Laboratory bioassays of entomopathogenic fungi for control of Delia radicum (L.) larvae

Laboratory soil bioassays were performed at economic field rates for in-furrow (3.85 x 10(6)spores/g dry soil) and broadcast (3.85 x 10(5)spores/g dry soil) applications with three isolates of Metarhizium anisopliae (F52, ATCC62176, and ARSEF5520) and one isolate of Beauveria bassiana (GHA). All isolates tested were infective to second instar Delia radicum (L.). The conditionally registered M. anisopliae isolate (F52) performed best killing an average of 85 and 72% of D. radicum larvae at the high and low concentration, respectively. The mean LC50 and LC95 of F52 against second instar D. radicum was 2.7 x 10(6) and 1.8 x 10(8)spores/g dry soil, respectively. The use of F52 in an integrated management program is discussed.     

Isolationin vitro ofStrongwellsea castrans [Fungi: Entomophthorales] a pathogen of adult cabbage root flies,Delia radicum [Dipt.: Anthomyiidae]

The entomogenous fungusStrongwellsea castrans was isolatedin vitro for the first time, by incubating conidia projected from infected cabbage root flies (Delia radicum) in a simple, semi-defined liquid medium comprising dextrose, yeast extract and lactalbumin hydrolysate buffered to pH 7. The fungus grew as long unitunicate hyphae. After transfer to a solid nutrient medium, multinucleate hyphal bodies were formed which developed a thick, laminated wall. Neither conidia nor resting spores developed in liquid or on solid media and the fungus survived successive sub-culturing only in liquid media. Using the API-ZYM system, tests on extracts on hyphae ofS. castrans were positive for 11 enzymes but there were no consistent differences in enzyme profiles betweenS. castrans and fungi of the related genusErynia.      

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.     

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.     

Orientation behavior of newly hatched larvae of the cabbage maggot,Delia radicum (L.) (Diptera: Anthomyiidae), to volatile plant metabolites

Newly hatched larvae of the cabbage maggot, Delia radicum(L.), responded to various olfactory stimuli from their host plants and oriented themselves by the concentration gradients of these stimuli. Allyl and ethyl isothiocyanate (NCS), characteristic metabolites of host Brassicaceae, elicited positive taxis, but at a higher concentrations were repellent. Benzyl NCS was neutral; only at the highest concentration was it slightly repellent. Phenyl, cyclohexyl, and butyl NCS were repellent in the highest amounts used. Volatile compounds emanating prevailingly from surface parts of plants were both attractive (hexanol, hexanal, cis-3-hexen-1-ol, linalool) and repellent (hexylacetate, cis-3-hexenylacetate, benzaldehyde, myrcene, terpinene, -pinene, limonene). While the attractiveness was associated with NCS group and with unsaturated and saturated alcohols and aldehydes with an optimal sixcarbon chain length, the repellency was probably caused by a cyclized carbon chain and an acetate group. The activity of a compound was strongly influenced by its concentration.     

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.     

Sensilla of the larvae of Delia radicum L., D. Floralis F. and D. Antiqua MG. (diptera : Anthomyiidae)

A comparative SEM study of the sensilla of larval Delia radicum, D. floralis and D. antiqua (Diptera : Anthomyiidae) was undertaken. All had a dorsal organ and an anterior organ. These may contain olfactory receptors, contact chemo- and mechanoreceptors. Delia radicum and D. floralis also possessed a ventral organ, which is a possible chemo- and mechanoreceptor. Campaniform (mechanoreceptor) and hair sensilla, which may be humidity receptors, were present on the body segments.     

Arabidopsis thaliana leaf-surface extracts are detected by the cabbage root fly (Delia radicum) and stimulate oviposition

Abstract. Oviposition of the cabbage root fly, Delia radicum (Diptera, Anthomyiidae) is stimulated by leaf‐surface extracts of Arabidopsis thaliana (L.) Heynh. (Brassicaceae) ecotype Columbia. The leaf surface of A. thaliana, similar to that of many other crucifers, contains glucosinolates and CIF (‘cabbage identification factor’; 1,2‐dehydro‐3‐thia‐4,10,10b‐triaza‐cyclopenta[.a.]fluorene‐1‐carboxylic acid). These compounds stimulate receptor neurones of the tarsal sensilla of D. radicum whereas additional, unknown compounds are detected by other receptor neurones.     

Binomial sampling as a cost efficient sampling method for pest management of cabbage root fly (Dipt., Anthomyiidae) in cauliflower

A binomial (presence–absence) sampling plan has been developed based on the relationship between the proportion of cauliflower plants having visible cabbage root fly eggs ( Delia radicum L.) exposed on the soil surface around the plant stem and the mean density of eggs per plant. The Kono–Sugino's model was fitted to a total of 125 population estimates, each based on 10 plant samples collected from cauliflower fields in 1994 and 1995 (P=0.001; R²=0.64). When the model was compared with an independent data set consisting of 39 population estimates collected in 1995, an analysis of covariance showed no significant differences between the regression lines. The efficiency of the binomial method was compared with absolute sampling in terms of relative precision and cost efficiency. The binomial method had a high coefficient of variation, RV ≈ 0.85, due to large biological error. In spite of this, binomial sampling was more cost efficient than the applied soil sampling when between 10 and 30 plants were examined for the presence of visible eggs.     

Exchange of Inoculum of Beauveria bassiana (Bals.) Vuill. (Hyphomycetes) Between Adult Flies of the Cabbage Maggot Delia radicum L. (Diptera: Anthomyiidae)

Adult cabbage maggots ( Delia radicum L.) were exposed to dry conidia of isolates of several hyphomycetous fungi by placing them in a centrifuge tube containing conidia, then releasing them into small screened plastic cages. Mortality was assessed after 48, 120 and 160 h. A Beauveria bassiana isolate (P89 from Musca domestica ) caused the highest mortality after 48 h, resulting in 100% mortality and 100% infection. Isolate L90 ( B. bassiana ) and one Metarhizium anisopliae isolate (ARSEF 2521) also caused fatal infection in more than 50% of the flies. To investigate exchange of inoculum, flies were placed in a small container with a dry powder formulation containing B. bassiana (Mycotrol ® ) on the bottom. The flies were removed to small screened cages containing untreated flies. This experiment confirmed the ability of flies to pass inoculum to other flies. In a similar experiment, one treated fly was placed in each cage with one untreated fly. When each fly died, one untreated fly was added to each cage after the dead fly was removed. This study showed that fly to fly transfer of fatal doses of inoculum was possible for a series of at least six flies. When female flies were exposed to the inoculum, then transferred to small cages containing males and an oviposition substrate, no eggs were laid. Further studies are being conducted to develop a system where flies attracted to a trap will be inoculated with the fungus and spread it to a field population.     

Cold resistance and overwintering survival of the cabbage root fly,Delia radicum (Anthomyiidae), and its parasitoid,Trybliographa rapae (Cynipidae), in England

Summary Overwintering Delia radicum (L.) in a field of swedes (Brassica napus L.) near Ascot, Berks., England, were exposed to soil temperatures below 10°C on 176 days from 21 October 1983 to 22 April 1984, but no temperatures below 0°C were recorded. Collections of D. radicum taken at monthly intervals from 1 November 1983 to 30 April 1984 showed that parasitism by the cynipid Trybliographa rapae (Westw.) and by the staphylinid Aleochara bilineata Gyll. was the main source of mortality. A substantial increase in parasitism by A. bilineata occurred during November, but much of the increase was by superparasitism of pupae previously parasitized by T. rapae. Mortality from causes other than parasitism was greater in the November and December collections (c. 22%) and in the spring (c. 12%) than during the winter (c. 3%) and could not be attributed to low temperatures.In all collections, most of the adult D. radicum (c. 90%) emerged within 230°D_5.6. The mean number of °D_5.6 to eclosion did not change from 1 November to 5 March but decreased significantly by 2 April. Late-emerging adults remired 259 to 992°D_5.6 to eclosion and no changes in the nean number of °D occurred among collections.Among unparasitized D. radicum, individual supercooling points showed a strong peak at c.-23°C. A significant proportion of pupae with supercooling points above-20°C were found only in the 1 November 1983 and the 30 April 1984 collections. The high supercooling points in the November collection may have comprised apparently healthy but moribund individuals, whereas in the April collection they may have included individuals that had initiated postdiapause development. The mean supercooling point of individuals in the low category (supercooling points 20°C) did not vary among monthly samples. Parasitism by T. rapae increased the variability in supercooling points, resulting in a few individuals with lower, and many more with higher supercooling points than among unparasitized individuals. The mean supercooling point increasing from the collections of November and December to those of January to April.Puparia containing unparasitized D. radicum pupae were heavier and contained more water than those with parasitized pupae, but neither group showed significant ranges over winter. Supercooling points were positively correlated with puparial live weight among unparasitized but not among parasitized pupae. Supercooling points were not correlated with water content for either group.Parasitism did not affect the occurrence or concentration of sugars and polyhydric alcohols (all<1% of fresh weight), and trehalose, glucose and mannitol were the most abundant. D. radicum can be considered to be over-protected from lethal freezing in the pupal stage and its high supercooling capacity in England may persist because it is conferred by the structural properties of the dipteran puparium and pupa within it and therefore is not subject to selection pressures.     

Effect of temperature on the pathogenicity of entomopathogenic nematodes (Steinernema and Heterorhabditis spp.) to Delia radicum

Susceptibility of last instarlarvae of Delia radicum to Steinernema feltiae, S. carpocapsae,S. arenarium, Heterorhabditismegidis and H. bacteriophora wasevaluated in the laboratory at 10 °C,15 °C and 20 °C. S. feltiaewas the only species that killed the larvae at10 °C; S. carpocapsae, S.arenarium and H. megidis were effectiveat 15–20 °C whereas H.bacteriophora killed the maggot only at20 °C. The temperature significantlyaffected the host searching ability of alltested species. Mobility was reduced at lowtemperatures. Significant effects of the hostpresence on nematode mobility were found forS. feltiae, S. arenarium and H. megidis but not for S. carpocapsaeand H. bacteriophora. The dynamics of theattachment to and penetration into the hostwere monitored for S. feltiae at10 °C, 15 °C or 20 °C and forS. carpocapsae at 20 °C. In theperiod of 6–30 hours after inoculation, S.carpocapsae attached in higher number at20 °C than did S. feltiae at alltemperatures. At 20 °C, S.carpocapsae penetrated the host only after 30hours while S. feltiae penetrated alreadyafter 15, 9, 6 hours at 10 °C,15 °C and 20 °C, respectively.     

Comparison of nectar use and preference in the parasitoid Trybliographa rapae (Hymenoptera: Figitidae) and its host,the cabbage root fly,Delia radicum (Diptera: Anthomyiidae)

This study investigated differences in flower preferences between the parasitoid Trybliographa rapae Westwood (Hymenoptera: Figitidae) and its host, the economically important pest of cruciferous crops, the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae). The data obtained were used to suggest selective food plants in conservation biological control programmes for control of D. radicum. The attraction of both insect species to floral odours emitted from nine different plant species, their ability to access nectar from four of these species and the effect of the most promising plant species on insect longevity were determined. Naive T. rapae females were significantly attracted to flower odours from Fagopyrum esculentum Moench. (Polygonaceae) and repelled by Coriandrum sativum L. (Apiaceae) and Borago officinalis L. (Boraginaceae). In addition, T. rapae gained weight when exposed to F. esculentum, Anethum graveolens L. (Apiaceae) and Lobularia maritima Desv. (Brassicaceae). In contrast, naive D. radicum females showed attraction to most of the flowers. The longevity of both T. rapae and D. radicum increased significantly when they were provided with flowering A. graveolens and F. esculentum. In addition to the laboratory studies, a semi-field experiment was made to study the impact of flowering F. esculentum on the ability of T. rapae to parasitise D. radicum larvae. Significantly more larvae were parasitised in cages where a floral resource was present. The findings are discussed in the context of a Brassica agroecosystem.     

Comparative biology of two rosette crown-feeding flies of the genus Botanophila (Dipt., Anthomyiidae) with potential for biological control of their thistle hosts

The comparative biology of two anthomyiid flies with potential for biological control of their host thistles, Botanophila turcica on Carthamus lanatus and Botanophila spinosa on Onopordum acanthium , was studied using field surveys and collections, and by rearing collected eggs and larvae in the laboratory in southern France. The thistle hosts are significant weeds outside their native range, particularly in Australia. Both flies attack the rosette meristems of their hosts prior to flowering. Larval stages are described together with natural attack rates (21–33% of field plants) and the mortality of field-collected larvae reared in the laboratory. A successful rearing protocol for these flies is also described. The results of preliminary host-specificity tests showed that both species are highly specific, being restricted to their host genus in the tests conducted. Furthermore, Botanophila turcica could not complete development on safflower (a congener of its natural host) under natural conditions. Botanophila turcica had an adult activity period that lasted 6 months from late autumn and laid fewer eggs per host plant than B. spinosa , which was active for 2 to 3 months in spring. Only one parasitoid was observed, an endoparasitic eucoilid, Trybliographa sp., which attacked both fly species, causing 18–23% mortality.     

Tarsal chemoreceptors and oviposition behaviour of the cabbage root fly (Delia radicum) sensitive to fractions and new compounds of host-leaf surface extracts

Abstract. Contact chemoreception plays a decisive role in host selection and oviposition behaviour of the cabbage root fly, Delia radicum L. (Diptera, Anthomyiidae). Glucosinolates (mustard oil glucosides) are known to be perceived by the flies, and when sprayed on paper leaf-models induce oviposition. Recently it has become clear that other non-volatile types of compounds must also be involved in host selection.
A pair of ventro-medial C sensilla on die fifth tarsomere respond strongly to a novel compound called tentatively 'cabbage identification factor' (CIF), but not to sucrose, glucose, fructose and proline. CDF is a new non-glucosinolate oviposition stimulant. A single neurone in each sensillum is activated by this compound and the same is true for glucosinolates. In some flies a mixture of bom types of stimuli evoked an apparent mononeural spike train, whereas in odiers spikes of two separate cells were activated. The significance of this variability is not yet clear.
The new stimulant, CIF, does not evoke responses in glucosinolate receptors in the D sensilla. The involvement of the C₃ sensilla in the detection of host-specific compounds constitutes the first known function for C sensilla in D. radicum. CIF appears to be present in leaf surface extracts from the host-plant Brassica oleracea in quantities as low as 1 ng per gram leaf. In spite of this low level, it stimulates oviposition significantly better than glucobrassicin at higher concentrations, which up till now was known as the most powerful stimulant for D.radicum.     

The relationship between cabbage root fly (Delia radicum) larval feeding and the freeze-dried matter and sugar content of Brassica roots

Five genotypes of swede (Brassica napus var. napobrassica), two genotypes of kale (B. oleracea var. acephala), and two genotypes of rape (B. napus var. napus) were each inoculated at the 8–10 true leaf stage with five cabbage root fly (Delia radicum) eggs. The percentage pupation after larval feeding on individual plant genotypes ranged from 45 to 78%, and the mean pupal weight from 6.5 to 13.0 mg. After 5 weeks, larval feeding damage had reduced root weight by up to 47%, compared with uninoculated plants. The dry matter content of undamaged roots was higher in the kales and rapes than in the swedes. Whilst the dry matter content of the rapes and swedes were not changed by D. radicum damage, that of the kales was elevated. The ethanol-soluble sugar content of the root was reduced in all cases by D. radicum larval damage. However, the effect of D. radicum damage on the concentrations of individual sugars (glucose, fructose and sucrose) was crop- and genotype-dependent. In the roots of kales and rapes, the glucose and fructose concentrations were either very low or unaffected by D. radicum damage, whilst both glucose and fructose were generally reduced in swede roots by D. radicum damage. The root sucrose concentration was either reduced or not significantly affected by D. radicum damage in all of the crop types tested. The percentage pupation and the mean pupal weight of D. radicum were inversely correlated to root freeze-dried matter content. D. radicum pupal weight was positively correlated with root fructose, glucose and ethanol-soluble sugar contents.     

Preference of the cabbage root fly, Delia radicum (L.), for coloured traps: influence of sex and physiological status of the flies, trap background and experimental design

Abstract. Catches of Delia rudicum (L.) (Diptera: Anthomyiidae) were compared in water traps that reflected predominantly wavelengths shorter (violet and blue traps) and longer (green and yellow traps) than 500 nm.Traps were positioned in choice and no-choice situations against backgrounds of bare soil and weeds in the field and against backgrounds of brown and green paper in the laboratory.The physiological status of the flies was modified in the laboratory by denying them access to food sources and oviposition sites.
Males discriminated significantly more clearly than females between yellow and blue traps.The discrimination between yellow and blue traps was significantly more pronounced when the traps were presented in the choice than in the no-choice situation in both sexes.Green background (weeds and green paper) was highly preferred for landing and thus competed with the traps to such an extent that few flies were caught when non-preferred violet and blue traps were sited on green backgrounds.Flies seldom landed on the brown background (soil and brown paper) which resulted in the relative increase of catches in the non-preferred violet and blue traps.The preference for yellow traps was innate even in young flies with immature egg-follicles.Females that were ready to lay eggs, even those deprived of an oviposition site till the age of 8 days, also preferred yellow traps.In the no-choice situation, flies deprived of food landed with the same frequency in yellow and blue traps.Food deprivation, however, did not affect preference for yellow traps over the blue traps presented in a choice situation.     

Biochemical and taxonomic characterization of bacteria associated with the crucifer root maggot (Delia radicum)

The crucifer root maggot, Delia radicum, is an important pest of cruciferous crops; however, little is known about its digestive biochemistry or resident gut microbiota. A culturing approach was used to survey the types of micro organisms associated with eggs, midgut, and faeces of larvae feeding on rutabaga. All bacteria isolated from the midgut and faecal materials were Gram-negative bacilli. Nine types of culturable bacteria were identified within the midgut based on analysis of 60 kDa chaperonin sequences and were generally gamma-Proteobacteria, primarily Enterobacteriaceae. Carbohydrate utilization patterns, select biochemical pathways, and hydrolytic enzymes were examined using the API(R) system for each of the nine groups, revealing an exceptionally broad metabolic and hydrolytic potential. These studies suggest that resident alimentary tract microorganisms have the potential to contribute to host nutrition directly as a food source as well as by providing increased digestive potential.     

A bait formulated with Metarhizium anisopliae for the control of Musca domestica L. (Dipt., Muscidae) assessed in large-scale laboratory enclosures

The entomopathogenic fungus Metarhizium anisopliae was formulated into a bait for assessment against Musca domestica (housefly). Its efficacy was tested by placing either one, two or four baits on the floor of a 10 m³ polythene cubicle and releasing 100 female and 50 male M. domestica. One, two or four baits had equal effects and, between 95.2 and 100% of flies were killed after 10 days. In a second experiment, the durations of visits by single or pairs of flies to the baits and subsequent pick-up of conidia were recorded. Single flies remained in the baits for up to 33 min and picked up a mean of 38 235 ± 8291 conidia. When pairs of flies were exposed, the individuals picked up a mean of 95 879 ± 23 838 conidia, which was significantly more (P < 0.05) than the single flies, although the mean duration of the visits was not significantly different (P > 0.05). However, the numbers of conidia picked up by the flies did not correlate with the duration of the visit. Lastly, 25 female and 25 male flies were exposed in 0.027 m³ arenas, to 10 M. anisopliae- killed houseflies, showing sporulating hyphae. After 8 days, 97.3% of female flies and 100% of male houseflies had succumbed to infection with M. anisopliae. The implications of these observations are discussed.     

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.