The selective use of floral resources by the hoverfly Episyrphus balteatus (Diptera: Syrphidae) on farmland

The use of flowers of non-crop plants by the syrphid Episyrphus balteatus in margins of cereal fields was assessed quantitatively. G-tests and the ‘C’ index of Murdoch (1969) were used to compare the use and abundance of twenty-seven plant species by adult flies from June to August in the UK. The flowers of several plant species were used selectively by hoverflies throughout the season while the relative importance of others changed with date. The prospects for managing the field-margin flora to enhance biocontrol by hoverflies is discussed.     

The case for headland set-aside: consideration of whole-farm gross margins and grain production on two farms with contrasting rotations

Spreadsheet calculations were used to compare headland set-aside with rotational set-aside in terms of gross margin and grain production on two farms with contrasting rotations. At Broom's Barn, Suffolk there was a five course rotation consisting of sugar beet and four cereals, while at Bunny Park, Nottinghamshire oilseed rape was the break crop, followed by three cereals. For both farms a sensitivity analysis was used to investigate the effect of the proportion of the farm required to be set aside, the extent of headland yield reduction and the cereal price on the outcome of the spreadsheet calculations. In general headland set-aside out-performed rotational set-aside. Yields on headlands were always less than the main body of the field, but it was on the turning headlands where yield was particularly depressed. Thus the advantage, in terms of gross margin, of setting aside the headlands was greatest when the requirement could be fulfilled by fallowing most turning headlands, but no non-turning headlands. Generally, rotational set-aside reduced grain production more than headland set-aside, but when the spreadsheet models were adjusted to maintain the area of sugar beet, the situation was reversed. In this case headland set-aside produced a larger gross margin and had the greatest impact on grain production. An extension of the analysis is to ask the question: even if set aside is not an option, is it worthwhile to crop rather than fallow headlands? For cereals and oilseed rape the answer is in the affirmative; the gross margin for headlands remains positive, even when prices are much reduced, because the arable area payment more than offsets the variable costs. This does not hold for crops such as sugar beet that are not eligible for arable area payments. An additional benefit from headland set-aside is its potential to enhance the environment through increased habitat diversity and the provision of ‘buffer zones’ to prevent agrochemicals from drifting into hedges and watercourses.     

Reduced pesticide inputs on cereal field margins: the effects on butterfly abundance

Abstract. 1. On a study farm in Hampshire where large blocks of cereal fields had the pesticide inputs on their headlands experimentally and selectively reduced (the practice known as 'conservation headlands'), numbers of butterflies were monitored over 4 years by using transect counts.
2. Consistently more butterflies were seen flying over field edges sprayed under the conservation headland regime compared to those that were fully sprayed.
3. A comparison of changes in butterfly abundance on the study farm containing conservation headlands with data from the National Butterfly Monitoring Scheme indicated that population increases in some species may result from the use of conservation headlands.
4. The implications of resource provisioning and the potential reduction of spray drift into field-margin habitats are discussed in relation to farmland butterflies.     

Fenologia y seleccion de habitat de las especies de sirfidos afidofagos (Dipt.: Syrphidae) mas frecuentes en cultivos cerealeros y forrajeros en la provincia de buenos aires,argentina

Phenology and habitat selection of the aphidophagous syrphid species most frequently found in crops and pastures in the Province of Buenos Aires, Argentina. The paucity in ecological studies on aphidophagous syrphid flies (Diptera, Syrphidae) of the neotropical region is particularly pronounced in Argentina. In order to increase the database on these natural enemies, the phenology and habitat selection of six syrphid flies (Dipt., Syrphidae):Syrphus phaeostigma (L.);Allograpta obliqua (Wied.);Allograpta exotica (Wied.);Pseudodorus clavatus (L.);Platycheirus carposcalis (L.) andOcyptamus argentinensis (Thorn.) were studied in the Province of Buenos Aires (Argentina). The moment of the year in which adults, eggs, larvae and pupae of these species are found was recorded. The phenologies found for the species in our area are similar to those found for other species of the same genera in other parts of the world. These aphidophagous syrphids are not evenly distributed in all the systems sampled, evidencing a preference for either one of the following types of habitat: cereal crop, lucerne, soya, bushes or prairies. These results are potentially useful in terms of crop and pest management practices.

     

Some factors influencing the occurrence and site of oviposition by aphidophagous Syrphidae (Diptera)

Syrphids were not deterred from ovipositing on suitable plants by the presence of other syrphid eggs, larvae or larval gut contents. Heavy infestations of Aphis fabae Scop, on bean plants (Viciafaba L.) induced Platycheirus manicatus (Meig.) to lay preferentially on neighbouring uninfested plants. Such behaviour was not found for Syrphus species. Nor did flowers, a source of adult food, stimulate oviposition nearby. The site of oviposition in relation to Brevicoryne brassicae L. on brussels sprouts (Brassicae oleracea gemnifera L.) varied markedly according to species: in similar conditions Syrphus luniger Meig. laid over 50% of its eggs touching aphids and less than 1% on uninfested plants, whereas P. manicatus laid less than 5% touching aphids and over 50% on uninfested plants. Most eggs were laid close to the edge of the leaf, especially by Platycheirus species, e.g. P. scutatus Meig. which laid over 90% within 5 mm of the edge of the leaf.     

Cereal density and N-fertiliser effects on the flora and biodiversity value of arable headlands

Modern intensive farming caused pronounced changes to the European arable flora. Many species adapted to less intensive traditional farming declined severely, as did the potential of unsown arable vegetation to support higher trophic levels. To reverse these trends, various agri-environment measures were introduced. One such measure is to manage cereal headlands as conservation headlands, involving strict restrictions on pesticide and fertiliser use. An additional modification to management which could reduce crop competition and thus deliver benefits to arable plants is cereal sowing at reduced rates. However, little is known about its benefits to rare and declining arable plants, or to species of value to higher trophic levels, and whether it can be implemented without concomitant increase in undesirable weeds. We set up identical two-factorial experiments in winter wheat and spring barley, combining a nitrogen fertiliser versus no fertiliser treatment with cereal sowing at economic rates versus sowing at rates reduced by 75 %, with added sowing of a mixture of rare arable species. Both experiments also included an uncropped but cultivated control equivalent to another agri-environment measure. Our results show that reduced cereal sowing in conservation headlands can benefit rare and declining species, as well as arable plant diversity, without necessarily resulting in a concomitant increase in undesirable weeds. While such benefits tended to be larger in uncropped cultivated controls, conservation headlands have the advantage of not requiring land being taken out of production. Moreover, as shown in this study, their benefits to arable plants can be maximised by reduced sowing.     

Use of selected flowering plants in greenhouses to enhance aphidophagous hoverfly populations (Diptera: Syrphidae)

The addition of floral resources in a crop is the most commonly used conservation biological control strategy. The influence of additional floral resources on the abundance of aphidophagous syrphids has been studied in Mediterranean sweet-pepper greenhouses, in southeast Spain. Sweet alyssum and coriander were the plant species used as flowering plants, distributed in the greenhouse in several monospecific patches. In our first experiment the influence on syrphid pre-imaginal stages (larvae and pupae) was studied and adult stages were studied in a second experiment. A higher number of pre-imaginal syrphids was recorded in two replicated greenhouses where flowers were introduced, compared with two control greenhouses (without additional floral resources). To evaluate the effect on adults, 4 greenhouses were divided into 2 plots in each greenhouse and flowers were introduced in one plot per greenhouse. More hoverfly adults were observed in the plots where flowers had been introduced than in the control. The three most abundant syrphid species found were Eupeodes corollae, Episyrphus balteatus and Sphaerophoria rueppellii. Specimens from these species were dissected, and their pollen content was analysed to assess the food potential of the introduced flowers. The three syrphid species fed on pollen from both the flowering plants, as well as on sweet-pepper pollen. This conservation biological control strategy is an effective method to enhance native syrphid populations in Mediterranean sweet-pepper greenhouses.     

Body size, reproductive allocation, and maximum reproductive rate of two species of aphidophagous Coccinellidae exploiting the same resource

To test the predictions of allometric analyses of laboratory data on aphidophagous ladybirds, a study was carried out on a small [Propylea quatuordecimpunctata (L.); dry female body mass 3.7 mg] and large species (Coccinella septempunctata L.; 15.4 mg) (both Coleoptera: Coccinellidae) of predatory ladybird, which regularly exploit cereal aphids. In 2003–2006, females of C. septempunctata and in 2006 P. quatuordecimpunctata were collected at 2‐ to 5‐day intervals during the 30‐day period around the peak in cereal aphid abundance, and the number of eggs they laid in the following 24 h in the laboratory was recorded. In addition to the number of eggs laid, clutch mass, live weight, and scutum width of ovipositing females and the sizes of the clutches laid in the field were recorded. As predicted, the reproductive allocation in both species was similar. The weight of the eggs of C. septempunctata (0.20 mg) and P. quatuordecimpunctata (0.18 mg) differed little, and the proportion of body mass allocated to daily reproduction (ca. 12%) was identical in both species. In addition, the maximum number of eggs laid per day in the field by the large species was, as predicted, greater than by the small species. Interestingly, the size of the egg clutches laid by C. septempunctata in the field was similar to the daily oviposition of field‐collected adults recorded in the laboratory, whereas for P. quatuordecimpunctata it was significantly smaller. The role of morphology and physiology of ladybirds in structuring aphidophagous ladybird guilds is discussed.     

Seasonal monitoring of Drosophila suzukii and its non-crop hosts in Wuhu,Eastern China

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a serious pest that prefers fresh fruits and is native to Southeast Asia. In our study, apple cider vinegar bait traps were used to capture and monitor the population dynamics of this native pest in Wuhu City, China, from May/June 2017 to May 2018. The research was conducted at 15 locations in two fruit orchards in Wuhu. Traps caught more adults in general in a Meiling blueberry orchard than in a Xicun mixed orchard, and the highest trap counts occurred near harvest time (October). Females had more mature eggs from September to November, and the number of mature eggs declined thereafter. We found several non-crop hosts, which can provide food and reproductive resources for D. suzukii and are common in forests and field margins. By comparing the number of captured adults in the Meiling and Xicun orchards, we found that blueberry was preferred by D. suzukii among the fruits in our search. Fruit ripening times differed among crops; therefore, fly populations moved between crop and non-crop habitats during the year or had varying population dynamics on different crops in different seasons. The D. suzukii population and the number of mature eggs decreased in summer and winter but increased in spring and autumn. Drosophila suzukii had higher survival rates with blueberry than those with other fruits, and D. suzukii could use four non-crop species growing around the orchards as host plants.     

The effect of different host plants on the reproduction and longevity of Nysius natalensis

Nysius natalensis Evans (Hemiptera: Orsillidae) is a pest of sunflower in South Africa. Adults invade sunflower fields from their weedy hosts which occur inside crop fields and on surrounding headlands. The host plant suitability for survival and reproduction as well as the effect of within‐generation host switching was studied on different wild host plants and sunflower. Life history parameters used to assess host plant suitability were F₁ adult survival, pre‐oviposition period, fecundity, and longevity. Nymphs and adults were provided with stems and seeds of five host plants, viz., Amaranthus hybridus L. (Amaranthaceae), Portulaca oleracea L. (Portulacaceae), Chenopodium album L. (Chenopodiaceae), Conyza albida Spreng. (Asteraceae), and sunflower, Helianthus annuus L. (Asteraceae). Nymphs were reared on crushed seed of the five plant species. After completion of the nymphal stage, emerging adults of each host plant group were provided with seed of a different host plant species for food. Adults did not survive long on stems only and very few eggs were laid. Seeds of the host plant species were shown to be an essential source of nutrients for N. natalensis reproduction, whereas the vegetative plant parts were unsuitable. Nymphal food and host‐plant switching between the nymphal and adult stages significantly affected the pre‐oviposition period. Nymphal and adult food source also affected female longevity. The number of eggs laid was not influenced by nymphal food, but was influenced by adult food and the switch between nymphal and adult food. The comparative attractiveness of sunflower and wild host plants for oviposition was also investigated and showed that females preferred to lay eggs on wild host plants, compared with sunflower. These results may explain why N. natalensis will lay their eggs on sunflower after weeds in the vicinity are controlled, or senesce toward the end of the growing season.     

Seed inoculation with beneficial rhizobacteria affects European corn borer (Lepidoptera: Pyralidae) oviposition on maize plants

Larvae of Ostrinia nubilalis (Hübner) cause significant damage to maize ears and reduce market value of fresh sweet corn. Females rely on volatile cues to locate and oviposit preferentially on maize plants. In addition, oviposition behavior of females is influenced by soil management practices as they usually lay more eggs on maize plants grown on conventional soil than on organic soils that harbor rich microbial diversity. Since some plant growth‐promoting rhizobacteria (PGPR) are known to mediate plant health via suppression of soil pathogens and enhanced uptake of nutrients; we hypothesized that inoculation of maize seeds with PGPR will alter emission of maize volatile and reduce the attractiveness of plants to ovipositing O. nubilalis. Plants treated with the single PGPR strain Bacillus pumilus INR‐7, two PGPR mixtures (Blend‐8 or Blend‐9) or untreated plants were presented to O. nubilalis females in oviposition choice bioassays. Headspace volatile organic compounds (VOCs) from the plants were analyzed by gas chromatography–mass spectrometry (GC–MS). Ostrinia nubilalis laid significantly fewer eggs on PGPR‐treated plants compared to untreated plants. In two‐choice oviposition experiments, significantly higher numbers of eggs were laid on untreated plants compared to PGPR‐treated plants. PGPR‐treated plants emitted fewer VOCs than untreated plants which, in part, explains the relatively fewer eggs on PGPR‐treated plants. These results indicate that selected PGPR treatments can alter maize plant volatiles with important ramifications for plant‐insect interactions. The implication of this finding is discussed in the context of integrated management of soil health to improve crop resistance to biotic stressors.     

The distribution and abundance of predatory arthropods overwintering on farmland

Soil samples (0·04 m^-2) were taken from December to January in 1981-82 and 1982-83 from five crop and two non-crop habitats on farmland in Hampshire to quantify the distribution and abundance of overwintering polyphagous predatory arthropods. Total numbers of overwintering polyphagous predators were greater in field boundaries, winter-sown cereals and established grassland than in the other four habitats. Many individual species overwintered in significantly higher densities in field boundaries than in any other habitat; others predominated in woodland, grassland and winter-sown cereals. The carabids Agonum dorsale and Demetrias atricapillus, probably the most important predators of cereal aphids, overwintered almost entirely in field boundaries.     

Influence of crop background on natural enemies of aphids on Brussels sprouts

The most abundant natural enemies of aphids on Brussels sprout crops were Syrphidae, different species being attracted differentially to weedy or weed-free plots according to whether they were more host-plant-orientated (e.g. Melanostoma spp., Platycheirus spp.) and thus affected directly by the background, or more aphid-orientated (e.g. Syrphus balteatus) and so less affected by background than by aphid numbers. Oviposition by Melanostoma spp. was usually much greater in weedy sprout crops than on sprouts in bare soil, and their eggs were also very abundant on weeds. Eggs of other syrphid species were scarcer on weeds. In contrast to Melanostoma, Platycheirus spp. usually oviposted preferentially on sprouts growing in bare soil. Oviposition by S. balteatus was in response to aphid abundance and thus tended to become greater on sprouts in bare soil. Notably more adults of non-aphido-phagous Syrphidae were caught over weedy than over non-weedy Brussels sprout plants. Anthocoris nemorum nymphs and adults were very common on sprout plants and weeds in the weedy crop but were scarce on sprouts in bare soil; A. nemorum oviposited on white and yellow charlock (Raphanus raphanistrum and Sinapis arvensis) occasionally. Parasitism of Brevicoryne brassicae by Diaeretiella rapae appeared to be related to aphid numbers and was only indirectly influenced by the crop background. Field experiments with green and brown cloth backgrounds showed that some syrphids were attracted to green; A. nemorum was relatively scarce over both artificial backgrounds. It is concluded that decreased natural enemy action is partly responsible for the initially greater abundance of B. brassicae in a weed-free crop of Brussels sprouts than in a weedy crop.     

Natural Fusarium Grain Infection Level in Wheat, Barley and Oat after Early Application of Fungicides and Herbicides

In Norway, early application of fungicides against cereal leaf diseases (before Zadoks 60) is common practice amongst farmers. Whether this procedure has any effect on Fusarium infection of the mature grain has been little investigated. To evaluate effects on Fusarium grain infection, cereal grains were sampled during 1996, 1997 and 1998 from 12 field trials where early spraying against fungal diseases in spring wheat, spring barley and oats was carried out. Percentage infected grains and frequency of different Fusarium species was analysed in every grain sample. The effect of fungicides, glyphosate and postemergence herbicides on Fusarium grain infection was studied. Significant increase in Fusarium infection was detected in fungicide‐treated plots compared with untreated plots. Fusarium avenaceum and F. tricinctum were the most frequent species detected. The internal ranking of Fusarium species remained the same after spraying. No significant effects were found on the level of Fusarium infection after glyphosate treatment in autumn or herbicide treatment during the growing season.     

High effectiveness of tailored flower strips in reducing pests and crop plant damage

Providing key resources to animals may enhance both their biodiversity and the ecosystem services they provide. We examined the performance of annual flower strips targeted at the promotion of natural pest control in winter wheat. Flower strips were experimentally sown along 10 winter wheat fields across a gradient of landscape complexity (i.e. proportion non-crop area within 750 m around focal fields) and compared with 15 fields with wheat control strips. We found strong reductions in cereal leaf beetle (CLB) density (larvae: 40%; adults of the second generation: 53%) and plant damage caused by CLB (61%) in fields with flower strips compared with control fields. Natural enemies of CLB were strongly increased in flower strips and in part also in adjacent wheat fields. Flower strip effects on natural enemies, pests and crop damage were largely independent of landscape complexity (8–75% non-crop area). Our study demonstrates a high effectiveness of annual flower strips in promoting pest control, reducing CLB pest levels below the economic threshold. Hence, the studied flower strip offers a viable alternative to insecticides. This highlights the high potential of tailored agri-environment schemes to contribute to ecological intensification and may encourage more farmers to adopt such schemes.     

Ecological relationships between non-cultivated plants and insect predators in agroecosystems: the case of Dittrichia viscosa (Asteraceae) and Macrolophus melanotoma (Hemiptera: Miridae)

Species of the genus Macrolophus (Hemiptera: Miridae) are thought to be effective predators in reducing the numbers of several pests in vegetable crops. These predators are omnivorous as in addition to prey they also utilize plant sap for growth and development. Populations of these predators build in non-crop host plants and provide inoculum that augments natural control of insect pests in adjacent crops. However, to enhance their effectiveness in crops requires knowledge of their trophic relationships with host plants. In this study, the ecological relationships between the predator Macrolophus melanotoma (Costa) ( =  M. caliginosus Wagner) and its most important natural host plant Dittrichia viscosa L. (W. Greuter) (Asteraceae) were investigated in the laboratory and in field studies. A 2-year field study of M. melanotoma populations on D. viscosa was made using the percentage of plants infested by C. inulae as a measure of aphid prey abundance. The field studies revealed that M. melanotoma populations were present throughout the year on D. viscosa reaching highest numbers in June and July despite very low levels of aphid infested plants. Laboratory life table studies were used to compare the survival and reproduction of the predator on D. viscosa leaves alone and leaves plus aphid prey (Capitophorus inulae (Passerini)). Predators reared on D. viscosa leaves plus aphid prey had an average developmental time of 16.73 days, fecundity was 69.55 eggs/female and the intrinsic rate of population increase was 0.0614/day. When fed only leaves, the developmental time was 21.13 days, fecundity was 10.80 eggs/female and the intrinsic rate of population increase was 0.0229/day. The results of the two studies suggest an important role for D. viscosa in conserving and augmenting M. melanotoma in agro ecosystems, and in the development of natural control augmentation strategies in vegetable crops.     

Microorganisms associated with the retting of flax treated with the herbicide glyphosate

Greater numbers of fungi were isolated from stems of flax following treatment with the herbicide glyphosate than from untreated stems although there was also a general increase in numbers with time. The fungal genera isolated were the same from both treated and untreated plants, the most common being Cladosporium, Aureobasidium, Epicoccum and Botrytis with Cladosporium being predominant. Populations of bacteria were generally not enhanced after glyphosate treatment. Partial dew-retting of crops resulted in the reduction in numbers of Cladosporium compared with conventionally-treated flax. The increase in numbers of fungi was associated with an increase in retting. Overretting also occurred, particularly in discrete pale areas on the stem. These were associated with colonisation by Botrytis cinerea and the tensile strength of fibres from these areas was 15 times weaker than from surrounding darker areas of the stem. Light microscopy showed death of cells after glyphosate application, followed by invasion and degradation of the epidermis and cortex by fungi and other microorganisms. Fibre bundles were partially dissociated but the individual fibres remained largely intact as did the xylem and medulla.     

Outdoor evaluation of herbicide resistant strains of Anabaena variabilis as biofertilizer for rice plants

Application of diazotrophic cyanobacteria, Anabaena variabilis, as biofertilizer for rice cultivation has a beneficial effect on crop productivity and maintenance of soil fertility. However, periodic applications of herbicides used to obtain high crop productivity are not only detrimental to weeds but to biofertilizer strains of cyanobacteria also. Therefore, research was undertaken to isolate four herbicide resistant strains (Arozin-R, Alachlor-R, Butachlor-R and 2,4-D-R) and a multiple herbicide resistant strain (MHR) of natural isolates of A. variabilis exhibiting resistance against these common rice field herbicides. The outdoor survivability of mutant strains and the productivity of rice crop (IR-36) were evaluated by inoculating the wild type and herbicide resistant mutant strains of A. variabilis in the presence and absence of recommended field dosages of test herbicides. No difference in survival and biofertilizer potentials of the herbicide resistant strains was observed in herbicide treated or in untreated conditions. Highest survivability (87%) was exhibited by MHR relative to other mutants. Highest growth and grain yield (76%) were recorded in plants treated with MHR as compared to uninoculated control rice plants. In conclusion, the mutant strains of A. variabilis had stable resistance to herbicides under outdoor conditions in flooded soils. Not only did the herbicide resistance strains increase growth of rice relative to the uninoculated pots, they were more beneficial for rice growth than the wild type strain. Responsible Editor: Richard W. Bell.     

The effects of organic and conventional fertilizers on cereal aphids and their natural enemies

• 1 Aphids are important pests of spring cereals and their abundance and the impact of their natural enemies may be influenced by fertilizer regime.
• 2 We conducted a 2‐year field study investigating the effects of organic slow‐release and conventional fertilizers on cereal aphids, hymenopteran parasitoids and syrphid predators and considered how the effects of fertilizers on barley morphology and colour might influence these species.
• 3 Barley yield was greater in conventionally fertilized pots. Barley morphology was also affected by treatment: vegetative growth was greater under conventional treatments. Barley receiving organic fertilizers or no fertilizer was visually more attractive to aphids compared with plants receiving conventional fertilizers.
• 4 Aphids were more abundant in conventionally fertilized barley but the reason for this increased abundance was species specific. Metopolophium dirhodum was responding to fertilizer effects on plant morphology, whereas Rhopalosiphum padi was sensitive to the temporal availability of nutrients.
• 5 Syrphid eggs were more numerous in conventionally fertilized pots, whereas the response of parasitoids appeared to be dependent on the abundance of aphids, although the number of parasitoid mummies was low in both years.
• 6 This research shows that the fertilizer treatment used can affect numerous characteristics of plant growth and colour, which can then influence higher trophic levels. This knowledge might be used to make more informed fertilizer application choices.