Abundance Of Pollen Beetles Research Articles

Earlier flowering of winter oilseed rape compensates for higher pest pressure in warmer climates

Abstract Global warming can increase insect pest pressure by enhancing reproductive rates. Whether this translates into yield losses depends on phenological synchronisation of pests with their host plants and natural enemies. Simultaneously, landscape composition may mitigate climate effects by shaping the resource availability for pests and their antagonists. Here, we study the combined effects of temperature and landscape composition on pest abundances, larval parasitism, crop damage and yield, while also considering crop phenology, to identify strategies for sustainable management of oilseed rape (OSR) pests under warming climates. In all, 29 winter OSR crop fields were investigated in different climates (defined by multi‐annual mean temperature, MAT) and landscape contexts in Bavaria, Germany. We measured abundances of adult pollen beetles and stem weevil larvae, pollen beetle larval parasitism, bud loss, stem damage and seed yield, and calculated the flowering date from growth stage observations. Landscape parameters (proportion of non‐crop and OSR area, change in OSR area relative to the previous year) were calculated at six spatial scales (0.6–5 km). Pollen beetle abundance increased with MAT but to different degrees depending on the landscape context, that is, increased less strongly when OSR proportions were high (1‐km scale), interannually constant (5‐km scale) or both. In contrast, stem weevil abundance and stem damage did not respond to landscape composition nor MAT. Pollen beetle larval parasitism was overall low, but occasionally exceeded 30% under both low and high MAT and with reduced OSR area (0.6‐km scale). Despite high pollen beetle abundance in warm climates, yields were high when OSR flowered early. Thereby, higher temperatures favoured early flowering. Only among late‐flowering OSR crop fields yield was higher in cooler than warmer climates. Bud loss responded analogously. Landscape composition did not substantially affect bud loss and yield. Synthesis and applications: Earlier flowering of winter OSR compensates for higher pollen beetle abundance in warmer climates, while interannual continuity of OSR area prevents high pollen beetle abundance in the first place. Thus, regional coordination of crop rotation and crop management promoting early flowering may contribute to sustainable pest management in OSR under current and future climatic conditions.

Fruit quantity and quality of strawberries benefit from enhanced pollinator abundance at hedgerows in agricultural landscapes

Animal pollinators are in a serious decline due to habitat loss, isolation and landscape fragmentation, putting pollination services to crops at risk. Hedgerows have been repeatedly emphasized as landscape elements that provide nesting and food resources, connect fragmented habitats and could thus facilitate crop pollination. However, the beneficial and potentially also detrimental impacts of hedgerows on crop pollination remain poorly studied. Here, we analysed the effects of pollinators and herbivorous pollen beetles (Meligethes spp.) on quantity and quality of strawberries from phytometer plants located at forest-connected hedgerows, isolated hedgerows and on grassy margins without any hedgerows. Higher pollinator abundance increased strawberry weight, whereas pollen beetle abundance reduced strawberry weight. Strawberry weight was significantly reduced by 29% at isolated hedgerows and 32% on grassy margins, compared to berries at connected hedgerows. Plants placed at forest-connected hedgerows produced more high quality strawberries with 90% classified as “marketable”, whereas only 75% of strawberries from plants at isolated hedgerows, 48% of strawberries from plants on grassy margins and 41% of strawberries from self-pollinated control plants where classified as marketable. Consequently, increased habitat connectivity through hedgerows enhanced the commercial value of strawberries from 9.27 € per 1000 strawberries for plants grown on grassy margins to 14.95 € for plants located at forest-connected hedgerows. Correspondingly, pollinator abundance was highest on phytometer plants at forest-connected hedgerows, lowest on grassy margins and intermediate at isolated hedgerows. Pollen beetle abundance on phytometer plants was not affected by hedgerows.Our study highlights the importance of hedgerows and habitat connectivity for promoting pollination services in agricultural landscapes, with economically important benefits for crop quantity and quality.

Effect of flower traits and hosts on the abundance of parasitoids in perennial multiple species wildflower strips sown within oilseed rape (Brassica napus) crops

Reducing the use of insecticides is an important issue for agriculture today. Sowing wildflower strips along field margins or within crops represents a promising tool to support natural enemy populations in agricultural landscapes and, thus, enhance conservation biological control. However, it is important to sow appropriate flower species that attract natural enemies efficiently. The presence of prey and hosts may also guide natural enemies to wildflower strips, potentially preventing them from migrating into adjacent crops. Here, we assessed how seven flower traits, along with the abundance of pollen beetles (Meligethes spp., Coleoptera: Nitidulidae) and true weevils (Ceutorhynchus spp., Coleoptera: Curculionidae), affect the density of parasitoids of these two coleopterans in wildflower strips sown in an oilseed rape field in Gembloux (Belgium). Only flower traits, not host (i.e. pollen beetles and true weevils) abundance, significantly affected the density of parasitoids. Flower colour, ultraviolet reflectance and nectar availability were the main drivers affecting parasitoids. These results demonstrate how parasitoids of oilseed rape pests react to flower cues under field conditions. Similar analyses on the pests and natural enemies of other crops are expected to help to develop perennial flower mixtures able to enhance biological control throughout a rotation system.

Characterization of the pollen beetle, Brassicogethes aeneus, dispersal from woodlands to winter oilseed rape fields.

Many crop pests rely on resources out of crop fields; understanding how they colonize the fields is an important factor to develop integrated pest management. In particular, the time of crop colonization and damage severity might be determined by pest movements between fields and non-crop areas. Notably, the pollen beetle, Brassicogethes aeneus, previously named Meligethes aeneus, one of the most important pests of winter oilseed rape, overwinters in woodlands. As a result, its abundance increases in oilseed rape fields near wooded areas. Here, we assessed the spatio-temporal patterns of the dispersal from woodlands to oilseed rape fields in diversified landscapes of a same region. We observed on four dates the abundance of pollen beetles in 24 fields spread in the Eure department, France. We modeled the abundance as a result of the dispersal from the neighboring woodlands. We compared the modalities of dispersal corresponding to different hypotheses on the dispersal origin, kernel shape and sources of variability. Within oilseed rape the distance to the edges of woodlands is not the main determinant of pollen beetle abundance. On the contrary, the variability of the abundance between fields is largely explained by the dispersal from neighboring woodlands but there is considerable variability between dates, sites and, to a lesser extent, between fields. The two dispersal kernels received similar support from the data and lead to similar conclusions. The mean dispersal distance is 1.2 km but seems to increase from a few hundred meters the first week to more than two kilometers the fourth, allowing the pollen beetles to reach more distant OSR fields. These results suggest that early varieties away from woodlands and late varieties close to the woodlands may limit attacks at the time when oilseed rape is the most sensitive.

Meteorological and landscape influences on pollen beetle immigration into oilseed rape crops

Heavy reliance on pesticide inputs to maintain crop yields has been an important aspect of agricultural intensification. Insecticide use has had detrimental impacts on pollinators and natural pest control agents, contributing to a decline in associated ecosystem services, and has also led to resistance development in pest populations. Throughout Europe, in oilseed rape (Brassica napus L.) crops, prophylactic use of insecticides against pollen beetles (Meligethes aeneus F. also known as Brassicogethes aeneus) has led to such issues, and there is an urgent need to develop more sustainable pest management practices for the crop. Although advice is available to oilseed rape growers regarding control thresholds, it may not be adhered to due to the expense of pollen beetle monitoring relative to the inexpensive cost of pyrethroid insecticides. Thus, the key to reducing prophylactic insecticide applications may lie with improved, less labour intensive methods of pollen beetle monitoring. For these to be realized, a better understanding is needed of the effects of agri-landscape features and meteorological conditions on pollen beetle immigration into the crop. In this study, based on data from four years of pollen beetle monitoring on a total of 41 field sites, we model the effects of meteorological (wind speed and direction, rainfall and accumulated temperature) and landscape (areas of woodland, residential gardens, the current and previous seasons’ oilseed rape crops, and lengths of hedgerows and treelines) variables on directional sticky trap catches, at both the single trap and field scales. Meteorological variables, particularly accumulated temperature and wind speed were more important than landscape variables in predicting the abundance of pollen beetles immigrating into OSR fields. Sticky traps that were facing downwind caught more beetles than those that were facing across-wind or upwind; this is the first study to show at a landscape-scale, direct evidence for use of upwind anemotaxis by pollen beetles at the point of entry during immigration into the crop. At the field scale, the area of oilseed rape grown in the previous season was found to be positively related to trap catch, but no relationships with other landscape variables were found. Optimally-placed monitoring traps could complement existing decision support systems to reduce pollen beetle monitoring effort and encourage use of insecticides only when control thresholds are breached, thus enhancing the sustainability of oilseed rape production. Knowledge of the area of oilseed rape crops grown during the previous season in the surrounding landscape could contribute to risk assessment of potential pest pressure for individual OSR crops.

Impact of oilseed rape crop management systems on the spatial distribution of Brassicogethes aeneus (Fabricius 1775): Implications for integrated pest management

The pollen beetle is one of the most important oilseed rape pests wherever the crop is grown. If no control measures are applied, it can cause a greater than 50% reduction in yield. The over-use of insecticides (especially pyrethroids) to control the pollen beetle has led to the development of resistance. Thus, alternative control strategies are required. A field trial with three experimental fields with different contributions of turnip rape as a trap crop was established during the growth season of 2013–2014. A grid of GPS points was established on each field. Pollen beetle abundance was recorded at each GPS point by beating into trays, and damage was assessed by dissection of buds from terminal racemes. Data analysis was performed by two-way analysis of variance and the appearance of pollen beetle adults was processed in a geographic information system (GIS). Statistically significant differences were found in terms of the density of the pollen beetle population between trap crop plants and oilseed rape plants. Control thresholds on each oilseed rape field were not exceeded, whereas the density of the pollen beetle population on trap crop plants was greater by up to 40 fold, regardless of the contribution of trap crop plants. The data indicate that support systems should use sampling strategies that incorporate spatial information to model crop loss more accurately and that there may be the potential for spatially targeted applications of insecticides to optimize the influence of natural enemies in oilseed rape.

Biological pest control and yields depend on spatial and temporal crop cover dynamics

Summary Modern agricultural landscapes are dynamic systems with interannually changing proportions of different crop types. However, the effects of spatiotemporal changes in crop area on crop yields and crop–herbivore–antagonist interactions have been rarely considered, in contrast to documented beneficial effects of semi‐natural habitats on biological pest control at local and landscape scales. In this study, we examined how the proportion of oilseed rape (OSR) fields in a landscape and the annual increase or decrease in OSR cover due to crop rotation affect OSR herbivores, their natural enemies and crop yield. During two study years, we examined the abundance of adult and larval pollen beetles, parasitism of pollen beetle larvae by a parasitic ichneumonid and crop yields (seed weight per plant) in the edge and centre of 36 OSR fields. The fields differed in the proportion of OSR in the surrounding landscape at 1‐km radius and in the interannual change in the proportion of OSR from the previous year to the respective study year. Adult pollen beetle abundance decreased in one study year and larval pollen beetle abundance and parasitism rates decreased in both study years with spatially increasing OSR proportion in the landscape, indicating dilution effects on both trophic levels. Crop yield was positively affected by spatially increasing proportions of OSR. An interannual increase in the proportion of OSR led to the dilution of pest species, but had no significant effect on yield or parasitism rate. Synthesis and applications. The negative effects of pollen beetles on yields despite regular insecticide applications underpin the need for improved techniques for controlling this pest. Our results emphasize the potential to enhance crop yields by the management of spatiotemporal crop cover dynamics within landscapes. We recommend that future management schemes should coordinate the spatial aggregation and annual dynamics of oilseed rape (OSR) cover in a landscape as a potential way to reduce pest impacts in intensively managed OSR fields.

Does insecticide application in a winter oilseed rape field influence the abundance of pollen beetle Meligethes aeneus in nearby ornamental flowers and vegetables?

Pollen beetle is a pest that attacks oilseed rape as well as many other brassicaceous crops, garden vegetables and ornamental flowers. The present study was primarily carried out to investigate whether insecticide application in brassicaceous field crops might influence the abundance of pollen beetles in nearby private garden flowers and vegetables. At peak emergence of the new generation of pollen beetles, a significantly higher number of beetles were found in flowers, and in window traps, alongside untreated as opposed to alongside treated sections of the winter oilseed rape (WOSR) field. However, the type of flower played a role in the number of pollen beetles found in the flowers. The presence of pollen beetles in both ornamental and wild flowers was also significantly influenced by the direction of placement of the flowers. No pollen beetle, neither overwintering nor newly emerged, was observed in any of the brassicaceous vegetables placed along the field. The number of pollen beetles in the WOSR field strongly influenced the number of pollen beetles in nearby flowers of preference to the beetles, and insecticide treatment with Biscaya (thiacloprid) against pollen beetle in oilseed rape may thus help, indirectly, to protect nearby garden flowers from damage.

Effects of nitrogen fertilization on insect pests, their parasitoids, plant diseases and volatile organic compounds in Brassica napus

Nitrogen (N) availability is a key factor influencing the yield of Brassica napus L. Thus, mineral fertilization is widely used to improve the quality and quantity of seeds. In this study, we conducted field experiments to determine the impact of nitrogen fertilization on B. napus pests, their parasitoids and plant diseases. The results showed that N treatment had an impact on the abundance of pollen beetles (Meligethes aeneus Fab.) and cabbage seed weevils (Ceutorhynchus obstrictus Marsh.) as well as dark spot disease (Alternaria brassicae (Berk.) Sacc.). Since pest abundance was not correlated with the flower and silique numbers, the feeding and oviposition sites, plant smell bouquets were analysed to determine potentially attractive or repellent volatile organic compounds. We detected 19 different compounds among which acetic acid and several lipoxygenase pathway products were emitted at higher levels from N-treated plants. Emission of a few other terpenoid compounds was correlated with the pest abundance in field conditions. Abundance of parasitoids of both pests was related to the host availability rather than to the fertilization treatment. Therefore, we suggest that plant chemical cues play a minor role in localization of hosts in close proximity to parasitoid. Dark spot disease levels decreased with increasing N availability, possibly reflecting enhanced emissions of acetic acid, a known antifungal volatile. This study demonstrates the effects of N fertilization on bud and flower volatile bouquets, which might play a role in B. napus insect pest host selection and in resistance to fungal plant diseases. Further studies are necessary to investigate the behavioural responses of insects to the changed volatile bouquets.

Local and landscape determinants of pollen beetle abundance in overwintering habitats

The development of integrated pest management strategies requires that the semi‐natural habitats scattered across the landscape are taken into account. Particular determinants of insect pest abundance in overwintering habitats just before they migrate onto crops appear to be poorly known and of crucial importance for understanding patterns of crop colonization and pest population dynamics at the landscape scale. The emergence of pollen beetle Meligethes aeneus F. was studied in grassland, woodland edge and woodland interior over a 3‐year survey in France using macro‐emergence traps. A suite of variables at the local and the landscape scale was assessed for each trap, aiming to identify potential relevant habitat indicators. The effects of habitat characteristics were evaluated using partial least square regressions. It was found that M. aeneus can overwinter in all types of habitat but that particular habitat characteristics at the local and landscape scales may explain their abundance in overwintering sites more than the types of habitat: relative altitude, litter thickness, soil moisture and proximity to the previous year's oilseed rape fields appear to be positively correlated with abundance of adults over the 3 years. Hence, the abundance of emerged pollen beetles depends on both the landscape configuration of the previous year's oilseed rape fields around overwintering sites and local habitat characteristics. Landscape configuration may determine population flow towards overwintering sites in the late summer, and local habitat characteristics may influence survival rates during the winter. The findings of the present study provide valuable insight into the role of semi‐natural habitats as a source of pests, patterns of crop colonization in the spring, and the influence of landscape on pollen beetle abundance.

Effect of crop management and landscape context on insect pest populations and crop damage

Understanding the determinants of insect–plant interactions and pest population dynamics at multiple spatial scales is a pre-requisite for developing innovative crop protection strategies and increasing the sustainability of agroecosystems. In a two-year study, we investigated the relative influence of local crop management and landscape context on pollen beetle (Meligethes spp.) abundance and damage at 8 different spatial scales around 42 oilseed rape fields using a multi-model inference approach. We found that pest abundance was mainly determined by the proportion of grassland and woodland in the landscape at scales ranging from 1500m to 2000m. Pollen beetle damage was affected both by local management and landscape predictors at scales ranging from 1500m to 2000m. Indeed, damage was negatively correlated with the nitrogen nutrition index of the plants and positively correlated with the proportion of woodland in the landscape at a large scale. Our multi-scale approach revealed that landscape complexity determines pollen beetle abundance in the spring and that nitrogen nutrition of the plants influences crop ability to compensate bud abortions resulting from pest attacks. The results are discussed in relation to crop management, pest dispersal ability and landscape structure.

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

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.