The effectiveness of traps used currently for monitoring populations of the cabbage root fly (Delia radicum)

Six different types of traps were compared for capturing adults of Delia radicum. Cone traps caught so few flies that it seems inadvisable for them to be used for monitoring populations of this pest. All the other traps tested were suitable for monitoring D. radicum populations. When expressed on a trap for trap basis, the large 1800 cm² Canadian traps caught most flies. When expressed as the numbers of flies caughthnit area of trapping surface, most flies were caught in the water traps. Similar numbers of D. radicum, D. platura, syrphids, blowflies and a tachinid, Eriothrix rufomaculatus were caught per unit area on each of three different vertical sticky traps. Although water traps have the advantage that they catch about 5 times as many females D. radicum/unit area as the most effective vertical sticky traps of a comparable size, their disadvantage is that they catch about 10 times as many beneficial syrphids. The reasons why water traps are so effective against D. radicum are discussed, with details of how to convert water-trap data to sticky-trap equivalents, and vice versa.     

Effects of the angle of inclination of traps on the numbers of large Diptera caught on sticky boards in certain vegetable crops

The angle of inclination of the surface on which flies prefer to land in vegetable crops was studied in field plots and in field-cages using one-sided sticky traps aligned in one plane but orientated in eight directions. The four Delia species studied, D. antiqua, D. floralis, D. platura and D. radicum, preferred to land on horizontal surfaces, indicating that they are likely to be trapped in largest numbers on traps with a horizontal trapping surface, such as water traps. This trend was even more pronounced with the Syrphidae. In contrast, greatest numbers of the carrot fly, Psila rosae, were caught on the lower surface of traps inclined at 45° to the vertical. The advantages of using traps inclined in this way for trapping P. rosae are that more flies are caught on such surfaces, the sticky trapping compound is protected from the adverse effects of rain, and the traps are highly selective.

---

Résu,é L'angle d'inclinaison de la surface sur laquelle les mouches préfèrent atterrir dans les cultures de légumes a été examiné dans la nature, dans des parcelles et dans des cages, en utilisant des pièges englués sur un côté, alignés dans le même plan, mais orientés dans 8 directions. Les 4 espèces de Delia étudiées: D. antiqua, D. floralis, D. platura, D. radicum, ont préféré atterrir sur des surfaces horizontales, ce qui implique qu'elles sont probablement prises en plus grand nombre sur des pièges avec une surface de capture horizontale, comme des pièges liquides. Cette tendance est encore plus prononcée chez les Syrphidae. A l'opposé, de nombreuses mouches de la carotte, Psila rosae, ont été capturées sur la face inférieure de pièges inclinés de 45°. Il est avantageux d'utiliser des pièges inclinés de cette façon contre P. rosae parce que, d'une part ils sont très efficaces, d'autre part le produit actif est protégé de la pluie et enfin, le piège est très sélectif.

     

Effect of trap background on cabbage root fly landing and capture

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

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.

---

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.

     

Field evaluation of the combined deterrent and attractive effects of dimethyl disulfide on Delia radicum and its natural enemies

Delia radicum (L. 1758) is a major pest of cabbage crops in northern Europe. Due to more constraining laws relating to insecticide use, new strategies to control this pest are urgently needed. Manipulating insect behavior through infochemicals is a promising approach. The recent identification of dimethyl disulfide (DMDS) as a compound that both attracts the main predators of D. radicum and inhibits oviposition by the fly gives a challenging opportunity to develop such strategy. The aim of the present study was to confirm such potential of DMDS, in the field. Through the 8 weeks of the first egg laying peak of the fly we assessed, the potential of artificially increasing the levels of this molecule in the close vicinity of broccoli plants to 1/attract predators, 2/stimulate predatory activity and 3/limit damage done by the fly. Despite a lower number of D. radicum eggs as food resource, DMDS effectively increased predator catches in treated plots (119 Aleochara bilineata (Gyllenhal, 1810) caught in treated plot, while only 21 in control plots). However, damages done by the fly were of the same magnitude order in treated plots than in control ones. Number of D. radicum larvae and pupae recovered in plant roots were similar, despite the important decrease in eggs laid. This result, together with the observation that the numbers of eggs predated in artificial patches were lowered in the presence of the molecule, seems to indicate that increasing DMDS amounts disturbed the foraging activity of the fly predators. Consequences of these findings for the future of DMDS use in crop protection against D. radicum are discussed.     

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.     

Evaluation of commercial and field‐expedient baited traps for house flies,Musca domestica L. (Diptera: Muscidae)

A comparison of nine commercial baited fly traps on Florida dairy farms demonstrated that Terminator traps collected significantly more (13,323/trap) house flies (Musca domestica L.) than the others tested. Final Flight, Fly Magnet, and FliesBeGone traps collected intermediate numbers of flies (834‐2,166), and relatively few were caught with ISCA, Advantage, Fermone Big Boy, Squeeze & Snap, or OakStump traps (<300). Terminator traps collected about twice as many flies (799.8/trap) as FliesBeGone traps (343.8) when each trap was baited with its respective attractant, but when the attractants were switched between the two trap types, collections were significantly lower (77‐108) than was observed with traps baited with their respective attractant. Solutions of molasses were significantly more attractive to house flies than honey, maple syrup, or jaggery (date palm sugar). Field‐expedient traps constructed from discarded PET water bottles were much less effective than commercial traps, but painting the tops of such traps with black spray paint resulted in a six‐fold increase in trap capture.     

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.

---

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.

     

Recycling of entomopathogenic nematodes in Delia radicum and in other insects from cruciferous crops

Larvae of Deliaradicum Linnaeus (Diptera: Anthomyiidae) wereexposed to Steinernema feltiae Filipjev(Rhabditida) to study the ability of thenematodes to fulfill their life cycle (recycle)in this host. In addition, the recycling ofSteinernema and Heterorhabditis(Rhabditida) species was studied in larvae ofthe following insects: Meligethes spp.Stephens (Coleoptera: Nitidulidae),Dasyneura brassicae Winnertz (Diptera:Cecidomyidae), Ceutorrhynchus assimilisPaykull, C. pallidactylus Marsham (Coleoptera: Curculionidae) and Mamestrabrassicae Linnaeus (Lepidoptera: Noctuidae).All larval instars of D. radicum werestudied (larvae live and pupate in soil)whereas the final instars of the remaininginsects were studied (larvae only pupate in soil).On average, the following numbers of infectivejuveniles were produced in the different hosts:1,200–1,400 in C. assimilis; 700–1,300 inMeligethes spp. and 47,000 in M.brassicae. In D. radicum, around 400infective juveniles were produced on average inthe smallest larvae and around 3,500 in thelargest larvae. The highest number of nematodesrecorded in a D. radicum larva (thirdinstar) was 9,500 infective juveniles. Thenumber of nematodes produced in D.radicum cadavers was positively related to thesize of the insect host, but large variationwas observed.     

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

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

---

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

     

Improving the selectivity of water traps for monitoring populations of the cabbage root fly

Traps placed within brassica crops to monitor changes in cabbage root fly activity could be made more selective by painting black the inner wall of the standard fluorescent yellow water-traps. Traps could also be made more selective by covering them with cylinders of Netlon mesh, although this procedure reduces the numbers of cabbage root fly caught by about 70%. Of the single-coloured traps tested, those painted “marigold” yellow were the most selective in capturing female cabbage root flies. Although white and certain blue traps were as effective as the best yellow traps at capturing cabbage root flies, such traps should be avoided, as they catch 4–5 times as many of the closely-related bean seed fly. The presence of bean seed flies makes cabbage root fly identification more difficult and adds considerably to the time required to sort trap catches.     

Trap cropping to control Delia radicum populations in cruciferous crops: first results and future applications

This study evaluates the efficacy of a new approach to the control of Delia radicum populations. We suggest associating the primary crop with a trap crop that is expected to be more attractive to D. radicum females and to attract and sustain their natural enemies such as Aleochara bilineata and A. bipustulata. Various cruciferous species were compared in terms of their preference for adult D. radicum females, and performance, as estimated by larval survival. Laboratory results were complemented by field experiments in which the selected trap crops were associated with broccoli plants. The following results were obtained. Of the six different cruciferous plant species tested, Delia radicum females showed a strong preference for Chinese cabbage, with turnip also being attractive. Following the laboratory results, turnip was chosen as a trap crop because it was easier to cultivate and presented good preference and performance. In the field experiments, Aleochara adults were present in higher numbers in plots associated with turnips than in pure broccoli plots. The presence of Aleochara adults in plots with turnips improved plant protection; as fewer broccoli plants were attacked, the attacked plants were less severely damaged, and more D. radicum pupae were parasitised than in pure broccoli plots. Delia radicum females did not lay fewer eggs on broccoli plants associated with turnips. Moreover, protection and parasitism were more effective in the rows closest to the central row of turnips, suggesting that Aleochara adults limit their activity to its immediate vicinity.     

Effect on radish pests by application of insecticides in a nearby spring oilseed rape field

Chemical control of insect pests is often necessary to ensure high yields of field crops. The aim of the present study was to study whether field pesticide use influences amount of pest damage in neighbouring garden crops. Spring oilseed rape, OSR (Brassica napus L.), was established in Southern Sweden as an example of an agricultural field crop. One half of the OSR field was treated with insecticides to control flea beetles (Phyllotreta spp., Chrysomelidae) and pollen beetle (Meligethes aeneus Fab., Nitidulidae). Radish (Raphanus sativus L.) was used as an example of a common garden crop and it was sown as four replications at three different distances and on four occasions during the season. Care was taken to protect the radish plots from pesticide due to wind drift during applications. Damage to the radish by flea beetle and cabbage root fly (Delia radicum L., Anthomyiidae) along with unspecified leaf damage was recorded. Significantly lower damage by flea beetles was found on cotyledons of radish adjacent to the insecticide treated side of the OSR field compared to the untreated side in radishes from the first sowing. Unspecified damage to true leaves was also less abundant on radishes at the treated side of the OSR field as compared to the untreated side, in all three of the radish harvests analysed. However, radish plot distance from the OSR field did not influence leaf damage. Root fly damage rates in radish did not differ significantly between those adjacent to the treated and untreated sides of the OSR. Damage rates were, however, higher in the radish plots closest to the OSR field in the first sowing, which coincides with the appearance of the first ovipositing females after overwintering as pupae elsewhere. Generally, insecticide treatment in the agricultural field appeared to influence overall damage in the neighbouring garden crop, despite the fact that the garden crop was protected against wind drift of the insecticides during applications.     

Changes in flight track angles of cabbage root fly, Delia radicum, in diffuse clouds and discrete plumes of the host-plant volatile allylisothiocyanate

Flight tracks of female cabbage root fly, Delia radicum (L.), in odourless air, and in difuse clouds and discrete plumes of the host-plant volatile allylisothiocyanate (ANCS), were investigated. In diffuse ANCS D. radicum flew upwind with a smaller mean straight leg track angle with respect to the wind than in odourless air. In discrete ANCS, a larger mean straight leg track angle and a larger range of track angles occurred than in diffuse odour. The frequency distribution of these angles may have been bi-modal. It is suggested that perceived changes in odour concentration may alter the flight track angle. This behaviour is compared to the odour-modulated anemotaxis of male moths locating pheromone sources.

---

Résumé Changements des angles de vol de Delia radicum en présence de nuages diffus ou de panaches discontinus d'allylisothiocyanate, substance volatile émise par la plante-hôte.Nous avons étudié les chemins de vol des D. radicum femelles, en air pur, avect des émissions diffuses ou dicontinues de l'allylisothiocyanate (ANCS), substance volatilede la plante-hôte. En présence d'ANCS diffus, D. radicum vole contre le vent. Ce vol présente des portions droites faisant un angle avec la direction du vent; l'angle moyen de ce crochets est plus petit que celui observé en air pur. En présence d'ANCS discontinu, l'angle moyen est plus grand qu'en atmosphère diffuse et surtout l'histogramme de valeur de ces angles est bimodal.On peut envisager que la perception de changements dans la concentration de l'odeur peut modifier l'angle de vol. Un tel comportement est à comparer à l'anémotaxie contre le vent, modulée par l'odeur, observée chez les papillons mâles décelant une source de phéromones.

     

Effect of hunger on yellow water trap catches of hoverfly (Diptera: Syrphidae) adults

1 An experiment was conducted in a winter wheat field using yellow water traps at crop height and at ground level, near to and distant from flowers, to test the hypothesis that such traps are seen as a source of food by flower‐feeding adult hoverflies and are therefore likely to selectively trap hungry individuals. Hoverflies caught in each trap were counted and identified and the amount of pollen in their guts was assessed. Ratios of numbers of hoverflies seen in the wheat crop to numbers caught in nearby traps were compared for the different treatments. 2 Most hoverflies were caught in crop‐high traps but they included a high proportion of individuals with empty guts. The taxa were: Episyrphus balteatus (De Geer), Metasyrphus corollae (F.) (these species together accounted for over 90% of the individuals trapped), with Sphaerophoria spp., Syrphus spp., Scaeva pyrastri (L.), Melanostomini and unidentified others making up the rest. 3 Significantly fewer hoverflies were captured in low than in high traps. The ratios of numbers trapped to numbers observed, in flower and in no flower treatments would be expected to be the same if the traps were not selective. This was supported for low traps. With high traps, however, there was a highly significant difference between the ratios (71.34 and 126 : 8, respectively). 4 Flies captured in high traps had less pollen in their gut than those captured in low ones. At each distance, more E. balteatus captured in high traps were in pollen category 1 (< 20 grains) than in any other category. The opposite state was seen in low trap catches, where most flies were in category 5 (> 5000 grains). Median pollen categories were 2 (21–200 grains) and 4 (1501–5000 grains) for flies caught in high and low traps, respectively. 5 The ecological selectivity of traps according to their height and the physiological condition of the targeted individuals is a problem likely to affect many trapping systems apart from the one described in this paper.     

The role of odour and visual cues in the pan-trap catching of hoverflies (Diptera: Syrphidae)

Coloured pan traps are frequently used to attract and catch insects, such as in the monitoring of populations of beneficial insects in classical or conservation biological control. They are also used in the evaluation of the recovery of insect populations after disturbance and in many other situations where an estimate of relative insect numbers is required. However, the fact that traps may be visible to the insects over a considerable distance can influence the interpretation of catch data. This difficulty may arise, for example, if traps along a transect can attract insects from some or all of the other transect positions. This study compared the effect of different coloured traps on attraction and catch of hoverflies. The hypothesis was that completely yellow traps would attract hoverflies from a distance, while traps that were green outside and yellow inside would catch fewer flies because only those from above or near the trap can see the yellow stimulus. A subsidiary hypothesis was that rose water would enhance hoverfly capture rates. For the two main hoverfly species captured, Melanostoma fasciatum (Macquart) and Melangyna novaezelandiae (Macquart), significantly more individuals were caught in completely yellow traps than in yellow and green or in completely green traps. Moreover, the addition of rose water increased the number of hoverflies caught significantly. It is suggested that if a measure of hoverfly numbers relating to a particular distance along a transect is required, consideration should be given to the ability of hoverflies to see yellow traps from a distance. The use of traps that are green outside would more accurately reflect the local abundance of hoverflies. If higher trap catches of hoverflies are needed for statistical purposes, rose water can enhance catches.     

Behavioural responses to dimethyl disulphide by Aleochara bilineata and Aleochara bipustulata

Adult Aleochara bipustulata L. and Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) are predatory on immature stages of cabbage root fly Delia radicum (L.) (Diptera: Anthomyiidae). Larvae of the two Aleochara are parasitoids of D. radicum pupae. Female Aleochara lay eggs near D. radicum puparia; the newly‐hatched Aleochara larvae enter puparia and consume the contents. Delia radicum‐infested roots of brassicas give off dimethyl disulphide (DMDS). In the field, DMDS attracts adult Aleochara to pitfall traps but does not enhance the biological control of D. radicum. In the present study, we investigate the behavioural responses of the Aleochara to DMDS in still air, as well as in moving air in a Y‐tube olfactometer, and also investigate the influence of DMDS on host selection. In larvae of both Aleochara species, DMDS induces a restricted‐area search in still air, resulting in elevated frequencies of attack of D. radicum puparia close to a source of DMDS. In the olfactometer, newly‐emerged virgin adults of both sexes of both Aleochara species choose alternatives to DMDS, older recently‐mated females are attracted to DMDS, and older males and older mate‐deprived females show no preference. Mating status of males determines the switch of their response to DMDS from avoidance to indifference. We conclude that DMDS is an important cue for host‐finding, although other cues are involved in mate‐finding. We discuss the implications for use of DMDS to enhance D. radicum mortality and for parasitism of nontarget species if A. bipustulata is introduced to Canada for biological control of D. radicum.     

Flight periodicity ofProstephanus truncatus and longevity of attraction to synthetic pheromone

Double-sided sticky traps were baited with polythene vials containing synthetic components of the aggregation pheromone ofProstephanus truncatus (Horn) and used to investigate the effect of time of day on capture of this insect.P. truncatus exhibited a bimodal pattern of flight activity with a major peak between 18.00 and 21.00 h, and a smaller peak between 07.00 and 09.00 h. The effective life of the pheromone bait was also investigated over 33 days. The highest numbers ofP. truncatus were caught during the first 8 days and the majority of the beetles were caught within 14 days. Catches then showed a steady decline. Captures of the predatory histeridTeretriosoma nigrescens Lewis, were much lower than those ofP. truncatus and showed fluctuations which did not appear related to numbers of its prey. Environmental factors such as rainfall, temperature, wind and trap positioning appeared to influence results, especially when considered over a short time scale.     

Effect of beetle size on predation of cabbage root fly eggs by ground beetles

Laboratory studies were done to determine the numbers of cabbage root fly (Delia radicum L.) (Diptera: Anthomyiidae) eggs eaten by sixty species of ground beetles (Coleoptera: Carabidae) collected from a range of habitats. For 35 species that were between 2.7 mm and 10 mm long, there was a linear relationship between the numbers of eggs eaten and beetle length. For each 1 mm increase in length above 2.7 mm, an additional 18 eggs were eaten/beetle/day. Eight further species within the above size range did not eat any fly eggs, as these species are known to be either phytophagous or to feed on moving prey. Large numbers of eggs were eaten by beetles in 13 of the 25 genera tested. Based on size, maximum numbers of eggs were eaten by 7 species of Agonum Bonelli, 5 species of Amara Bonelli and seven species of Bembidion Latreille. Only one of the 6 species of Pterostichus Bonelli tested, P. strenuus (Panz.), ate the expected numbers of eggs, the other species being too large to feed from such small prey items as cabbage root fly eggs. The numbers of beetles larger than 10 mm that ate eggs was highly variable and so 10 mm was considered the upper size limit of carabid predators of cabbage root fly eggs.     

Comparison of traps for the control of sheep blowfly in the U.K.

The ability of three commercially available trap types to catch Lucilia (Diptera: Calliphoridae) blowflies was assessed on three sheep farms in southwest England in 2008. The aim was to evaluate their relative value for the control of ovine cutaneous myiasis (sheep blowfly strike) on farms. There was a highly significant difference between the total number of female Lucilia caught per day by the traps, with an Agrilure Trap (Agrimin Ltd, Brigg, U.K.) catching more than the other trap types (Rescue Disposable Fly Trap, Sterling International, Spokane, U.S.A.; Redtop Trap, Miller Methods, Johannesburg, South Africa). However, there was no significant difference between the traps in the numbers of female Lucilia sericata (Meigen) caught. Nevertheless, consideration of the rate at which female L. sericata were caught over time showed that the Agrilure trap did not begin catching until about 30 days after its initial deployment. It subsequently caught L. sericata at a faster rate than the other two traps. The data suggest that the freeze‐dried liver bait used in the Agrilure trap required a period of about 30 days to become fully rehydrated and decompose to the degree required to attract and catch L. sericata. Once the bait was attractive, however, the trap outperformed the other two traps in terms of the rate of L. sericata capture. The Agrilure trap would appear to be the most effective of the designs tested for use against sheep blowfly and blowfly strike in the U.K., but care would be needed to ensure that the traps were deployed in advance of the blowfly season so that the bait was suitably aged when trapping was required.