Further investigations of the host range of the carrot fly, Psila rosae (F.)

Techniques were developed for testing umbelliferous species against naturally-occurring populations of carrot fly in the field. The most efficient technique involved exposure of plants to either first or second generations of the insect in the field, followed by caging of infested plots and trapping of emerged flies in water in yellow water dishes. In a series of field experiments between 1981 and 1989 inclusive, a total of 132 umbelliferous species and sub-species were tested against carrot fly. Seventy-eight of these proved to be new hosts, 27 were confirmed as hosts and 27 failed to support any carrot flies. Six non-umbelliferous plant species failed to be colonised by carrot fly. Sources of variability in investigations of the host range of insects are discussed.     

Behavioural responses of the carrot fly larva, Psila rosae, to carrot root volatiles

ABSTRACT. The behaviour of the carrot fly larva, Psila rosae F. (Diptera, Psilidae), was investigated in the presence of six concentrations of thirty-four volatiles associated with carrot root and of trans -methyl-iso-eugenol, a constituent of carrot herb oil. Bomyl acetate, 2,4-dimethyl styrene, α-ionone, SbT-ionone and biphenyl were the most consistently preferred compounds. Klinotaxis and klinokinesis were the orientation responses near the stimulus source. Trans -2-nonenal was the most consistently avoided compound. Extracts derived by steam distillation of carrot roots and by concentration of vapour from roots were resolved, by gas liquid chromatography, into forty-five and twenty-two major constituents, respectively. The five preferred compounds are micro-components of these extracts, collectively representing 1% and 0.6% of root extract oil and vapour, respectively. It is suggested that these secondary plant constituents are specific host finding cues for the larva, and that frara-2-nonenal is a carrot defence compound.     

Monitoring populations of the carrot fly, Psila rosae, with sticky and water traps

The relative, effectiveness of Rebell®, small cylinder, large cylinder, windmill and water traps, the five types of trap used currently for monitoring populations of the carrot fly, Psila rosae, was assessed in nine field experiments, three in south west Lancashire, four in the Fens (Suffolk, Norfolk, Cambridgeshire), one in East Suffolk and one at Wellesbourne, Warwickshire. Regression analysis of the numbers of flies caught on each type of trap against the numbers caught on the Rebell® trap indicated that each trap samples a constant proportion of the fly population relative to the other traps. Therefore, provided the fly population was sufficiently large for insects to be caught on the least effective traps, any of the five traps would monitor adequately fluctuations in carrot fly populations. However, the Rebell® trap caught 4–17 times as many flies/trap and 5–7 times as many flieshnit area of trap as any of the other traps tested.
Operators considered the Rebell® trap to be the easiest to use. However, it was more expensive than any of the other traps tested.     

Olfactory responses of the omnivorous generalist predator Dicyphus hesperus to plant and prey odours

This paper describes a method for studying the neighbourhood (dispersal) movement of pest insects that overcomes the major problems associated with release/recapture experiments. The method has been developed using the carrot fly, Psila rosae (Fab.) (Diptera: Psilidae), as the experimental insect. It involves building up a large population of insects in an area free of other host plants, and then, as the insects disperse in the spring, monitoring the fall‐off in numbers of insects with increasing distance. Estimates of the fall‐off in numbers of the carrot fly were obtained by using sticky traps to monitor changes in fly numbers in 11 small plots of carrots drilled 130–1300 m away from the site at which the flies emerged (emergence site) in the spring. A strong linear relationship (r² = 0.96) was obtained between the log₁₀ numbers of flies caught in each plot and the log₁₀ distance the plot was from the emergence site. Few flies were caught more than 1 km from the emergence site. A linear relationship (r² = 0.86) was also obtained between the date when 50% of the flies were caught in each plot and the distance the plot was from the emergence site. The date of 50% capture was delayed by 1 day for each 100 m the given plot was away from the emergence site. This suggests that when carrot flies move to find new crops, the population moves about 100 m day^?1. About one million flies would have to be released in conventional release/recapture experiments to obtain data as robust as those collected using the current method. The major breakthrough of this method is that dispersal can be estimated for an insect species that, although a major pest of field crops of carrots and parsnips, is exceptionally difficult to rear, even in relatively small numbers, under controlled‐environment conditions.     

Carrot fly cultivar preferences: some influencing factors

Abstract. 1. Factors affecting cultivar preferences by the carrot fly Psila rosae F. were examined in choice tests using foliage from carrot lines representing extremes of resistance and susceptibility to attack.
2. Flies were offered a choice to oviposit on foliage, artificial substrates impregnated with leaf surface extracts or enclosed in vapours of different cultivars to establish the importance of contact and olfactory stimuli. Susceptible cv. Danvers Half Long 126 foliage was preferred over that of resistant cvs. Clause's Sytan Original and Tip-Top. But, whereas the Sytan leaf surface extract was as effective as that of Danvers, the surface extract of Tip-Top was very much inferior as an oviposition stimulant. By contrast, Sytan and Tip-Top foliar vapours were both more attractive to the fly than that from Danvers.
3. Headspace vapours over Sytan foliage evoked significantly higher electroantennogram responses than those from Danvers.
4. Cold-trapped foliar volatiles of Sytan and Danvers were analysed by gas chromatography linked with antennographic detection. Foliage of Sytan released, among other chemo-stimulants, higher levels of host plant attractants, i.e. green leaf aldehydes and the phenylpropanoids, trans-asarone and trans-methylisoeugenol.
5. These findings indicate that olfactory and contact chemostimuli may be involved in preferences shown by the carrot fly for carrot cultivars, but these factors alone do not fully account for the preferences observed.     

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.

     

A FIELD TEST FOR HOST-PLANT DEPENDENT SELECTION ON LARVAE OF THE APPLE MAGGOT FLY,RHAGOLETIS POMONELLA

Host-plant dependent fitness trade-offs refer to traits that enhance the performance of an insect on one plant species to its detriment on others. Such trade-offs are central to models of sympatric speciation via host shifts, but have proven difficult to empirically demonstrate. Here, we test for host-plant dependent selection on larvae of apple (Malus pumila L.)- and hawthorn (Crataegus mollis L. spp.)-infesting races of Rhagoletis pomonella (Walsh). Samples of larvae were reared in the field and under protective conditions in a garage. Our rationale was that the garage should slow rates of fruit rot relative to the field, relaxing selection pressures associated with declining fruit quality. Four findings emerged from the study. (1) Larvae suffered higher mortality in fruits in the field than the garage. (2) The increase in mortality was greater for larvae in haws. (3) Larvae possessing the alleles Me 100, Acon-2 95, and Mpi 37, three allozymes displaying host-related differentiation in R. pomonella that map to linkage group II in the fly, left fruits earlier than other genotypes. (4) Allele frequencies for Me 100, Acon-2 95, and Mpi 37 were significantly higher in both apple and haw larvae surviving the field versus the garage treatment. Our results suggested that field conditions favored larvae that rapidly developed and left rotting fruits. Since these individuals tended to possess the alleles Me 100, Acon-2 95, and Mpi 37, frequencies of these allozymes were higher in the field. Selection on larvae was directional for Me 100, Acon-2 95, and Mpi 37 (or linked genes) in both host races. We previously showed that these same alleles can be disfavored in the pupal stage, especially in the apple race, where they correlate with premature diapause termination. Fitness trade-offs in Rhagoletis may therefore be due as much to differences in the relative strengths of directional selection pressures acting on different life stages as to disruptive selection affecting any one particular stage. The necessity to consider details of the entire life-cycle highlights one of the many challenges posed to documenting fitness trade-offs for phytophagous insects.     

LARVAL X‐RAY IRRADIATION INFLUENCES PROTEIN EXPRESSION IN PUPAE OF THE ORIENTAL FRUIT FLY,BACTROCERA DORSALIS

The sterile insect technique (SIT) was developed to eradicate the new world screwworm from the southern United States and Mexico, and became a component of many area‐wide integrated pest management programs, particularly useful in managing tephritid fruit flies. SIT is based on the idea of rearing and sterilizing male pests, originally by ionizing radiation, and then releasing into field, where they compete for and mate with wild females. Mating with sterile males leads to reduced fecundity to lower pest populations. There are concerns with the use and distribution of radioisotopes for SIT programs, which have led to developing X‐ray irradiation protocols to sterilize insects. We considered the possibility that X‐ray irradiation exerts sublethal impacts aside form sterilizing insects. Such effects may not be directly observable, which led us to the hypothesis that X‐ray irradiation in one life stage creates alterations in biological fitness and protein expression in the subsequent stage. We tested our hypothesis by irradiating larvae of Bactrocera dorsalis. There are two major points. One, exposing larvae to X‐ray treatments led to reduced adult emergence, fecundity, fertility, and flight capacity from the corresponding pupae and emerged adults. Two, the X‐ray treatments led to substantial expression changes in 27 pupal proteins. We assorted the 67 spots representing these proteins into three groups, metabolism, development, and structure. Our interpretation is these X‐ray induced changes in biological performance and protein expression indicate their adult counterparts may be disabled in their abilities to successfully compete for and mate wild females in native habitats.     

四川省山蚋亚属一新种记述(双翅目,蚋科)

继作者于2005年首次发现并记述四川省山蚋亚属二新种之后,报道四川省山蚋亚属另1新种,Simulium (Montisimulium)jiajinshanense sp.nov.(夹金山山蚋).本新种与报告自中国的S.(M.)tibetense Deng et al.,1993(西藏山蚋)and S.(M.)moxiense Chen et al.,2005(磨西山蚋),阿塞拜疆的S.(M.)assadovi(Djafarav,1956),亚美尼亚的S.(M.)litshkense(Rubtsov,1947),哈萨克斯坦的S.(M.)quattuordecimfiatliatum(Rubtsov,1947)和塔吉克斯坦的S.(M.)quattuordecimfilum Rubtsov,1947相似,均具14条呼吸丝,但新种可依据食窦弓具中突,两性生殖器的特殊形态,茧简单和呼吸丝特殊分枝等综合特征和上述近缘种相区别.     

不同地区小菜蛾种群羧酸酯酶的毒理学性质研究

在1995～1997年对湖北武汉、河北张家口地区小菜蛾Plutella xylostella(L.)种群的抗药性进行了研究。结果表明对阿维菌素的抗性和台湾敏感种群相比,武汉种群抗性为4.3倍,张家口种群抗性为1.8倍;对马拉硫磷的抗性武汉和张家口种群分别为2.2和2.9倍;对氟铃脲的抗性分别为3.2和0.5倍;对溴氰菊酯的抗性分别为2.4和1.7倍。对羧酸酯酶(Care)的研究结果表明,三个种群幼虫CarE对a-乙酸萘酯或β-乙酸萘酯(a或β-NA)水解活性差异显著,但成虫Care活性没有明显差异。武汉和张家口种群幼虫CarE对a-NA和β-NA的亲和力没有明显差异,但是武汉种群幼虫Care对底物的亲和力高于张家口种群。敏感品系Care对a—NA的亲和力明显高于对β-NA,相差约3倍。不同类型的抑制剂对小菜蛾幼虫CarE的抑制能力不同。增效磷和对氧磷对敏感品系CarE水解a-NA具有明显的抑制作用,分别比对武汉种群Care的抑制作用大4.577倍(SVl)和2.576倍(对氧磷)。