Cornicle Secretion Research Articles

Strategies Involved in the Location of Hosts by the ParasitoidAphidius erviHaliday (Hymenoptera: Braconidae: Aphidiinae)

Abstract The parasitoidAphidius erviHaliday uses both semiochemical and physical cues to locate and recognize its main host, the pea aphidAcyrthosiphon pisum(Harris). In wind tunnel studies, it was demonstrated that plant volatiles, particularly those induced by aphid feeding, are important long-range cues in the initial stages of host location. Furthermore,A. ervidistinguished between plants damaged byAc. pisumand those damaged by the nonhost aphidAphis fabae(Scop.). Host-induced volatiles were emitted by young broad bean plants (Vicia faba) in sufficient quantities to elicit a flight response from female parasitoids after 40 aphids had been feeding for 72 h. Aphids confined to a single leaf caused systemic production of herbivore-induced volatiles throughout the plant. Previous experiences with hosts or host-related cues heightened parasitoid responses to host-induced volatiles and also triggered responses to other plant volatiles. This learning ability provides the parasitoid with behavioral plasticity to adapt its responses to suit prevailing foraging opportunities.A. ervifemales also responded to synthetic aphid sex pheromones in wind tunnel experiments, and attempts are being made to manipulate field populations using host pheromone lures. Contact kairomones in the host cuticle and cornicle secretion appear to be involved in host recognition and acceptance byA. ervifemales. In addition, visual cues play a role in host location and recognition, with color being an important short-range cue. Color alone stimulated attack responses;A. ervifemales attacked green aphids in preference to brown aphids and showed attack responses toward yellow paint pigments enclosed in glass capillary tips.

Biological and chemical characterization of a kairomone excreted by the bean aphids, Aphis fabae Scop. (Hom., Aphididae) and its effect on the predator Metasyrphus corollae Fabr. I. Isolation, identification and bioassay of aphid‐kairomone

Abstract: The results obtained are summarized as follows: (1) the active compounds of aphid's odour stimulated the syrphid females to deposit significantly higher percentages of eggs. These chemical compounds could be isolated by the solvent n‐pentane. (2) Gas chromatography mass spectral analysis of n‐pentane fractions of aphid's odour revealed the presence of several active peaks of hydrocarbon compounds. The active peaks ranged from docosane (C22) to octacosane (C28). Also, GC‐mass spectral analysis of n‐pentane fractions of the aphid‐extract supernatant showed the same chain of hydrocarbon compounds which is present in the aphid odour. (3) Bioassay of the different cosane compounds showed that the different concentrations of tricosane, tetracosane, pentacosane and hexacosane have a kairomonal effect on the syrphid females and the second concentration of C23CII, C24CII, C25CII and C26CII stimulated the syrphid females to deposit a significantly higher percentage of eggs. While hexacosane (C26) was the most abundant hydrocarbon compound in aphid kairomone, tricosane (C23) was the most active hydrocarbon compound. (4) Bioassay of the different mixtures of cosane compounds showed that HCM1, HCM2, HCM3, HCM4, HCM5 and HCM6 have a kairomonal effect on the syrphid females. The highest percentage of eggs was laid under the effect of the fourth mixture (HCM4) which contains tricosane (C23), tetracosane (C24), pentacosane (C25), hexacosane (C26) and octacosane (C28). (5) The chain of non‐volatile hydrocarbon compounds of aphid‐kairomone is secreted along with the cornicle secretion which contains volatile compounds. This kairomone stimulate the oviposition of syrphid females when it is received mechanically by the antennae. (6) The present study showed the importance of the different mixtures of cosane compounds as aphid‐kairomone. The use of aphid‐kairomone could be promising in aphid biological control instead of the heavy use of insecticides.

Contact kairomones mediating the foraging behavior of the aphid hyperparasitoid Alloxysta victrix (Westwood) (Hymenoptera: Charipidae)

A variety of host-related substances was assessed in relation to their ability to induce arrestment and antennal examination behavior in adult females of the aphid hyperparasitoid Alloxysta victrix (Westwood). In laboratory bioassays, whole-body homogenates of both unparasitized host aphids [Myzus persicae (Sulzer)] and those parasitized by the primary parasitoid Aphidius colemani Viereck failed to elicit a response. However, significant kairomonal activity was associated with aphid cornicle secretions, aphid honeydew, and solvent extracts of parasitized aphids. Solvent extracts of unparasitized aphids (in either hexane or butan-1-ol) failed to elicit arrestment or antennal examination behavior in hyperparsitoid females. The response to aphid honeydew was significantly lower in “experienced” females than in naive individuals, suggesting that even relatively strong innate responses can be modified by learning.

Effect of Adult Experience on in-Flight Orientation to Plant and Plant–Host Complex Volatiles inAphidius erviHaliday (Hymenoptera, Braconidae)

Abstract The effect of adult experience on in-flight orientation to plant–host complex volatiles by Aphidius ervi Haliday was studied in a wind tunnel bioassay, using Acyrthosiphon pisum (Harris), maintained on broad bean plants ( Vicia faba ) as host. A short oviposition experience (15 s) on the plant–host complex (PHC) was sufficient to induce a drastic decrease of flight propensity and stimulated a foraging behavior characterized by intense walking activity. However, flight activity resumed to normal levels 1 h after the oviposition experience on the PHC occurred. For parasitoids conditioned on the PHC for at least 1 min the recorded proportion making oriented flights to the PHC was significantly higher than that for naive females. In contrast, oviposition experience in the absence of plant material did not influence the A. ervi flight response. Oviposition attempts on aphid dummies without egg release did not reduce flight activity. When A. ervi females were exposed to glass beads coated with Ac. pisum cornicle secretion, a priming effect was observed, resulting, compared with naive females, in a significantly higher rate of oriented flights to the PHC. In contrast, oviposition attempts visually induced by colored aphid dummies did not influence flight behavior. A strong reaction to volatile cues from uninfested plants was induced by oviposition experience on newly infested broad bean plants. This appears to be a case of associative learning. In fact, uninfested broad bean plants are basically unattractive to naive A. ervi females. The results demonstrate that adult experience has a considerable influence on A. ervi behavior and may have important implications for biological control of natural pest aphid populations.

Aphid alarm pheromone (E)-?-farnesene: A host finding kairomone for the aphid primary parasitoidAphidius uzbekistanicus (Hymenoptera: Aphidiinae)

The present study aimed to test the possible function of the aphid alarm pheromone (E)-β-farnesene (EBF) as a host finding kairomone for aphid primary parasitoids. Extracts of volatile emissions of undisturbed aphids and of aphids under parasitoid attack were obtained by air entrainment. Extracts of cornicle secretions were gained by disturbing aphids and taking their secretions into solution. Extracts were compared by gas chromatography. Only air entrainments of aphids under attack and solvent extracts of cornicle secretions contained the alarm pheromone. In Y-tube olfactometer bioassays, femaleA. uzbekistanicus were attracted to aphid groups under attack of parasitoids, presumably by released EBF. High concentrations of synthetic EBF (1.4 µg to 5.7 µg) also attractedA. uzbekistanicus females. Females with oviposition experience reacted more readily to lower concentrations of EBF than females without experience. In experiments designed as Petri-dish bioassays, the test animals could contact filter paper discs that were treated with solutions containing EBF. Behavioural effects like antennation or stinging attack were not observed. With computer video analysis of parasitoid movements, some effects onA. uzbekistanicus behaviour were detected, again indicating attraction to EBF. As the volatile aphid alarm pheromone attractedA. uzbekistanicus females, it can be concluded that this chemical stimulus acts as a host finding kairomone for this parasitoid species. However, its effect over long distances seems to be limited due to the relatively high concentrations required for reactions. Of two other parasitoid species examined (P. volucre andL. testaceipes) onlyP. volucre was also significantly attracted to the volatile EBF in the Y-tube olfactometer.

The role of physical cues in the regulation of host recognition and acceptance behavior ofAphidius ervi Haliday (Hymenoptera: Braconidae)

The role of color and shape in the host recognition and acceptance behavior ofAphidius ervi Haliday was studied. A quantitative analysis of the oviposition behavior ofA. ervi was carried out with a computer-aided analysis of 150 video-recorded oviposition sequences on its natural host,Acyrthosiphon pisum (Harris). The importance of visual stimuli was assessed in a choice condition bioassay, observing the behavioral reaction of female parasitoids to various test materials flame-sealed into glass capillaries. Glass beads 2 and 6 mm in diameter and a flat arena were coated with cornicle secretion ofA. pisum, and their acceptance rates by both naive and experienced female parasitoids were assessed under no-choice conditions. In most cases,A. ervi females switched from random searching to attack position when the host was within a range of 1 cm, suggesting that host recognition is regulated in part by cues acting before physical contact. The glass capillary bioassay indicated that visual cues are important factors in the host recognition and acceptance phases. Pea aphid color alone can elicit the oviposition response of naiveA. ervi females, and this response is enhanced when color is combined with aphid shape. The cornicle secretion ofA. pisum stimulated an oviposition response which was stronger in naive females ofA. ervi than in experienced ones and was not significantly affected by the glass bead size or flat surface. These results, along with those from previous studies, suggest that manipulation of the oviposition behavior ofA. ervi is feasible under laboratory conditions.

Kairomonal effect of an aphid cornicle secretion onLysiphlebus testaceipes (Cresson) (Hymenoptera: Aphidiidae).

In laboratory bioassays, whole-body homogenates and fresh cornicle wax of Rhopalosiphum padi(L.) (the bird-cherry oat aphid) elicited antennal examination and attack behavior in naive females of the polyphagous aphidiid parasitoid, Lysiphlebus testaceipes (Cresson). No such response was elicited by either homogenates or cornicle wax of Aphis nerii(Boyer de Fonscolombe) (another known host of the parasitoid) or by preparations of the aphid alarm pheromone, (E)-β-farnesene. The response to R. padiproducts was independent of rearing host and appears to be innate. Application of R. padicornicle wax to the dorsum of a nonhost aphid [Acythosiphum pisum(Harris)] increased the frequency with which this species was attacked by L. testaceipes.There was a tendency for the kairomonal activity of the cornicle secretion to decline as the wax dried, although parasitoid attack behavior was still elicited by wax which had been allowed to dry for up to 30 min before testing.

Host plant iridoid-based chemical defense of an aphid,Acyrthosiphon nipponicus, against ladybird beetles

A Rubiaceae-feeding aphid,Acyrthosiphon nipponicus, is seldom attacked by the ladybird beetle,Harmonia axyridis. A potent deterrent against the beetle was isolated from the aphid and identified as paederoside, an iridoid glycoside originating in the aphid's host,Paederia scandens. The iridoid content was as high as 2% of the intact body weight, and a large portion was found in the cornicle secretion.

Alarm pheromone secretion by insecticide‐susceptible and ‐resistant Myzus persicae treated with demeton‐S‐methyl; aphid dispersal and transfer of plant viruses

SUMMARYThe insecticides demeton‐S‐methyl and pirimicarb induced cornicle secretion, and thereby alarm pheromone release, in Myzus persicae. Secretion was earliest in young and insecticide‐susceptible aphids.In laboratory experiments to assess the behavioural significance of this effect, demeton‐S‐methyl applied to colonies of R1 (moderately resistant) aphids killed the majority, but caused the remainder to disperse. The timing and degree of dispersal depended on the size and composition of the colonies. Beet yellows virus was transferred by dispersed aphids, but less frequently when recipient indicator seedlings were treated with demeton‐S‐methyl. R2 (strongly resistant) aphids soon dispersed from colonies containing susceptible nymphs (which secrete alarm pheromone early) and transmitted readily even to treated seedlings.The non‐persistent potato virus Y was transferred by dispersed R: aphids and no protection was afforded by treatment of the seedlings.

Composition of triglycerides from aphids of six different families and from different seasonal forms of Aphis evonymi

The triglyceride compositions of extracts and cornicle secretions of specimens from a range of aphid families were examined by mass spectrometry and found to support earlier evidence that there is little correlation between taxonomic position and chemical constitution. Parasites developing within Myzus persicae preferentially consumed the typical aphid triglycerides which contain hexanoic (C 6), sorbic (C 6:2), myristic (C 14), and palmitic (C 16) acid moieties, so that when parasitism was advanced, only triglycerides with three long-chain fatty acids per molecule remained. The adult parasites themselves contained very little triglyceride. Triglycerides of Aphis evonymi and Aphis fabae were similar and varied in composition regularly throughout the year. In the apterous and alate (summer) viviparae, there were equal amounts of myristoyl (C 14) and palmitoyl (C 16) triglycerides, while in fundatrices and fundatrigeniae (spring forms) myristoyl was predominant. Males collected in autumn resembled the spring forms. However, oviparae and eggs of these and other species differed considerably from the other seasonal forms, in having more hexenoic (C 6:1), sorbic (C 6:2), and myristoleic (C 14:1) acid moieties.

Aphid Cornicle Secretions Ineffective Against Attack by Parasitoid Wasps 1

Cornicle secretions have been reported to serve multiple functions in aphids. Of particular interest are reports that these sticky secretions serve to defend aphids against attack by predators and parasites. Dixon (1958) observed that the aphid, Microlophium evansi (Theobald) will smear its cornicle secretions on the mouthparts of the coccinellid, Adalia decempunctata (L.) allowing the aphid to escape from the temporarily immobilized predators. Edwards (1966) observed parasitoid wasps ( Aphidius ) trapped in aphid cornic1e secretions in the field.

A comparison of triglycerides from aphids and their cornicle secretions

Direct mass spectrometry of extracts showed that body triglycerides from 30 species of aphids contained the same fatty acid radicals, C 6 (hexanoyl), C 6:2 (sorboyl), C 14 (myristoyl), and C 16 (palmitoyl) as did the cornicle secretions, but in many species the proportions of hexanoyl and/or palmitoyl triglycerides were greater in the body. When cornicle secretions were collected progressively so as to draw increasingly upon body fat reserves, their composition changed gradually towards that of the body extracts. All summer forms of Myzus persicae had similar body triglycerides, even when selected for resistance to organophosphorus insecticides, or bred for 3 months on an artificial diet. The composition of body triglycerides was also independent of colour in two aphid species in which pink and green forms were compared. Body extracts contain enough triglycerides for their composition to be determined in single aphids and the use of body extracts allows examination of aphids lacking cornicles and of specimens that do not give cornicle secretion because of low body turgor. Although, as in the case of cornicle secretions, the triglyceride composition of body extracts was not well correlated with taxonomic position, body extracts provide a second chemical characteristic that can be used to define a particular species.

Chemistry of the secretion from the cornicles of various species of aphids

The cornicle secretions from 28 species of aphids were examined directly by mass spectrometry and, in selected cases, by chemical and chromatographic methods. The major components of the secretions are triglycerides, the acid moieties of which are hexanoic, hexadienoic (sorbic), tetradecanoic (myristic), and hexadecanoic (palmitic) acids, with smaller amounts of C 12 and C 18:1 acids. The mixtures from the different species fall into six groups which are readily distinguished by mass spectrometry. The composition was independent of the host plant or of the stage of development where these have been investigated. Biochemical classification is not consistent with morphological classification in the species examined.

Trans-β-farnesene, Alarm Pheromone of the Green Peach Aphid, Myzus persicae (Sulzer)

THE chemical structure of the repellent odour found in the cornicle secretion of the aphid M. persicae1 has been identified as trans-β-farnesene.

Observations on Aphid Cornicle Secretions

Physiological and chemical observations were made on the cornicle secretions of Myzus persicae (Sulzer), Acyrthosiphon pisum (Harris), and a Chaitophorus sp. If appropriately stimulated, a droplet of fluid, about 150µ in diameter, appeared at the tip of the cornicles; this droplet hardened in about 20 seconds. Chemically, the hardened droplets were composed primarily of triglycerides. Myristic acid was the major fatty acid moiety of the trigly-cerides.