Chlorotic feeding injury by the black pecan aphid (hemiptera: aphididae) to pecan foliage promotes aphid settling and nymphal development

Black Pecan Aphid (Hemiptera: Aphididae) Management on Pecan When Gibberellic Acid Is Applied Concurrently With Broad-Spectrum Insecticides

Aphids (Hemiptera: Aphididae) are serious pests of pecan foliage (Carya illinoinensis [Wangenh.] K. Koch). The black pecan aphid, Melanocallis caryaefoliae (Davis) (Hemiptera: Aphididae), feeds on pecan foliage and elicits leaf chlorosis that can cause defoliation. In contrast, the blackmargined aphid, Monellia caryella (Fitch) (Hemiptera: Aphididae), and yellow pecan aphid, Monelliopsis pecanis Bissell (Hemiptera: Aphididae), feed on pecan foliage but do not elicit chlorotic feeding injury. Application of gibberellic acid (GA3) to pecan foliage reduces chlorotic foliar injury and nymphal populations of the black pecan aphid. GA3 has potential to manage black pecan aphid later in the season when broad-spectrum insecticides are used to control direct pests of pecan nuts but also inadvertently induce aphid outbreaks. Here, broad-spectrum insecticides were used with GA3 or aphicides in orchard trials for 2 yr. Populations of aphids and natural enemies along with chlorotic feeding injury on foliage were assessed. When used concurrently with GA3 or aphicides, broad-spectrum insecticides did not flare black pecan aphid populations. However, combined populations blackmargined aphids and yellow pecan aphids were higher in treatments with GA3 than with an aphicide or in the control treatment during one of two years. Application of GA3 or the aphicide often led to significantly less chlorotic injury than observed in the control. Surprisingly, natural enemies were not significantly affected by broad-spectrum insecticides when applied concurrently with GA3. These results show that GA3 can be used as part of a late-season IPM strategy to protect foliage from localized chlorotic leaf injury elicited by the black pecan aphid.

Multisite Seasonal Monitoring of Pecan Aphids and Their Parasitoid in Commercial Pecan Orchards

Aphids are important pests of pecans in Georgia. Although previous studies conducted seasonal monitoring of pecan aphids, these studies were done at a single experimental site. In addition, only a few seasonal monitoring studies have tracked pecan aphid mummies parasitized by the aphid parasitoid, Aphelinus perpallidus Gahan. The objective of this study was to assess the seasonal phenology of yellow pecan aphid (Monelliopsis pecanis Bissell), blackmargined aphid [Monellia caryella (Fitch)], black pecan aphid [Melanocallis caryaefoliae (Davis)], aphid mummies, and adult A. perpallidus in four Georgia commercial orchards, with varying aphid management regimes, in 2019 and 2020. Comparison of overall aphid and parasitoid numbers between sites revealed few consistent annual patterns in both years. Aphid seasonal trends were consistent among sites and followed the patterns seen in previous studies, with the yellow aphid complex peaking in May, June, September, and October and black pecan aphids peaking in late September and October. Despite varying levels of insecticide application between sites, aphid phenology followed a similar seasonal pattern and remained low, throughout both growing seasons. This may indicate that growers can apply low frequencies of insecticides and still achieve pecan aphid control. Parasitism numbers were highest in the low insecticide frequency site compared with the other three sites. Mummies varied in their correlation with yellow aphid complex and black pecan aphid numbers. Parasitoid numbers typically followed the cycle of their host throughout the season.

Gibberellic acid decreases Melanocallis caryaefoliae (Hemiptera: Aphididae) population density and chlorotic feeding injury to foliage in pecan orchards

BACKGROUND

Melanocallis caryaefoliae (Davis), Monellia caryella (Fitch), and Monelliopsis pecanis Bissell (Hemiptera: Aphididae) attack pecan foliage (Carya illinoinensis [Wangenh.] K. Koch). Unlike M. caryella and M. pecanis, feeding by M. caryaefoliae triggers a physiological change within foliage mimicking natural leaf senescence; it can lead to defoliation. Pretreatment of pecan foliage with gibberellic acid (GA₃ ) mitigates M. caryaefoliae-elicited physiological disturbances. GA₃ application to pecan was evaluated for efficacy regarding effects on M. caryaefoliae populations and possible negative side-effects on two natural enemy species and on return bloom of pecan.

RESULTS

All GA₃ treatment rate schedules significantly reduced M. caryaefoliae nymphs but not adults or adults and nymphs of M. caryella or M. pecanis. Percentage leaf chlorosis elicited by M. caryaefoliae was significantly reduced by GA₃ (i.e., 39.5 to 197.7 g a.i./ha). No negative side-effects of GA₃ treatment were detected regarding certain key natural enemy species or on return bloom of pecan.

CONCULUSION

Application of GA₃ to the orchard canopy protects foliage from senescence-like physiological responses triggered by M. caryaefoliae. This reduces detrimental leaflet chlorosis, both senescence and abscission processes and horticulturally significant feeding injury. Additionally, the absence of apparent negative side-effects on key natural enemies and return bloom is suggestive of a practical means for efficacious non-insecticidal control of M. caryaefoliae populations in orchards. This novel protective effect of GA₃ against aphid-elicited, senescence-like physiological responses may merit investigation as an IPM tool to manage aphid species eliciting similar senescence-like damage to other crop species. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Synthesis and characterization of bio-based quaternary ammonium salts with gibberellate or l-tryptophanate anion

Numerous biologically active acids can be transformed into an ionic form in a facile way and combined with appropriate quaternary ammonium cation to improve their application properties or biological activity. This study describes the synthesis of new quaternary ammonium salts with anions of gibberellic acid, a common plant growth regulator from the gibberellin group, or l-tryptophan, an important precursor of auxin biosynthesis. The surface-active tetrapentylammonium ion and natural substances such as acetylcholine, choline, and quinine were the sources of cations. Novel salts of gibberellic acid and l-tryptophan were obtained with high yields exceeding 97% as a result of the metathesis reaction or the neutralization of quaternary ammonium hydroxides. Phase transition temperatures, thermal and chemical stability, and solubility in solvents with different polarities were determined for all obtained salts. On the basis of studies regarding the influence of synthesized salts on the post-harvest longevity and quality of leaves of Convallaria majalis, it was established that the biological activity of the natural plant regulators in most cases was maintained. Therefore, it can be concluded that the conversion of the active substance into the form of a quaternary ammonium salt results in obtaining novel forms of plant growth regulators with favourable physicochemical properties while maintaining the efficacy of the biological active ingredients.

Graphic abstract

O3-Induced Leaf Senescence in Tomato Plants Is Ethylene Signaling-Dependent and Enhances the Population Abundance of Bemisia tabaci

Elevated ozone (O3) can alter the phenotypes of host plants particularly in induction of leaf senescence, but few reports examine the involvement of phytohormone in O3-induced changes in host phenotypes that influence the foraging quality for insects. Here, we used an ethylene (ET) receptor mutant Nr and its wild-type to determine the function of the ET signaling pathway in O3-induced leaf senescence, and bottom-up effects on the performance of Bemisia tabaci in field open-top chambers (OTCs). Our results showed that elevated O3 reduced photosynthetic efficiency and chlorophyll content and induced leaf senescence of plant regardless of plant genotype. Leaf senescence in Nr plants was alleviated relative to wild-type under elevated O3. Further analyses of foliar quality showed that elevated O3 had little effect on phytohormone-mediated defenses, but significantly increased the concentration of amino acids in two plant genotypes. Furthermore, Nr plants had lower amino acid content relative to wild-type under elevated O3. These results provided an explanation of O3-induced increase in abundance of B. tabaci. We concluded that O3-induced senescence of plant was ET signal-dependent, and positive effects of O3-induced leaf senescence on the performance of B. tabaci largely resulted from changes of nutritional quality of host plants.

Boom and bust: rapid feedback responses between insect outbreak dynamics and canopy leaf area impacted by rainfall and CO2

Frequency and severity of insect outbreaks in forest ecosystems are predicted to increase with climate change. How this will impact canopy leaf area in future climates is rarely tested. Here, we document function of insect outbreaks that fortuitously and rapidly occurred in an ecosystem under free-air CO₂ enrichment. Over the first 2 years of CO₂ fumigation of a naturally established mature Eucalyptus woodland, we continuously assessed population responses of three sap-feeding insect species of the psyllid genera Cardiaspina, Glycaspis and Spondyliaspis for up to ten consecutive generations. Concurrently, we quantified changes in the canopy leaf area index (LAI). Large and rapid shifts in psyllid community composition were recorded between species with either flush (Glycaspis) or senescence-inducing (Cardiaspina, Spondyliaspis) feeding strategies. Within the second year, two psyllid species experienced significant and rapid population build-up resulting in two consecutive outbreaks: first, rainfall stimulated Eucalyptus leaf production increasing LAI, which supported population growth of flush-feeding Glycaspis without impacting LAI. Glycaspis numbers then crashed and were followed by the outbreak of senescence-feeding Cardiaspina fiscella that led to significant defoliation and reduction in LAI. For all three psyllid species, the abundance of lerps, protective coverings excreted by the sessile nymphs, decreased at e[CO₂ ]. Higher lerp weight at e[CO₂ ] for Glycaspis but not the other psyllid species provided evidence for compensatory feeding by the flush feeder but not the two senescence feeders. Our study demonstrates that rainfall drives leaf phenology, facilitating the rapid boom-and-bust succession of psyllid species, eventually leading to significant defoliation due to the second but not the first outbreaking psyllid species. In contrast, e[CO₂ ] may impact psyllid abundance and feeding behaviour, with psyllid species-specific outcomes for defoliation severity, nutrient transfer and trophic cascades. Psyllid populations feeding on Eucalyptus experience rapid boom-and-bust cycles depending on availability of suitable foliage driven by rainfall patterns and leaf phenology.

Response of Solanum tuberosum to Myzus persicae infestation at different stages of foliage maturity

Young leaves of the potato Solanum tuberosum L. cultivar Kardal contain resistance factors to the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) and normal probing behavior is impeded. However, M. persicae can survive and reproduce on mature and senescent leaves of the cv. Kardal plant without problems. We compared the settling of M. persicae on young and old leaves and analyzed the impact of aphids settling on the plant in terms of gene expression. Settling, as measured by aphid numbers staying on young or old leaves, showed that after 21 h significantly fewer aphids were found on the young leaves. At earlier time points there were no difference between young and old leaves, suggesting that the young leaf resistance factors are not located at the surface level but deeper in the tissue. Gene expression was measured in plants at 96 h postinfestation, which is at a late stage in the interaction and in compatible interactions this is long enough for host plant acceptance to occur. In old leaves of cv. Kardal (compatible interaction), M. persicae infestation elicited a higher number of differentially regulated genes than in young leaves. The plant response to aphid infestation included a larger number of genes induced than repressed, and the proportion of induced versus repressed genes was larger in young than in old leaves. Several genes changing expression seem to be involved in changing the metabolic state of the leaf from source to sink.

Induced senescence promotes the feeding activities and nymph development of Myzus persicae (Hemiptera: Aphididae) on potato plants

The effect of dark-induced senescence on Solanum tuberosum L. (Solanales: Solanaceae) plants was assessed on the feeding behavior and performance of the green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). Senescence was induced by covering the basal part of the plant with a black cloth for 5 d, avoiding the light passage, but keeping the apical buds uncovered. The basal part of control plants was covered with a white nonwoven cloth. The degree of senescence was determined by measuring the chlorophyll content of the covered leaves. The performance and feeding behavior of M. persicae were studied on the uncovered nonsenescent apical leaves. The aphid's performance was evaluated by measuring nymphal mortality and prereproductive time. Aphid feeding behavior was monitored by the electrical penetration graph technique. In plants with dark-induced senescence, the aphids showed a reduction in their prereproductive time. Aphids also spent more time ingesting sap from the phloem than in control plants and performed more test probes after the first sustained ingestion of phloem sap. These data suggest that M. persicae's phloem activities and nymph development benefit from the nutritional enrichment of phloem sap, derived from dark-induced senescence on potato plants. The induced senescence improved plant acceptance by M. persicae through an increase in sap ingestion that likely resulted in a reduction in developmental time.

Application of plant growth regulators mitigates chlorotic foliar injury by the black pecan aphid (Hemiptera: Aphididae)

BACKGROUND

Black pecan aphid, Melanocallis caryaefoliae (Davis) (Hemiptera: Aphididae), feeding elicits localized chlorotic injury to pecan foliage [Carya illinoinensis (Wangenh.) K Koch] and apparent acceleration of leaf senescence and defoliation. The ability of certain plant growth regulators (PGRs) (forchlorfenuron, gibberellic acid and aviglycine) to prevent M. caryaefoliae from triggering pecan leaf chlorosis and senescence-like processes was evaluated on two dates in both 2006 and 2007. Treatments were applied to orchard foliage and used in laboratory leaf-disc bioassays to assess possible reduction in aphid-elicited chlorosis and concomitant effects on aphid mortality and development.

RESULTS

Foliage pretreated with forchlorfenuron + gibberellic acid prior to being challenged with aphids resulted in significantly less aphid-elicited chlorosis than did control or aviglycine-treated leaf discs. No PGR affected aphid mortality; however, development time was increased by forchlorfenuron + gibberellic acid in 2006 and by aviglycine + gibberellic acid on one date in 2007.

CONCLUSION

Certain PGRs possess the potential for usage on pecan to protect foliar canopies from M. caryaefoliae via changes in the susceptibility of the host leaf to senescence-like factors being introduced by feeding aphids. This protective effect on host foliage and the associated suppressive effect on development of feeding aphids might also be relevant to pest management programs on other aphid-crop systems in which aphid-elicited chlorosis and senescence-like processes can limit profitability.