Host plan preferences of Oscinella spp. (Diptera: Chloropidae) in the laboratory

The oviposition preferences of Oscinella frit, O. vastator, O. nitidissima, O. albiseta andO. nigerrima for differenct Gramineae were investigated in the laboratory. O. frit, laid most eggs on oats, Lolium multiflorum and Festuca rubra, relatively few eggs were laid on barley and virtually none on Dactylis glomerata None of the other Osinella species oviposted on cereals. Of the other species, O. vastator appeared to be the most polyphagous and the preferred hosts were L. multiflorum, Lolium perenne and Festuca pratensis; few eggs were laid on either F. rubra, Agrostis tenuis or Poa pratensis. The host ranges of the remaining species were much more limited. Although a few eggs were laid by O. nitidissima on Lolium, the preferred host was A. tenuis. Oscinella albiseta oviposited only on D. glomerata whilst nearly all the eggs laid by O. nigerrima were deposited on shoots of Arrhenatherum elatius. The distribution of eggs by O. frit on L. multiflorum and A. tenuis was different from that on oats; on grasses most eggs were laid inside withered leaf sheaths whereas on oats most were deposited inside the coleoptile. The oviposition sites of O. nitidissima, O. nigerrima and O. albiseta on their respective host grasses were similar to those of O. frit on grasses. O. frit laid most eggs on grasses which were at the five-leaf stage and tailoring.     

The invasion and development of the cereal cyst-nematode, Heterodera avenae in the roots of autumn-and spring-sown cereals

Observations were made at 2 or 4 wk intervals from December to harvest on all stages of Heterodera avenae in winter oats growing on infested land. Second-stage larvae were present in all soil samples except on 5 and 20 July. Invasion and development of larvae was slow during winter. The nodal and seminal roots of winter oats were both heavily invaded by the nematode; larvae which invaded seminal roots tended to become male whereas those in nodal roots tended to become female. There was a small second invasion in August. Females were first observed on the roots of winter oats on 17 May, 214 days after the crop was sown and 62 days after the first fourth-stage larva was observed. The nodal roots of spring barley contained few H. avenae larvae whereas these roots were heavily invaded in winter wheat and oats. In spring barley the nodal roots were developing in June and July when few second-stage larvae were in the soil whereas in winter oats and wheat the nodal roots were growing rapidly in April when larvae were most numerous, and so were heavily invaded.     

The effect of barley yellow dwarf virus on field populations of the cereal aphids, Sitobion avenae and Metopolophium dirhodum

The numbers of cereal aphids, especially Metopolophium dirhodum in 1979, and Sitobion avenae in 1980, were significantly increased on BYDV infected wheat and oats in 1979, and wheat, barley and oats in 1980. The differences were probably caused by attraction of alates of each species to virus infected plants which had changed colour as a result of their infection. Significantly more alates of M. dirhodum were found on virus infected oats in 1979, and of S. avenae on oats and barley in 1980, although not on wheat in either year. probably because the colour contrast in wheat was less intense than in the other crops. Flight chamber experiments with alates of both species confirmed their visual attraction to virus-infected leaves. The interaction between virus, vector and host plants is discussed with reference to the ecology of virus spread.     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

Diamondback moth females oviposit more on plants infested by non‐parasitised than by parasitised conspecifics

Abstract 1. When offered a choice, female diamondback moths (Plutella xylostella) oviposited more eggs on plants with non‐parasitised conspecific larvae than on plants with parasitised larvae. 2. The leaf area consumed by parasitised larvae was significantly lower than that by non‐parasitised larvae. However, this quantitative difference in larval damage did not explain the female’s ability to discriminate between plants with parasitised and non‐parasitised larvae, as females showed an equal oviposition preference for plants infested by higher or lower densities of non‐parasitised larvae. 3. Pupal weight and duration of the larval stage of P. xylostella were independent of whether larvae were reared on plants that were previously infested by either non‐parasitised or parasitised larvae. 4. The larval parasitoid Cotesia vestalis did not distinguish between plants infested by non‐parasitised larvae and plants infested by larvae that had already been parasitised by conspecific wasps. 5. Based on these data, it can be concluded that the moth oviposition preference for plants infested by non‐parasitised conspecifics relative to plants infested by parasitised conspecifics was not explained by plant quality or by the attractiveness of plants towards wasps. It is hypothesised that one of the reasons for this preference is avoidance of plants where a relatively high risk of parasitism is expected due to the emergence of parasitoids from the parasitised host larvae.     

Comparison of the potential rate of population increase of brown and green color morphs of Sitobion avenae (Homoptera: Aphididae) on barley infected and uninfected with Barley yellow dwarf virus

Life tables of brown and green color morphs of the English grain aphid, Sitobion avenae (Fabricius) reared on barley under laboratory conditions at 20 ± 1°C, 65% ± 5% relative humidity and a photoperiod of 16 : 8 h (L : D) were compared. The plants were either: (i) infected with the Barley yellow dwarf virus (BYDV); (ii) not infected with virus but previously infested with aphids; or (iii) healthy barley plants, which were not previously infested with aphids. Generally, both color morphs of S. avenae performed significantly better when fed on BYDV‐infected plants than on plants that were virus free but had either not been or had been previously infested with aphids. Furthermore, when fed on BYDV‐infected plants, green S. avenae developed significantly faster and had a significantly shorter reproductive period than the brown color morph. There were no significant differences in this respect between the two color morphs of S. avenae when they were reared on virus‐free plants that either had been or not been previously infested with aphids. These results indicate that barley infected with BYDV is a more favorable host plant than uninfected barley for both the color morphs of S. avenae tested, particularly the green color morph.     

Effects of long-term barley monoculture on plant-affecting soil microbiota

Effects of soil microbiota on shoot and root growth of barley were tested in a greenhouse tube-growing system. Tubes were filled with a mixture of pure sand and various percentages of soils sampled from plots in three long-term field experiments measuring effects of various crop rotations on yield. Using 3% soil in the sand-soil mixture, shoot dry weight of barley test plants was reduced by about 35% and root depth by about 40% in soils from monoculture plots as compared to soils from crop-rotation plots. Typical root symptoms on poorly growing barley plants started as distinct dark-brown zones which then rapidly spread over the whole root system until the root tips ceased to grow. As tested in one experiment, the barley monoculture soil also affected wheat and oats, but to a lesser degree than it did barley. Most of the depressing effects of monoculture soil on barley were eliminated when soil samples were treated with metalaxyl or heated to 65°C for 2 hours. A Pythium sp. frequently isolated from barley roots showing typical symptoms affected barley, wheat and oats in the same way as did barley monoculture soil.     

Lacewings (Chrysopidae,Neuroptera) in cereal agrocenoses of the forest-steppe of Western Siberia

Twelve species of lacewings: Chrysopa altaica, Ch. commata, Ch. perplexa, Ch. phyllochroma, Ch. dasyptera, Ch. carnea, Ch. formosa, Ch. intima, Ch. perla, Ch. prasina, Ch. septempunctata, and Nineta inpunctata were found in cereal agroecosystems of the forest-steppe zone of Western Siberia. The dominant species were Ch. carnea and Ch. phyllochroma. The biological characteristics, seasonal dynamics of the abundance of lacewings in the agrocenoses of winter rye, spring wheat, and oats are given. The abundance of larval and adult lacewings in the spring wheat agrocenosis was not affected by the level of chemicalization (upon condition of the rational use of insecticides), tillage variant, and predecessor crop. In the years when the density of lacewings was low, no differences in their population were found between the agrocenoses of wheat (after fallow), winter rye, oats, vetch-oats, canola, barley, and barley with melilot. In the years characterized by relatively high abundance of lacewings, they occurred more frequently in the crop rotations with wheat after fallow and with oats. These plants were settled by cereal aphids to the greatest extent. In all the years studied, the density of lacewings on alfalfa was 2–2.8 times as great as that on wheat after fallow.     

Effects of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) damage on sugarcane yield

Feeding by lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae), larvae on sugarcane (a complex hybrid of Saccharum spp.) causes leaf damage, dead hearts, and dead plants that can result in stand and yield loss. A 2-yr greenhouse experiment was conducted to examine sugarcane variety and plant age-specific feeding responses to E. lignosellus. Plants growing from single-eye setts of three varieties were exposed to a single generation of E. lignosellus larvae beginning at the three-, five-, and seven-leaf stages. Results indicated that the physical damage and resulting yield loss of plants attacked by E. lignosellus larvae were dependent on the variety and leaf stage at which they were infested. Significantly more plant damage was observed in all three varieties when infested at the three- than at the seven-leaf stage. Larvae caused significantly more plant damage and reduced yield in CP 89-2143 than in CP 78-1628. Tiller production increased in CP78-1628 and CP 88-1762 when infested at the three-leaf stage, whereas tiller production, biomass and sugar yield decreased in CP 89-2143 when infested at all leaf stages, compared with the untreated control. There was no reduction in yield when CP 78-1628 was infested at the three- or five-leaf stages. Biomass was reduced in CP 88-1762 when plants were infested at any of the leaf stages, but sugar yield was reduced only when infested at the seven-leaf stage. These results indicate that compensation in response to E. lignosellus damage was variety dependent and declined with the delay in infestation time.     

Wheat stem sawfly‐infested plants benefit from parasitism of the herbivorous larvae

1 Parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck and their herbivorous host the wheat stem sawfly Cephus cinctus Norton, a pest of wheat Triticum aestivum, were investigated for yield in T. aestivum grown in the field. 2 Wheat stem sawfly‐infested stems had a higher yield potential than uninfested stems. However, final reproductive output was not significantly different between ears on infested stems that supported complete larval development compared with ears on uninfested stems. 3 Stems containing parasitized larvae and stems containing larvae that died before completing their development had a higher mean number of seeds and seed weight, when accounting for number of fertile spikelets of each ear, than either infested with live larvae and uninfested stems. 4 The results obtained suggest that larval feeding prevented infested stems from attaining their yield potential, and that the negative impact of the pest on wheat yield was reduced when late instar sawfly larvae were parasitized. Even though some feeding occurs before parasitism, this early damage has a comparatively low impact on yield. 5 This is the first study to show a yield benefit and enhanced plant fitness due to the wheat stem sawfly parasitoids B. cephi and B. lissogaster. This results from the maintenance of increased seed number and seed weight in the higher yielding stems that are preferentially infested by this pest.     

Efficacy of imidacloprid for control of cereal leaf beetle (Coleoptera: Chrysomelidae) in barley

The toxicity of imidacloprid to the cereal leaf beetle, Oulema melanopus (L.), was measured under laboratory and field conditions. Insect mortality and plant damage were determined from artificial and natural infestations of O. melanopus applied to various growth stages of barley. All rates of imidacloprid formulated and applied as a seed treatment caused >90% mortality to cereal leaf beetle larvae when barley was infested with eggs at the 4-leaf stage, but were ineffective when barley was infested with eggs at the early tillering or flag-leaf stages of barley. This window of susceptibility influenced results obtained in field trials where peak larval emergence did not occur until the early tillering stage of barley. The resulting mortality in plants from treated seeds never exceeded 40% in the field. Foliar imidacloprid, however, caused >90% mortality in the field, and may be another option in the management of the cereal leaf beetle.     

Can herbivore‐induced plant volatiles inform predatory insect about the most suitable stage of its prey?

The leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) is a specialist herbivore, all of whose mobile stages feed on the leaves of salicaceous plants. Both the larval and adult stages of the ladybird Aiolocaria hexaspilota (Coleoptera: Coccinellidae) are dominant natural enemies of the larvae of the leaf beetle. To clarify the role of plant volatiles in prey‐finding behaviour of A. hexaspilota, the olfactory responses of the ladybird in a Y‐tube olfactometer are studied. The ladybird adults show no preference for willow plants Salix eriocarpa that are infested by leaf beetle adults (nonprey) over that for intact plants but move more to the willow plants infested by leaf beetle larvae (prey) than to intact plants. Moreover, ladybird larvae show no preference for willow plants infested by leaf beetle larvae or adults over intact plants. Using gas chromatography‐mass spectrometry, six volatile compounds are released in larger amounts in the headspace of willow plants infested by leaf beetle larvae than in the headspace of willow plants infested by leaf beetle adults. In addition, the total amount of volatiles emitted from willow plants that are either intact or infested by leaf beetle adults is much smaller than that from willow plants infested by leaf beetle larvae. These results indicate that volatiles from S. eriocarpa infested by P. versicolora inform A. hexaspilota adults about the presence of the most suitable stage of their prey, whereas A. hexaspilota larvae do not use such information.     

Seasonal changes in the free amino acids of oat and barley phloem sap in relation to plant growth stage and growth of Rhopalosiphum padi

The concentrations and composition of free amino acids in phloem sap from two cultivars of oats and barley, both susceptible to the aphid Rhopalosiphum padi, were determined by means of high performance liquid chromatography. Sap was collected from excised aphid stylets at three developmental stages (seedlings, tillering plants and plants undergoing stem elongation) from plants given or not given fertiliser and grown outdoors. In connection, the growth of individual R. padi nymphs was estimated at the same phenological stages on plants grown in the greenhouse. The content of free amino acids was consistently higher in seedlings than in plants at the early tillering stage. Only in seedlings did the addition of fertiliser increase amino acid levels. Barley phloem sap contained more free amino acids than that of oats when fertiliser was added and at later developmental stages. Phloem sap of oats and barley showed similar patterns in their composition of free amino acids at the seedling stage, but as the plants grew older the patterns became increasingly different. Plants given fertiliser had higher amounts of dicarboxylic amino acids (glutamic and aspartic acid) than unfertilised plants. The concentrations of γ-amino butyric acid, glycine, histidine, and methionine were very low in all treatments. The relative growth rates of R. padi nymphs were low when amino acid content was low and vice versa. The results are discussed in relation to host plant suitability and plant resistance mechanisms.     

Studies on the horizontal migration of dipterous stem borers (Oscinella spp.) in direct drilled Italian ryegrass

The distance stem boring dipterous larvae e.g. Oscinella frit L. migrate in direct drilled Italian ryegrass (Lolium multiflorum) was investigated. First, adjacent contrasting swards of Italian ryegrass or Cocksfoot (Dactylis glomerata) were grown which were, respectively, expected to be either infected with large populations of larvae or likely to be free of larvae. Sampling revealed that these expectations were realised. Swards were then desiccated by herbicide, and subsequently direct drilled with Italian ryegrass. Over 50% of the larvae in original, infested part of the sward migrated to infest tillers of the newly sown ares. The distance larvae migrated was gauged by assessing how far they were found from the perimeter of a previously uninfested area which had been reseeded. Most larvae migrated 20 cm or less, but a small proportion appeared to migrate several metres, apparently passing many suitable host tillers as they did so.deceased September 1989     

Biology,host preferences and fitness of <Emphasis Type="Italic">Oulema melanopus</Emphasis> (Coleoptera: Chrysomelidae), a recent invasive pest in Western Canada

The developmental parameters and fitness of a recent invasive insect pest of cereals in western Canada, the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae), were compared on live plants and excised leaves of commercial cultivars of potential cereal hosts including wheat (winter and spring), oats, barley, corn, rye and triticale. Host preference and utilization within the fundamental host range of O. melanopus differed. The biological parameters differed significantly when the larvae were reared on excised tissues versus on live host plants. In both studies, wheat (winter and spring), oat (cv. Morgan) and barley were the most preferred hosts in terms of development, survivorship, adult weights and fecundity. Prolonged development with low fitness gains was noted on corn. Although the development on hosts such as rye and triticale was prolonged and adult fitness was low, the survivorship was high on these hosts. Hence, these crops can act as secondary hosts for the beetle in its new eco-region. Larvae fed foliage of Waldern, a local oat cultivar, had increased developmental time and lower survivorship compared with other cereal hosts. Despite differences in fitness gains among hosts, similar numbers of eggs were laid on all hosts. Hence, the oviposition choice of O. melanopus may not be driven by fitness gains alone and it may indicate adaptive strategy to hosts in newer environments.     

Bionomics of aphids reared on cereals and some Gramineae

In controlled temperature, light and relative humidity, Metopolophium dirhodum and Sitobion avenae multiplied more on young Proctor barley than on Blenda oats, and less on Cappelle wheat. Rhopalosiphum padi increased in number fastest on barley and slowest on oats. More survived, and generation lengths seemed shorter, on barley for M. dirhodum and S. avenae and on wheat for R. padi. Tests with young cereals outdoors generally agreed with those in controlled conditions. On mature plants, there were more M. dirhodum on barley, more R. padi on wheat and more S. avenae on oats than on the other cereals. Given a free choice in large cages outdoors, most aphids were found on barley. When allowed to choose between grasses, more M. dirhodum were on Dactylis glomerata, Poa pratensis and Festuca pratensis, more R. padi on Lolium perenne and F. pratensis, and more S. avenae on D. glomerata and L. perenne. Most aphids of all species combined were on F. pratensis, Lolium and Phleum, and fewest on Festuca rubra and Holcus mollis.     

Host location by the fruit fly parasitoid Diachasmimorpha krausii: role of fruit fly species,life stage and host plant

• 1 Diachasmimorpha krausii is a braconid parasitoid of larval tephritid fruit flies, which feed cryptically within host fruit. At the ovipositor probing stage, the wasp cannot discriminate between hosts that are physiologically suitable or unsuitable for offspring development and must use other cues to locate suitable hosts.
• 2 To identify the cues used by the parasitoid to find suitable hosts, we offered, to free flying wasps, different combinations of three fruit fly species (Bactrocera tryoni, Bactrocera cacuminata, Bactrocera cucumis), different life stages of those flies (adults and larvae) and different host plants (Solanum lycopersicon, Solanum mauritianum, Cucurbita pepo). In the laboratory, the wasp will readily oviposit into larvae of all three flies but successfully develops only in B. tryoni. Bactrocera tryoni commonly infests S. lycopersicon (tomato), rarely S. mauritianum (wild tobacco) but never C. pepo (zucchini). The latter two plant species are common hosts for B. cacuminata and B. cucumis, respectively.
• 3 The parasitoid showed little or no response to uninfested plants of any of the test species. The presence of adult B. tryoni, however, increased parasitoid residency time on uninfested tomato.
• 4 When the three fruit types were all infested with larvae, parasitoid response was strongest to tomato, regardless of whether the larvae were physiologically suitable or unsuitable for offspring development. By contrast, zucchini was rarely visited by the wasp, even when infested with B. tryoni larvae.
• 5 Wild tobacco was infrequently visited when infested with B. cacuminata larvae but was more frequently visited, with greater parasitoid residency time and probing, when adult flies (either B. cacuminata or B. tryoni) were also present.
• 6 We conclude that herbivore‐induced, nonspecific host fruit wound volatiles were the major cue used by foraging D. krausii. Although positive orientation to infested host plants is well known from previous studies on opiine braconids, the failure of the wasp to orientate to some plants even when infested with physiologically suitable larvae, and the secondary role played by adult fruit flies in wasp host searching, are newly‐identified mechanisms that may aid parasitoid host location in environments where both physiologically suitable and unsuitable hosts occur.

     

Control of stem nematode, Ditylenchus dipsaci Coat race'), by aldicarb and resistant crop plants

Aldicarb at 1.5 or 4.5 kg ha^-1 applied around the seeds at sowing greatly increased the yields of a range of crop plants in soil heavily infested with stem nematode (Ditylenchus dipsaci, ‘oat race’). Yield responses could be largely explained by stem nematode control in onions, field beans, peas, Manod oats and maize but not in wheat, Maris Tabard oats, lucerne or sugar beet. Aldicarb lessened stem nematode attacks and lessened stem nematode increase in host plants. The supposedly resistant oat Manod was susceptible, whereas Maris Tabard was resistant, as were Peniarth, Pennal, Panema, Pennant, Maris Quest and Milford, whose resistances derive from Grey Winter. Maris Tabard outyielded resistant Panema, Peniarth and Pennal and susceptible Maris Osprey and Manod on infested soil. ‘Tulip root’ is not an infallible guide to susceptibility of oats to stem nematode. We advocate using a mixture of nematode populations in breeding for resistance to stem nematodes.     

A COMPARATIVE STUDY OF THE GROWTH OF WILD OATS (AVENA FATUA L. AND A. LUDOVICIANA DUR.) AND OF CULTIVATED CEREALS WITH VARIED NITROGEN SUPPLY

Growth analysis of wild oats ( Avena fatua and A. ludoviciana ) grown in pots with different levels of nitrogen supply showed many similarities to spring barley, winter oats and winter wheat.
Small differences that could affect competition between wild oats and cereals occurred mainly in the seedlings. Wild oat seedlings were smaller than the corresponding cultivated cereals in total dry weight, total nitrogen content, leaf area and number of shoots. However, very young wild oat plants had higher net assimilation rates than the cultivated cereals and soon caught up and passed them. The difference in net assimilation rate did not persist, and in the later stages of growth differences in dry-matter production depended mainly on differences in leaf area. Another important difference between wild oats and cultivated cereals was that 98–100% of the wild oat seeds and none of the crop seeds were dormant 2 months after harvest.
Ear emergence in wild oats spread over a longer period, the range of ear heights was greater and the tallest ears were taller than in the corresponding cultivated cereals. Assimilation in the ear appeared to account for less of the total dry matter of the plants of wild and cultivated oats than of wheat. The wild oats produced more seeds per plant than the cultivated cereals, but the 1000-grain weight, and hence the total dry weight of seeds, was lower in the weeds than in the crop.
Addition of nitrogen to the soil affected the growth of the wild oats in the same ways as the cultivated cereals; they took up the same amount of nitrogen per plant as winter oats and winter wheat but more than spring barley.
It is concluded that wild oats are most susceptible in the seedling stage to competition from the crop and that nitrogenous fertilizer applied to an infested field is unlikely to alter the balance between the yields of crop and of wild oats.     

A study on common bean cultivars to identify sources of resistance against the black bean aphid,Aphis fabae Scopoli (Hemiptera: Aphididae)

Black bean aphid is an important common bean pest in the world. Aphids damage crops both directly by their feeding and by spreading viruses. Also, they indirectly damages with excretion honeydew and smokes moulds growth through some physiological processes and transmission of viruses. Resistant cultivars application is the main strategy to control Aphis fabae Scopoli. In this experiment, different lines and cultivars were infested with five wingless adult aphids. After 7 and 14?days, plants were evaluated and aphid population was counted and recorded. After 45?days when plants reached to the flowering stage, test was repeated. Result showed that there was a significant difference among cultivars in number of adult aphid in two-leaf stage. Most of the number of adult at the first week in two-leaf stage observed on Goynok cultivar that had significant difference to other lines and cultivars. Number of adults and nymphs among the line and cultivar at flowering stage did not show significant difference. Number of deployed aphids after two weeks was significantly higher than the first week that observed in all cultivars. Totally, the most resistant cultivar was Sayad and the most susceptible cultivar was Goynok.