susceptible shoots on resistant roots. Partial loss of resistance was observed after detachment of leaves and excision of leaf disks from resistant plants. Aphids fed longer on excised resistant plant tissue compared with intact resistant plants; however, compared with excised plant tissue of the susceptible cultivar, the time spent on feeding was shorter, indicating resistance was not completely lost. Our findings caution against the use of excised leaf material for aphid resistance bioassays.     

Cadmium uptake in Elodea canadensis leaves and its interference with extra‐ and intra‐cellular pH

This study investigated cadmium (Cd) uptake in Elodea canadensis shoots under different photosynthetic conditions, and its effects on internal (cytosolic) and external pH. The plants were grown under photosynthetic (light) or non‐photosynthetic (dark or in the presence of a photosynthetic inhibitor) conditions in the presence or absence of CdCl₂ (0.5 μm ) in a medium with a starting pH of 5.0. The pH‐sensitive dye BCECF‐AM was used to monitor cytosolic pH changes in the leaves. Cadmium uptake in protoplasts and leaves was detected with a Cd‐specific fluorescent dye, Leadmium Green AM, and with atomic absorption spectrophotometry. During cultivation for 3 days without Cd, shoots of E. canadensis increased the pH of the surrounding water, irrespective of the photosynthetic conditions. This medium alkalisation was higher in the presence of CdCl₂. Moreover, the presence of Cd also increased the cation exchange capacity of the shoots. The total Cd uptake by E. canadensis shoots was independent of photosynthetic conditions. Protoplasts from plants exposed to 0.5 μm CdCl₂ for 3 days did not exhibit significant change in cytosolic [Cd²⁺] or pH. However, exposure to CdCl₂ for 7 days resulted in increased cytosolic [Cd²⁺] as well as pH. The results suggest that E. canadensis subjected to a low CdCl₂ concentration initially sequesters Cd into the apoplasm, but under prolonged exposure, Cd is transported into the cytosol and subsequently alters cytosolic pH. In contrast, addition of 10–50 μm CdCl₂ directly to protoplasts resulted in immediate uptake of Cd into the cytosol.     

Feeding on tea GH19 chitinase enhances tea defense responses induced by regurgitant derived from Ectropis grisescens

Multiple isoforms of chitinases participate in plant defense against outside invaders. However, the functions of hydrolase family 19 (GH19) chitinases on pest control remain largely unknown. Here we reported the isolation and functional analysis of a gene CsChi19, which encodes a GH19 endochitinase protein of 332 amino acid residues from tea plant (Camellia sinensis). CsChi19 expression levels were upregulated in response to mechanical wounding, infestation by two important pests: the tea geometrid Ectropis grisescens and the tea green leafhopper Empoasca (Matsumurasca) onukii, a fungal pathogen Colletotrichum fructicola, and treatment with two phytohormones: jasmonic acid (JA) and salicylic acid. CsChi19 was heterologously expressed in Escherichia coli, and its catalytic function was further elucidated. The protein could hydrolyze colloidal chitin, and the optimum temperature and pH for its activity was 40°C and pH 5.0. CsChi19 were found to be toxic to tea pests when they were fed on artificial diets containing this protein. Interestingly, the regurgitant derived from E. grisescens fed with artificial diets containing CsChi19 protein induced stronger expression of CsMPK3, more JA burst, more accumulation of defense-related secondary metabolites, and more emission of volatiles than the regurgitant derived from E. grisescens fed only with artificial diets. Our results provide first evidence that CsChi19 is involved in mediating a novel defense mechanism of tea plant through altering the composition of the regurgitant.     

Resident spiders as predators of the recently introduced light brown apple moth,Epiphyas postvittana

The invasive light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), has not reached damaging levels on crops in California (USA), suggesting that its populations and impact are limited by generalist natural enemies. In a series of laboratory experiments, we examined resident spiders as predators of E. postvittana larvae on two host plants, the ornamental Australian tea tree, Leptospermum laevigatum (Gaertn.) F. Muell (Myrtaceae), and the weed French broom, Genista monspessulana (L.) L.A.S. Johnson (Fabaceae). Of three abundant spider species in Australian tea tree, two hunting spiders measurably reduced the numbers of E. postvittana larvae and plant damage, whereas a web‐weaving spider had no detectable impact. The adult stage of the dominant hunting spider Anyphaena aperta Banks (Anyphaenidae) consumed E. postvittana larvae, but neither large nor small juveniles had statistically detectable effects on numbers of larvae. However, plant damage was reduced in the presence of large juvenile A. aperta, suggesting that A. aperta may also have non‐consumptive effects on the feeding behavior of E. postvittana larvae. Anyphaena aperta consumed larvae only when larval densities exceeded a low threshold in a functional response experiment, leading to a type III functional response. Adult A. aperta showed no preference for different E. postvittana instars, whereas Cheiracanthium mildei L. Koch (Miturgidae), an abundant hunting spider on French broom, showed a partial preference for late‐instar larvae. The generalist feeding habits of the spiders may have precluded strong prey preferences. Results show that hunting spiders may help limit E. postvittana populations in California, and that they may in turn reduce the impact of E. postvittana on its host plants.     

Bacillus thuringiensis plants expressing Cry1Ac,Cry2Ab and Cry1F are not toxic to the assassin bug,Zelus renardii

Cotton‐ and maize‐producing insecticidal crystal (Cry) proteins from the bacterium, Bacillus thuringiensis (Bt), have been commercialized since 1996. Bt plants are subjected to environmental risk assessments for non‐target organisms, including natural enemies that suppress pest populations. Here, we used Cry1F‐resistant Spodoptera frugiperda (J.E. Smith) and Cry1Ac and Cry2Ab‐resistant Trichoplusia ni (Hübner) as prey for the assassin bug, Zelus renardii (Kolenati), a common predator in maize and cotton fields. In tritrophic studies, we assessed several fitness parameters of Z. renardii when it fed on resistant S. frugiperda that had fed on Bt maize expressing Cry1F or on resistant T. ni that had fed on Bt cotton expressing Cry1Ac and Cry2Ab. Survival, nymphal duration, adult weight, adult longevity and female fecundity of Z. renardii were not different when they were fed resistant‐prey larvae (S. frugiperda or T. ni) reared on either a Bt crop or respective non‐Bt crops. ELISA tests demonstrated that the Cry proteins were present in the plant at the highest levels, at lower levels in the prey and at the lowest levels in the predator. While Z. renardii was exposed to Cry1F and Cry1Ac and Cry2Ab when it fed on hosts that consumed Bt‐transgenic plants, the proteins did not affect important fitness parameters in this common and important predator.     

Feeding by sugarcane aphid,Melanaphis sacchari,on sugarcane cultivars with differential susceptibility and potential mechanism of resistance

Feeding behavior of Melanaphis sacchari Zehntner (Hemiptera: Aphididae) was studied on sugarcane, Saccharum spp. (Poaceae), cultivars HoCP 91‐555 (resistant), LCP 85‐384 (moderately resistant), and L 97‐128 (susceptible) using the electrical penetration graph (EPG) technique. Constitutive concentrations of total phenolics and available carbohydrates, water potential at the whole‐leaf tissue level, and free amino acids (FAAs) in phloem sap extracts, and in honeydew produced by aphids fed on L 97‐128 and HoCP 91‐555 were determined. Cultivar did not influence time for M. sacchari to access phloem sieve elements. Total time in sieve elements was ca. two‐fold greater on L 97‐128 than on HoCP 91‐555, whereas it did not differ from LCP 85‐384 in either cultivar. The mean duration of individual events associated with phloem sap ingestion was ca. 50% shorter on both HoCP 91‐555 and LCP 85‐384 than on L 97‐128. Although cultivar effects were not detected for levels of total phenolics, available carbohydrates, and water potential, two free essential amino acids, histidine and arginine, were absent from phloem sap in HoCP 91‐555. Two free essential amino acids, leucine and isoleucine, and two free non‐essential amino acids, tyrosine and proline, were absent from honeydew of aphids fed on HoCP 91‐555. These results suggest that despite apparent biosynthesis of some FAAs, the absence of important FAAs in the phloem sap of HoCP 91‐555 and the inability of M. sacchari and its endosymbionts (e.g., Buchnera) to derive specific free essential and non‐essential amino acids from other ingested molecules, possibly along with other unidentified factors, underlie the pest's decreased phloem sap ingestion and consequently reduced growth potential on HoCP 91‐555.