L. R. Nault

Aphid Alarm Pheromone: Isolation, Identification, Synthesis

A broadly interspecific aphid alarm pheromone was isolated from several economically important species of aphids and identified as trans-β-farnesene.

Effects of sinigrin on host selection by aphids.

The feeding response of six aphid species to sinigrin, a mustard oil glucoside, was investigated. Sinigrin was a powerful phagostimulant for Hyadaphis = (Lipaphis) erysimi and Brevicoryne brassicae, whose host ranges are restricted primarily to the Cruciferae. H. erysimi was induced to feed on ten non‐host species when leaves were systemically treated with sinigrin. To a lesser degree, the polyphagous Myzus persicae, which feeds widely among the Cruciferae, was stimulated to feed on sinigrin treated non‐host leaves. Two polyphagous species, Aphis fabae and Acyrthosiphon = (Aulacorthum) solani, which are not pests of the Cruciferae, and the oligophagous Acyrthosiphon pisum which is restricted to the Leguminosae, were deterred by sinigrin‐treated broadbean leaves, with the latter species showing the greatest response to treatment.

COMPARATIVE RESPONSE OF APHIDS TO THE ALARM PHEROMONE, (E)-ß- FARNESENE

Threshold dosage and type of dispersive response by aphids to the alarm pheromone, (E)‐ß‐farnesene, were determined for fourteen species in the subfamilies Aphidinae and Chaitophorinae. Dosage required to disperse 50% of the most and least sensitive species was 0.02 ng and 100 ng, respectively. Some species dispersed at low dosages by walking and at high dosages by falling; others dispersed only by walking regardless of dosage. Sensitivity to alarm pheromone and type of dispersive response are interrelated with aggregation density and whether the aphid is myrmecophilous.

Roles of interplant movement, acoustic communication, and phototaxis in mate-location behavior of the leafhopper Graminella nigrifrons

SummaryMale Graminella nigrifrons leafhoppers (Cicadellidae: Homoptera) employ a “call-fly” strategy to find virgin females on oat host plants. Males observed in isolation during daylight hours exhibit a high rate of interplant movement, calling from the lower canopy on each plant visited. Virgin and mated females exhibit little interplant movement. They differ from one another in that virgin females perch on the upper half of plants, whereas mated females perch on the lower half of plants. The positioning of females in the plant canopy is influenced by light. Unlike mated females, virgin females respond to male calls by emitting their own acoustic signals. When virgin females are present on plants visited by males, interplant movement of males ceases, and a localized-upward search of the female bearing plant ensues. Male search is influenced by light. Regardless of whether virgin females were confined to the upper or lower portion of plants, direction of male search was towards a light source used to illuminate above or below the plant canopy. These findings suggest that interplant movement by males and sedentary behavior by females prior to mate recognition and their use of acoustic and phototactic sensory modalities after mate recognition represent previously unrecognized adaptations to problems associated with the use of vibrational signals on plants.

Influence of Aster Yellows Phytoplasma on the Fitness of Aster Leafhopper (Homoptera: Cicadellidae)

Abstract This study revealed that feral aster leafhoppers, Macrosteles quadrilineatus Forbes, exposed to aster yellows phytoplasma live longer and may lay more eggs than nonexposed leafhoppers. Aster leafhoppers were reared on asters infected with either of 2 strains of aster yellows phytoplasma or uninfected asters. After eclosion, adults were placed on uninfected healthy lettuce or oat plants and transferred periodically. The life span of test leafhoppers and the number of offspring they produced were compared. Females reared on noninfected aster plants lived for an average of 19 d, those reared on ‘severe’ and ‘bolt’ strain aster yellows phytoplasma-infected plants lived 26 and 28 d, respectively. The mean number of offspring produced by females reared on the bolt strain of aster yellows phytoplasma-infected asters was almost twice the number produced by nonexposed leafhoppers. The life span of feral leafhoppers or the number of eggs laid did not differ for leafhoppers maintained on either oats or lettuce after exposure to aster yellows phytoplasma-infected asters. Female leafhoppers lived twice as long as males. Our results suggest that the aster leafhopper may have had a long association with aster yellows phytoplasma. The longer life and higher fecundity of phytoplasma-infected leafhoppers may influence disease dynamics of aster yellows in lettuce.

Spatial pattern analysis of the incidence of aster yellows disease in lettuce

The degree of aggregation of lettuce plants infected by aster yellows phytoplasma (AYP) was investigated in 12 fields from three experiments. Position of diseased and healthy plants was mapped in a 6–9×12-m section of each field; for most analyses, fields were divided into 10-plant quadrats. Mean disease incidence (p) ranged from 0.01 to 0.30. The frequency of diseased plants was described by the beta-binomial distribution, with an index of aggregation (θ) ranging from 0 to 0.17, positively correlated withp, and generally increasing over time within a field. Distance-class analysis revealed a core-cluster size of only a few plants. However, spatial autocorrelations ofp between quadrats were not significant, indicating that the scale of spatial pattern was small, generally less than 10 plants. An overall measure of aggregation was given by the slope parameter of the binary form of the power law, in which the log of the calculated variance is regressed on the log of the theoretical variance for a binomial distribution. The slope was 1.18 and significantly different from 1. Results for this “simple-interest” disease are interpreted in relation to the persistent transmission of AYP by its aster leafhopper vector.

Multiple alarm pheromones in aphids

In Drosophila, the resistance to PTC was found to be genetically controlled and its polymorphism widely spread among laboratory and natural populations ( D e e r y & Parsons, 1972). The biochemical basis of this polymorphism is not known yet, except that larvae of the mutant ebony (which is more susceptible to PTC than the wild-type) contain less dopa-oxidase than larvae of the wild-type strain and it is known that PTC is an inhibitor of dopa-oxidase (Parsons, 1963).

Survival in Dalbulus leafhopper vectors improves after exposure to maize stunting pathogens

Using D. maidis and pathogen isolates collected at three field sites along an altitudinal gradient in Mexico, we compared survival in leafhoppers exposed to healthy maize to those exposed to maize infected with one of four isolates of maize stunting pathogens: two isolates of the corn stunt spiroplasma (CSS, Spiroplasma kunkelii) and two of the maize busby stunt phytoplasma (MBSP). Survival improved after exposure to either plant pathogen under both the cooler and warmer environmental conditions D. maidis is likely to encounter during the dry season. Survival varied among leafhoppers from the different field sites, suggesting that gene flow between these populations is limited. The leafhoppers responded differently to the four isolates (i.e., we noted significant population by exposure interactions), but we found no difference between MBSP and CSS exposure. Finally, we found evidence of local adaptation in one leafhopper population to sympatric, as compared to allopatric, plant pathogens. We have shown with this and our earlier study that aspects of the interaction phenotype in the association between D. maidis and the plant pathogens are mutualistic and that this association has considerable potential as a model for studies of local adaptation.

Alarm pheromone of the spotted alfalfa aphid,Therioaphis maculata buckton (Homoptera: Aphididae)

An alarm pheromone, C15H24, was isolated from the spotted alfalfa aphid,Therioaphis maculata. The IR, PMR, and [13C]NMR data showed that this alarm pheromone is germacrene A (structure IIIa). The negative plain curve in the ORD of the alarm pheromone implies that the pheromone is (−)-germacrene A (structure IIIb).

Assembly and Accumulation Sites of Maize Mosaic Virus in Its Planthopper Vector

The morphology, assembly, and accumulation sites of rhabdovirus particles in Peregrinus maidis planthoppers infected with a Hawaiian isolate of maize mosaic virus (MMV) were studied. These particles were usually bullet-shaped, but were sometimes bacilliform, and averaged 234 and 247 nm, respectively, in length and 60 nm in width. They were found in most acini of the principal and accessory salivary glands and in brain, nerve ganglia, leg muscle, foregut, midgut, trachea, epidermis, and fat and connective tissues. In most tissues MMV particles accumulated mainly within intracytoplasmic, dilated cisternae that were connected to the perinuclear space. However, in the salivary glands virus particles accumulated mainly in intercellular and extracellular spaces and were found in secretion vesicles. MMV particles appeared to bud from three types of membranes: (i) inner, and rarely outer, nuclear membranes of cells in most tissues examined; (ii) intracytoplasmic membranes, e.g., endoplasmic reticulum in salivary glands; and (iii) plasma membranes of salivary gland cells and nerve axons. The plasma membrane has not been reported previously as a budding site for plant rhabdoviruses, although it is known as a major assembly site for animal rhabdoviruses.