Russell F. Mizell

Feeding by the leafhopper, Homalodisca coagulata, in relation to xylem fluid chemistry and tension

Abstract Feeding by the adult leafhopper [Homalodisca coagulata (Say)], a polyphagous xylem feeder, was monitored in response to changes in xylem tension, and the concentration of amino acids, organic acids and sugars in xylem fluid. Models were constructed based on diurnal feeding patterns on a preferred host, Lagerstroemia indica L. Feeding rate (measured by excretion rate) was best correlated with the concentration of the amides. Correlation coefficients of other amino acids were low. Models were tested by monitoring feeding rates diurnally on Pyrus communis L. and Vitis hybrid cv. Suwannee, and during midday on L. indica subjected to water stress. Only total amino acids, amides and glutamine were correlated with feeding on P. communis and on Vitis. When L. indica were subjected to a high level of water stress, feeding during midday was associated with xylem tension, and not the concentration of chemical variables. Feeding rate decreased exponentially as a function of xylem tension; feeding ceased above a tension of about 2.1 MPa. Models were substantially improved when compounds were expressed on a ratio basis. Feeding rate was best correlated with the ratio of amides to total organic compounds (RAM) in the diurnal experiments. In the stress experiment, amides/xylem tension provided the best correlation. Net energy gain (Xneg) of an insect feeding on xylem fluid was described by the equation: Xneg = 0.70(Xe) - Excoef(Xt − P), where 0.70(Xe) = net energy content of xylem fluid, Excoef = the extraction coefficient, Xt = xylem tension and P = the Poiseuilles law-derived pressure to account for fluid movement through stylets.

Metabolism of amino acids, organic acids and sugars extracted from the xylem fluid of four host plants by adult Homalodisca coagulata

The efficiency of amino acid, organic acid and sugar metabolism was quantified for adult Homalodisca coagulata (Say) (Homoptera: Cicadellidae) by comparing chemical profiles of xylem fluid (food source) and insect exudate. Leafhoppers were confined in Parafilm® sachets to stems of 4 host plants: [Baccharis halimifolia (L.), Lagerstroemia indica (L.), Prunus salicina (Lindl.), Prunus persica (L.), Batsch]. Insect feeding rates (0.09‐0.27 ml h−1***), exudate osmolarity (7.8–12.8 mM) and exudate composition (mainly inorganic entities) were characteristic of a xylem feeder. Total organic solute concentration in the xylem fluid of B. halimifolia, L. indica, P. salicina and P. persica was ca. 9.4, 13,8, 5.5 and 1.8 mM, respectively. Nineteen protein amino acids, 7 organic acids and 3 or 4 sugars were identified in the xylem fluid. Total amino acids, organic acids and sugars were metabolized with ca. 99% efficiency. Glutamine, asparagine, arginine and citric, malic and succinic acids, the predominant organic compounds in the xylem fluid of all four plant species, were metabolized with greater than 99% efficiency. Cysteine (51%), methionine (74%) and oxalic acid (77%) were metabolized with the lowest efficiency. The primary nitrogenous waste was NH+4; uric acid or urea were not detected. Nitrogen retention was generally less than 60% of dietary nitrogen. High feeding rates, ammonotelism and an extremely high metabolic efficiency of organic compounds permit H. coagulata to subsist on the dilute and skewed chemical profile of xylem fluid.

Amino acids as determinants of host preference for the xylem feeding leafhopper, Homalodisca coagulata (Homoptera: Cicadellidae).

SummaryHomalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in its selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.

Scientific Notes: Toxicity of Imidacloprid to Selected Arthropod Predators in the Laboratory

Imidacloprid, BAY NTN 33893, 1-[(Chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro1H-imidazol-2-amine, is an insecticide being developed worldwide by Bayer AG and in the U.S. by the Mobay Corporation (Anonymous 1990). This nitromethylene compound is a broad-spectrum, systemic insecticide which has shown activity against sucking insects such as Homoptera and some Coleoptera, Diptera and Lepidoptera. It also has shown excellent potential in seed and soil applications (Schmeer et al. 1990, Dewar & Read 1990). Imidacloprid has no known activity against phytophagous mites or nematodes (Elbert & Overbeck 1990). Mobay anticipates registration of imidacloprid on many commodities including vegetables, field crops, fruit, turf and ornamentals. Imidacloprid is a category 3 or 4 compound, depending upon formulation, and is relatively non-toxic to mammals (Elbert & Overbeck 1990). The systemic properties of imidacloprid may be useful with respect to activity against pests and selectivity to beneficial species. However, control of many target pests will require foliar applications which may also affect beneficial arthropods. The objective of this study was to determine the toxicity of imidacloprid to selected beneficial arthropods commonly found in agroecosystems. The 240 FS formulation (240 g ai/liter) of imidacloprid, obtained from Mobay Corporation, was used in the bioassays. Dilutions tested varied by predator response (Table 1), and 127.4 ppm active ingredient, the recommended concentration for foliar application, was used as the 1X rate. Laboratory tests of the toxicity of imidacloprid residues to the following predatory species were conducted: adults of the mirid, Deraeocoris nebulosus (Uhler); larvae in the last instar and adults of the coccinellid, Olla v-nigrum (Mulsant); adults of the coccinellid, Hippodamia convergens (Guerin-Meneville); adult females of the phytoseiid mites, Neoseiulus collegae (De Leon), Phytoseiulus macropilis (Banks), and Proprioseiopsis mexacanus (Garman); eggs and adults of the chrysopid, Chrysoperla rufilabris (Burmeister) from a Georgia colony and adults from a Texas colony; and adults of the lygaeid, Geocoris punctipes (Say). Some of the predators were collected in the field; however, the predatory mites and C. rufilabris were obtained from laboratory cultures. The female mites were from a one-year-old colony and had been adults for approximately 5-10 days. The Georgia C. rufilabris were from a one-year-old colony and had been adults for 15-30 days when tested. C. rufilabris from Texas were from a 2to 3-year-old colony and were approximately 5 days old when tested. Predators were provided water, a 1:1:1, honey:glycerin:water solution and/or wheast before and during the tests. All predators collected in the field were tested within 3 h of collection. Tests were conducted by exposing the predators to plastic petri dishes or diet cups with lids (29.6 ml) dipped in solutions of water + imidacloprid + Triton 1956 (0.1 mllliter)

Spatiotemporal Patterns and Dispersal of Stink Bugs (Heteroptera: Pentatomidae) in Peanut-Cotton Farmscapes

ABSTRACT In the southeast United States, a field of peanuts, Arachis hypogaea L., is often closely associated with a field of cotton, Gossypium hirsutum L. The objective of this 4-yr on-farm study was to examine and compare the spatiotemporal patterns and dispersal of the southern green stink bug, Nezara viridula L., and the brown stink bug, Euschistus servus (Say), in six of these peanut-cotton farmscapes. GS+ Version 9 was used to generate interpolated estimates of stink bug density by inverse distance weighting. Interpolated stink bug population raster maps were constructed using ArcMap Version 9.2. This technique was used to show any change in distribution of stink bugs in the farmscape over time. SADIE (spatial analysis by distance indices) methodology was used to examine spatial aggregation of individual stink bug species and spatial association of the two stink bug species in the individual crops. Altogether, the spatiotemporal analyses for the farmscapes showed that some N. viridula and E. servus nymphs and adults that develop in peanuts disperse into cotton. When these stink bugs disperse from peanuts into cotton, they aggregate in cotton at the interface, or common boundary, of the two crops while feeding on cotton bolls. Therefore, there is a pronounced edge effect observed in the distribution of stink bugs as they colonize the new crop, cotton. The driving force for the spatiotemporal distribution and dispersal of both stink bug species in peanut-cotton farmscapes seems to be availability of food in time and space mitigated by landscape structure. Thus, an understanding of farmscape ecology of stink bugs and their natural enemies is necessary to strategically place, in time and space, biologically based management strategies that control stink bug populations while conserving natural enemies and the environment and reducing off-farm inputs.

Physiological and behavioral adaptations of three species of leafhoppers in response to the dilute nutrient content of xylem fluid

Abstract Physiological and behavioral processes of three species of leafhoppers were examined in relation to the extremely dilute content of their food source (xylem fluid). Segregated sexes of Homalodisca coagulata (Say), Homalodisca insolita (Wlk.) and Cuerna costalis (F.) were caged on two hosts, Lagerstroemia indica L. and Catharanthus roseus (L.). Excreta was analyzed and compared to the composition of xylem fluid of the hosts during day and night feeding. Both xylem fluid and insect excreta were analyzed for amino acids, organic acids and sugars and excreta was also analyzed for common excretory products. Efficiencies of metabolic conversion of organic compounds (defined by quantity ingested versus quantity excreted), and total nitrogen and carbon retention were calculated. Diurnal feeding patterns as well as total daily ingestion rates were recorded. Four primary similarities were noted in diet utilization regardless of leafhopper species, host species or sex: (1) excretion of ammonia as the primary waste product; (2) high efficiency of conversion for all organic compounds ingested from xylem fluid; (3) high daily feeding rates (100–300 times dry body weight per day and (4) adjustment of feeding rates to diurnal fluctuations in xylem fluid chemistry. Although these processes were operative for all leafhoppers examined, the extent of their usage and subsequent energy gain and nitrogen accumulation varied greatly with host species and insect sex. These processes maximize efficiency of diet utilization and are discussed in relation to nutritional and caloric requirements of xylem feeding insects.

Egg parasitoids of Homalodisca coagulata (Homoptera: Cicadellidae).

The glassy-winged sharpshooter, Homalodisca coagulata (Say), is native to the southeastern United States. It has existed in southern California since about 1990 (Sorensen & Gill 1996), and has become an economic problem as a vector of the pathogenic bacterium Xylella sp., that is the cause of leaf scorch disease in oleander. H. coagulata also feeds on citrus and many other plants. In October 1995, the mymarid wasp Gonatocerus ashmeadi Girault was reared from egg clusters of H. coagulata collected on citrus leaves in Santa Paula, California (Triapitsyn & Phillips 1996). This finding prompted us to conduct a limited survey of egg parasitoids of H. coagulata in California and also in the southeastern United States to assess the feasibility of a biological control program against this pest. Prior to this study, published information concerning natural enemies of H. coagulata was limited to the work by Turner & Pollard (1959) in Georgia. Egg masses of H. coagulata are rather conspicuous and thus easy to locate on the underside of leaves. The female leafhopper covers its eggs with a white, chalky material, which may have a bactericidal effect, and spreads this material over the eggs using the tarsi. Parasitized eggs turn black before parasitoids exit through characteristic emergence holes. To obtain parasitoids, leaves with H. coagulata egg masses were collected and held in plastic containers. Upon emergence, parasitoids were placed directly in 70% ethyl alcohol and later identified by the senior author. In California (1996-1997), parasitized H. coagulata eggs were collected on various ornamental plants on the University of California, Riverside campus. Eggs collected early in spring were not parasitized. During summer, G. ashmeadi was found in all samples from southern California and in rather large numbers (up to 80% of eggs were parasitized in Riverside in the July 1997 samples). Three other species of Gonatocerus-G. capitatus Gahan, G. incomptus Huber and G. novifasciatus Giraultwere collected in very small numbers, and only early in spring in Fillmore by University of California Cooperative Extension (Ventura Co.) researchers. Gonatocerus capitatus and G. novifasciatus have not been previously reared from eggs of H. coagulata whereas G. incomptus was a known parasitoid of this sharpshooter species in Georgia (Huber 1988). Earlier studies in Monticello, Florida (R. F. M., unpublished data) estimated average parasitism of H. coagulata eggs there at ca. 80%. During July and August 1997, we collected egg masses of H. coagulata from crape myrtle (Lagerstroemia indica L.) and citrus trees grown at the University of Floridas North Florida Research and Education Center. In July samples, more than 90% of ca. 300 emerged parasitoids were G. ashmeadi. One female was identified as G. morrilli (Howard), and the rest belonged to an undescribed Zagella sp. (Trichogrammatidae). In August samples, however, Zagella sp. was by far the dominant parasitoid of H. coagulata eggs. The genus Zagella

LEAFHOPPER VECTORS OF PHONY PEACH DISEASE: FEEDING SITE PREFERENCE AND SURVIVAL ON INFECTED AND UNINFECTED PEACH, AND SEASONAL RESPONSE TO SELECTED HOST PLANTS

The feeding site acceptance and adult survival of 2 leafhoppers, Homalodisca coagulata (Say) and H insolita (Walker), the vectors of phony peach disease (PPD), were determined on branches of uninfe...

Differential utilization of nutrients during development by the xylophagous leafhopper, Homalodisca coagulata

Utilization of nutrients at different stages of development was examined for the xylophage, Homalodisca coagulata (Say). Survivorship and consumption rates of second‐instar, fourth‐instar and adult leafhoppers were measured daily on the hosts Lagerstroemia indica L. and Euonymus japonica Thumb. Rates of consumption, assimilation efficiencies and daily assimilation of nitrogen, carbon, and individual organic compounds were calculated based on chemical analyses of xylem fluid and insect excreta. Gross growth efficiencies of diet utilization were also estimated by comparing biomass of young adults to estimates of nutrient utilization of the two host species.

Effects of total dietary nitrogen and nitrogen form on the development of xylophagous leafhoppers

The influence of primary nutrients on the development of the leafhopper Homalodisca coagulata (Say) was examined using Glycine max (L.) Merrill subjected to treatments using different forms of nitrogen fertilization (urea and nitrate) and inoculation with Rhizobium bacteria. Concentrations of amino acids, organic acids, carbohydrates, and ureides in xylem fluid varied with treatment; differences were most pronounced in young plants (6 weeks after planting), and subsided as plants aged. Plants receiving urea fertilization had lower concentrations of organic nitrogen and carbon, but more balanced profiles of amino acids. Leafhoppers on urea-fertilized plants had much higher success in development (62 to 87% survival to adult stage) than H. coagulata developing on nitrate-fertilized plants (31-42%). The sex ratio of successfully developed adults varied greatly with treatments, indicating that female survival was much higher on urea-fertilized plants. Males and females utlilized diets differently as indicated by the carbon and nitrogen content of adult carcasses. Consumption rates and nitrogen assimilation efficiencies were higher for young (third instar) leafhoppers on urea-fertilized plants. Instar duration and total time of development were not affected by treatment. Highest rates of success in development on diets providing the lowest (yet most balanced) concentrations of total nitrogen, amino acids, and organic compounds underscored the importance of nutrient balance for leafhopper development. Arch. Copyright 1999 Wiley-Liss, Inc.