Eve Veromann

Insect pests and their natural enemies on spring oilseed rape in Estonia : impact of cropping systems

To investigate the impact of different cropping systems, the pests, their hymenopteran parasitoids and predatory ground beetles present in two spring rape crops in Estonia, in 2003, were compared. One crop was grown under a standard (STN) cropping system and the other under a minimised (MIN) system. The STN system plants had more flowers than those in the MIN system, and these attracted significantly more Meligethes aeneus, the only abundant and real pest in Estonia. Meligethes aeneus had two population peaks: the first during opening of the first flowers and the second, the new generation, during ripening of the pods. The number of new generation M. aeneus was almost four times greater in the STN than in the MIN crop. More carabids were caught in the MIN than in STN crop. The maximum abundance of carabids occurred two weeks before that of the new generation of M. aeneus, at the time when M. aeneus larvae were dropping to the soil for pupation and hence were vulnerable to predation by carabids.

Relative attractiveness of Brassica napus, Brassica nigra, Eruca sativa and Raphanus sativus for pollen beetle (Meligethes aeneus) and their potential for use in trap cropping

Oilseed rape (Brassica napus) is a valuable crop, attacked by several insect pests, of which the pollen beetle (Meligethes aeneus) is one of the most widespread and important in Europe. The relative attractiveness for the pollen beetle of Brassica nigra, Eruca sativa and Raphanus sativus was compared with that of spring oilseed rape, to assess the potential of these plant species as trap crops for the pest. At early growth stages, B. nigra and R. sativus were more attractive to over-wintered adult pollen beetles than B. napus. At the bud and flowering stages, B. nigra was the most attractive while E. sativa was the least attractive. At flowering, B. nigra was more attractive for oviposition than the other species. Thus, of the species tested, B. nigra has the most potential as a prospective trap crop to protect spring oilseed rape before flowering when it is at its most vulnerable developmental phase, due to its faster development and its acceptability both for feeding and oviposition to overwintered pollen beetle adults. Raphanus sativus was accepted both for feeding and oviposition, but pollen beetle larvae failed to develop in its flowers; it therefore has the potential for use as a dead-end crop. At the end of the growing season, both E. sativa and R. sativus, as late-flowering species, attracted the new generation of pollen beetles and thereby have potential to extend the effectiveness of a trap-cropping system at this time.

The relative attractiveness of Brassica napus, B. rapa, B. juncea and Sinapis alba to pollen beetles

It is often suggested that weeds from the same family as the crop plant may increase insect pest damages by providing shelter and additional oviposition opportunities. We compared the relative attractiveness of Brassica rapa L., B. juncea L., Sinapis alba L. and B. napus L. (Capparales: Brassicaceae) to the pollen beetle and its hymenopteran parasitoids in field conditions. Our results revealed that none of the investigated plants increased the pest abundance on B. napus plants. On the contrary, B. juncea and S. alba lured beetles away from B. napus during its damage-susceptible stage. The parasitism rate of pollen beetle larvae was the highest on B. juncea plants, indicating that cruciferous weeds could improve the natural control of the pollen beetle by providing additional hosts for parasitoids. Therefore, close relatives of oilseed rape might be used to trap pollen beetle adults, but also to support populations of natural enemies that could decrease the number of beetles.

Do cropping system and insecticide use in spring oilseed rape affect the abundance of pollen beetles (Meligethes aeneus Fab.) on the crop

Abstract The impact of minimised (MIN – no plough, direct drilling, no pesticides) and standard (STN – plough, standard application of pesticides) cropping systems on the abundance of old (previously overwintered) and new generations of Meligethes aeneus (Fabricius) (Nitidulidae, Coleoptera) was assessed in spring oilseed rape in 2003 – 2005 in Estonia. Old generation M. aeneus were more abundant in STN than in MIN crops, despite the application of insecticide, probably because the latter reduced M. aeneus damage to the buds, making STN crops more attractive to M. aeneus seeking feeding and oviposition resources. The abundance of new generation M. aeneus showed a strong linear increase over the 3 years, on both MIN and STN systems. In 2005, the abundance of new generation M. aeneus was significantly greater in the STN than in the MIN field. The study showed that the application of insecticides promotes population increase in new generation M. aeneus.

Potential of parasitoids to control populations of the weevil Ceutorhynchus obstrictus (Marsham) on winter oilseed rape

Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) is a major pest of oilseed rape in Europe and North America. The last decade has seen growing interest in the occurrence, importance and efficiacy of its parasitoids as biocontrol agents. The infestation of pods by C. obstrictus larvae and their parasitism rates were assessed in a total of nine commercially-grown crops and fifteen experimental plots of winter oilseed rape in 2004–2007. Pod samples were collected at the pod maturation stage and incubated in emergence traps. Emerged larvae, their exit holes and parasitoids were counted and identified; the percentage of infested pods and parasitism rates were calculated. Pod infestation by larvae increased continuously over the study period. The parasitism level was lowest in 2005 and increased thereafter up to 96%. The most abundant parasitoid was Trichomalus perfectus (Walker), but Mesopolobus morys (Walker) and Stenomalina gracilis (Walker) (Hymenoptera: Pteromalidae) were also reared from host larvae. This study showed that naturally-occurring ectoparasitoids of C. obstrictus were capable of becoming established as viable populations and have the potential to contribute to biological control of C. obstrictus.

Ground Beetles as Predators of Oilseed Rape Pests: Incidence, Spatio-Temporal Distributions and Feeding

Ground beetles or carabids are amongst the most abundant invertebrate predators in fields of oilseed rape in Europe. The immature stages of the six major pests of oilseed rape i.e., cabbage stem flea beetle, pollen beetle, cabbage seed weevil, cabbage stem weevil, rape stem weevil and brassica pod midge, are vulnerable to predation by carabids when they are in or on the soil from mid-September to mid-July. About 42 species of carabid are common in rape fields. The community composition varies between countries, between spring and winter crops and with crop management, as species differ in distribution and habitat requirements. The ten most widespread and dominant species are A. similata, Anchomenus dorsalis, Bembidion lampros, Harpalus affinis, Harpalus rufipes, Loricera pilicornis, Nebria brevicollis, Poecilus cupreus, Pterostichus melanarius and Trechus quadristriatus. A field-scale study found within-field spatio-temporal coincidence of T. quadristriatus and Pterostichus madidus with cabbage stem flea beetle eggs, of A. similata, N. brevicollis and Asaphidion spp. with pollen beetle larvae, and of A. dorsalis with larvae of cabbage stem weevil, cabbage seed weevil and brassica pod midge. Carabid within-field distributions are influenced by their life cycles, habitat preferences, mobility and food availability. Evidence of predation from analysis of gut contents of field-collected individuals and laboratory feeding trials is reviewed in relation to carabid functional morphology, prey size and diel periodicity of activity. Feeding trials suggest that Clivina fossor also has potential as a predator of oilseed rape pests. The implications for biocontrol-based integrated pest management are discussed.

Flea beetle (Chrysomelidae: Alticinae) species composition and abundance in different cruciferous oilseed crops and the potential for a trap crop system

Flea beetles are significant insect pests of cruciferous oilseed crops in northern Europe. A two-year small-scale field experiment was performed to determine the species complex and abundance of flea beetles (Chrysomelidae: Alticinae) associated with eight cruciferous oilseed plants: Brassica juncea (L.) Czern., Brassica napus L. var. oleifera subvar. annua, Brassica nigra (L.) Koch, Brassica rapa L. var. oleifera subvar. annua, Camelina sativa (L.) Crantz, Eruca sativa Mill., Raphanus sativus L. spp. oleifera (DC) Metzg. and Sinapis alba L. Their relative attractiveness to flea beetles was compared to assess their potential for use within a trap crop system for spring oilseed rape. Adults of six species of flea beetles were found on the test plants. Phyllotreta undulata Kutsch. was the most abundant species followed by Phyllotreta nigripes (Fabr.), Phyllotreta nemorum L. and Phyllotreta vittata (=striolata) (Fabr.), while Phyllotreta atra (Fabr.) and Chaetocnema concinna Marsh. were occasionally present. The species composition of flea beetles on seven of the investigated plant species was fairly similar but differed significantly on C. sativa. The flea beetle species discriminated between the tested host plants, with a general gradient in attraction from E. sativa > B. juncea > B. nigra > R. sativus > S. alba > B. rapa > B. napus through to C. sativa. Brassica juncea and B. nigra developed faster and at early growth stages were more attractive to overwintered adult flea beetles than B. napus and therefore had potential as trap plants to protect spring rape. R. sativus and E. sativa, despite their development rate being slower than B. napus were also more attractive to flea beetles. Thus, further experiments with a complex of attractive early season and late-season plant species (multiple trap crops) should be undertaken.

Reliability of the entomovector technology using Prestop-Mix and Bombus terrestris L. as a fungal disease biocontrol method in open field

Botrytis cinerea Pers.:Fr. is a major plant pathogen, and a new approach is needed for its control in strawberry to minimise the increasing use of synthetic fungicides. The biofungicide Prestop-Mix, which contains Gliocladium catenulatum, is effective against Botrytis infections; however, the need for frequent applications increases the costs for farmers. Here, we demonstrate that bumble bees, Bombus terrestris L., effectively disseminate the preparation onto flowers in open field conditions. Over the course of three years, we found a highly significant decrease in the rate of Botrytis infection. Pathogen control was achieved with relatively low numbers of G. catenulatum spores per flower, even using flowers that are not highly attractive to bumble bees. An even distribution of spores was detected up to 100 m from the hives, either due to primary inoculation by bumble bees or secondary distribution by other flower visitors such as honey bees and solitary bees. We showed that the application of a biocontrol agent by bumble bees is reliable for the use of environmentally friendly pest control strategies in northern climatic conditions. This low cost technology is especially relevant for organic farming. This study provides valuable information for introducing this method into practice in open strawberry fields.

Effects of land use on infestation and parasitism rates of cabbage seed weevil in oilseed rape: Landscape effects on Ceutorhynchus obstrictus infestation and parasitism rates

BACKGROUND This study investigated how infestation rates of an important oilseed rape pest, the cabbage seed weevil (Ceutorhynchus obstrictus) and rates of parasitization by its parasitoids are affected by land use, up to 1000 m from 18 focal fields. RESULTS The mean proportion of C. obstrictus-infested pods per plant was 8% (2-19.5%). Infestation rates were higher if the adjacent habitat was a herbaceous semi-natural habitat than if it was either another crop or a woody habitat. Infestation rates were positively related to the area of herbaceous semi-natural vegetation, permanent grassland and wheat (which followed oilseed rape in the crop rotation) at a spatial scale of at least 1 km. The mean parasitism rate of C. obstrictus larvae was 55% (8.3-87%), sufficient to provide efficient biocontrol. Parasitism rates were unrelated to adjacent habitats, however, they were positively related to the presence of herbaceous linear elements in the landscape and negatively related to permanent grasslands at a spatial scale of 200 m. CONCLUSION Proximity of herbaceous elements increased both infestation rates and parasitism, while infestation was also related to landscape factors at larger distances. The findings provide an empirical basis for designing landscapes that suppress C. obstrictus, at both field and landscape scales.

Comparison of sampling methods for estimating the abundance of Meligethes aeneus on oilseed crops

Meligethes aeneus, the pollen beetle, is a major pest of cruciferous oilseed crops in Europe. Two sampling methods for estimating the abundance of pollen beetle adults on Brassica napus, B. nigra, B. juncea, Sinapis alba were compared: beating plants over a tray and yellow water traps (YWT). The dynamics of beetle abundance at different plant growth stages and in different weather conditions was investigated in 2010 and 2011. Abundance was significantly greater in samples collected by beating than in the YWT. Beetle dynamics differed significantly with the sampling method. Beating caught most beetles during the green–yellow growth stage of plants; after that, their number decreased substantially. The number of beetles sampled by the YWT also fluctuated and, in addition, reflected the abundance of the new generation. The density of pollen beetles in different crop plants was not uniform; the beating method caught most in S. alba whereas YWT caught most in B. nigra. We conclude that the beating method is effective as an early warning system for growers whereas YWT are more effective for long-term continuous monitoring of pollen beetles.