Pecan Aphid Research Articles

Pecan Aphid Complex and Their Management

Pecan Aphid Complex and Their Management

A molecular approach to unravel trophic interactions between parasitoids and hyperparasitoids associated with pecan aphids.

Advances in molecular ecology can overcome many challenges in understanding host-parasitoid interactions. Genetic characterization of the key-players in systems helps to confirm species and identify trophic linkages essential for ecological service delivery by biological control agents; however, relatively few agroecosystems have been explored using this approach. Pecan production consists of a large tree perennial system containing an assortment of seasonal pests and natural enemies. As a first step to characterizing host-parasitoid associations in pecan food webs, we focus on aphid species and their parasitoids. Based on DNA barcoding of field-collected and reared specimens, we confirmed the presence of 3 species of aphid, one family of primary parasitoids, and 5 species of hyperparasitoids. By applying metabarcoding to field-collected aphid mummies, we were able to identify multiple species within each aphid mummy to unravel a complex food web of 3 aphids, 2 primary parasitoids, and upward of 8 hyperparasitoid species. The results of this study demonstrate that multiple hyperparasitoid species attack a single primary parasitoid of pecan aphids, which may have negative consequences for successful aphid biological control. Although further research is needed on a broader spatial scale, our results suggest multiple species exist in this system and may suggest a complex set of interactions between parasitoids, hyperparasitoids, and the 3 aphid species. This was the first time that many of these species have been characterized and demonstrates the application of novel approaches to analyze the aphid-parasitoid food webs in pecans and other tree crop systems.

Evaluation of two methods for monitoring the blackmargined pecan aphid and its predators

The present study aimed to evaluate, qualitatively and quantitatively, yellow sticky traps and entomological net in the monitoring of Monellia caryella (Fitch, 1855) (Hemiptera: Aphididae) and its predators in a pecan plantation in Santa Maria, Rio Grande do Sul, Brazil. This plantation was implemented on 1.2 ha in February 2012 with the Barton and Shawnee varieties at a spacing of 7 m x 7 m. Twenty pecan plants were randomly selected to sample the blackmargined pecan aphid and its predators. From November 2014 to May 2015, 13 collections were carried out with yellow sticky traps and an entomological net. A total of 898 arthropod specimens were collected, 50.9% of which were from yellow sticky traps and 49.1% from the entomological net trap. Regarding the yellow sticky traps, only M. caryella was identified at the species level, with the predators identified at the taxonomic levels of order (Araneae) and family (Coccinellidae; Coleoptera). In terms of the entomological net, all the insects of interest at the species level were identified. There was a significant difference only between the averages in the number of Araneae specimens, with the highest density found in the yellow sticky traps. Both methods provided the correct identification of M. caryella and efficiently recorded its population peak. It is concluded that yellow sticky traps are effective for monitoring M. caryella, while the entomological net is suitable for monitoring and correctly identifying species of natural enemies of the insect pest in pecan plantations.

Canopy hedge pruning in pecan production differentially affects groups of arthropod pests and associated natural enemies

Controlling canopy growth and size through pruning techniques in perennial agroecosystems is often crucial to maximizing productivity. However, the implications of modifying canopy architecture for arthropod management are often overlooked. We studied the effects of hedge pruning on pests and natural enemies on mature pecan trees by assessing the abundance of: 1) leaf-dwelling aphids and mites, 2) visually detectable injuries caused by black pecan aphids [Melanocallis caryaefoliae (Davis)] and Phylloxera spp., 3) aphid parasitoids and parasitized hosts (aphid mummies), and 4) predatory mites. Additionally, we assessed the prevalence of entomopathogens that dwell on the orchard floor, under the trees. Hedge pruning decreased Phylloxera infestation but increased pressure from scorch mites and the yellow aphid complex. Black pecan aphid abundance responded inconsistently, but their damage was consistently reduced in hedged canopies. Predatory mites were only affected by hedging in the second year when higher populations were observed. Although parasitoid wasp abundance was not affected by hedging, more parasitized aphids (mummies) were observed in trees that did not receive pruning in the first year. Also, higher activity of entomopathogens was observed in soil cores collected under hedged trees in the first year but lower in the second. Taken together, the effects of hedge pruning pecan canopies were case-specific, and cannot be generalized across pests or natural enemies. Nevertheless, structural and environmental variation across seasons and within hedge pruning systems clearly have implications for crop protection in pecans and other perennial systems.

Toxicity of Photorhabdus luminescens and Xenorhabdus bovienii bacterial metabolites to pecan aphids (Hemiptera: Aphididae) and the lady beetle Harmonia axyridis (Coleoptera: Coccinellidae)

Toxicity of the metabolites of two bacteria, Photorhabdus luminescens and Xenorhabdus bovienii, symbionts of entomopathogenic nematodes, were tested in the laboratory against the multicolored Asian lady beetle, Harmonia axyridis, the black pecan aphid, Melanocallis caryaefoliae, and the blackmargined aphid, Monellia caryella. Bacterial broth prepared from both P. luminescens and X. bovienii demonstrated high levels of toxicity equivalent to the pyrethroid insecticide bifenthrin and caused higher insect mortality than tryptic soy broth plus yeast extract (TSY) (blank control) against M. caryella; broth culture of P. luminescens was more effective than TSY against M. caryaefoliae. At the levels tested, the metabolites were not toxic to H. axyridis.

Control of Curculio caryae (Coleoptera: Curculionidae) with Reduced Rates of a Microbial Biopesticide

Control of Curculio caryae (Coleoptera: Curculionidae) with Reduced Rates of a Microbial Biopesticide

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.

Impact of a biorational pesticide on the pecan aphid complex and its natural enemies

The pecan weevil, Curculio caryae (Horn) (Coleoptera: Curculionidae), and the pecan aphid (Hemiptera: Aphididae) complex: black pecan aphid, Melanocallis caryaefoliae (Davis), blackmargined aphid, Monellia caryella (Fitch), and yellow pecan aphid, Monelliopsis pecanis Bissell are major pests of pecan production. Management is primarily based on chemical insecticides, and alternative control methods need to be explored. Prior field tests showed that the microbial insecticide Grandevo® (based on Chromobacterium subtsugae) can suppress C. caryae at similar rates to insecticides, and a laboratory test showed that Grandevo is toxic to M. caryaefoliae. However, it was unknown if Grandevo applications targeted towards C. caryae also impact the pecan aphid complex and aphid natural enemies. Hence, we initiated a field study to determine the impact of two rates of Grandevo (2.24 and 3.36 kg/ha) on aphid, Coccinellidae (Coleoptera) and Chrysopidae (Neuroptera) populations. Both Grandevo rates, in both years of the study, suppressed M. caryaefoliae in comparison to the negative control. Only the standard chemical insecticide regimen suppressed M. caryella and M. pecanis combined populations during both years of the experiment. In 2016, both Grandevo rates had more abundant natural enemy populations compared with the chemical insecticide regimen, and the higher Grandevo rate (3.36 kg/ha) had more natural enemies than the non-treated control. In 2017, all treatments had comparable populations of natural enemies. These findings suggest that a microbial insecticide can manage multiple insect pests while preserving the natural enemy community.

Effects of Aphicides on Pecan Aphids and Their Parasitoids in Pecan Orchards.

Simple SummaryInsecticide application is the primary method for aphid management in commercial pecan orchards in the U.S. However, over-reliance and non-judicious insecticide use has led to numerous downsides, including insecticide resistance and impairment of beneficial insects. It is important to assess the efficacy and potential non-target impact of insecticides in order to create sustainable management programs. The objective of this study was to assess three insecticides (flonicamid, sulfoxaflor, and afidopyropen) on pecan aphids and their parasitoid 7, 14, and 21 days post-application in 2019 and 2020. In 2019, non-treated trees had up to 9-fold more aphids than treated trees 7 days post-application, but these differences diminished by 14 and 21 days after treatment application. Although aphid numbers were low during 2020, non-treated trees had more aphids in the lower canopy than most treated trees 7 days post-application. These differences diminished for the later assessments. Surprisingly, there was no significant difference in abundance of parasitoid adults or mummies between non-treated trees and treated trees. The results of this study indicate that growers have multiple products for aphid management, thus allowing product rotation to slow development of aphid resistance.Aphids are important pests of pecans. Traditionally, insecticides have been the primary method of management. However, over-reliance and non-judicious use has led to resistance and damage to natural enemy populations. Therefore, frequent assessment of insecticides is necessary in order to monitor resistance development and non-target impacts. Aphicides, flonicamid, sulfoxaflor, and afidopyropen were assessed for their effects on pecan aphids and parasitoid, Aphelinus perpallidus, in a mature pecan orchard in 2019 and 2020. Post-application assessments were performed 7, 14, and 21 days post-application. Leaf samples from non-treated trees had greater aphid numbers than treated trees 7 days post-application with differences diminishing throughout the other two treatment periods in 2019. In 2020, aphid numbers were lower but leaf samples from non-treated trees had more aphids than treated trees 7 days post-application in the lower canopy. These differences again diminished 14 and 21 days post-application. There was no difference among treatments in number of parasitoid adults or mummies. These findings indicate that pecan growers have multiple potential options available for aphid management that do not negatively impact the primary pecan aphid parasitoid. Implications of the results on pecan aphid management are discussed.

Insecticide Efficacy Against Pecan Aphids and Pecan Leaf Scorch Mites, 2018

Insecticide Efficacy Against Pecan Aphids and Pecan Leaf Scorch Mites, 2018

Insecticide Efficacy for Controlling Pecan Aphids, 2018

Insecticide Efficacy for Controlling Pecan Aphids, 2018

Establishment of Beauveria bassiana as a fungal endophyte in pecan (Carya illinoinensis) seedlings and its virulence against pecan insect pests

Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of the world’s pecans. Several insect pests and various plant diseases reduce crop yield directly destroying nutmeats, or indirectly through effects on foliage and shucks, reducing photosynthesis. Beauveria bassiana is a well-studied, commercialized fungal entomopathogen that when applied inundatively is an effective biocontrol agent against certain pecan pests. In addition to being used in inundative biocontrol, B. bassiana can exist as an endophyte in many plant species and has been shown in some cases to reduce pest damage when present as an endophyte. The potential for B. bassiana to exist as an endophyte in pecan had not been explored previously. We tested whether B. bassiana could endophytically colonize pecan seedlings by seed soaking, seed coating and soil drenching. Results indicated that B. bassiana became established in the roots, leaves and stems of pecan seedlings. Establishment was verified using molecular techniques as well as completing Koch’s postulates on the re-isolated fungus, infecting two susceptible insect hosts (Galleria mellonella and Tenebrio molitor) and a target pest (Curculio caryae). Subsequently we explored whether the established endophytic fungus suppressed two pecan aphid species. In a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryella) were reduced when placed on leaves of pecan that were colonized endophytically with B. bassiana, relative to control leaves. Our study demonstrates the ability to establish endophytic B. bassiana in pecan and the potential to apply this capability in pecan pest management. Additional research is needed to determine the utility of the endophytic approach against various insect and plant pathogens and to measure efficacy under field conditions.

DISTRIBUTION OF THE BLACK PECAN APHID ON PECAN LEAF SURFACES: AN OVERVIEW

Three species of aphids regularly attack pecan, Carya illinoinensis, foliage. Two of them, i.e., the blackmargined aphid and the yellow pecan aphid, are predominantly distributed on the lower leaf surface, as are adults and nymphs of most tree-feeding aphid species. This surface provides aphids protection from rain, solar radiation, honeydew dropped by aphids on leaves above and the protruding leaf veins of the lower leaf surface protect from dislodgement by the movement and abrasion of other leaves. However, nymphs of the third species, i.e., black pecan aphid (BPA), do not follow this distribution pattern. Although adult BPA are mostly found on the lower surface, nymphs are distributed about equally between both leaf surfaces. BPA nymphs need to remain stationary to elicit chlorotic feeding lesions and this may explain their movement to the upper leaf surface. Natural enemies spending more time searching the lower surface coupled with BPA nymphs staying in one location to feed provides the best explanation for the observed distribution of BPA nymphs and adults. BPA nymphs that do not remain stationary to elicit chlorotic lesions face higher mortality (in the absence of predators), take longer to develop and result in smaller adults. Thus, BPA nymphs likely move to the upper leaf surface as a predator avoidance strategy.

TEXAS RESULTS: IMIDACLOPRID RESISTANCE IN BLACKMARGINED PECAN APHIDS

During the 2011 and 2012 growing seasons, 46 separate laboratory tests of blackmargined pecan aphid (BMA) populations from 11 Texas counties were tested against imidacloprid. All testing was conducted in a laboratory setting by placing BMA alataes on treated foliage and recoding mortality and first instar production after 24, 48 and 72 h of continuous exposure. Results after 72 h of continuous exposure to imidacloprid treated foliage ranged from 85% survival and 165 first instars to 0% survival and no reproduction. This range of control indicated that there are areas of resistance in Texas. When difficult to control populations were detected, populations were retested against products with different modes of action (IRAC Groups 4C, sulfoxaflor; Group 9B, pymetrozine and Group 9C, flonicamid) effective control was achieved. Where imidacloprid was effective against blackmargined aphid populations, effective control was also achieved by another IRAC Group 4A insecticide – clothianidin. Based on two years of test results, recommendations to producers for management actions to reduce or prevent resistance to imidacloprid in BMA populations include: 1) rotate IRAC group numbered products; 2) do not use more than two consecutive applications of the same IRAC group numbered product per season; 3) where possible, treat only problem varieties or areas; and 4) do not base your treatment decision just on the presence of honeydew.

Performance of 19 Pecan Cultivars and Selections in Southern Georgia

Nineteen pecan (Carya illinoinensis) clones were evaluated over a period of 18 years in a test orchard located in southern Georgia. Clones tested were primarily U.S. Department of Agriculture selections, but two grower-discovered cultivars, Jubilee and Surprize, were also trialed. Annual yields were measured for each tree in the test throughout the test period and the alternate bearing intensity of each cultivar was calculated. Average annual in-shell nut production in years 1–10 ranged from 12 lb in the precocious USDA 76-4-41 to 0 lb in the non-precocious USDA 72-8-4. Wide variation was seen in nut production of trees in years 11–18, averaging from 10 to 60 lb nut yield per year. A subsample of nuts was taken from each tree annually and percent kernel, nuts per pound, specific gravity, and nut volume were determined. Significant differences were found between clones for each of these traits. Differences were also found for the presence of damage from pecan scab [Fusicladium effusum (synonym Cladosporium caryigenum)] and black pecan aphid (Melanocallis caryaefoliae). Most clones were not acceptable for use in Georgia due to small nut size or poor kernel quality, but two clones merit further testing in this region. USDA 70-3-34 produced a large nut with good quality and scab resistance, but needs to be evaluated with mechanical crop thinning to improve kernel quality in high crop-set years. USDA 74-1-12 produced good yields of excellent quality, medium-sized pecans and should be trialed with greater tree numbers. Several other clones were found to have traits of interest to pecan breeding programs including: pecan scab resistance, large nut size, and high kernel percentage. Results of this trial suggest that cultivar development programs in Georgia should place greater selection emphasis on large nut size.

Control of Key Pecan Insect Pests Using Biorational Pesticides

Key pecan insect pests include the black pecan aphid, Melanocallis caryaefoliae (Davis), pecan weevil, Curculio caryae (Horn), and stink bugs (Hemiptera: Pentatomidae). Alternative control tactics are needed for management of these pests in organic and conventional systems. Our objective was to evaluate the potential utility of several alternative insecticides including three plant extract formulations, eucalyptus extract, citrus extract-8.92%, and citrus extract-19.4%, and two microbial insecticides, Chromobacterium subtsugae (Martin et al.) and Isaria fumosorosea (Wize). In the laboratory, eucalyptus extract, citrus extract-8.92%, citrus extract-19.4%, and C. subtsugae caused M. caryaefoliae mortality (mortality was reached approximately 78, 83, and 96%, respectively). In field tests, combined applications of I. fumosorosea with eucalyptus extract were synergistic and caused up to 82% mortality in M. caryaefoliae. In laboratory assays focusing on C. caryae suppression, C. subtsugae reduced feeding and oviposition damage, eucalyptus extract and citrus extract-19.4% were ineffective, and antagonism was observed when citrus extract-19.4% was combined with the entomopathogenic nematode, Steinernema carpocapsae (Weiser). In field tests, C. subtsugae reduced C. caryae damage by 55% within the first 3d, and caused 74.5% corrected mortality within 7 d posttreatment. In the laboratory, C. subtsugae and eucalyptus extract did not cause mortality in the brown stink bug, Euschistus servus (Say). Applications of C. subtsugae for suppression of C. caryae, and eucalyptus extract plus I. fumosorosea for control of M. caryaefoliae show promise as alternative insecticides and should be evaluated further.

Distribution of the black pecan aphid, Melanocallis caryaefoliae, on the upper and lower surface of pecan foliage

AbstractThree aphid species regularly feed on pecan [Carya illinoinensis (Wangenh.) K. Koch (Juglandaceae)] foliage: the black pecan aphid, Melanocallis caryaefoliae (Davis), the yellow pecan aphid, Monelliopsis pecanis Bissell, and the blackmargined aphid, Monellia caryella (Fitch) (all Hemiptera: Aphididae). Adults of M. caryaefoliae and both the nymphs and adults of M. pecanis and M. caryella mainly feed on the lower surface of leaves. Nymphs of M. caryaefoliae appear unique by frequently feeding on the upper surface of pecan leaves. This is risky behavior given the environmental hazards (e.g., rain, solar radiation, and dislodgement) associated with the upper surface. Thus, we determined the leaf surface distribution of M. caryaefoliae on trees in an orchard and on pecan seedlings in the laboratory. A pecan orchard survey found all three aphid species and stages predominantly on the lower leaf surface, except for the nymphs of M. caryaefoliae, which were evenly distributed between upper and lower leaf surfaces. This survey also found aphidophagous lacewing (Neuroptera) larvae predominantly on the lower leaf surface, whereas ladybird beetle (Coleoptera: Coccinellidae) larvae were more evenly distributed between upper and lower surfaces. Laboratory experiments using single or multiple pecan aphid species revealed M. caryaefoliae distribution on pecan seedlings similar to orchard data. Nymphal M. caryaefoliae require nearly 2 days to elicit chlorotic feeding lesions on leaves; without these lesions, nymphal development is hindered. The similar distribution of nymphs of M. caryaefoliae on both leaf surfaces likely reflects a strategy of predator avoidance allowing a proportion of the population to survive.

Seasonal Abundance of Aphids and Aphidophagous Insects in Pecan.

Seasonal occurrence of aphids and aphidophagous insects was monitored for six years (2006–2011) from full leaf expansion in May to leaf fall in October in “Desirable” variety pecan trees that were not treated with insecticides. Aphid outbreaks occurred two times per season, once in the spring and again in the late summer. Yellow pecan and blackmargined aphids exceeded the recommended treatment thresholds one time and black pecan aphids exceeded the recommended treatment levels three times over the six seasons. Increases in aphidophagous insect abundance coincided with aphid outbreaks in five of the six seasons. Among aphidophagous insects Harmonia axyridis and Olla v-nigrum were frequently collected in both the tree canopy and at the ground level, whereas, Coccinella septempunctata, Hippodamia convergens were rarely found in the tree canopy and commonly found at the ground level. Green lacewing abundance was higher in the ground level than in the tree canopy. Brown lacewings were more abundant in the tree canopy than at the ground level. Dolichopodid and syrphid fly abundance, at the ground level increased during peak aphid abundance in the tree canopy. Application of an aqueous solution of fermenting molasses to the pecan foliage during an aphid outbreak significantly increased the abundance of ladybeetles and lacewings and significantly reduced the abundance of yellow pecan, blackmargined and black pecan aphids.

Immigrant inviability in yellow pecan aphid

1. Host-associated differentiation (HAD) may be an important driver of parasite biodiversity. The sympatric occurrence of host-associated populations features prominently in studies documenting HAD but this neither confirms nor denies that the lineages arose in sympatry. It does raise the question of what maintains such structure despite the proximity of populations in space and time. 2. We tested for immigrant inviability in yellow pecan aphid Monelliopsis pecanis Bissell, a species previously shown to be host associated, using a laboratory reciprocal transplant experiment on pecan and water hickory. 3. Immigrant inviability on the alternative host is present in yellow pecan aphid. Immigrants to both hosts were significantly less fecund than residents and their nymphs were significantly less viable. Future studies should establish the genetic and non-genetic (maternal effects) basis of immigrant inviability in yellow pecan aphid in order to be certain about its contribution to pre-mating reproductive isolation. 4. Since aphids are cyclic parthenogens, inviability of both immigrants and their offspring has the potential to contribute to total pre-mating reproductive isolation. This is different than the case of obligate sexually reproducing organisms where offspring viability is a post-mating reproductive isolating mechanism. We discuss the implications of this for estimating the contributions of immigrant and offspring inviability to total reproductive isolation in aphids.