摘要:

SUMMARYSorghum midge,Contarinia sorghicolaCoq. (Diptera: Cecidomyiidae) is an important pest of grain sorghum, and host‐plant resistance is one of the most effective means of controlling this pest. We studied the antibiosis mechanism of resistance in sorghum toC. sorghicolain a diverse array of midge‐resistant and midge‐susceptible genotypes. Data were recorded on adult emergence, postembryonic developmental period, number of mature eggs in the ovary, fecundity, larval survival from artificially implanted eggs; and the tannins, soluble sugars, and protein content of 10‐day old and mature grains during the 1982‐91 rainy and post‐rainy seasons.Adult emergence was significantly lower in the midge‐resistant genotypes compared with the susceptible controls. Initiation of adult emergence was delayed by 4–8 days on DJ 6514, IS 8571, IS 9807, IS 10712, IS 19474, IS 19512, ICSV 830 and ICSV 197. Postembryonic developmental period was prolonged on DJ 6514, IS 15107, IS 3461, IS 7005, IS 19474, ICSV 831 and ICSV 197. However, the delay in adult emergence or the extended developmental period was not observed during the post‐rainy season in some genotypes. These differences in the expression of antibiosis to midge in resistant genotypes over seasons may be attributed to the effect of environmental conditions on the insect development and chemical composition of sorghum grain. Amounts of tannins and proteins were generally greater in the midge‐resistant lines compared with the susceptible ones (except tannins in DJ 6514) while the soluble sugars were low in the midge‐resistant lines (except TAM 2566). These differences in chemical composition of the grain between genotypes and variations over seasons have been discussed in relation to the expression of antibiosis mechanism of resistance to the sorghum midge. Antibiosis to sorghum midge was also evident in terms of smaller size of larvae, lower number of eggs in the ovary, reduced fecundity, and larval survival. Midge‐resistant lines have diverse effects on the biology of this insect. Antibiosis along with other components of resistance can be used to develop cultivars with stable res

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04920.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYRecords of wheat bulb fly egg(Delia coarctata)population densities in fields sampled throughout East Anglia in the autumns of 1953–1990 are presented. In descending order of risk, fallow, potato, pea (mainly vining), sugar beet and oilseed rape are the main crops preceding wheat or barley which attract oviposition. A declining trend of egg populations observed over the study period may be associated with climatic changes as well as with the elimination of fallow in the rotation and the dramatic increase in the use of insecticides against the pest. Negative correlations(P<0.05) in mean annual egg numbers were found with departures from average of July temperature and January air or soil temperature; positive correlations (P<0.05) with departure from average of August raindays. Stepwise regression analysis was used to identify the most important relationships of meteorological variables with mean annual egg numbers, or the proportion of fields sampled with egg numbers in excess of the action threshold of 2.5 million eggs/ha. Up to 59% of the variation in the annual proportion of fields above threshold was accounted for in a regression equation using departures from average of July temperature, August raindays and the percentage of average of October (preceding year) rainfall. Estimated mean annual egg populations and the proportion of fields above threshold showed a good fit with the observed values. The findings are discussed and compared with previous work. The forecasting model may be readily incorporated as a regional risk‐prediction component of a knowledge‐based system for the management of wheat bulb fly control. Regional forecasts of wheat bulb fly oviposition from this work should be tested and modified as necessary according to experience or changing climatic or agricultural fa

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04921.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYThe abundance and species composition of syrphid adults in herbicide‐treated and untreated headlands was recorded in a replicated within‐field experiment conducted over a two‐year period. The highest numbers of the most abundant syrphid species,Episyrphus balteatus,were recorded in the untreated headland strips. Analysis of the behaviour of the adult flies showed that they were retained in the untreated strips because they were foraging on the flowering non‐crop plants.The distribution of syrphid eggs between herbicide treated and untreated headland replicates was examined. A significant positive relationship between the numbers of eggs per aphid and weed density was detected during June in the second year of the study. This is in part attributed to the tendency ofMelanostomafemales to oviposit on non‐crop plants.The implications of the implementation of a modified herbicide regime in the headlands of cereal fields for the biological control of cereal aphids by syrphid larvae is

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04922.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYInfestation of banana and plantain suckers by nematodes(Pratylenchus good‐eyi, Radopholus similisandHelicotylenchus multicinctus)and weevils(Cosmopolites sordidus)increased with time from establishment in a field of eight different cultivars. There was a strong association between nematode and weevil infestation; suckers infested with nematodes were more than four times more likely to be infected by weevil than suckers without nematodes. Weevil damage, measured by percentage coefficient of infestation (PCI) at harvest of the bunch, was higher on a plantain (cv. Gonja) and on an east African highland cooking banana (cv. Lusumba) than on the sweet and multi‐purpose cultivars. There was a correlation between numbers of male weevils caught in a plot and the mean PCI measured in the plot, but no correlation with female numb

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04923.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYThree extraction methods were compared for the recovery of bibionid larvae from grassland soil samples. Only wet‐sieving followed by flotation in a saturated salt solution yielded bibionids. No larvae were recovered either with modified Tullgren funnels or by slow immersion of soil cores into a saturated salt solution. The efficiency with which larval bibionid populations can be estimated is poor. Generally, smaller cores yielded more larvae per volume of soil. Most bibionids were found in the top 4 cm of soil. It is concluded that 10 cm diameter and 6–8 cm deep soil cores are an acceptable compromise between efficiency and sampling effort but sample size will largely be determined by the resources available for processing of samp

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04924.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYAll life stages of the western flower thrips(Frankliniella occidentalisPergande) were tested for their response to the fumigant methyl bromide and dose response curves were established. Pseudo‐pupae were the most tolerant stage with a calculated LD99 of 53.1 mg litre“1h at 15oC with a gas concentration of 13.5 mg litre”1, but no survivors were found in any test above a concentration time product of 40 mg litre“1h. Standard 4 h fumigations achieving a CTP of 54 mg litre”1h that are used to control other pests are therefore likely to give very high levels of control of western flow

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04925.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYFungus gnat adults transportedFusarium oxysporumf.sp.radicis‐lycopersicifrom Petri dish culture and infected host plants to the roots and hypocotyls of healthy tomato and bean plants. The source of the fungus did not affect the ability of fungus gnats to transport the fungus to healthy hosts. The presence of fungus gnat larvae in media in which young tomato plants were grown did not increase the incidence of plant infection by the pathogen. Fungus gnat adults appear to aid in the dissemination ofF. oxysporumf.sp.radicis‐lycopers

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04926.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYComponents of partial resistance [disease incidence (DI), infection frequency (IF), latent period (LP), spores per lesion (SPL)] were assessed on glasshouse‐grown barley seedlings following inoculation with spore suspensions ofRhynchosporium secalisat growth stage 12 (Zadoks, Chang&Konzak, 1974). Four experiments were carried out at different times during 1988. Three spring barley cultivars [two from Cyprus (cvs Kantara and Athenais) and one from the UK (cv. Triumph)] were used in the first three experiments. In the fourth experiment eight additional UK cultivars with NIAB resistance ratings ranging from 3 to 9 were used. Two races ofR. secaliswere used in the first three experiments and three in the fourth.The three cultivars, Kantara, Athenais and Triumph, were examined in all four experiments and significant differences detected for virtually all components of partial resistance in each. Differences, however, were often small and ranking of cultivars varied in different experiments. The greater susceptibility of cv. Kantara compared to cv. Athenais, observed under field conditions in Cyprus, would not be anticipated from the small differences in components of partial resistance observed in these experiments, but, for these cultivars, the possibility of a marked genotype x environment interaction cannot be discounted.Mean values for the components of partial resistance differed in the four experiments. LP was correlated with mean glasshouse temperature from inoculation to the onset of sporulation but differences in IF and SPL were not correlated with temperature. For these components, light quality and/or duration appeared to be more important.Overall, there were no differences between races but significant race X cultivar interactions were observed in two experiments.In the fourth experiment, examining 11 cultivars, there were significant differences between cultivars for all components of partial resistance. IF and LP were correlated but neither of these components was correlated with SPL indicating independent control of this latter component. Both IF and LP were correlated with field performance (NIAB ratings) but there was no correlation with SPL. However, combining IF with mean values of SPL restricted to the 5 days following the end of the LP, produced the best correlation(r= 0.92) with NIAB ratings.Problems of assessing components of partial resistance and possible means of improving assessments are discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04927.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYThe effect of root temperature on growth and yield of rockwool‐grown tomato plants infected withPhytophthora cryptogeawas investigated. Measurements of shoot and root growth were taken at high (25oC) and low (15oC) root temperatures during the generative phase of growth. The growth of roots of healthy andP. cryptogea‐infectedtomato plants in rockwool blocks was higher in plants grown with roots at 25oC than at 15oC after 60 days and a similar effect was found in slabs after 98 days. Under sub‐optimal conditions for growth the disease became severe when root temperatures were low. Growth of roots was greatest when roots were maintained at a high temperature in combination with an ambient air temperature ofc.15oC and the response was greater in cv. Counter than cvs Calypso and Marathon. Water‐soluble carbohydrates of roots were higher in those produced in blocks than slabs and were reduced by infection compared to healthy plants with roots at 15oC and 25oC. Reduced transpiration rates were found 17 days after inoculation in symptomless plants grown at a root temperature of 25oC. Infection, regardless of the temperature of the roots or cultivar, led to reduced stem growth. The plants grown at 25oC were taller than those with a root temperature of 15oC. After 9 wk of harvest, the cumulative fruit yields in infected cvs Counter and Calypso grown at 25oC were comparable to that in healthy plants grown at either temperature and cumulative fruit numbers followed a similar pattern. High root temperatures led to delayed fruit ripening between weeks 3–10 and a larger number of unripe fruit. The weight of unripe fruit from infected plants grown at 25oC at the terminal harvest was higher than from healthy plants with roots maintaine

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04928.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYPopulation levels ofScaphytopiusspp., possible sharpnosed leafhopper vectors of blueberry stunt disease (BBSD), were monitored during 1989,1990 and 1991, using yellow sticky traps and a D‐Vac power aspirator.Scaphytopius magdalensis(Prov.),S. frontalis(Van D.) and 5.acutus(Say) had two population peaks, one after the petal fall stage and a larger second peak in late Summer to early Autumn. Healthy cv. Bluecrop highbush blueberry(Vaccinium corymbosumL.) plants were placed under stunt‐diseased bushes in the field for 2‐wk periods during 1989 and 1990. These plants and some of the leafhoppers trapped during 1990 and 1991 were tested for mycoplasma‐like organism (MLO) infection with a DNA probe that detected BBSD‐associated MLO. The percentage of plants and the number ofScaphytopiusspp. that were MLO‐positive tended to follow the same bimodal distribution found in the population studies. BBSD transmission tests were performed withScaphytopiusspp. collected from the field. Stunt‐related MLO transmission was achieved withS. magdalensis, S. acutusan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1993.tb04929.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY