Comparative study of the antennal sensilla of five species of root maggots: Delia radicum L., D. floralis F., D. antiqua Mg., D. platura MG. (Diptera : Anthomyiidae) and Psila rosae F. (Diptera : Psilidae)

A comparative study of the antennal sensilla of Delia radicum L., D. floralis F., D. antiqua Mg., D. platura Mg. (Diptera : Anthomyiidae) and Psila rosae F. Diptera Psilidae) is undertaken. For both sexes of each species, the type, distribution, and density of sensilla are determined. All 5 species have trichoid (olfactory) and grooved (olfactory) sensilla. Basiconica I (blunt) sensilla (olfactory) are found on each of the species examined, except D. platura. Basiconica II (tapered) (olfactory) and clavate (olfactory) sensilla are found only on Delia species. Also, only Delia species have single-chambered, dorsal pits, and these contain basiconic II pit sensilla (olfactory). Common to all 5 species is a multi-chambered ventral pit (olfactory). In the ventral pit, all 5 species have grooved pit sensilla (olfactory). In addition to this type of sensillum the Delia species have smooth-walled conical pit sensilla (hygro-/thermosensitive) and P. rosae has granular pit sensilla (hygro-/thermosensitive). Smooth-walled tapered pit sensilla (hygro-/thermosensitive) are found in D. radicum. Similarities and differences in the density of surface sensilla between dorsal and ventral funicular surfaces, male and female flies, and oligophagous (D. antiqua, D. radicum, D. floralis and P. rosae) and polyphagous (D. platura) species are compared. Several differences in sensillum density between the dorsal and ventral funicular surfaces are observed, but these do not fit into a consistent trend. Except for D. radicum, there are differences in sensillum density between male and female flies. For the oligophagous species, females have a greater sensillum density, whilst for the polyphagous D. platura males have a greater sensillum density. Comparisons between species show the greatest differences between the Delia species and P. rosae, and within the 4 Delia species, differences in sensillum density do not correlate with host range or body size.     

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.     

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.     

Evaluating the enemies hypothesis in a clover‐cabbage intercrop: effects of generalist and specialist natural enemies on the turnip root fly (Delia floralis)

• 1 The relative importance of the resource concentration hypothesis and the enemies hypothesis was investigated for the turnip root fly Delia floralis in a cabbage–red clover intercropping system compared with a cabbage monoculture.
• 2 Delia floralis egg densities were measured as well as the activity‐densities of generalist predators in a field experiment during two growing seasons. In the second year, a study of egg predation with artificially placed eggs was conducted, in addition to a predator exclusion experiment, to estimate total predation during the season. Parasitization rates were estimated from samples of pupae.
• 3 Delia floralis oviposition was greater in the monoculture during both years. The predator activity‐densities differed between treatments and study years. The known natural enemies of Delia spp., Bembidion spp. and Aleochara bipustulata showed a strong response to a cultivation system with higher activity‐densities in the monoculture. The response, however, appeared to be caused primarily by habitat preferences and not by D. floralis egg densities.
• 4 The reduction in the number of D. floralis pupae in the intercropping may be explained by a disruption in oviposition behaviour caused by the presence of clover because neither predation, nor parasitization rates differed between cultivation systems.

     

Aleochara suffusa andA. bilineata (Col.: Staphylinidae) as parasitoids of brassica root flies in northern Norway

A sample ofDelia puparia collected in late autumn from a brassica field at Tromsø, northern Norway, was investigated to study the level of parasitism byAleochara. BothA. suffusa andA. bilineata were reared from puparia of the cabbage root fly,Delia radicum, and the bean seed flies,D. florilega and/orD. platura. Only two specimens ofA. bilineata emerged from puparia of the turnip root fly,D. floralis. BothAleochara species hibernated in the larval state and both pupated inside the host puparium. Most specimens ofA. suffusa emerged from small hosts (D. florilega/D. platura), whereas the majority of A.bilineata emerged from host species of larger size (D. radicum/D. floralis). The time to develop from first instar larva to adult was similar for bothA. suffusa andA. bilineata. Parasitoids developing in large hosts emerged later than those in small hosts, the delay being the same for both species ofAleochara.     

Antennal sensilla and sexual dimorphism of the adult ladybird beetle Semiadalia undecimnotata Schn. (Coleoptera: Coccinellidae)

The antennal receptors of the adult male and female ladybird beetle, Semiadalia undecimnotata (Coleoptera: Coccinellidae), were examined by scanning and transmission electron microscopy. Twelve types of receptors were characterized and grouped into 5 morphological classes: Böhm, trichoid, coeloconic, basiconic, and chetiform sensilla. Sensory function was determined on the basis of sensillar ultrastructure and electrophysiological response. Olfactory sensilla are confined in both sexes to the 2 terminal antennal segments. In contrast, gustatory and mechanosensitive organs are present along the entire length of the antennae. Sexual dimorphism of antennal receptors is limited to the latter 2 functional classes. The principal characteristics of this dimorphism are the following: a) males possess 540 sensilla (all types), while females possess only 500; b) males exhibit 2 types of taste receptors not present in females; c) females exhibit one type of mechanoreceptor absent in males; d) the 3 sex-specific types of sensilla, which occupy the same position in males and females, are confined to the inner side of the antennae. The possible role of male-specific sensilla in intersexual communication is discussed.     

Relationships between turnip root fly (Delia floralis) larval development and the sugar content of swede (Brassica napus ssp. rapifera) roots

Eight genotypes of swede (Brassica napus L. ssp. rapifera [Metz.] Sinsk.) at the 8–10 true leaf stage were inoculated with five, 10 or 20 eggs of the turnip root fly Delia floralis (Fall). The roots were sampled, with control roots, after 6 weeks of larval development. D. floralis root damage, as measured by reduction in root weight, was found to be linked to inoculation level. Neither D. floralis egg numbers nor swede genotype had a significant effect on the percentage of larvae developing to pupation. Mean pupal weight varied by a factor of ×1.4 and consistently decreased with increasing egg inoculation level. Changes in the root concentrations of glucose, sucrose and fructose were measured. All swede genotypes showed a similar response in their sugar concentrations after root damage. Glucose and fructose concentrations were reduced whilst sucrose concentration remained unaffected. The concentrations of glucose and fructose were highly correlated. Pupal weight, used as a measure of larval development, was significantly correlated with the concentrations of individual and total sugars in the roots. The implications of sugar responses to damage in brassicas, and the correlation between sugar concentrations in the roots and D. floralis pupal weights are discussed.     

Ultrastructure of the funicular sensilla of the cabbage root fly,Delia radicum L. (Diptera : Anthomyiidae)

A transmission electron microscope study of the funicular sensilla of the cabbage root fly, Delia radicum, (Diptera : Anthomyiidae), showed 4 types of surface sensilla and 5 types of pit sensilla. The ultrastructure of the surface sensilla indicated all had a primary olfactory function. These include thick-walled multiporous trichoid sensilla, thin-walled multiporous basiconic sensilla (with 2 subtypes), thin-walled multiporous clavate sensilla, and grooved sensilla with channels at the base of each of the grooves. Clavate sensilla had 2 types of dendrites, one tubular, the other “scrolled”. This 2nd type may indicate an additional thermosensitive function. The dorsal pits contained thin-walled multiporous basiconic sensilla with a tapered tip. The ventral pits contain 3 types of sensilla, which have no wall pores and an inflexible socket. These may contain thermo- and/or hygroreceptors and include smooth-walled conical-, smooth-walled tapered- and striated pit sensilla. The 4th type is a grooved pit sensillum similar to the surface type.     

Female-derived sex pheromone mediates courtship behaviour in the parasitoid Lariophagus distinguendus

Brassiceye^®traps baited with ethylisothiocyanate were modified and used to collect live adults of Delia radicum(L.) and Delia floralis(Fallén) (Diptera: Anthomyiidae) from the field to observe the prevalence of Entomophthora muscae(Cohn) Fresenius and Strongwellsea castransBatko & Weiser. The traps were highly effective and selective for D. radicumand D. floralis. Of the flies identified, 98.4% in 1996 and 93.7% in 1997 were either D. radicumor D. floralis. In 1997 the maximum mean catch was as high as 82 flies per trap per day, and more than 80% of these were females.During both seasons E. muscaecaused relatively high levels of mortality in adult populations of D. radicumand D. floralis. The fungus caused a total infection level of 17.9% in 1996 and 47.7% in 1997 with infection peaks of 82.4% in 1996 and 87.5% in 1997. Both years, a significant positive correlation was found between E. muscaeprevalence and temperature. One infection peak was observed for S. castransin 1996, and during that season the total S. castransinfection level was 18.0%. In 1997, the total S. castransinfection level was as low as 8.1%. There is no strong indication that the prevalence of E. muscaeor S. castransdiffers between either the fly species or sexes within species.     

Reproductive strategies and parasitization behavior of Ageniaspis citricola, a parasitoid of the citrus leafminer Phyllocnistis citrella

We describe the number, distribution, and function of sensilla located on different organs of Lobesia botrana (Lepidoptera: Tortricidae) females using scanning electron microscopy, selective staining, and contact electrophysiology. The tarsi of the prothoracic legs bear contact chemo‐mechanoreceptor sensilla chaetica (5–13 per tarsomere), arranged in rings mainly concentrated on ventral surfaces, and different mechanosensory structures (sensilla chaetica, sensilla squamiformia, sensilla campaniformia, and spines). A single contact chemo‐mechanoreceptor sensillum chaeticum is present between the claws on the pretarsus. The ventral surface of the ovipositor lobes is covered with numerous mechanosensory sensilla chaetica of different types, out of which 10 have a contact chemosensory function. Putative contact chemo‐mechanoreceptor sensilla were also observed on the proboscis and antenna. Longitudinal rows of alternated sensilla styloconica and basiconica are present on the distal part of the proboscis, and rings of sensilla chaetica are present at the antennal tip. The sensilla on these body parts may play different roles in the selection of an oviposition site.     

Morphology of the antennal sensilla of the cabbage root fly,Delia radicum L. (Diptera : Anthomyiidae)

The antennal sensilla of Delia radicum L. (Diptera : Anthomyiidae) were studied by scanning electron microscopy. On the scape and pedicel, grooved socketed bristles and setiferous plaques were found. There are 4 types of surface sensilla on the funicle: trichoid, basiconic, clavate, and grooved. Their numbers and distribution are described. There are 3–4 single-chambered pits on the dorsal surface of the funicle of both sexes and these contain basiconic sensilla. On the ventral surface, there is one multi-chambered pit, which contains 5 types of sensilla: grooved s., smooth-walled conical s., smooth-walled tapered s., striated s. and a novel type, flattened sensilla. These results are compared with previously published studies on several other fly species.     

Field and glasshouse studies on components of resistance to root fly attack in swedes

Field trials in two years indicated that egg-laying antixenosis was the major component of resistance in swede cvs Angus and Melfort against root flies (Delia floralis and D. radicum). Between four and eight times as many D. floralis eggs were laid on the susceptible cv. Doon Major as on the resistant cv. Angus. The degree of antixenosis effective against D. radicum was more variable in 1985, due to low numbers of adult flies, but in 1986, when adult fly numbers were higher, D. radicum laid 34 times as many eggs on susceptible cv. Sator Øtofte as on Angus. Root antibiosis against larval feeding is a second but less important component of resistance against D. floralis. In egg inoculation tests, 1.3-2.0 times more D. floralis pupae developed on Doon Major than on Angus or Melfort. Larval feeding on resistant cultivars was restricted to surface root tissue only, compared with deeper tunnelling on susceptible cultivars. Tolerance to root damage may also occur under certain conditions. Although increased dry matter content was significantly correlated with root antibiosis, its effect on larval feeding was apparently not due to increased tissue hardness. It seems likely that chemical differences in the outer root tissues influence larval feeding and development.     

Comparison of the sensitivity of four Delia species to host and non-host plant compounds

Abstract. The behavioural facilitation hypothesis, tested in the present study, suggests that evolution of host-plant shifts by phytophagous insects is based on the preadaptation of insects to the chemistry of potentially novel plant hosts. Thus, closely-related insects should have similar sensitivities to compounds that are shared by different host plants. The chemoreception is investigated for four phytophagous flies, Delia radicum, Delia floralis, Delia antiqua and Delia platura (Diptera, Calyptratae: Anthomyiidae), belonging to the same genus but developing mainly on different plant families, with particular secondary plant compound profiles. In addition, the carrot fly, Psila rosae, an acalyptrate Diptera, is included as an unrelated species that is associated with completely different host plants. For the comparison, the known oviposition stimulants of the cabbage root fly (glucobrassicin, sinalbin, sinigrin and a thia-triaza-fluorene compound; CIF-1) present on the cabbage leaf surface were chosen. Responses from prothoracic tarsal sensilla are recorded to contact stimulation in a dose-dependent manner. Among the different flies tested, only D. radicum responds to all the compounds. By contrast, D. floralis is only sensitive to CIF-1, and not specifically on the C₅ sensillum, a finding that is in conflict with previously published results. This discrepancy is possibly an indication of the variability among flies originating from different cultures or habitats. With the exception of sinigrin at high concentration, the various compounds tested do not stimulate D. antiqua or D. platura. However, the carrot fly appears to be completely insensitive to sinigrin even at the highest tested concentration of 10⁻¹ M. The responses of the contact-chemoreceptor neurones to the selected compounds therefore provide little evidence of common sensitivities that would explain host shift in Delia species and specialization at the physiological level. The wide divergence within closely-related species and rearing cultures appears to indicate that the sensitivity and distribution of sensory receptor neurones is very variable on an evolutionary scale.     

Morphology and distribution of antennal sense organs and diversity of mouthpart structures in Odontopus nigricornis (Stall) and Nezara viridula L. (Hemiptera)

Sensilla on the antennae and labial tip of the adult hemipteran bugs, Odontopus nigricornis Stall (Pyrrhocoridae) and Nezara viridula L. (Pentatomidae) (Hemiptera) were examined with an electron microscope in order to study their morphology, distribution, and possible chemo- and mechanoreceptive functions for food detection. The antenna contains 2 types of sensilla trichodea and 3 types of sensilla basiconica on the flagellar segments. S. trichodea are most abundant in both insects. Long slender hairs with elevated bases, and slightly shorter hairs with flexible sockets at the bases are common in both species. However, on each antennal segment of O.nigricornis, 1 or 2 rows of very long trichodeal hairs with longitudinal grooves and blunt tips are visible. At the periphery, S. basiconica with bulbous bases were also observed in addition to sensilla chaetica. The tripartite apex of the labium in both species consists of 2 lateral lobes and an apical plate. Each lateral lobe possesses a field of 11 thick-walled uniporous peg sensilla and long non-porous hair sensilla. Mandibular stylets of O.nigricornis have barbs, which may help in penetrating the hard seed coat. These insects made circular holes while feeding on the seed. A possible mechanism of feeding is discussed.     

Some observations onStrongwellsea castrans [Zygomycetes: Entomophthorales], a parasite of root flies [Delia spp.], in the south of Scotland

Root flies,Delia radicum (L.) andD. floralis (Fallén) (Diptera: Anthomyiidae), trapped in swede crops in the south of Scotland, were infected withStrongwellsea castrans Batko and Weiser (Zygomycetes: Entomophthorales). The pathogen was associated mainly with females of the 1st and 2nd generations ofD. radicum and of the single generation ofD. floralis. Disease incidence showed time-lagged density dependence. Greatest sustained infection levels were recorded in the coolest wettest season. Higher proportions ofD. radicum were infected in the headland than in the crop. Unbaited yellow water traps caught greater proportions of infected flies than traps baited with mustard oil (allyl isothiocyanate). The reasons for high levels of infection in Scotland are discussed.

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Résumé Les mouches des racines,Delia radicum (L.) etD. floralis (Fallén) [Diptera: Anthomyiidae] attrapées dans la culture du rutabaga dans le sud de l'écosse, étaient contaminées parStrongwellsea castrans Batko & Weiser [Zygomycetes: entomophthorales]. Le pathogène était surtout associé aux fe nelles de la lère et de la 2ème générations deD. radicum et de la seule génération deD. floralis. Les cas de maladie montraient avec retard leur dépendance avec la densité des mouches. Les niveaux d'infection les plus grands étaient enregistrés pendant la saison la plus froide et la plus humide. Les bordures en friche des parcelles hébergeaient de plus grandes proportions deD. radicum infectés que les cultures. Des pièges jaunes sans appat ont attrapé de plus grandes proportions de mouches que lorsqu'ils étaient appatés avec de l'huile de moutarde (allyl-isothiocyanate). Les raisons qui expliquent pourquoi les niveaux d'infection en écosse sont plus élevés qu'ailleurs sont discutées.

     

Effects of plant competition and herbivore density on the development of the turnip root fly (Delia floralis) in an intercropping system

In this study, interactive effects of plant competition and herbivory on plant quality and herbivore development were examined in a greenhouse experiment where cabbage plants [Brassica oleracea L. var. capitata (Brassicaceae)] were intercropped with red clover [Trifolium pratense L. (Fabaceae)]. Cabbages were grown with two red clover densities and attack rates by the root feeding herbivore the turnip root fly, Delia floralis Fall. (Diptera: Anthomyiidae). Above ground and below ground cabbage biomass was reduced through intercropping and larval damage. Intercropping also resulted in lower nitrogen and higher carbon root levels compared with levels in the roots of monocultured cabbage. Furthermore, both root nitrogen and carbon levels increased with herbivory. Root neutral detergent fibre (NDF) and lignin content increased in response to both increased plant competition and higher egg densities. For lignin, an interaction effect was observed in the form of elevated levels in intercropped plants subjected to larval damage, while levels in roots of monocultured cabbage remained unchanged. The quality changes brought about by clover competition affected D. floralis development negatively, which resulted in reduced pupal weight. In addition, increased egg density also decreased larval growth. The effects on the development of D. floralis in relation to host plant quality are discussed. Handling editor: Gimme Walter     

Fine sturcture of an antennal sensory organ ('vésicule olfactive') of Speophyes lucidulus Delar. (cave Coleoptera of the Bathysciinae subfamily)

The study of the ‘vésicule olfactive’ of the Speophyes antenna by means of electron microscopy, shows that it is a highly complex sensory organ.The organ of the ninth and tenth article is composed of two rooms, one above the other (the spheric room and the periarticular gutter) whereas the organ of the seventh article has an additional cavity, the intermediary room. The different parts contain various sensory receptors: pine-cone sensilla with porous ducts and innervated by one or sometimes two neurons. These sensilla have structural modifications which are related to sexual maturity; claviform pegs innervated by two neurons; star-shaped pegs innervated by five neurons; black pegs innervated by four neurons. The star-shaped pegs and the black pegs are associated with a lamellar structure arising from modified dendrite. Because of the diversity of sensilla the ‘vésicule olfactive’ is thought to serve multiple functions.     

Relationship between structure and function of antennal chemo-, hygro-, and thermoreceptive sensilla in Periplaneta americana

Summary On the antennae of Periplaneta americana, 25 chemo-, hygro- or thermosensitive sensilla were investigated electrophysiologically and, after marking, by transmission and scanning electron microscopy. A clear-cut relationship of functional types to structural types was observed. Two different stimulus conducting structures were observed: a) pore tubules which are found only in smooth, single-walled sensory pegs and b) secretion-filled canals which occur only in grooved double-walled sensilla. Temperature and humidity-sensitive receptors occur only in double-walled sensilla with secretion material as the stimulus conducting system. Olfactory sensory cells were found in both types, however, those with a specific sensitivity for short-chain n-alcohols are restricted to single-walled pegs with pore tubules, while those which are most sensitive to short-chain n-acids and amines are found in double-walled sensilla, sometimes together with thermosensitive units. The stimulus conducting systems may control the access of odorous substances to the dendritic membranes and thus contribute to the discriminatory properties of the sensilla.Supported by the Deutsehe Forschungsgemeinschaft (Al 56/6)     

Fine structure of tarsal sensilla in the taiga tick Ixodes persulcatus (Ixodinae)

The first tarsal segment of the taiga tick bears 4 general types of sensilla (except for sensilla forming the Haller's sensory organ on the dorsal surface of the tarsus): tactile mechanoreceptor sensilla of 3 types, contact chemo-mechanoreceptor sensilla of 2 types, and double-walled pore sensilla. One of these types, the chemo-mechanoreceptor upper-pore sensilla, was found only in the Ixodinae, and not found in the examined representatives of the Amblyomminae. This type of sensilla was also found in the palpal receptor organ of the ixodid and argasid ticks.     

Functional anatomy of sensory structures on the antennae of Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae)

The ultrastructure and distribution of sensilla on the antennae of the cabbage stem flea beetle, Psylliodes chrysocephala, were investigated using scanning and transmission electron microscopy techniques. Eight different sensillar types were distinguished. These were; hair plate sensilla, sensilla chaetica, three types of sensilla trichodea, sensilla basiconica, grooved peg sensilla and styloconic sensilla. The sensilla chaetica are known to be gustatory receptors. Ultrastructure indicates that the hair plate sensilla and sensilla trichodea type one are probably mechanoreceptors, whilst the sensilla styloconica are probably thermo-hygro receptors. These thermo-hygroreceptors are unusual in that they are innervated by two sensory cells (one hygroreceptor and one thermoreceptor) rather than the more usual triad. The remaining four sensillar types all have a porous hair shaft, indicating an olfactory role. One of these (the grooved peg sensillum) may also have a thermoreceptive function. No sexual dimorphism was found in the structure, number or distribution of the antennal sensilla.