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Keywords:

  • Brassica napus ;
  • Meligethes aeneus ;
  • Meligethes viridescens ;
  • natural insecticides;
  • organic production

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Pollen beetles, Meligethes spp. (Coleoptera: Nitidulidae), are among the most damaging pests of oilseed rape (Brassica napus L.). Increasing populations of pyrethroid-resistant pollen beetles coupled with the prohibition of synthetic pest control products in organic farming means that other direct control methods are needed. A laboratory study was therefore conducted to evaluate the effect of natural products, combinations of natural products and additives as well as natural and synthetic insecticides on mortality of pollen beetles. In addition, field trials under both integrated and organic production were conducted to evaluate the efficacy of six natural products, nine combinations of natural products, two synthetic insecticides (integrated-production trials only), two natural insecticides and two additives to reduce pollen beetles. The laboratory trial, using both a curative and preventive approach, showed that two of the eight natural products (lavender oil and stone meal) caused a mortality of over 98% within the first day of application. The other natural products were only partially effective compared with the untreated control. In the field trials, the natural products reduced the number of pollen beetles 1 day after application compared with the untreated control in both trial years and production systems. Promising substances were stone meal, Silico-Sec and liquid manure. Nevertheless, the efficacy was not consistent, and no effect on oilseed rape yield was observed. In spite of this, these products have the potential to control pollen beetles under field conditions with comparable effects to synthetic insecticides. Further research should therefore focus on timing and frequency of applications as well as on the formulation of the natural products to increase the persistency of the products under field conditions.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Oilseed rape (Brassica napus L.) is a useful crop to grow in rotation because its early harvest allows the seeding of the following crop comparatively early in the summer. It suppresses weeds fairly well, which is particularly interesting in organic farming. Oilseed rape yields a valuable oil for food purpose, which is highly demanded from both food retailers and consumers. Furthermore, interest in environmentally friendly oilseed rape production has increased. Nevertheless, oilseed rape production may suffer from infestations of pollen beetles, Meligethes aeneus (F.) and Meligethes viridescens (F.) (Coleoptera: Nitidulidae). Pollen beetles are a widespread and major pest of winter- and spring-sown oilseed rape and other cruciferous crops in Europe (Williams 2010). In an EU-wide survey conducted between 1995 and 1998, pollen beetles were found to be the most abundant pest (Garbe et al. 2000; Richardson 2008).

Adult pollen beetles infest oilseed rape in spring during the green-to-yellow bud stage, attracted by both olfactory and visual cues (Evans and Allen-Williams 1994; Cook et al. 2002, 2007a; Jönsson et al. 2007). Adults and to a lesser extent emerging larvae damage the flower buds while feeding, causing important yield losses (Hansen 2004; Slater et al. 2011). Feeding damage by pollen beetles and oilseed rape yield were negatively correlated (Zaller et al. 2008). Despite this, well-fertilized oilseed rape plants can compensate for insect injury, thereby reducing yield losses (Hansen 2004), because they can develope auxiliary shoots (Tatchell 1983). More specifically, oilseed rape yield has a strong positive correlation with nitrogen input (Rathke et al. 2006). In contrast, plants with limited nitrogen fertilizer have difficulty in compensating for losses caused by pests. In organic agriculture in particular, the nitrogen supply for the oilseed rape crops is often limiting. As a consequence of damage compensation, pod-filling then becomes unsynchronized, making it difficult to determine the best time for the harvest.

Because no pollen-beetle-resistant oilseed rape cultivars are currently available, pyrethroid insecticides are widely used for the control of pollen beetles. However, the resistance of pollen beetles to pyrethroids is now a widespread problem in Europe (Slater et al. 2011) and in Switzerland (Derron et al. 2004). Moreover, according to the Swiss production scheme ‘Extenso’ for small-grain cereals and oilseed rape, the application of insecticides, fungicides and plant growth regulators is prohibited (Jäggi 2003). Likewise, no direct control measures against this pest insect are registered and available for organic oilseed rape production in Switzerland (Ordinances 910.18 and 910.181). Consequently, a wide variety of cultural and biological management strategies have been proposed for reducing pollen beetle infestations, such as using early-flowering oilseed rape varieties (Hiltbrunner et al. 2011), conservation strips (Büchi 2002), conservation tillage for parasitoid and predator enhancement (Nilsson 2010; Rusch et al. 2011), trap cropping (Hokkanen 1991; Cook et al. 2006, 2007a,b) and push–pull strategies, which use behavioural manipulation that make the crop unattractive to the pests (push) while luring them towards an attractive source (pull) from where they are subsequently removed (Cook et al. 2007a,b). In addition, a number of plant essential oils were shown to repel pollen beetles (Mauchline et al. 2005; Cook et al. 2007a,b), and various entomopathogenic fungi were effective against pollen beetles under laboratory conditions (Butt et al. 1998; Husberg and Hokkanen 2001; Pilz and Keller 2006; Kuske et al. 2011).

These strategies may be promising for reducing the numbers of pollen beetles before they invade a field, but once infestation has occurred, direct control measures against this pest are required to protect the crop from major damage. Pest control measures that make use of natural products may offer strategies for controlling pollen beetles under field conditions, especially in low-input and organic agriculture. To our knowledge, there is only little information available on the direct control of pollen beetles with natural products (Weiher et al. 2007; Mauchline et al. 2013) and for pyrethrum in the field (Weiher et al. 2007). The aim of this study was therefore to evaluate selected natural products for their ability to reliably control pollen beetles under both laboratory and field conditions in both ‘Extenso’ and organic production.

Material and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Selection of natural products

Products were selected based on the literature on the control of other small coleopteran pests or other insect species, as well as on recommendations by organic growers. Two synthetic insecticides (integrated-production trials only), two natural insecticides registered for other insect pests, six natural products, nine combinations of natural products and two additives were tested (table 1). Application rates of the products were according to recommendations of the retailers or the input list for organic production (FiBL, 2013).

Table 1. Products evaluated for their efficacy against pollen beetles (Meligethes spp.) in laboratory and field trials
Product nameIngredientsManufacturer/Distributor
Insecticides
Synthetic
Karate ZeonLambda-CyhalothrinSyngenta Agro AG, Basel, Switzerland
AudienzSpinosadOmya AG, Oftringen, Switzerland
Natural
Pyrethrum FSPyrethrin and sesame oilAndermatt Biocontrol AG, Grossdietwil, Switzerland
NeemAzalAzadirachtin AAndermatt Biocontrol AG, Grossdietwil, Switzerland
Natural products
Stone meal (Ur)Calcium carbonate (3%), silica oxide (59%)Hauert Biorga, Grossaffoltern, Switzerland
Stone meal (Napf)Calcium carbonate (12%), silica oxide (58%)Ulrich & Partner GmbH, Zell LU, Switzerland
Silico-SecSilica oxide (96.5%)ISS Pest Control AG, Dietikon, Switzerland
SilkabenFinely ground minerals such as silica, bentonite, algal limestoneReichmuth AG, Romanshorn, Switzerland
SurroundKaolin (95%)Stähler Suisse SA, Zofingen, Switzerland
AshWooden ash from woodchip heatingGassmann, Rümlang, Switzerland
Frangula alnus Bark of Frangula alnus as fine powderHänseler AG, Herisau, Switzerland
Lavender oilOil of Lavendula angustifoliaHänseler AG, Herisau, Switzerland
Eucalyptus oilOil of Eucalyptus globulus,E. fructosa and E. smithiiHänseler AG, Herisau, Switzerland
Calamus oilCalamus oilHänseler AG, Herisau, Switzerland
Teak oilTeak oilOBI Bülach, Bülach, Switzerland
Liquid manureNot determined in details; cattle manure (70%), pig manure (30%)Götsch, Zurich-Seebach, Switzerland
Additives
TelmionRape oilOmya AG, Oftringen, Switzerland
Nu-Film-17Pine oilAndermatt Biocontrol AG, Grossdietwil, Switzerland
PromanalParaffin oilAndermatt Biocontrol AG, Grossdietwil, Switzerland
Starch glueCereal starchCOOP Bau und Hobby, Basel, Switzerland

In the field trials, natural products, which were ineffective in the first trial year, were difficult to handle, or which had other disadvantages were eliminated and replaced with other promising compounds in the second year.

Laboratory trial

Pollen beetle populations naturally occurring in the study area were collected from an untreated oilseed rape field and stored in mesh-lidded jars in a refrigerator (4°C) without food but with an oilseed rape leaf until use for the experiment. Pollen beetles were removed from the refrigerator immediately before being used for the experiment.

Two synthetic insecticides (Karate Zeon; Syngenta Agro AG, Basel, Switzerland and Audienz; Omya AG, Oftringen, Switzerland), one natural insecticide (NeemAzal; Andermatt Biocontrol AG, Grossdietwil, Switzerland), five natural products (stone meal (Napf), Silico-Sec, Surround, lavender oil and eucalyptus oil) and two natural additives (Telmion and Nu-Film-17), as well as the combinations stone meal/Telmion, Silico-Sec/Telmion and Surround/Telmion (table 1) were tested for their effect on pollen beetles using a curative and preventive approach. The curative approach is defined as applying a pest control product after pest invasion took place, whereas a preventive approach is defined as applying a pest control product before pest invasion took place, respectively. To test curative efficacy, 20 pollen beetles were transferred to a transparent, mesh-lidded Plexiglas box shaped like a quadratic truncated pyramid (bottom area 10 cm × 8 cm, height 13 cm, top area 10 cm × 12 cm). Thereafter, the products were applied to the pollen beetles using an enclosed spray booth (Spray-Lab, Schachtner Gerätetechnik, Ludwigsburg, Germany) with one nozzle (Lechner Antidrift IDK 120-02, 500 l/ha, 4 bar). For testing preventive efficacy, the products were applied to the empty mesh-lidded Plexiglas boxes, and thereafter, 20 pollen beetles were placed inside. In both test systems, the stone meal treatment was applied using a sieve. After application of the products, the Plexiglas boxes were carefully closed and placed in a climatic chamber at 22°C, 70% r.h. and L14:D10. A cotton-wool plug (40 mm × 14 mm; IVF Hartmann AG, Neuhausen, Switzerland) was placed at the bottom of each Plexiglas box and periodically moistened with tap water to prevent the pollen beetles from drying out. Flower pollen (Reformhaus Dropa, Zurich, Switzerland) was also added as food. Three replicates were used for each treatment, for a total of 60 insects. Pollen beetle mortality was recorded one and 5 days after application of the products. The trial included an untreated control and a water control.

Field trials

Field trials were conducted in 2006–2007 and 2007–2008 under both ‘Extenso’ and organic production. The fields were situated in the main agricultural midland area of Switzerland near Zurich (MeteoSwiss norm value: average mean temperature, 8.5°C; average mean precipitation, 1042 mm). Certified seeds of winter oilseed rape (cv. Rémy) were used in all trials. In both years, sowing was carried out with a small-plot seeder (Hege 76; Maschinen GmbH, Waldenburg, Germany) at a row spacing of 0.18 m for ‘Extenso’ in 2006–2007 and 2007–2008 as well as in organic production in 2006–2007, and with a normal farm seeder (MS 8200; MaterMACC, San Vito al Tagliamento, Italy) with a row spacing of 0.45 m in organic production in 2007–2008, respectively. Plots were harvested using a threshing machine (Wintersteiger plot combine, Nurserymaster Elite, Ried im Innkreis, Austria), and mean yield per treatment was determined for all but the organic trial in 2008, when a heavy stem weevil (Ceutorhynchus napi Gyll.) infestation interfered with plant ripening. Harvested seeds were dried, and yield (kg/a) was adjusted to 100% dry matter content. Soil management as well as fertilization, slug control and weed management was conducted according to good agricultural practice for ‘Extenso’ and organic production in Switzerland (Table S1).

Plot size per treatment was 29 m2 (11 m × 2.64 m). The trials under ‘Extenso’ and organic production consisted of twelve and ten treatments, respectively. Each field trial comprised four replications using a randomized complete block design. Liquid products were applied using a knapsack sprayer (Birchmeier Sprühtechnik AG, Stetten, Switzerland) with a boom (2.5-m-long five nozzles, 0.5 m distance, Lechler Antidrift IDK 120.02, 4 bar) with a spraying volume of 500 l/ha. Stone meals and ash were hand-dusted over the plants with a sieve in the respective treatment. Each trial included an untreated control. All treatments and their application rates are listed in table 2.

Table 2. Products applied and application rate for the control of Meligethes spp. present in winter oilseed rape field trials under ‘Extenso’ and organic production systems in 2006–2007 and 2007–2008
Product nameYearExtensoOrganic
Application rate (l, kg or m3/ha)a
  1. – –, treatment not applied in the respective trial.

  2. a

    Spraying volume of 500 l water/ha. Stone meals and ash were hand-dusted over the plants with a sieve in the respective treatment.

Untreated control2006–2007  
Karate Zeon2006–20070.15 l– –
Audienz2006–20070.2 l– –
Pyrethrum FS2006–20071 l– –
NeemAzal2006–20073 l– –
Telmion2006–200710 l– –
Promanal2006–200710 l10 l
Eucalyptus oil2006–200710 l– –
Eucalyptus oil + Nu-Film-172006–2007– –10 l + 0.5 l
Eucalyptus oil + Nu-Film-172006–2007– –25 l + 0.5 l
Calamus oil + Teak oil2006–20075 l + 10 l– –
Lavender oil2006–200710 l– –
Lavender oil + Nu-Film-172006–2007– –10 l + 0.5 l
Lavender oil + Nu-Film-172006–2007– –25 l + 0.5 l
Stone meal (Ur)2006–2007– –500 kg
Frangula alnus bark2006–200720 l20 l
Liquid manure2006–200720 m320 m3
Untreated control2007–2008  
Audienz + Telmion2007–20080.2 l + 10 l– –
Telmion2007–200810 l10 l
Silico-Sec + Telmion2007–200825 kg + 10 l25 kg + 10 l
Silkaben + Telmion2007–200825 kg + 10 l25 kg + 10 l
Stone meal (Napf)2007–2008500 kg500 kg
Stone meal (Napf) + Nu-Film-172007–2008500 kg + 10 l500 kg + 10 l
Stone meal (Napf) + starch glue2007–2008500 kg + 100 kg500 kg + 100 kg
Stone meal (Ur) + Nu-Film-172007–2008500 kg + 10 l– –
Ash + starch glue2007–2008300 kg + 60 kg300 kg + 50 kg
Lavender oil2007–200810 l10 l
Liquid manure2007–200820 m320 m3

Pollen beetle density was assessed according to the EPPO protocol (2005) by counting the number of pollen beetles on 25 randomly chosen main shoots from the centre of each plot early in the morning on the main shoots 1 day before (except for the trials under ‘Extenso’ in 2007), one or 2 days and three, four or 5 days after application of the products. The growth stage was noted at the days of counting according to Lancashire et al. (1991) to determine whether the economic threshold value for insecticide application was reached. In Switzerland, the economic threshold value is three pollen beetles at BBCH 53–57 and five pollen beetles at BBCH 57–61 for winter oilseed rape, respectively.

Data analysis

For the laboratory trial, the relative efficacy (of each treatment as compared to the untreated control) was calculated for both the curative and the preventive approach (Abbott 1925). The relative efficacy was calculated as follows: efficacy (%) = [(number of pollen beetles in the untreated control – number of pollen beetles in the treatment)/number of pollen beetles in the untreated control] * 100. The effect of the products on mortality of pollen beetles in the laboratory, on the number of pollen beetles on oilseed rape blossoms at each counting as well as on oilseed rape yield was analysed using a one-way anova in randomized blocks. A Tukey HSD test (P < 0.05) was used to determine significant differences of products on the parameters measured. Data were log-transformed where required to meet the assumptions for anova but non-transformed data are presented in the text and in tables. All statistical analyses were performed using R 2.13.0 (Development Core Team 2011).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Laboratory trial

The efficacy of the products differed significantly 1 day after treatment in both test systems (curative: F14,28 = 28.27; P < 0.001; preventive: F14,28 = 4.10; P < 0.05). In both test systems, two of the eight natural products, namely stone meal and lavender oil as well as the synthetic product Audienz, caused a pollen beetle mortality rate of more than 98.0% day after application (table 3).

Table 3. Relative efficacy (%) (±SE) of synthetic and natural products on pollen beetles (Meligethes spp.) in the laboratory trial one and 5 days after a curative (pollen beetles added before treatment) or preventive (pollen beetles added after treatment) application, respectively
Product nameApplication rate (l or kg/ha)aCurativePreventive
Pollen beetles added before treatmentPollen beetles added after treatment
1 day5 days1 day5 days
  1. Means in each column followed by different letters indicate significant differences (one-way anova in randomized blocks, Tukey HSD, P < 0.05); SE, standard error of the mean.

  2. a

    Spraying volume of 500 l water/ha. Stone meals and ash were hand-dusted over the plants with a sieve in the respective treatment.

Untreated control 0.00 ± 0.00 g0.00 ± 0.00 f0.00 ± 0.00 d0.00 ± 0.00 de
Water control500 l−1.77 ± 1.77 g−3.43 ± 4.76 f−0.57 ± 2.58 d−7.57 ± 3.38 e
Karate Zeon0.075 l84.67 ± 2.24 ab75.93 ± 7.97 ab89.80 ± 3.06 a81.67 ± 3.97 a
Audienz0.2 l99.10 ± 0.90 a100.00 ± 0.00 a100.00 ± 0.00 a100.00 ± 0.00 a
NeemAzal3 l 28.90 ± 3.78 defg19.53 ± 6.43 def17.80 ± 6.12 cd13.17 ± 7.59 cde
Stone meal (Napf)500 kg100.00 ± 0.00 a100.00 ± 0.00 a98.50 ± 1.50 a100.00 ± 0.00 a
Stone meal (Napf) + Telmion500 kg + 10 l −1.77 ± 1.77 g100.00 ± 0.00 a−1.77 ± 1.77 d97.10 ± 2.90 a
Silico-Sec25 kg16.13 ± 3.94 efg10.57 ± 3.84 ef7.37 ± 3.57 d13.07 ± 9.34 cde
Silico-Sec + Telmion25 kg + 10 l 62.03 ± 7.92 abcd62.33 ± 5.85 abc52.80 ± 6.18 b40.13 ± 9.75 bc
Surround30 kg3.80 ± 2.14 fg0.33 ± 3.23 f0.20 ± 3.23 d3.10 ± 4.25 de
Surround + Telmion30 kg + 10 l 28.53 ± 1.64 defg25.13 ± 5.09 cdef36.37 ± 11.25 bc43.63 ± 11.89 b
Lavender oil10 l 100.00 ± 0.00 a100.00 ± 0.00 a100.00 ± 0.00 a100.00 ± 0.00 a
Eucalyptus oil10 l 49.70 ± 25.81 bcde50.67 ± 19.79 bcd5.73 ± 4.11 d−2.27 ± 4.10 e
Telmion10 l 75.47 ± 7.97 abc38.23 ± 5.48 bcde58.10 ± 9.05 b28.90 ± 1.80 bcd
Nu-Film-1710 l 39.83 ± 2.33 cdef45.57 ± 12.53 bcde36.13 ± 11.25 bc15.90 ± 4.79 bcde

Stone meal in combination with Telmion was not effective 1 day after application. In contrast, Telmion applied on its own caused mortality of pollen beetles of 75.47% and 58.10% in the curative and preventive treatment, respectively, 1 day after the application. The efficacy of the standard insecticide Karate Zeon 1 day after application was 84.67% and 89.80% in the curative and preventive treatment, respectively, while that of the other natural products ranged between 0.00% and 62.00%. Surprisingly, the efficacy of eucalyptus oil was 49.70% in the curative approach, while it proved ineffective in the preventive approach. Limited pollen beetle mortality was recorded in the water control treatment in either approach (table 3).

The products differed significantly in efficacy 5 day after treatment in both test systems (curative: F14,28 = 27.63; P < 0.001; preventive: F14,28 = 54.98; P < 0.001). In both test systems, three of the eight natural products, namely stone meal, lavender oil and stone meal in combination with Telmion as well as the synthetic product Audienz, caused a pollen beetle mortality rate of more than 97.00% (table 3). The efficacy of the standard insecticide Karate Zeon 1 day after application was 75.93% and 81.67% in the curative and preventive treatment, respectively. Surprisingly, the efficacy of eucalyptus oil was 50.67% in the curative approach, while it proved ineffective in the preventive approach. Limited pollen beetle mortality was recorded in the water control treatment in either approach (table 3).

Field trials

Weather conditions and pressure of pollen beetles

Weather conditions were cold and windy during oilseed rape blossom development in spring 2007, while spring 2008 was exceptionally rainy. Before application of the products, in 2007, pollen beetle pressure in the organic trial was 2.02 ± 0.12 (3 April; BBCH 53). In 2008, number of pollen beetles before treatment was 0.61 ± 0.03 (17 April; BBCH 55) for ‘Extenso’ and 1.70 ± 0.05 (17 April; BBCH 52) for organic production.

Impact on pollen beetle number

In the trial under ‘Extenso’ production conducted from 2006–2007, the number of pollen beetles found on the blossoms of the main shoot varied significantly depending upon the products used one (F11,33 = 0.19; P < 0.001) and four (F11,33 = 0.11; P < 0.001) days after application (table 4).

Table 4. Mean number (±SE) of pollen beetles (Meligethes ssp.) per main shoot one and 4 days after the application of the products in the field trial with winter oilseed rape under ‘Extenso’ production in 2006–2007
Product name1 day4 days
  1. Means in each column followed by different letters indicate significant differences (one-way anova in randomized blocks, Tukey HSD, P < 0.05). SE, standard error of the mean.

Untreated control2.10 ± 0.50 cd2.65 ± 0.48 bc
Karate Zeon0.25 ± 0.13 a0.48 ± 0.38 a
Audienz0.53 ± 0.14 ab0.55 ± 0.18 ab
Pyrethrum FS0.63 ± 0.04 abc1.65 ± 0.20 abc
NeemAzal1.10 ± 0.29 abcd1.68 ± 0.30 abc
Telmion1.05 ± 0.26 abcd0.83 ± 0.29 abc
Promanal1.35 ± 0.22 bcd1.95 ± 0.50 abc
Lavender oil1.45 ± 0.26 bcd2.13 ± 0.29 abc
Eucalyptus oil2.23 ± 0.35 d3.13 ± 0.90 c
Calamus oil + Teak oil1.08 ± 0.14 abcd1.90 ± 0.05 abc
Frangula alnus bark0.83 ± 0.28 abcd1.38 ± 0.26 abc
Liquid manure0.65 ± 0.11 abc0.58 ± 0.11 abc

In the trials conducted under organic production (2006–2007), pollen beetle numbers did not differ in the trial plots before the products were applied (F9,29 = 0.08; P > 0.05) (table 5).

Table 5. Mean number (±SE) of pollen beetles (Meligethes spp.) per main shoot before and one and 4 days after the application of the products in the field trial with winter oilseed rape under organic production in 2006–2007
Product nameBefore treatment1 day4 days
  1. Means in each column followed by different letters indicate significant differences (one-way anova in randomized blocks, Tukey HSD, P < 0.05); ns, not significant. SE, standard error of the mean.

Untreated control2.11 ± 0.36 ns1.14 ± 0.21 b5.35 ± 0.60 c
Stone meal (Ur)2.21 ± 0.53 ns0.31 ± 0.05 a1.87 ± 0.42 a
Telmion2.32 ± 0.34 ns0.95 ± 0.15 ab3.37 ± 0.33 abc
Promanal1.97 ± 0.22 ns0.75 ± 0.15 ab3.70 ± 0.55 abc
Lavender oil 2% + Nu-Film-171.69 ± 0.41 ns0.81 ± 0.03 ab4.36 ± 0.21 bc
Lavender oil 5% + Nu-Film-172.01 ± 0.15 ns0.56 ± 0.05 ab5.07 ± 0.42 c
Eucalyptus oil 2% + Nu-Film-171.66 ± 0.08 ns0.99 ± 0.17 ab4.50 ± 0.25 bc
Eucalyptus oil 5% + Nu-Film-172.13 ± 0.73 ns1.10 ± 0.22 b4.28 ± 0.32 bc
Frangula alnus bark2.10 ± 0.06 ns0.92 ± 0.07 ab2.80 ± 0.38 abc
Liquid manure1.97 ± 0.39 ns0.58 ± 0.19 ab2.38 ± 0.45 ab

The number of pollen beetles on the blossoms of the main shoot varied significantly one (F9,29 = 0.03; P < 0.01) and four (F9.29 = 0.04; P < 0.001) days after application of the products (table 5). Only stone meal significantly reduced pollen beetle number one and 4 days after application (by 3.6- and 2.8-fold, respectively), while liquid manure reduced their numbers 2.2-fold 4 days after application compared with the untreated control (table 5).

In the 2007–2008 trial conducted under ‘Extenso’ production, the number of pollen beetles did not differ in the trial plots before application of the products (F11,33 = 0.19; P > 0.05) to the blossoms of the main shoot (table 6).

Table 6. Mean number (±SE) of pollen beetles (Meligethes spp.) per main shoot before and one and 3 days after the application of the products in the field trial with winter oilseed rape under ‘Extenso’ production in 2007–2008
Product nameBefore treatment1 day3 days
  1. Means in each column followed by different letters indicate significant differences (one-way anova in randomized blocks, Tukey HSD, P < 0.05); ns, not significant; SE, standard error of the mean.

Untreated control0.50 ± 0.06 ns2.88 ± 0.23 g3.65 ± 0.13 e
Audienz + Telmion0.58 ± 0.09 ns0.80 ± 0.18 cde1.40 ± 0.26 abcd
Telmion0.68 ± 0.08 ns1.43 ± 0.18 ef1.65 ± 0.32 bcd
Silico-Sec + Telmion0.70 ± 0.11 ns0.58 ± 0.12 bcd0.65 ± 0.22 ab
Silkaben + Telmion0.63 ± 0.12 ns1.18 ± 0.18 def1.33 ± 0.36 abcd
Stone meal (Napf)0.60 ± 0.06 ns0.33 ± 0.10 abc1.58 ± 0.27 bcd
Stone meal (Napf) + Nu-Film-170.78 ± 0.14 ns0.10 ± 0.04 ab0.43 ± 0.12 a
Stone meal (Napf) + starch glue0.58 ± 0.16 ns0.30 ± 0.10 abc1.95 ± 0.27 cde
Stone meal (Ur) + Nu-Film-170.63 ± 0.13 ns0.08 ± 0.02 abc0.93 ± 0.16 abc
Ash + starch glue0.40 ± 0.04 ns0.03 ± 0.02 a1.60 ± 0.23 bcd
Lavender oil0.63 ± 0.11 ns1.75 ± 0.22 fg2.65 ± 0.30 de
Liquid manure0.68 ± 0.13 ns1.08 ± 0.18 def1.98 ± 0.47 cde

However, number of pollen beetles did vary significantly among treatments one (F11,35 = 0.02; P < 0.001) and three (F11,35 = 0.03; P < 0.001) days after application (table 6). Except for lavender oil, all of the products applied significantly reduced the number of pollen beetles on the blossoms compared with the untreated control 1 day after application by up to 28.8-fold for the treatment using stone meal (Napf) and Nu-Film-17, while the reduction for liquid manure was only 2.6-fold. Three days after application of the products, Silico-Sec and Telmion significantly reduced pollen beetle numbers by 5.6-fold, stone meal and Nu-Film-17 by 8.5-fold and liquid manure by 1.8-fold compared with the untreated control.

In the 2007–2008 trial conducted under organic production, pollen beetle number did not differ prior to application of the products (F9,29 = 0.19; P > 0.05) (table 7). However, two (F9,29 = 0.03; P < 0.001) and five (F9,29 = 0.01; P < 0.001) days after application of the products, the number of pollen beetles on the blossoms of the main shoot varied significantly depending on the products used (table 7).

Table 7. Mean number (±SE) of pollen beetles (Meligethes spp.) before and two and 5 days after the application of the products in the field trial with winter oilseed rape under organic production in 2007–2008
Product nameBefore treatment2 days5 days
  1. Means in each column followed by different letters indicate significant differences (one-way anova in randomized blocks, Tukey HSD, P < 0.05); ns, not significant; SE, standard error of the mean.

Untreated control1.55 ± 0.09 ns6.00 ± 0.37 g4.05 ± 0.03 de
Telmion1.60 ± 0.08 ns3.23 ± 0.25 ef2.15 ± 0.33 bc
Silico-Sec + Telmion1.85 ± 0.18 ns0.83 ± 0.10 ab1.00 ± 0.10 a
Silkaben + Telmion1.60 ± 0.22 ns1.38 ± 0.11 abc1.50 ± 0.10 ab
Stone meal (Napf)1.75 ± 0.15 ns2.05 ± 0.31 cde2.65 ± 0.18 c
Stone meal (Napf) + Nu-Film-171.78 ± 0.07 ns0.75 ± 0.11 a0.95 ± 0.03 a
Stone meal (Napf) + starch glue1.85 ± 0.04 ns1.68 ± 0.29 cde2.75 ± 0.08 c
Ash + Starch glue1.68 ± 0.18 ns1.35 ± 0.18 abc2.25 ± 0.13 bc
Lavender oil1.63 ± 0.17 ns5.20 ± 0.33 fg4.40 ± 0.10 e
Liquid manure1.58 ± 0.17 ns2.50 ± 0.13 de3.00 ± 0.20 cd

Two days after the application all products, but lavender oil, significantly reduced the number of pollen beetles by as much as 8.0-fold for stone meal (Napf) and Nu-Film-17, by 7.2-fold for Silico-Sec and Telmion, while the reduction was 2.4-fold for liquid manure. Five days after product application, Silico-Sec and Telmion reduced pollen beetle numbers by 4.0-fold, while stone meal and Nu-Film-17 had reduced it by 4.2-fold and liquid manure by 1.3-fold compared with the untreated control (table 7).

Oilseed rape yield

None of the products improved the grain yield of oilseed rape in any of the trials (mean yield over all treatments: 2007, ‘Extenso’ production: 25.64 ± 0.34 kg/a, F11,33 = 0.007; P > 0.05; organic production: 29.25 ± 0.64 kg/a, F9,29 = 0.02; P > 0.05; 2008, ‘Extenso’ production: 40.94 ± 0.61 kg/a, F11,35 = 0.01; P > 0.05; organic production: trial not harvested due to stem weevil infestation) (data not shown).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

In this study, natural products were evaluated in the laboratory and the field for their efficacy to control pollen beetles. To our knowledge, this is the first study to report the screening of various natural products on field efficacy against pollen beetles once field infestation begun. In all field trials, all of the products applied reduced pollen beetle numbers compared with the untreated control in both trial years, except for eucalyptus oils in the trial under ‘Extenso’ production in 2007. The highest reduction in pollen beetle number was achieved with stone meal alone and with stone meal in combination with a wetting agent. However, no effects on yield of winter oilseed rape were observed. This is in contrast to what was expected. Therefore, laboratory trials were conducted to elucidate the potential of the natural products to reduce pollen beetles under controlled environmental conditions. The laboratory trial using both a curative and a preventive approach showed that only two of the eight natural products, namely lavender oil and stone meal, caused a mortality of pollen beetles higher than 98.0%. The other natural products were only partially effective.

In the current investigation, lavender oil was shown to cause very high mortality of pollen beetles in the laboratory trials. This is in line with findings from another laboratory trial in which lavender oil was observed to cause mortality of pollen beetles (Pavela 2011). Under field conditions, however, no pollen-beetle-reducing effect of lavender oil was observed, which is in contrast to other findings (Mauchline et al. 2013). This might be due that the efficacy of volatile plant essential oils was reduced by spraying the product compared with the lavender packed in the sachets as applied by Mauchline et al. (2013). In contrast, eucalyptus oil had an efficacy rate of only 5.7% in the preventive compared with 49.7% in the curative test. Products based on plant essential oils (Isman 2006) as well as plant powders (Paul et al. 2009; Ndomo et al. 2010) were shown to have contact, fumigant, repellent and antifeedant activity against pest insects, and such products are successfully used to control coleopteran pests during storage. Although both lavender oil and eucalyptus oil showed promising effects under laboratory conditions, they neither caused a reduction in pollen beetle numbers in the field trials. This might be due to the fact that the mode of action, as hypothesized for a variety of essential oils (Lee et al. 2008), is the vapour phase. Consequently, oils might lose their insecticidal activity (Li et al. 2011) when applied under field conditions (Isman 2006) as opposed to indoor conditions where the volatile components of essential oils cannot evaporate into the environment and are therefore effective over a prolonged period. Unlike volatile plant essential oils, powder formulations of plant oils (Li et al. 2011) or plants applied as a powder (Ndomo et al. 2010; Mauchline et al. 2013) seem to have longer persistency. In the present study, only F. alnus was tested as a plant-powder formulation. Six days after application, its pollen-beetle-reducing activity was higher than that of the plant essential oils screened. However, this product caused phytotoxicity, resulting in a yield reduction of about 10%. Although this yield reduction was not significant, such high losses are not tolerable for a farmer. Consequently, this product was excluded from further testing.

Interestingly, small-scale farmers in Africa mix their dried beans with botanicals or add ash or fine sand to protect them from bruchid infestation (Paul et al. 2009). The observation that the stone meal treatment caused mortality of pollen beetles in the laboratory and reduced pollen beetles in the field indicates that it might be encouraging to further develop this product group. Furthermore, other natural products based on silica oxide, such as Silico-Sec, showed promising persistency in both field trials. In the laboratory trials, mortality of pollen beetles caused by the kaolin-containing product Surround was only moderate. This is consistent with findings by Glenn et al. (1999) that contact with the hydrophobic kaolin dust did not cause initial death of the arthropod pests. This observation would support the fairly low direct mortality caused by Silico-Sec and Surround in the current laboratory trial. It is likely that the mode of action of the dusty products, such as stone meal and Silico-Sec, would cause abrasion and sorption of cuticular waxes in pollen beetles, leading to slower death, as demonstrated in the case of small coleopteran pests of stored products (Mewis and Ulrichs 1999). Under field conditions, such dusty products might even have multiple impacts on arthropod pests: first, they might cause a change in the appearance of the plants, thereby impeding the invasion by insect pests such as pollen beetles, which use visual cues for host plant location. Second, the dusty layer might lead to behavioural alterations or even disruption of pollen beetle movement, feeding or egg laying, as observed for arthropod pests of tree fruit, which were treated with a hydrophobic kaolin layer (Glenn et al. 1999). Third, dusty products could result in reduced mobility of the insects, causing them to fall off the plants.

Liquid manure is occasionally used by organic growers to protect oilseed rape plants from pollen beetle infestation. This treatment seems promising according to the presented field studies; however, its efficacy was not consistent. Growers assume that the odour emanating from the treated plants may repel pollen beetles. Together with the change in colour of the plants, the attracting volatile cues of oilseed rape during flowering may be masked. These combined effects therefore might contribute to the reduction in the number of pollen beetles observed in all field trials. Only one study was found dealing with the effect of cow urine on pests. Paul et al. (2007) observed a reducing effect on bean beetle, Ootheca bennigseni _Weise (Coleoptera: Chrysomelidae), feeding on bean plants treated with diluted cow urine. However, environmental concerns about using liquid manure could arise because of increasing ammonia emissions, harmful effects on bees and other beneficial organisms.

Because they are active flyers, pollen beetles are highly mobile pest insects. Direct and effective control measures are essential once the pest insect has begun to invade the oilseed rape field in the yellow bud stage, the most susceptible stage for damage. Consequently, reliable products should have a curative effect and demonstrate a degree of persistency, as well as being fast-acting. The results of this study showed that certain natural products, especially those containing minerals, caused mortality of pollen beetles under laboratory conditions. These products might have the potential to regulate pollen beetles under field conditions by even showing comparable effects to synthetic insecticides. However, these effects were not yet reliable as to recommend any or the natural products for regular field application. Nitrogen fertilization was shown to impact the abundance of pollen beetles directly as well as the bud and flower volatile bouquets, which might play a role host location by the pest insect (Veromann et al. 2013). Additionally, because well-fertilized oilseed rape plants can compensate pollen beetle damage and thus yield losses (Hansen 2004), nitrogen fertilization is an important factor in crop management. Therefore, the effects of additionally applied nitrogen fertilizer in combination with direct control with natural products and cultural strategies might contribute to the achievement of consistent results for the control of pollen beetles under field conditions. Such field trials are currently ongoing to better understand the complex interaction of oilseed rape variety, fertilizer application, pollen beetle infestation and application of natural pesticides on oilseed rape yield. The results of these trials will elucidate the potential of such a combined approach to improve yield security and grain yield of oilseed rape for both ‘Extenso’ and organic production. For example, grain yield of the variety Rémy reached 21.2 kg/a averaged over the 43 organic farmers harvesting it in 2007. In 2008, the average grain yield (various varieties) for Swiss organic farmers was 16.2 kg/a, but 39% of the area originally planted with oilseed rape could not be harvested, mainly due to insect pest infestation. Because a number of the natural products tested in the current study demonstrated promising efficacy in the laboratory trial as well as comparable efficacy over a short time period in the field trials, their potential to reduce pollen beetles might be increased by improving their formulation, application rate, application technique, number of applications or a combination of these factors. Additionally, direct effects of the natural products on oilseed rape plants and natural antagonists of pollen beetles should be investigated. Detailed studies with the most promising natural products from the current laboratory and field trials are under way to address the above-mentioned factors in order to develop practicable and economically sound strategies to control pollen beetles.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

The authors would like to thank the growers for kindly providing the fields where the field trials were conducted. Their thanks also go to E. Uhlmann and collaborators at Agroscope Reckenholz-Tänikon Research Station ART for preparing and managing the field trials at Agroscope and helping at the harvest at the farmers' sites. We would also like to express our gratitude to Dr. T. Steinger, Agroscope Changins-Wädenswil (ACW), for his valuable comments on the manuscript. Bio Suisse and IP SUISSE funding for parts of this work are gratefully acknowledged.

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  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information
FilenameFormatSizeDescription
jen12086-sup-0001-TableS1.docWord document39KTable S1. Agronomic practice and experimental specific treatments for the field trials conducted under ‘Extenso’ and organic production in 2006–2007 and 2007–2008 for the control of pollen beetles (Meligethes spp.) in Switzerland.

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