Influence of trap surface on the numbers of insects caught in water traps in brassica crops

The contribution of the various surfaces of a water trap to the trap's overall effectiveness was studied in brassica crops by painting black different parts of fluorescent-yellow water-traps. Three pest species, Delia radicum (L.), D. platura (Meig.), and Meligethes aeneus (Fab.)/Meligethes viridescens (Fab.), together with blowflies and syrphids, were caught in large numbers. Each insect responded differently to the yellow/black traps. The numbers of insect caught indicated that the area of trap involved in capturing D. radicum was effectively twice the surface area of the water. Yellow traps for monitoring D. radicum populations could be made more selective by painting the inner wall black, as such traps caught similar numbers of D. radicum to all-yellow traps but 50% fewer D. platura, Meligethes sp. and blowflies, and 95% fewer syrphids.     

Effect of trap background on cabbage root fly landing and capture

Pieces (600 mm × 800 mm) of coloured board, plastic sheeting and woven materials, place beneath water traps prevented the traps from becoming soiled during rainy weather. Such backgrounds are not recommended for use with traps for monitoring populations of the cabbage root fly (Delia radicum L. — Diptera: Anthomyiidae), however, as, instead of increasing trap catch they reduced the numbers of female flies caught by 70%–90%. The main effect was that the visually attractive stimuli from the introduced backgrounds competed with those from the trap. A white background competed with a white trap on a direct fly/unit area basis. Green backgrounds stimulated males to land and the vertical stems of both real and artificial grass induced trivial flights that resulted in greater numbers of males entering traps resting on short grass. Most females were caught over bare soil. To minimize the variation in catch between traps used for monitoring cabbage root fly populations, the background beneath each trap should be similar. For maximum capture, the background should be of grass for male flies and of bare soil for female flies. Care is required if data from traps within mulched crops are used to make pest control decisions, as they will underestimate considerably the numbers of flies in such crops.     

Laboratory studies on aestivation in the cabbage root fly (Delia radicum)

Laboratory experiments at 16°–30°C showed that the cabbage root fly can only be induced into aestivation during the early part of the pupal stage. The relationship between the percentage of pupae entering aestivation (y) and the average daily temperature (T) was the same under both constant and alternating temperatures. The percentage of pupae entering aestivation at a particular temperature was given by y=13T–255. An additional 13% of the pupae entered aestivation for each degree rise between 20° and 27°C. There was no constant period of arrested development following the induction of aestivation. Aestivating pupae started to develop into flies as soon as the temperature fell below 20°C. The reinduction of aestivation occurred more readily than the initial induction. Insect survival was not reduced after a month of aestivation. The effects of aestivation on forecasting the time of the second (summer) generation of flies are discussed.

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Étude au laboratoire de l'estivation de la mouche du Chou (Delia radicum)

Résumé Au laboratoire, à 10°–30°C, l'induction de l'estivation ne peut être obtenue qu'avec des pupes formées depuis peu.Le rapport pourcentage de pupes entrant en estivation (y) température journalière moyenne (T) a été le même, que la température soit constante ou alternée. La relation entre la température et ce pourcentage est donnée par y=13 T–255. Le pourcentage de pupes entrant en estivation a augmenté de 13% pour chaque élévation d'un degré entre 20° et 27°C. L'estivation une fois induite, la période d'arrêt de développement n'est pas constante. Dès que la température est devenue inférieure à 20°C, la formation d'imagos a commencé dans les pupes en estivation. Une nouvelle estivation a été plus facile à provoquer que l'estivation initiale. Le taux de survie des insectes n'avait pas diminué après un mois d'estivation. La discussion examine l'utilisation des conséquences de l'estivation dans la prédiction de la seconde génération d'adultes: génération d'été.

     

Effect of age on the responsiveness of peripheral chemosensory sensilla of the turnip root fly (Delia floralis)

The effect of insect age on the neural responsiveness of gustatory sensilla was investigated. Electrophysiological recordings were obtained from type A and type D sensilla on the pro- and meso-thoracic tarsi, and from sensilla on the labellum of the turnip root fly,Delia floralis (Fallen) in response to potassium chloride, sucrose and sinigrin. The age of the fly did have an effect on the numbers of sensilla responding to the test stimuli and on the magnitude of the response, but there was no consistent pattern in these effects among sensilla. The labellar sensilla were more responsive to sucrose than the tarsal sensilla and the proportion of flies whose labellar sensilla responded to sucrose was initially low, but increased after day 2 of adult life. In contrast, the number of flies whose tarsal sensilla responded to stimulation with sucrose was initially high and decreased as the flies aged. There was a similar decline in the proportion of tarsal sensilla responding to potassium chloride. Neither the proportion of flies whose tarsal sensilla responded to sinigrin nor the magnitude of the response was influenced by the age of the fly. These finding are discussed in relation to the feeding and host selection behaviour of the fly.     

The effect of colour of the substrate on the landing and oviposition behaviour of the cabbage root fly

Field and laboratory experiments were made in order to understand the relation between the spectral characteristic of a substrate and its attractiveness for Delia radicum (L.) (Diptera: Anthomyiidae) flies to land or oviposit. Landing females preferred substrates with high reflectance of green and particularly of yellow wavelengths, but substrates with a high proportion of the blue and green reflectance simultaneously (light blue and white) were also very attractive. Unattractive substrates had either low reflectance across the whole insect-visible spectrum (dark blue) or increased reflectance only in orange or red region of the spectrum (red) or a large proportion of UV reflectance (aluminium). Landing males were most attracted to the substrates with the highest total reflection. Oviposition attractiveness of a substrate grew with an increase in the proportion of reflectance in the blue and a decrease in the green regions of the spectrum. In addition, the oviposition attractiveness increased with increasing total reflection and contrast with the background, and decreased with a high proportion of UV reflectance.     

Physical and chemical factors influencing landing and oviposition by the cabbage root fly on host-plant models

Various plant models were used in both choice and no-choice tests in the laboratory to assess landing and oviposition preferences of the cabbage root fly,Delia radicum (L.). The main factor governing the site most suitable for landing was the conspicuousness of the object and not its shape. Oviposition was influenced considerably by the pre-conditioning of the females. Deprived females laid eggs even when denied access to both host plant chemicals and host-plant models. The dominant role of contact chemical stimuli in host acceptance was reconfirmed, but only a combination of physical and chemical stimuli appeared capable of eliciting normal oviposition. The combination of contact chemical stimuli and the presence of a stem on the test model had a synergistic effect on the numbers of eggs laid in both choice and no-choice situations. In choice bioassays, female cabbage root flies distinguished between models of different shapes, heights and sizes. The size and shape of the models appeared to be perceived in part after the flies had landed.     

Foliar form, colour and surface characteristics influence oviposition behaviour in the cabbage root fly Delia radicum

The effects of foliar form, colour and surface characteristics on the oviposition behaviour of the cabbage fly were investigated by presenting females with various leaf models made of paper. The models differed in shape, size, colour, surface coating, the presence of 3 dimensional folds and a stem. It was shown that in the presence of host leaf surface extracts physical factors can strongly influence oviposition behaviour. Females laid the most eggs around the base of bright green or yellow models having a stem, vertical folds and covered with a thin layer of paraffin. The vertical folds in the surface increased the chance of a behavioural transition from leaf run to stem run.

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Zusammenfassung Mit Hilfe von Papiermodellen von Kohlblättern wurde der Einfluss von visuellen und mechanischen Eigenschaften des Blattes auf das Eiablageverhalten der kleinen Kohlfliege, Delia radicum, untersucht. Die verwendeten Modelle unterschieden sich in Form, Grösse, Farbe, Oberflächen struktur und Stiel des Blattes. Es wurde gezeigt, dass physikalische Reize zusammen mit den chemischen Stoffe auf der Blattoberfläche stimulierend wirken. Ein natürliches Eiablageverhalten und die stärkste Eiablage wurde durch ein Modell ausgelöst, welches sich durch leuchtend grüne Farbe, Stiel und vertikale Falten und einen Paraffinnüberzug auszeichnete.

     

Relationship between root volatiles of some carrot cultivars and their resistance to the carrot fly, Psila rosae

Field experiments investigated the resistance of some carrot cultivars to Psila rosae. In addition, headspace vapour and steam distillate from the roots of resistant and susceptible varieties were compared by gas-liquid chromatography. The field data confirmed that resistance may operate by decreasing the numbers of eggs laid indicating a nonpreference by the female Psila. Root resistance to the larva was also confirmed but the mechanism was unclear. A new finding was that root resistance is independent of the effect of egg laying, some cultivars evincing one or the other effect and some such as Regulus Imperial displaying both. It was clear that root resistance to the larva is the crucial prerequisite in breeding resistant varieties.One consistent difference was detected by the chemical comparisons: intact roots of resistant varieties released substantially less volatiles. Specifically, Regulus released almost five times less of the volatiles already shown to positively influence host-finding behaviour by the larva.

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Résumé La résistance à P. rosae de quelques cultivars de carotte a été étudiée en plein champ. Parallèlement, les substances volatiles diffusées et celles extraites par la vapeur des racines de variétés résistantes et sensibles, ont été comparées en chromatographie gaz-liquide (GLC). Les résultats en champ ont confirmé que la résistance peut être due à une diminution du nombre d'oeufs pondus, révélant une absence d'attractivité pour les femelles de P. rosae. La résistance des racines aux larves a été aussi confirmée, mais les raisons n'en étaient pas claires. Un aspect nouveau est que la résistance des racines est indépendante de l'effet de la ponte, quelques cultivars présentant l'un ou l'autreeffet et certains, comme Regulus Imperial, manifestant les deux. Il est net que la résistance racinaire aux larves est la condition essentielle pour la sélection de variétés résistantes. Une différence importante a été mise en évidence par les comparaisons chimiques: les racines intactes de variétés résistantes libèrent nettement moins de substances volatiles. Précisément, Regulus a libéré 5 fois moins de substances volatiles déjà connues comme influençant positivement le comportement de découverte de l'hôte par la larve.

     

Completion of diapause in field populations of the cabbage root fly (Delia radicum)

The various diapause and post-diapause stages entered by cabbage root fly pupae during the overwintering period are shown schematically. Although diapause induction started in mid-Aug., the early-pupating insects did not develop further but were maintained in diapause by the warm autumn temperatures. Therefore, diapause development was simultaneous in all Wellesbourne pupae, whether of second or third generation origin. Diapause development started only in mid-Oct., when mean soil temperatures fell below 10°. In the field, 90% of the overwintering population of cabbage root fly pupae had completed pleted diapause by 5 March 1980, 17 Feb. 1981 and 18 Feb. 1982. This was equivalent to a duration of 19 weeks from mid-Oct. onwards, during the winters of 1979–80, 1980–81 and 1981–82 respectively. A further break between the completion of diapause and the warm conditions required to start post-diapause development also helps to condense the emergence of flies in the spring. Hence, an accurate forecast of the time of spring attack by populations of flies similar to those at Wellesbourne should be possible.This study was financed partly by the Commission of the European Communities as CEC Contract No. 0771.     

The effect of a chemical deterrent, released from the frass of caterpillars of the garden pebble moth, on cabbage root fly oviposition

The cabbage root fly, Delia radicum (L.), was deterred from laying eggs on cauliflower plants that had been sprayed with a suspension of the frass of caterpillars of the garden pebble moth, Evergestis forficalis (L.). Polar extracts of the frass deterred oviposition irrespective of the cruciferous plant species on which the caterpillars had been feeding. Non-polar extracts of the frass had no effect. Spraying plants with macerates from Brassica leaves stimulated fly oviposition whereas spraying plants with macerates from garlic mustard leaves deterred fly oviposition. Macerates from the leaves of all other plants tested had no effect. In field experiments the deterrent effect persisted 2–3 days after leaves were sprayed with frass extracts. Plants infested with feeding caterpillars and contaminated with only a few discrete frass pellets were as deterrent to the fly as those sprayed with frass suspensions.

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Résumé D. radicum a évité de pondre sur des pieds de chou-fleur, qui avaient été pulvérisés avec une suspension d'excréments d'E. forficalis. Les extraits polaires de ces excréments empêchent la ponte quelle que soit l'espère de crucifère sur laquelle les chenilles se sont alimentées. Les extraits non polares sont sans effet. Dans la nature, l'action dissuadante persiste 2 à 3 jours après la pulvérisation des feuilles avec les extraits d'excréments. La pulvérisation tous les deux jours a maintenu l'action dissuadante. Des plantes contaminées par des chenilles en train de s'alimenter et souillées par quelques crottes sont aussi dissuadantes pour la mouche que celles pulvérisées avec une suspension d'excréments.

     

A cabbage root fly oviposition deterrent in the frass of garden pebble moth caterpillars

The cabbage root fly, Delia radicum (L.), was deterred from laying eggs on cauliflower plants sprayed with a water-soluble extract of the frass of caterpillars of the garden pebble moth, Evergestis forficalis (L.), which had fed on a range of cruciferous species. Chemical analysis of the extract revealed the presence of a phenolic acid which was not present in the frass of larvae of two other Lepidoptera (Mamestra brassicae (L.) and Plutella xylostella (L.)) that had fed on the same range of cruciferous plants. The deterrent chemical was isolated and identified as sinapic (3,5-dimethoxy-4-hydroxycinnamic) acid. Spraying cauliflower plants with a buffered solution of the acid in water (0.1, 1 and 10 mM) reduced the numbers of cabbage root fly eggs laid by 60–70%. In field experiments, the deterrent effect persisted 5 days after leaves were sprayed with a buffered, aqueous solution of the acid (10 mM).

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Résumé D. radicum L. a pondu beaucoup moins sur des choux-fleurs pulvérisés avec un extrait (polaire) hydrosoluble d'excréments de chenilles de E. forficalis L. qui avaient consommé différentes crucifères. La pulvérisation des choux-fleurs avec une suspension aqueuse d'éluate de méthanol d'une colonne polyamide et d'éluate aqueux d'une colonne florosile a réduit respectivement de 50 et 66% le nombre d'oeufs pondus. L'analyse chimique des fractions actives révèle la présence d'un acide phénolique isolé et identifié comme acide sinapique (3,5-diméthoxy-4-hydroxycinnamique). Cet acide est absent des excréments des chenilles de Mamestra brassicae L. et Plutella xylostella L. qui avaient consommé la même gamme de crucifères. La pulvérisation des plants de choux-fleurs par une solution aqueuse tamponnée d'acide sinapique a réduit la ponte de D. radicum de 60 à 70%. Dans la nature, l'effet dissuasif persiste sur choux-fleurs 5 jours après la pulvérisation avec une solution aqueuse tamponnée à 10 mM d'acide sinapique.

     

Behavioural and chemosensory responses of the turnip root fly (Delia floralis) to glucosinolates

This study investigates the behavioural and neural mechanisms involved in the oviposition behaviour of the turnip root fly,Delia floralis (Fallen). Behavioural studies showed that glucosinolates modulated the oviposition behaviour of the flies on artificial leaves as well as the number of eggs laid in the soil at the base of these leaves. Electrophysiological responses to glucosinolates were obtained from type A and type D sensilla on the prothoracic and mesothoracic tarsi, as well as from the long contact sensilla on the labellum. The neural responses from these sensilla were positively correlated with the oviposition behaviour of the flies and with the number of eggs laid. Of the eleven glucosinolates tested in the behavioural and electrophysiological tests, the flies were most responsive to glucobrassicanapin, gluconapin and glucobrassicin. The type D tarsal sensilla were more responsive to the glucosinolates than either the type A tarsal sensilla or the labellar sensilla. The structure-activity investigations showed that slight modifications to the chemical composition of the glucosinolates resulted in changes in neural activity.     

Quantitative analysis of ovipositional behavior: Effects of a host-plant chemical on the onion fly (Diptera: Anthomyiidae)

Behavioral responses of female onion flies, Delia antiqua (Meigen), to hostplant cues were quantified during encounters of individual flies with onion plants and onion foliar surrogates. The behavioral repertoire of such females included sitting, grooming, running up and down foliar surfaces, extension of the proboscis such that the labellum contacted foliar and soil surfaces, movements of the tip of the abdomen over surfaces (surface probing), subsurface probing of soil crevices with the ovipositor, and oviposition. Sequences of behaviors preceding oviposition were probabilistic rather than highly stereotyped but generally followed the order given above. Foliar surrogates were used to determine the effects of n-dipropyl disulfide (Pr₂S₂) on the sequence of behaviors leading up to oviposition. The addition of a Pr₂S₂-treated surrogate to a cage increased the frequency of alighting on that surrogate but also increased alighting on a nearby foliar surrogate without Pr₂S₂. After alighting, females encountering surrogates treated with Pr₂S₂ had shorter latencies to proboscis extension and surface probing, spent less time sitting and grooming, and had runs of shorter duration. These females were also more likely to make the transition from probing of surfaces of foliage and soil to subsurface probing of soil crevices and oviposition. Thus, rather than mediating a particular step in the behavioral sequence, Pr₂S₂ played a role throughout the sequence leading up to oviposition. Collectively, these data and past studies on the onion fly support the hypothesis that egglaying is triggered by a temporal summation of inputs to the central nervous system from various sensory modalities rather than strict behavioral chaining, with each transition effected by some unique cue.     

Onion maggot feeding and development on heterogeneous sections of the onion bulb

When given a choice of feeding sites in laboratory arenas, Delia antiqua (Meigen) larvae exhibited a 3: 1 bias for internal vs outer sections of onion bulbs and distributed themselves non-randomly among identical preferred onion sections. Larval clustering did not appear to be correlated with increased fitness in the laboratory; larval development was identical across the range of densities from 1 to 50 larvae per onion. Larvae feeding on preferred internal sections developed 14% faster, were 38% heavier upon pupation, and were two times more likely to survive to the adult stage than larvae feeding on outer sections. D. antiqua larval food preference was therefore positively correlated with increased fitness.