Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass‐flowering prairie crop

One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass‐flowering crop grown intensively throughout the Canadian Prairies, canola has the potential to influence pollinator success across tens of thousands of square kilometers of cropland. Bumble bees (Bombus sp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass‐flowering crop on the abundance and phenology of bumble bees, and on another species of social bee (a sweat bee; Halictus rubicundus), by continuously deploying traps at different levels of canola cultivation intensity, spanning the start and end of canola bloom. Queen bumble bees were more abundant in areas with more canola cover, indicating that this crop is attractive to queens. However, bumble bee workers were significantly fewer in these locations later in the season, suggesting reduced colony success. The median collection dates of workers of three bumble bee species were earlier near canola fields, suggesting a dynamic response of colonies to the increased floral resources. Different species experienced this shift to different extents. The sweat bee was not affected by canola cultivation intensity. Our findings suggest that mass‐flowering crops such as canola are attractive to bumble bee queens and therefore may lead to higher rates of colony establishment, but also that colonies established near this crop may be less successful. We propose that the effect on bumble bees can be mitigated by spacing the crop more evenly with respect to alternate floral resources.     

Deposition and longevity of oviposition-deterring pheromone in the cabbage seed weevil

Abstract The cabbage seed weevil ( Ceutorhynchus assimilis Payk.) lays eggs singly into pods of oilseed rape ( Brassica napus L.) through punctures bored with the mouthparts, preferring pods not recently used for oviposition. A simple new choice test has been used to test individual components of egg-laying behaviour for their effect on oviposition site selection. It is confirmed that an oviposition-deterring pheromone (ODP) is deposited during abdomen brushing of the pod which follows egg-laying. Neither pin punctures, weevil feeding punctures, oviposition punctures nor eggs had any deterrent effect. Pods walked on by female weevils were not avoided by those laying eggs. Observations suggest that the ODP is sensed by contact chemoreceptors on the antennae. The deterrent effect lasted only 1–2 h. The implications of these findings on the adaptive significance of the pheromone and its possible use in pest control are discussed.     

Comparative assessment of the sensitivity of oilseed rape and wheat to limited water supply

The drought‐sensitivity of oilseed rape (OSR, Brassica napus cv. SW Landmark) was investigated, using the more widely studied crop species wheat (Triticum aestivum cv. Tybalt) as a benchmark. The water relations of OSR and wheat were compared in lysimeter and controlled environment experiments to test the hypothesis that the growth of OSR is restricted to a greater extent by soil drying than wheat and to determine whether the greater sensitivity results from differences in root or shoot traits. Plants were grown, with or without irrigation, in 1.2 m tall lysimeters packed with a sandy clay loam soil. The experiment was conducted in an open‐sided glasshouse to encourage air flow and to resemble a field environment as far as possible; plant population densities were equivalent to commercial crops. Irrigated OSR (evapo)transpired more water than wheat (498 vs. 355 mm), but had a comparable water use efficiency (WUE; 4.1 vs. 4.4 g DW mm^?1 H₂O). Oilseed rape showed a greater reduction in above‐ground growth (52% vs. 21%) and a smaller increase in WUE (27% vs. 45%) when water was withheld. Oilseed rape also responded to soil drying at a lower soil moisture deficit than wheat; transpiration rates fell below the potential of irrigated plants when plant available water remaining in the soil profile declined from 54 to 23% compared to 38 to 9% for wheat. The root hydraulic conductivity of young OSR plants, measured on root surface area basis, was about twice that of wheat, and was comparable on a root length basis. The results show that OSR was more sensitive to a restricted water supply than the benchmark species wheat and that the greater sensitivity resulted from differences in shoot, rather than root, characteristics. The root system of OSR was at least as efficient as wheat at extracting water from soil.     

Effects of crop plants on abundance of Pochonia chlamydosporia and other fungal parasites of root‐knot and potato cyst nematodes

The effects of a host plant on reproduction/abundance of fungal populations in relation to soil nutrients released by plants in the rhizosphere were studied. Abundance in the soil and potato rhizosphere of the fungi Paecilomyces lilacinus, Monographella cucumerina (CABI 380408) and Pochonia chlamydosporia var. chlamydosporia (Pc280, potato cyst nematode biotype) and P. chlamydosporia var. catenulata (Pc392, root‐knot nematode biotype) were assessed. The different ability of break crops (oilseed rape, sugarbeet and wheat) in the potato rotation to support Pa. lilacinus, Pochonia isolates Pc280 and Pc392 and abundance of the latter two isolates in soil and rhizosphere of potato plants infected with Meloidogyne incognita were also studied. Potato chits and crop seedlings were planted into boiling tubes containing 5000 chlamydospores or conidia g^?1 in acid washed sand (pH 6) and kept in a growth chamber at 20°C, and 16 h of light for up to 9 weeks. The abundance of the fungi in sand (fallow) differed significantly between fungal species, being in general less abundant in the absence than in the presence of the plant, although there was no interaction between plant species and fungal isolate. There was evidence of a different response to Me. incognita for Pc392 than for Pc280 but there was no significant effect of the presence of the nematode on the rate of increase of the fungus.     

Occurrence,Molecular Characterization and Vector Transmission of a Phytoplasma Associated with Rapeseed Phyllody in Iran

Symptoms of rapeseed phyllody were observed in rapeseed fields of Fars, Ghazvin, Isfahan, Kerman and Yazd provinces in Iran. Circulifer haematoceps leafhoppers testing positive for phytoplasma in polymerase chain reaction (PCR) successfully transmitted a rapeseed phyllody phytoplasma isolate from Zarghan (Fars province) to healthy rapeseed plants directly after collection in the field or after acquisition feeding on infected rapeseed in the greenhouse. The disease agent was transmitted by the same leafhopper from rape to periwinkle, sesame, stock, mustard, radish and rocket plants causing phytoplasma‐type symptoms in these plants. PCR assays using phytoplasma‐specific primer pair P1/P7 or nested PCR using primers P1/P7 followed by R16F2n/R2, amplified products of expected size (1.8 and 1.2 kbp, respectively) from symptomatic rapeseed plants and C. haematoceps specimens. Restriction fragment length polymorphism analysis of amplification products of nested PCR and putative restriction site analysis of 16S rRNA gene indicated the presence of aster yellows‐related phytoplasmas (16SrI‐B) in naturally and experimentally infected rapeseed plants and in samples of C. haematoceps collected in affected rapeseed fields. Sequence homology and phylogenetic analysis of 16S rRNA gene confirmed that the associated phytoplasma detected in Zarghan rapeseed plant is closer to the members of the subgroup 16SrI‐B than to other members of the AY group. This is the first report of natural occurrence and characterization of rapeseed phyllody phytoplasma, including its vector identification, in Iran.     

Milk production responses and rumen fermentation of dairy cows supplemented with summer brassicas

Forage brassicas, such as summer turnip (ST; Brassica rapa) and forage rape (FR; Brassica napus), are used as supplementary crops during summer. However, studies with lactating dairy cows fed these forages are limited and report inconsistent productive responses. The aim of this study was to determine dry matter intake, rumen fermentation and milk production responses of dairy cows in mid-lactation supplemented with and without summer (‘ST’ or ‘FR’) brassicas. Twelve multiparous lactating dairy cows were randomly allocated to three dietary treatments in a replicated 3 × 3 Latin square design balanced for residual effects over three 21-day periods. The control diet consisted of 16.2 kg DM of grass silage, 2.25 kg DM of commercial concentrate and 2.25 kg DM solvent-extracted soybean meal. For the other two dietary treatments, 25% of the amounts of silage and concentrates were replaced with FR or ST. The inclusion of forage brassicas had no effects on milk production (24.2 kg cow/day average) and composition (average milk fat and protein 43.2 and 33.6 g/l, respectively). Dry matter intake was 0.98 kg and 1.12 kg lower for cows supplemented with FR and ST, respectively, resulting in a greater feed conversion efficiency (1.35 kg milk/kg DM for ST and FR v. 1.27 kg milk/kg DM for the control diet). Intraruminal pH was lower for cows supplemented with ST compared to the control diet; however, it did not decrease below pH 5.8 at any time of the day. After feeding, the concentrations of total short-chain fatty acids (SCFAs) in rumen contents increased with ST supplementation compared to the control diet. Inclusion of FR in the diet increased the molar proportion of acetate (68.5 mmol/100 mmol) in total SCFA at the expense of propionate, measured 6 h after feeding of the forage. The molar proportion of butyric acid was greater with ST and FR supplementation (13.1 and 12 mmol/100 mmol, respectively) than in control cows. The estimated microbial nitrogen (N) flow was 89.1 g/day greater when supplementing FR compared to the control diet. Based on the haematological measures, the inclusion of summer brassica forages did not affect the health status of the animals. These results indicate that mid-lactation dairy cows fed brassicas are able to maintain production despite the reduced intake, probably due to improved rumen fermentation and therefore nutrient utilization.