Responses of <Emphasis Type="Italic">Phradis</Emphasis> parasitoids to volatiles of lavender, <Emphasis Type="Italic">Lavendula angustifolia</Emphasis>—a possible repellent for their host, <Emphasis Type="Italic">Meligethes aeneus</Emphasis>

Hymenopterous parasitoids of herbivorous insects can be useful biocontrol agents in integrated pest management strategies. However, the potential effects on these beneficials of new components in such strategies are often neglected. Essential oil of lavender, Lavendula angustifolia (Miller) (Lamiaceae), has recently been identified as a potential repellent in new control strategies being developed for the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a major pest of oilseed rape, Brassica napus L. (Brassicaceae). We tested the electrophysiological and behavioural responses of two common parasitoids of M. aeneus: Phradis interstitialis (Thomson) and P. morionellus (Holmgren) (both Ichneumonidae) using coupled gas chromatography-electroantennodetection (GC-EAD) and olfactometry techniques. Both species elicited electrophysiological responses to lavender oil volatiles, including two compounds known to be repellent to M. aeneus. However, the parasitoids gave no significant responses to the odours of lavender oil in behavioural bioassays and there was no evidence to suggest that lavender-treated oilseed rape plants would reduce host habitat location by parasitoids of the target pest.     

Effects of host plant species on the interaction between the parasitic wasp Diospilus capito and pollen beetles (Meligethes spp.)

1 Field studies were conducted in central Sweden to establish whether two host plants with high and low suitability for pollen beetles (Meligethes aeneus Fabr. [Coleoptera: Nitidulidae] and Meligethes viridescens Fabr.) affected the parasitoid Diospilus capito Nees [Hymenoptera: Braconidae]. 2 Samples of larvae were taken from fields with plots of white mustard, Sinapis alba L. and spring rape, Brassica napus L. in 1997 and 1998. Levels of parasitism and the survival and size of D. capito were measured to determine any influence of the host plant species. Survival and weights of pollen beetles from S. alba and B. napus were also measured. 3 Levels of parasitism between 8% and 29% were recorded. There was a significantly higher likelihood of being parasitized by D. capito for beetle larvae developing on S. alba than on B. napus. We argue that semiochemical or morphological properties of plant species could be responsible for differential parasitism by D. capito. 4 Neither survival of D. capito nor parasitoid size differed from hosts developing on S. alba or B. napus. Pollen beetle emergence was the same for both plant species, but beetles that developed on S. alba weighed less than those from B. napus. Results suggest that the partial resistance of S. alba to the pollen beetle will have no negative effects on the parasitoid D. capito.     

A study on the effects of insecticides on parasites of larvae of blossom beetles (Meligethes aeneus F., coleoptera: Nitidulidae)

Summary Three species ofIsurgus were found associated with flowering mustard plants at Trumpington, Cambridge, during late May and June.I. morionellus Holmgren, constituted 80% of the adult parasite population in 1960, and 74% in 1961. The remainder were mainlyI. heterocerus Thomson, with very small numbers ofIsurgus species C andDiospilus capito Nees (Hymenoptera, Braconidae). Dieldrin or DDT sprays severely reduced parasitism of the larvae of blossom beetles (Meligethes aeneus F.); sometimes no parasitised larvae were found after spraying, but in such cases there were only small numbers of blossom beetle larvae present.

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Zusammenfassung Vorausgegangene Untersuchungen an kleinen Schlägen und in Insekticid-Feldprüfungen haben bestätigt, daß DDT und Dieldrin sowohl Imagines wie Larvenstadien des Rapsglanzkäfers (Meligethes aeneus F.) vernichten. Erwachsene Parasiten der GattungIsurgus (Hym. Ichneumonidae) wurden auf den behandelten Flächen ebenfalls in geringerer Anzahl als auf angrenzenden nicht-gespritzten gefunden. Jedoch scheinen die Männchen dieser Gattung aktiver zu sein als die Weibchen; die Männchen besiedelten die bespritzten Flächen schneller und in größerer Anzahl wieder als die Weibchen.Gewöhnlich übertrifft die Anzahl der Rapsglanzkäfer die der adulten Parasiten um das Fünf-bis Sechsfache, und es wird vermutet, daß der Parasitismus in Feldbeständen wahrscheinlich kein wirksamer Bekämpfungsfaktor ist. Der Parasitierungsgrad der Rapsglanzkäfer-Larven variiert auf kleinen Schlägen zwischen 8 und 61% und war nach der Spritzung immer stark herabgemindert. Manchmal wurden überhaupt keine parasitierten Larven gefunden, doch waren in solchen Fällen auch nur geringe Mengen Rapsglanzkäferlarven vorhanden.Bei Trumpington, Cambridge, wurden auf blühenden Senfpflanzen Ende Mai und im Juni regelmäßig dreiIsurgus-Arten (Hym. Ichneumonidae) angetroffen.I. morionellus Holmgren bildete 1960 80% und 1961 74% der Population adulter Parasiten. Der Rest bestand hauptsächlich ausI. heterocerus Thomson und ganz geringen Zahlen einerIsurgus-Art C und vonDiospilus capito Nees (Hym. Braconidae).Zur Schätzung der Populationsdichte der Parasiten über wachsenden Pflanzen von Sareptasenf (Brassica juncea Coss.) und Sommerrübsen (Brassica campestris oleifera var.annua Metz) erwies sich Käscherstreifen als befriedigende Methode. Eine Klebfalle war weniger geeignet, da dabei ein größerer Anteil männliche Parasiten und weniger Weibchen gefangen wurde als beim Streifen.Feststellung der Larvenparasitierung erfolgte durch Präparation einer Anzahl von Rapsglanzkäferlarven in der Fixierungsflüssigkeit. Fixierungsgemische und alkoholhaltige Flüssigkeiten erwiesen sich als unbefriedigend, da sie die Larven der Rapsglanzkäfer wie die der Parasiten rasch härteten, wodurch die Auffindung der letzteren sehr erschwert wird. Eine Formol-Eisessig-Lösung ergab bessere Resultate.

     

The effect of insecticide application by dropleg sprayers on pollen beetle parasitism in oilseed rape

Dropleg sprayers apply pesticides below the flower horizon of oilseed rape plants and thus reduce unwanted side effects on pollinating insects. Whether this technique benefits parasitoids of seed and pollen feeding insect pests has not been studied earlier. To answer this question, we first assessed the vertical distribution of pests and parasitoids using a portable aspirator. In addition, parasitism rates of pollen beetle, Brassicogethes aeneus Fabricius (Coleoptera: Nitidulidae), by the larval parasitoid Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) were compared in conventional and dropleg sprayed fields over four years (2016–2019), using the neonicotinoids thiacloprid and acetamiprid. Our results show that seed and pollen feeders were mainly found in the flowering canopy, while the predominant location of parasitoids was species-specific. Among pollen beetle parasitoids, Phradis interstitialis Thomson (Hymenoptera: Ichneumonidae) was more abundant below flowering canopy (63% of total catch), whereas T. heterocerus was mainly caught in the flowering canopy (84% of total catch). In the spraying experiments, average parasitism rates of pollen beetles by T. heterocerus ranged between 55 and 82% in the untreated controls. In the dropleg spray treatments, parasitism rates did not differ significantly from control levels, with the exception of thiacloprid application in 2019. In contrast, conventional spray applications resulted in a reduction of parasitism rates by up to 37% compared to the control for at least one of the insecticides in three out of four years. The impact of conventional application differed between years, which may be explained by the temporal coincidence between spray application and the immigration of parasitoids into the crop. We conclude that dropleg spraying exerts lower non-target effects on the main biological control agent of pollen beetle.

     

Persistence of augmented Metarhiziumanisopliae and Beauveria bassiana in Finnishagricultural soils

The persistence and penetration into soilof surface-applied unformulated conidia of twoisolates of Metarhizium anisopliae and one of Beauveria bassiana at sites with clay, peat andtwo kinds of sand as their soil types and at depthsof from 0 to 20 cm was studied in 1988–1991 underconditions characterized by permanent snow cover andfrozen soil in the winter time. At 0–5 cm depth, M. anisopliae persisted throughout the experiment atall sites, clay being the most and peat the leastfavourable soil for persistence. Clay and one of thesandy soils were the least and peat the most conducivesoil to penetration of M. anisopliae from thesurface to deeper soil layers and persistence therein.Differences in persistence were evident between thetwo M. anisopliae isolates in the sandy and peatsites, but not in the clay site. Three yearspostapplication there were still enough infectiouspropagules of M. anisopliae in soil of allsites to infect over 80% of the Tenebriomolitor larvae used as baits in samples taken fromthe cylinders of all soils. All the augmentedpropagules of B. bassiana disappeared duringthe first winter after application in clay and one ofthe two sandy sites, but some persistence one yearpostinoculation was evident at 0–5 depth in one ofthe sand soils and at 0–5 and 5–10 cm depths in peat.     

Metarhizium anisopliae, a potential agent for the control of grape phylloxera

This investigation deals with the control effects of the insect pathogenic fungus Metarhizium anisopliae var. anisopliae on Daktulosphaira vitifoliae. In pot experiments, the soil surrounding phylloxera-infected grapes was inoculated with barley colonised with M. anisopliae. After thirty-two days, ineight of ten Metarhizium-applied pots nofresh phylloxera infections could be observed.In two of ten plants, a few fresh nodositiessingly occupied with phylloxera or phylloxeraeggs could be found. In all untreated plants,fresh nodosities with either single (two of sixplants) or multiple (four of six plants)occupation with phylloxera could be observed.M. anisopliae could be re-isolated in aconcentration of <1 × 10³ CFU g^$minus;1 soil dry weight from those pots with phylloxera-infected plants that had been treated with the fungus. The potential role of M. anisopliae in grape phylloxera management is discussed.     

Behavioral responses to host foodplants of two populations of the insect parasitoid Cotesia congregata (Say)

To test the hypothesis that natural enemy populations differ in their behavioral responses to plants or to plant allelochemicals, we compared two populations of the gregarious larval endoparasitoid, Cotesia congregata (Say) (Hymenoptera: Braconidae) that differed in their historical and present exposure to tobacco. The major hosts for both populations were Manduca sexta L. and M. quinquemaculata (Haworth) (Lepidoptera: Sphingidae), but these hosts were typically encountered on tobacco by parasitoids in one population (Upper Marlboro) and on tomato by parasitoids in another population (Wye). Early in the season, Wye parasitoids preferred to oviposit in M. sexta on tomato rather than on tobacco and Upper Marlboro parasitoids showed no preference; neither population showed any preference later in the season. Neither of the strains originating from the two populations showed a landing preference for tobacco or tomato in flight chamber trials, but Upper Marlboro parasitoids searched longer on tobacco than on tomato, and Wye parasitoids searched longer on tomato. When nicotine solutions were applied to tobacco leaf, searching responses of Upper Marlboro parasitoids were enhanced by 0.001–1.0% nicotine, and searching responses of Wye parasitoids were decreased by 0.01–1.0% nicotine. We speculate that population differences in searching responses to tobacco and nicotine may explain the differential parasitism responses found early in the season.     

Effects of insecticide application on parasitism rates of pollen beetle larvae (<Emphasis Type="Italic">Brassicogethes aeneus</Emphasis> (Fabricius)) by tersilochine parasitoids

Larval parasitoids can substantially reduce the population density of the pollen beetle [Brassicogethes aeneus (Fabricius), syn. Meligethes aeneus (Fabricius)]. The most abundant tersilochine parasitoids of pollen beetle are Tersilochus heterocerus, Phradis interstitialis and P. morionellus. The main activity of these parasitoids was observed in the period shortly before flowering to full flowering of oilseed rape. Insecticide applications during this period may have negative effects on parasitoids. In the present study, the effects of the insecticides Biscaya (a.i. thiacloprid), Mavrik (a.i. tau-fluvalinate) and Karate Zeon (a.i. lambda-cyhalothrin) applied during the bud or flowering stage of winter oilseed rape on parasitization of pollen beetle larvae by T. heterocerus were studied in 12 field trials at different locations in Germany in 2013–2015. The effects on parasitism by Phradis spp. were assessed in 2015. Parasitism of pollen beetle larvae by T. heterocerus was found in all field trials in all experimental years, but in most trials not before full flowering. Maximum percentage of parasitized larvae at different locations ranged between 3.4 and 16.8% in 2013, 8.3 and 22.4% in 2014 and from 11.1 to 29.1% in 2015. Levels of parasitism were not significantly different between the untreated control and insecticide treatments within each location. In contrast to T. heterocerus, Phradis spp. was not detected at all locations and not before flowering declining. In field trials at Lucklum and Puch, the maximum level of parasitism by Phradis spp. was 9.4 and 18.3%, respectively. No significant effect of insecticide application on parasitism by Phradis spp. was observed between the treatments. The results of this study showed that the insecticides used in the field trials did not affect parasitization of pollen beetle larvae by T. heterocerus and Phradis spp., regardless whether applied at the bud stage, at the beginning of flowering or full flowering.     

The making of a pest: recruitment of Meligethes aeneus onto oilseed Brassicas

Populations of the rapeseed pollen beetle Meligethes aeneus F. (Col., Nitidulidae) from areas with 0–16 years of history of intensive rapeseed growing were compared for key ecological characters. During the first 16 years of rapeseed cultivation the reproductive success of M. aeneus increased 200–300% over that of the beetles living on the natural host plants, cruciferous weeds. The increase was linear over time and statistically highly significant, and it did not appear to be related to food quality or to the size of the beetles. During the same period the tolerance to intraspecific competition decreased, possibly due to the relative absence of such competition on the new crop. Furthermore, the optimum population density for M. aeneus to maximize the size of its next generation on summer turnip rape was determined to be 0.5–1.0 beetles/plant, which is slightly below the economic threshold for chemical control (1 beetle/plant). Therefore the practical protection of the rapeseed yield also ensures the highest possible pest population size for the next year. These mechanisms may in part explain the particular noxiousness of the species as a pest all over Europe. In general these data show that after the introduction of a new crop plant into a region, significant changes during the recruitment process in a pestiferous insect may take place, contributing to the future pest status of the insect. It is suggested that such genetic and ecological changes in insects may be a more common mechanism than previously thought in initiating and sustaining pest outbreaks, and that conventional pest management methods may enhance that effect.     

Impact of the egg parasitoid Uscana lariophaga and the larval-pupal parasitoid Dinarmus basalis on Callosobruchus maculatus populations and cowpea losses

In West Africa, Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) and Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) parasitize the eggs and larvae, respectively, of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae), an important pest of stored cowpea. The impact of the parasitoids on pest populations was evaluated in clay pots similar to the ones used in traditional storage in Niger. At the beginning of the storage period, cowpeas were infested with one density of C. maculatus and with either one or both of the parasitoid species. If the parasitoids we inoculated as single species in stores, both D. basalis and U. lariophaga significantly suppressed the bruchid population, but the former did so more effectively than the latter. A combination of D. basalis and U. lariophaga resulted in the same suppression of bruchid populations as when D. basalis was the only parasitoid. Fifteen weeks after storage, the parasitoids reduced the number of grains damaged significantly by 38–56%. The effect of inoculating single or multiple parasitoid species on C. maculatus populations in an augmentation strategy is discussed.     

Field trials against Hoplia philanthus (Coleoptera: Scarabaeidae) with a combination of an entomopathogenic nematode and the fungus Metarhizium anisopliae CLO 53

The white grub, Hoplia philanthus Füessly (Coleoptera: Scarabaeidae), is a major pest of turf and ornamental plants in Belgium. Previously, the combination of lethal concentration of the entomopathogenic nematodes Heterorhabditis megidis or Steinernema glaseri with the entomopathogenic fungus Metarhizium anisopliae (strain CLO 53) caused additive or synergistic mortality to third-instar H. philanthus in the laboratory and greenhouse. In this present study, we examined this interaction under field conditions and compared a combination of a commercial formulation of Heterorhabditis bacteriophora (Nema-green^®) and M. anisopliae. Controls were M. anisopliae, chlorpyrifos (Dursban 5 Granules) and H. bacteriophora. Field applications (surface or subsurface) were made against a mixed population of second/third-instar H. philanthus at a sport field and lawn infested in the province of West-Flanders. In both trials, the combination of M. anisopliae with H. bacteriophora at 5 × 10¹² conidia/ha +2.5 × 10⁹ infective juveniles/ha resulted in additive or synergistic effects, causing more than 95% grub mortality when the nematodes was applied 4 weeks after the application of fungus. However, application of nematode, chlorpyrifos or fungus alone provided 39–66%, 42–60% (surface) and 33–76%, 82–100% or 37–65%, (subsurface) control of H. philanthus. We concluded that the pathogen combinations we tested are compatible elements of integrated pest management and are likely to improve control of H. philanthus larvae and perhaps other insect pests beyond what is expected from single application of the pathogen.     

Production of microsclerotia of the fungal entomopathogen Metarhizium anisopliae and their potential for use as a biocontrol agent for soil-inhabiting insects

Microsclerotia (MS), overwintering structures produced by many plant pathogenic fungi, have not been described for Metarhizium anisopliae. Three strains of M. anisopliae – F52, TM109, and MA1200 – formed MS in shake flask cultures using media with varying carbon concentrations and carbon-to-nitrogen (C:N) ratios. Under the conditions of this study, all strains produced MS, compact hyphal aggregates that become pigmented with culture age, in addition to more typical blastospores and mycelia. While all strains formed desiccation tolerant MS, highest concentrations (2.7–2.9 × 10⁸ L⁻¹ liquid medium) were produced in rich media with C:N ratios of 30:1 and 50:1 by strain F52. All three strains of M. anisopliae produced similar biomass concentrations when media and growth time were compared. Strain MA1200 produced higher concentrations of blastospores than the other two strains of M. anisopliae with highest blastospore concentrations (1.6 and 4.2 × 10⁸ blastospores ml⁻¹ on days 4 and 8, respectively) in media with the highest carbon and nitrogen concentrations. Microsclerotial preparations of M. anisopliae containing diatomaceous earth survived air-drying (to <5 % moisture) with no significant loss in viability. Rehydration and incubation of air-dried MS granules on water agar plates resulted in hyphal germination and sporogenic germination to produce high concentrations of conidia. Bioassays using soil-incorporated, air-dried MS preparations resulted in significant infection and mortality in larvae of the sugar beet root maggot, Tetanops myopaeformis. This is the first report of the production of sclerotial bodies by M. anisopliae and provides a novel approach for the control of soil-dwelling insects with this entomopathogenic fungus.     

Effect of brassicaceous plants on the survival and infectivity of insect pathogenic fungi

Studies were conducted to investigate potentialinteractions between brassicaceous plants, theisothiocyanates they produce and insectpathogenic fungi. Studies in vitro showedthat 100 ppm of 2-phenylethyl isothiocyanatecompletely inhibited growth of Metarhiziumanisopliae and Tolypocladiumcylindrosporum. T. cylindrosporum wassignificantly inhibited by 10 ppm 2-phenylethylisothiocyanate, but not by 1 ppm. M.anisopliae was not inhibited by 10 or 1 ppm2-phenylethyl isothiocyanate. The effect offreshly grated rutabaga on virulence of M.anisopliae to Galleria mellonella larvaewas also tested, resulting in reduced infectionby M. anisopliae. To study the effect ofplants in the Brassicaceae under morefield-like conditions fungi were added to soilwithout plants or at the bases of two differentplant species, Barbarea vulgaris and Eruca vesicaria sativa. Soil was sampled at 5,10 and 15 days to determine the concentrationof colony forming units (CFUs). Treatments withplants did not have fewer CFUs than thecontrol. Instead significantly fewer CFUsresulted when M. anisopliae was added topots with soil only than to pots with plants.There were no significant differences betweenthe two plant species in the number of CFUs atday 5. For days 10 and 15, however,significantly more M. anisopliae CFUswere found in pots containing E. vesicariasativa than B. vulgaris. T.cylindrosporum was less affected by thedifferent treatments than M. anisopliae.Our studies demonstrated that whileisothiocyanates can inhibit insect pathogenicfungi in Petri dishes, when using a morerealistic fungus/plant/soil microcosm no fungalinhibition was found.     

The parasitoid complex affecting Choristoneura rosaceana and Pandemis limitata in organically managed apple orchards

Parasitism and density of obliquebanded leafroller,Choristoneura rosaceana (Harris), and thethree-lined leafroller, Pandemis limitata(Robinson) (Lepidoptera: Tortricidae), were studied in 1998–2001 in organically managed apple orchards in the southern interior of British Columbia, Canada. The density of the overwintered generation of leafrollers in spring was significantly higher than thedensity of the first generation in summer. There was a significant inverse correlation between the density of leafrollers and the percent parasitism within generation and therefore parasitoids may play a role in controlling leafroller density. Parasitism of the overwintered generation (means between 5.5 and 24.7%) was significantly lower than parasitism documented in the summer generation (means up to 67.9%). The parasitoid complex recorded as emerging from these leafrollerpopulations in 1998–1999 included 30 species, of which eight have not been previously recorded in the literature as parasitoids of either leafroller species. The most frequently occurring parasitoids included Apophuasimplicipes (Cresson) and two species of Glypta(Hymenoptera: Ichneumonidae), Macrocentrus linearis (Nees), Meteorus trachynotus Viereck, Apantelespolychrosidis Viereck, Apanteles atra (Ratzeburg) and Microgaster epagoges Gahan (Hymenoptera: Braconidae), Colpoclypeus florus (Walker) and one Sympiesisspecies (Hymenoptera: Eulophidae). All of these more common parasitoids, except Glypta sp. 1 and M. epagoges, were recorded parasitizing leafroller hosts in both leafroller generations. The number of days to adult parasitoid emergence, when field collected parasitized hosts were held at 20°C, was recorded for four of the parasitoid species. Meteorus trachynotus was found to emerge early enough in spring toparasitize the few remaining overwintered early instar leafrollers. Glypta sp. 1, A. simplicipes and one Apanteles species emerged to coincide with the first generationin the summer.     

Entomogenous Fungi as Promising Biopesticides for Tick Control

When ticks were sealed in nylon tetrapacks and infected with the entomogenous fungi, Beauveria bassiana and Metarizium anisopliae and maintained in potted grass in the field, the fungal oil formulations (10⁹ conidia per ml) induced 100% mortality in larvae of Rhipicephalus appendiculatus and Amblyomma variegatum, whereas mortalities in nymphs varied between 80–100% and in adults 80–90%. The aqueous formulations (10⁹ conidia per ml) induced mortalities of 40–50% and reductions in egg hatchability of 68% (B. bassiana) and 48% (M. anisopliae) when sprayed on Boophilus decoloratus engorging on cattle. The strains of B. bassiana and M. anisopliae isolated from naturally infected ticks were also found to induce high mortalities in both R. appendiculatus and A.variegatum in tetrapacks placed in potted grass. Both aqueous and oil-based formulations were found to be effective, although the latter induced higher mortalities. These fungal strains in aqueous formulation (10⁸ conidia per ml) suppressed on-host populations of adult R. appendiculatus by 80% (B. bassiana) and 92% (M. anisopliae) when sprayed on tick-infested grass once per month for a period of 6 months. The feasibility of using entomogenous fungi for tick control in the field is discussed.     

Microbial pathogens of the coconut pest Oryctes rhinoceros: influence of weather factors on their infectivity and study of their coincidental ecology in Kerala,India

The rhinoceros beetle, Oryctes rhinoceros L., is an economically important pest of the coconut palm. Management of this pest has been accomplished using microbial agents viz., Oryctes virus (OrV) and an entomofungal pathogen Metarhizium anisopliae. Recently an opportunistic bacterial pathogen Pseudomonas alcaligenes has also been noticed to cause septicaemia in the grubs when under stress. To unravel the influence of abiotic weather factors and the interactions amongst these microbial pathogens, a 3 year study was conducted from September 1996 to August 1999 in three of the southern districts of Kerala, India. Of the 6627 grubs and 307 adults collected from various breeding sites of the pest, 5% of the grubs and 22% of the adults had natural virus infection, 3% larvae died of M. anisopliae mycosis and 20% larvae succumbed to bacterial septicaemia. Oryctes virus infection in grubs and adults was negatively correlated to minimum temperature (correlation co-efficient, r = –0.4, and –0.6 respectively, sample size, n = 0). Increase in relative humidity increased the fungal activity (r = 0.8) whereas, maximum temperature had a negative impact (r = –0.7). Occurrence of virus infection in grubs and adults was positively correlated (r = 0.6), supporting the contention of active transmission of the virus pathogen between these two stages. The bacterial septicaemia in the grubs was marginally correlated with virus infection and P. alcaligenes undermined the efficiency of the virus pathogen.     

Behavioural responses in three ichneumonid pollen beetle parasitoids to volatiles emitted from different phenological stages of oilseed rape

Pollen beetles (Meligethes spp.; Coleoptera: Nitiduliae) are a major pest of oilseed rape, Brassica napus L. (Brassicaceae) in northern Europe. Phradis interstitialis Thomson, P. morionellus Holmgr., and Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) are among the most frequent pollen beetle parasitoids. These three species differ in temporal occurrence, as well as in preferred host stage. The behavioural responses of female parasitoids to odours from oilseed rape at bud and flowering stage were evaluated in two‐choice experiments. The role of visual stimuli was examined by combining green and yellow colours with odour stimuli. All three species were attracted to odours from the bud stage of oilseed rape. Tersilochus heterocerus was attracted to odours of flowering rape, but the two Phradis species avoided the flower odours. However, when the odours of flowering rape were combined with yellow, and odours of the bud stage were combined with green, P. interstitialis was equally attracted to both stimuli, and T. heterocerus showed an increased preference for flower odours, while no effect of colours could be found in P. morionellus. The observed differences in responses between the parasitoids may reflect differences in their biology and may be involved in the niche segregation of these often coexisting species. The volatile blends released from the two phenological stages were identified and compared. Clearly, odours can be reliable cues for differentiating between oilseed rape in the bud and flowering stage. Of 20 identified compounds, 18 were released at a significantly higher rate from flowering plants. The terpenes sabinene, myrcene, limonene, and (E,E)‐α‐farnesene were the dominant volatiles in the bud and flower headspace. A group of aromatic compounds including benzaldehyde, methyl benzoate, and phenyl acetaldehyde were mainly released from flowering rape.     

Effects of non‐host plant odour on Meligethes aeneus during immigration to oilseed rape

The use of semiochemicals for the manipulation of the pollen beetle, Meliethes aeneus (Fabricius) (Coleoptera: Nitidulidae), is being investigated for potential incorporation into a push‐pull strategy for this pest, which damages oilseed rape, Brassica napus L. (Brassicaceae), throughout Europe. Previous laboratory behavioural studies using volatiles from non‐host plants showed that M. aeneus is repelled by the odour of lavender, Lavendula angustifolia Mill. (Lamiaceae), essential oil. This article reports on semi‐field and field trials to investigate this behaviour under more realistic conditions. Semi‐field experiments were conducted to assess the relative importance of olfaction at different points in host location behaviour by M. aeneus. The results showed that oilseed rape plants treated with lavender odour were less colonised by M. aeneus in comparison with an untreated control, but that the treatment effect was much reduced if the lavender odour was applied after colonisation. The field experiment demonstrated that lavender odour caused a significant reduction in the number of adult M. aeneus infesting the oilseed rape plants in the treatment plots compared to the control plots. Overall, these findings are very encouraging for the future development of a push‐pull pest control system.     

Overwintering survival and spring emergence inMeligethes aeneus: Effects of body weight, crowding, and soil treatment withBeauveria bassiana

High overwintering mortality was recorded forMeligethes aeneus in the field in Finland, ranging from 85 to 98% depending on the source of the overwintering population. The main factor explaining, variation in survival was the body weight of the beetles in the autumn: only the heaviest beetles survived. Body weight, on the other hand, was influenced by treatment of the rape field soil withBeauveria bassiana, resulting in a 50% decrease in winter survival compared with the reference. The soil treatment did not appear to have direct mortality effects (pathogenesis) on the beetle neither in the summer nor in the winter, and there was no apparent effect on survival of crowding of the insects at the overwintering site. Density dependence in overwintering survival ofM. aeneus may function through the availability of pollen food in the autumn, and intraspecific competition for it. Treatment of the rape field soil withB. bassiana may be a feasible way to increase, the winter mortality and to lower the pollen beetle populations, but requires further research.     

Management of pine wilt disease vectoring Monochamus alternatus adults using spray and soil application of Metarhizium anisopliae JEF isolates

Chemical control is widely used to control the Japanese pine sawyer beetle, Monochamus alternatus, but strong chemical regulations require an environmentally sound management strategy. In this work, we investigated the use of entomopathogenic fungi and their application as a means of practical pest management. Thirty-two diverse species of fungal isolates were assayed against adult pine sawyer beetles using a contact method under laboratory conditions, and four isolates showed over 70% virulence consequently. These isolates, two each of Beauveria bassiana and Metarhizium anisopliae were sprayed on the adult beetles at 1 × 10⁷ conidia/ml in plastic containers, respectively. The M. anisopliae-treated adult beetles showed 67% mortality. M. anisopliae isolates JEF-197 and JEF-279 demonstrated dosage-dependent insecticidal activity. Following the laboratory experiments, semi-field trials were conducted in young pine trees under high (RH 94%) and low (RH 35%) humidity conditions. In the high humidity conditions, most of the adult beetles stayed on the top of the branches. When the two M. anisopliae isolates were sprayed on the beetles, they showed ca. 50–70% insecticidal activity 11 days after application. In contrast, in low humidity conditions, the adult beetles tried to move off the branches and onto the soil. When the beetles reached the JEF-197 and JEF-279-treated soil, we measured >90% insecticidal activity. This work suggests that M. anisopliae was the most virulent entomopathogenic fungus against adult Japanese pine sawyer beetles, and this forest insect could be ecologically controlled by the spray and soil application of the M. anisopliae isolates.