Stimulation of oviposition by the cabbage root fly Erioischia brassicae

A study was made of physical and chemical aspects of oviposition stimulation in E. brassicae.It was shown that contact chemostimulation provided by host plant material stimulated the gravid female to probe with the ovipositor into cracks in which eggs were laid. Carbon disulphide stimulated oviposition at certain concentrations in water, but solutions of carbon disulphide and three other chemicals previously shown to stimulate oviposition were less effective in mixtures than the juice of swede, Brassica napus var. napobrassica, a favoured host. The addition of mangold juice or 20% sucrose solution to solutions of chemostimulants appeared to enhance oviposition.The most favourable soil for oviposition was of particles approximately 1 mm in diameter which may just permit the complete entry of the extended ovipositor, and provide irregularities against which eggs can be laid.

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Zusammenfassung Eine Untersuchung der physikalischen und chemischen Aspekte der Eiablage-Stimulation von Erioischia brassicae wurde durchgeführt.Es wurde gezeigt, daß chemischer Kontakt mit dem material der Wirtspflanze die trächtigen Tiere dazu veranlasste, Vertieferungen mit dem Ovipositor abzutasten, in welche dann Eier abgelegt wurden.Gewisse Konzentrationen wässriger Schwefelkohlenstofflösungen stellten einen Anreiz zur Eiablage dar. Jedoch waren Mischungen von CS₂-Lösungen mit vier anderen Reizstoffen weniger wirkungsvoll als der Saft des bevorzugten Wirtes, Brassica napus L. var napobrassica (L.) Rchb. (Steckrübe). Der Zusatz von Mangoldsaft oder 20%-iger Zuckerlösung zu Lösungen von chemischen Reizstoffen schien die Eiablage zu steigern.Der bevorzugte Boden für die Eiablage hatte eine Korngrösse von ungefähr 1 mm Durchmesser, welche wahrscheinlich das vollständige Eindringen des ausgestreckten Ovipositors gestattet und das günstigste Substrat zur Eiablage darstellt.

     

Effect of host plant odour on the behaviour of the adult cabbage root fly, Erioischia brassicae

Laboratory experiments showed that the odour of leaves of host plants stimulated an increase in activity in gravied female E. brassicae while the odour of non-host foliage had little effect. Males and non-gravid females showed very little response to the odour of both types of foliage. Other experiments failed to show any orientation of the flies towards sources of host plant odour, although more flies were caught in traps containing the juice expressed from a host plant than in those containing water. It is suggested that an unoriented activation of gravid female E. brassicae by host plant odour enhances their chance of being caught in traps emitting the odour, and of making contact with host plants in the field.

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Zusammenfassung Laborversuche zeigten, daß der Blattduft der Wirtspflanzen die Aktivität der trächtigen Weibchen von Erioischia brassicae steigert, während der Duft von Fremdlaub nur einen geringen Effekt hervorrief. Die Reaktion der männlichen und der jungen weiblichen Tiere auf den Duft beider Laubtypen war gleichmäßig schwach. Weitere Laborversuche zeigten keine Orientierung der Tiere auf die Quelle des Wirtspflanzenduftes, dennoch wurden mehr Tiere in Fallen gefangen, welche Wirtspflanzensaft enthielten als in solchen, die nur mit Wasser beschickt waren. Es wird angenommen, daß die trächtigen Weibchen von Erioischia brassicae durch den Wirtspflanzenduft unorientiert aktiviert werden und somit für sie eine grössere Möglichkeit besteht, in Fallen gefangen zu werden, die einen solchen Duft ausströmen, und in der Natur auch mit Wirtspflanzen in Kontakt zu kommen.

     

Factors affecting the behavioural responses of the adult cabbage root fly, Delia brassicae, to host plant odour

The behavioural responses of Delia brassicae to host plant odour were observed in a large wind tunnel (6×2.3×1.8 m). Only mated, gravid females showed oriented upwind responses to host plant odour; visual stimuli had no effect. There was a marked optimum in the odour concentration for upwind flight but higher concentration stimulated flight activity in both sexes. The response levels were higher and the degree of positive phototaxis lower in females released in the tunnel 1 hr before test, than in those tested without this preconditioning. The effects of handling on response level were complex; physical disturbance inhibited responses at intermediate intensities but increased it at high levels.

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Résumé Les réactions comportementales de Delia brassicae à l'odeur de la plante-hôte ont été étudiées dans un grand tunnel parcouru par un courant d'air (6×2,3×1,8 m). Les femelles fécondées et gravides ont, seules présenté une réaction orientée contre le vent à l'odeur de la plante-hôte; les stimulations visuelles ont été sans effet. La concentration en odeur a présenté un optimum marqué pour le vol contre le vent, mais une concentration plus élevée a stimulé le vol des deux sexes. Les niveaux de réaction étaient plus élevés et le degré de phototaxie plus bas chez les femelles libérées dans le tunnel une heure avant les expériences, que chez celles étudiées sans ce préconditionnement. Les effets des manipulations sur le niveau de réaction étaient complexes; les perturbations physiques ont inhibé les réactions aux intensités intermédiaires mais les ont augmentées aux intensités élevées.Bien que le comportement des femelles aurait pu être envisagé comme étant sous l'influence de deux systèmes de motivation contrôlant la ponte et la fuite, une étroite liaison entre les deux a paru exister, une perturbation physique stimulant simultanément les comportements de fuite et de ponte.

     

Comparison of the nutritive values of carbohydrates and related compounds to Erioischia brassicae

The cabbage root fly Erioischia brassicae (Bouché) must feed on carbohydrate but not on protein to mature its initial batch of eggs. From a laboratory assessment of the nutritive values of naturally occurring carbohydrates and related compounds, fructose, glucose, maltose, sucrose, melezitose, mannitol and sorbitol were highly nutritive. Except for melibiose which was intermediate the other compounds tested were of low nutritive value. These compounds were either inert (xylose, galactose), toxic or repellent. The toxic compounds when mixed with sucrose were either undetectable (L-arabinose) or stimulatory (D-arabinose). The repellent compounds acted either through the gustatory mechanisms of the fly (sorbose, dihydroxy-acetone) or by olfactory or chemo-contact stimulation (pyruvic acid). Highly nutritive sources of carbohydrates were present during April and May in the nectars of Anthriscus sylvestris (L.). Bernh. and Lamium album L. and during June and July in the nectars of Crataegus monogyna Jacq. and Heracleum sphondylium L. Dactylis glomerata L. was the most nutritive flower tested but in this and other nutritive wind-pollinated plants the nutrients must have been obtained from a source other than nectar.

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Zusammenfassung Die Kohlfliege Erioischia brassicae muß sich statt mit Eiweißen mit Kohlenhydraten ernähren, um den ersten Satz ihrer Eier fruchtbar zu machen. Untersuchungen des Nährwertes natürlich vorkommender Kohlenhydrate und verwandter Verbindungen ergaben, daß Fruktose, Glukose, Maltose, Rohrzucker, Melezitose, Mannitol und Sorbitol von hohem Nährwert sind. Melibiose hatte mittelmäßigen und alle anderen Verbindungen hatten niedrigen Nährwert. Sie waren entweder unwirksam (Xylose, Galaktose), giftig oder abstoßend.Wenn die giftigen Verbindungen mit Rohrzucker-Lösung gemischt wurden, riefen sie entweder Reaktionen hervor (D-Arabinose) oder nicht (L-Arabinose). Die abstoßenden Verbindungen wirkten entweder über den Geschmacksmechanismus der Fliege, über Geruch oder durch Chemo-Kontakt-reizung (Pyruvic acid). Nahrungsmäßig hochwertige Kohlenhydrat-Quellen kamen von April bis Mai im Nektar von Anthriscus silvestris und Lamium album und während Mai und Juni im Nektar von Crataegus monogyna und Heracleum sphondylium vor. Unter den geprüften Blüten war die von Dactylis glomerata die nährstoffreichste; jedoch müssen bei ihr und anderen windbefruchteten Arten die Nährstoffe einen anderen Ursprung als im Nektar haben.

     

Dispersal of the cabbage root fly

The dispersal rates of wild and culture cabbage root flies Erioischia brassicae were determined in release-recapture experiments at Wellesbourne in 1971–3. The experiments were concerned mainly with the first 7 days of adult life. The flies, released from nine locations in the area, were recaptured in yellow water-traps. Dispersal was affected by wind, rain and the terrain the flies were crossing. The flies least often recaptured were those released into the host crop when 6–12 days old. The results indicated the following pattern of behaviour. Flies moved little during the first 2 days of adult life but by the third day both sexes had dispersed to c. 100 m from the release point. Flies are known to mate about the fourth day and after this the males continued to disperse at c. 100 m per day for the three subsequent days. ‘Wild’ females from field-collected pupae carried out a ‘migratory’ flight, however, and dispersed at c. 1000 m per day during the fifth and sixth days, the days preceding the start of oviposition. Similar rates of dispersal were recorded from flies released across host crop and non-host crop areas. Some females did not stop at the first crop they encountered. The culture females from the laboratory-reared pupae dispersed only c. one-third of the distance of the wild females. There was considerable intermingling of local populations. The percentage recapture of young culture and wild flies released during the pre-oviposition period of this species was 38 ± 4 and 19 ±4 for males, and 15 + 2 and 8+1 for females, respectively. The dispersal range of the cabbage root fly is probably within a 2000–3000 m radius of the site of infestation.     

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.     

Upwind flight by the cabbage root fly, Delia radicum

ABSTRACT. In fourteen releases, most female D.radicum (L.) (Diptera, Anthomyiidae) flew upwind or at an angle to it of less than 77° regardless of the presence of host-plant odour. Females ready to lay eggs flew upwind without prior stimulation by odours from either a host crop or a trap releasing up to 3 ml/day of the attractant allylisothiocyanate. Upwind flight was more pronounced in flies from a diapause than from a continuous, non-diapause culture. Males from the non-diapause culture dispersed upwind and downwind in more or less equal numbers; old males flew mainly downwind. But, like the females, most males from the diapause culture flew upwind. Long-distance, odour-modulated anemotaxis did not appear to be used to locate distant host crops by either sex. It is concluded that the distances of insect orientation to plant odours recorded to date are only of intermediate range, and that long-range orientation to the odours of a host-plant still has to be proven. It is suggested that host-plant volatiles are involved not only in the final stage of host location but also in the first, and probably most important stage of host selection whilst the insect is still in flight.     

Role of visual and olfactory stimuli in host finding of adult cabbage root flies, Delia radicum

Visual host finding and form recognition by the cabbage root fly, Delia radicum, were studied using four shapes of yellow sticky traps as plant models. Cross, disc, and Y traps caught similar numbers of flies. Cross traps caught more females than vertical or horizontal rectangular traps. Black borders did not increase rectangle trap catches. Discs (8 cm diam.) at ground level caught more females than discs at 40 cm above ground. Larger discs (11.2 and 13.8 cm diam.) caught more females per trap than 8 cm diam. discs, but not as many per unit area.Volatile mustard oils were added to sticky cross traps as single and multiple-component baits. Traps with multiple-component baits did not consistently catch more females than single baited traps. Yellow traps baited with isothiocyanates caught 4–7 times as many females as clear plastic allylisothiocyanate (ANCS)-baited traps.Results indicated yellow discs or crosses at ground level beited with ANCS effectively monitored female D. radicum. Main factors affecting landing of female D. radicum are suggested to be color of substrate, height above ground, presence of host volatiles in vicinity, visual prominence, and area of attractive color. The view that host finding in some insects is mediated by complex responses to multichannel stimuli was supported.

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Résumé L'étude de la perception visuelle et de la reconnaissance des formes par les D. radicum adultes a été réalisée en utilisant des pièges jaunes gluants de quatre formes différentes comme leurres de plantes. Des pièges en croix, en disque et en Y ont permis la capture des mêmes nombres de mouches. Plus de femelles ont été capturées avec des pièges en croix qu'avec des pièges rectangulaires verticaux ou horizontaux. Les captures n'ont pas augmenté avec des pièges bordés de noir. Des disques de 8 cm de diamètre disposés au niveau du sol ont permis la capture de plus de femelles que des disques à 40 cm au-dessus du sol. La capture par piège a été supérieure avec des pièges de 11,2 et 13,8 cm de diamètre qu'avec ceux de 8 cm, mais moindre par unité de surface.Des essences volatiles de moutarde ont été ajoutées aux pièges en croix comme appâts simples ou composés. Les pièges avec appâtes composés n'ont pas été significativement plus efficaces que les pièges à appâts simples. Les pièges jaunes appâts avec de l'isothiocyanata ont entraîné la capture de 4 à 7 fois plus de mouches que des pièges en plastique transparent appâtés avec de l'allylisothiocyanate (ANCS). Les résultats ont montré que des disques ou des croix jaunes appâtés avec de l'ANCS au niveau du sol permettent d'organiser un avertissement agricole contre D. radicum. Les principaux facteurs intervenant dans l'atterrissage des femelles de D. radicum semblent être la couleur du substrat, l'élévation audessus du sol, le contraste visuel, la présence de substance de l'hôte dans le voisinage, et l'aire d'attractivité de la couleur. En conclusion, il est exact de considérer que la perception de l'hôte est provoquée chez quelques insectes par une réponse complexe à des stimuli multicanaux.

     

Chemosterilization of the cabbage root fly under field conditions

Removing hedgerow feeding sites from within 40, 80 or 160 m of cauliflower plots, failed to reduce populations of the cabbage root fly (Erioischia brassicae (Bouché)). Oviposition on the plots was unchanged but the efficiency of yellow water-traps was improved. Traps along-side cleared hedgerows caught more gravid than non-gravid females. In cages, 94% of the eggs laid were sterile when both sterilant baits containing tepa [tris-(i-aziridinyl) phosphine oxide] and hedgerow flowers were present. In the field, maximum egg-sterility rarely exceeded 30% when sterilant was present when natural sterility averaged 8%. Chemosterilization was an inadequate control since sufficient eggs and larvae survived to produce root-damage indices of 49 % in contrast to 2 % on insecticide-treated plants. Most eggs were sterile when chemosterilant baits were placed 0.75 m apart and bait was most effective when placed around the crop during the pre-oviposition period and through the crop at the time of maximum oviposition. Increasing the concentration of tepa failed to increase the effectiveness of the bait but a higher proportion of the eggs laid were sterile on large than on small plots. When chemosterilant treatments were stopped, egg-fertility gradually reverted to the natural level. Protracted immigration, an innate tendency for females to disperse, reductions in the competitiveness of sterile males, and the failure of males to re-disperse once sterilized, appeared to be the main factors limiting the levels of sterility in root-fly populations exposed to tepa-baited lures in the field.     

Influence of background on host-plant selection and subsequent oviposition by the cabbage root fly (Delia radicum)

The behaviour of female cabbage root flies during host plant selection was studied in the laboratory using brassica plants growing in backgrounds of bare soil, clover, grass, peas and four non-living materials. Gravid females landed about twice as often on brassica plants growing in bare soil than on comparable plants growing amongst non-host plants. Once a receptive female landed on a brassica plant, the female made, on average, four ‘spiral flights’ and two jumps on and off the plant before laying alongside the plant. Surrounding a brassica plant with a diverse background altered the behaviour of the flies, so that the spiral flights around the host plant were replaced by short hops between nearby vertical objects. The loss of contact and recontact with the host plant then prevented the females from accumulating sufficient contacts with the host plant to be stimulated to lay. Spiral flights around host plants appear to determine whether or not flies will lay alongside host plants. Flies in mixed plantings have a reduced rate of settling on the host plant, and a higher rate of locomotion, because they land frequently on non-host plants. Hence, visual stimuli appeared to have greater effects than, chemical or mechanical barriers in deterring flies from laying alongside brassica plants in diverse backgrounds. In ‘choice’ situations, backgrounds of real plants reduced oviposition alongside brassica plants by at least 50%. In ‘no-choice’ situations, flies laid similar numbers of eggs alongside all brassica plants irrespective of plant background or plant size. If numbers of fly eggs are to be reduced on commercial brassica crops by undersowing the crops with clover, plants growing in bare soil may also have to be included to provide the flies with sites preferred for oviposition.     

The diurnal periodicity and cycle of behaviour of the adult cabbage root fly (Erioischia brassicae)

Adult cabbage root fly (Erioischia brassicae (Bouché)) exhibited a diurnal periodicity in behaviour. Trapping tests indicated that the flies fed from hedgerow flowers in the morning, visited the crop in the early afternoon and returned to the hedges in the late afternoon. In the laboratory the flies also showed a cyclical pattern in behaviour. Feeding preceded oviposition by 3 days and this was reflected in the field by a relative increase in the movement of females away from the hedges and to the crop when they became gravid. The diurnal periodicity and the cycle in behaviour of males was similar to that of the females, indicating that some of the flies' movement was non-appetitive. The tendency of flies to stay for most of the day at hedges resulted in progressive declines in the numbers captured with increasing distances from hedges.     

Laboratory studies of non-preference resistance to cabbage root fly in radish

First generation progenies selected from four radish cultivars on the basis of their attractiveness to ovipositing cabbage root fly in the laboratory were compared in the same environment. There were significant differences between and within cultivars in their attractiveness for egg-laying, indicating that genetic variation existed and that selection had effected a heritable change. However, inconsistencies between experiments indicated that other, as yet unquantified, factors were compounded with the heritable component of non-preference resistance. There was no evidence to suggest that seed weight, leaf area, or hypocotyl size affected the attractiveness of the plants. The effects of eliminating any choice between selections was investigated in the laboratory by exposing 4-wk-old ‘high’ and ‘low’ preference selections of cv. Asmer Tip Top to the pest for 6 days. Three times as many eggs were laid on ‘high’ than on ‘low’ preference selections, indicating that the heritable non-preference resistance to cabbage root fly in Asmer Tip Top was maintained when no choice was offered to the flies, an essential requirement for ‘resistant’ cultivars in the field.     

Tolerance and antibiosis resistance to cabbage root fly in vegetable Brassica species

Four accessions of the wild species Brassica fruticulosa Cyrillo (Brassicaceae) were studied in order to identify its tolerance and antibiosis resistance to the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae), in comparison to a widely cultivated cauliflower cultivar and a rapid cycling Brassica oleracea L. line. Antibiosis was prominent, as the insects reared on resistant accessions showed reduced individual pupal weight, total pupal weight, adult dry weight, and the longest average fly eclosion time. Host plant resistance, however, did not affect the sex ratio of adult flies. A study of the root architecture of plants with and without root fly inoculation revealed differences in the structure within B. oleracea accessions. A long main root and a high number of lateral roots appeared to be important characteristics for a Brassica type, with a higher tolerance level to cabbage root fly attack.     

High-performance liquid chromatography of ecdysone metabolites applied to the cabbage butterfly, Pieris brassicae L

HPLC allowed separation of twelve major labeled compounds after injection of ³H-ecdysone into Pieris pharate pupae. These compounds were identified as six pairs of metabolites (3α and 3β epimers), comprising ecdysone, 20-hydroxyecdysone, 26-hydroxyecdysone, 20,26-dihydroxy-ecdysone and the polar metabolites P and 20-hydroxy-P. These last two products could not be enzymatically split by any hydrolase tested and are weak acids arising respectively from 26-hydroxyecdysone and 20,26-dihydroxyecdysone. They might be 26-oic compounds.Epimerization appears as a fundamental inactivation process in Pieris and could well be a general characteristic of closed systems (eggs and pupae). No significant amounts of hydrolyzable conjugates were detected in our biological system (pharate pupae and pupae).     

The distribution and analysis of cabbage root fly egg populations

The distribution of the egg stage of the cabbage root fly around brassica plants was studied at Wellesbourne on 0.05–0.4 ha plots during 1970 and 1971. The three generations of flies occurred at similar times in both years and the numbers of eggs collected generally decreased from the first to the third generation. Differences between generations demonstrated that each generation should be treated separately. The number of plant samples required for a given level of precision increased from the first to the third generation, indicating that experiments relying on egg counts should be planned to coincide with the first generation whenever possible. A sampling plan for the range of oviposition normally encountered during the three generations is illustrated for both one- and five-plant samples. For the same level of precision, estimates of the populations from five-plant samples required only 50% to 80% of the time of those from one-plant samples. When aestivation occurs the peak of oviposition in the second generation is difficult to determine, and designed experiments should not be undertaken. The negative binomial distribution failed to describe the clumping of the eggs for a complete generation, since a common k could not be fitted to the data. The distribution of the eggs was best described by Taylor's power law which showed that although sampling factors changed with generation, the value of the power did not. A value of 1.4 appears to be the index of aggregation characteristic of the egg stage of this species.     

Developmental instability in cabbage aphid (Brevicoryne brassicae) populations exposed to heavy metal accumulated host plants

Random deviations from the perfect symmetry of normally bilaterally symmetrical characters exist during individual development as a result of various environmental conditions. Fluctuating asymmetry (FA) is often used as a measurement of developmental instability, and within-environmental variation (CV_e) is also considered as an indicator of developmental deviations. These two parameters may indicate the quality of the environmental habitat of organisms. For herbivore insects, such as aphids, any change in their host plants conditions is important and directly affects their development. The presented investigation revealed that both Lead (Pb) and Copper (Cu) accumulation in different host plants resulted in a significant amount of deviations from bilateral symmetry in cabbage aphid (Brevicoryne brassicae). Cabbage aphid populations showed higher FA and CV_e on heavy metal accumulated cabbage and radish than on non-contaminated cabbage and radish plants. However, the pattern between developmental instability and fitness measurements was inconsistent. Thus, this study does not support the hypothesis that asymmetry is a valuable bioindicator of developmental instability.