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1.
The effect of azadirachtin and salannin, two triterpenoids isolated from seeds of neem (Azadirachta indica A. Juss), on the feeding response ofSpodoptera littoralis (Boisd.) andEarias insulana (Boisd.) larvae, was investigated. Styropor (foamed polystyrene) lamellae were painted on both sides with a mixture of 5% sucrose with different concentrations of either azadirachtin or salannin dissoled in methanol-water (3∶7). Azadirachtin strongly suppressed feeding inS. littoralis larvae even at 0.001%, whereas salannin showed some antifeedant activity at 0.005% and above. Larvae ofE. insulana were deterred from feeding on azadirachtin-treated lamellae even at 0.005%, whereas salannin was effective only at 0.01% and above. Azadirachtin applied on cotton leaves deterred larvae ofS. littoralis from feeding at all concentrations ranging between 0.001 and 0.02%.  相似文献   

2.
Synergism of mixtures of pyrethroids with organophosphorus (OP) compounds in insects is reviewed, and the toxicity of such combinations againstSpodoptera littoralis (Boisd.) larvae is reported. Mixtures of one of the pyrethroids cypermethrin, fenvalerate or deltamethrin with one of the OP compounds monocrotophos, profenofos, azinphos-methyl or acephate were assayed at different ratios as 24-h-old dipping residues on alfalfa, which was fed toS. littoralis larvae for 48 h. With most of the binary mixtures containing various OP concentrations in excess of those of the pyrethroids, synergism was demonstrated. In the pairs fenvalerate — azinphos-methyl, deltamethrin — azinphos-methyl and deltamethrin — profenofos, however, no synergism was found. In a detailed investigation with pyrethroid concentrations causing 20% mortality and OP concentrations giving a kill of no higher than ;10%, the above findings on synergism were amply confirmed. A cypermethrinmonocrotophos mixture showed synergism also on cotton leaves sprayed in the field. Synergism could not be demonstrated by topical application of pyrethroid — OP mixtures.  相似文献   

3.
The effect ofPhytophthora infestans on foliage growth and senescence of three potato cultivars was studied in two field experiments. Inoculum or fungicide was applied in different frequencies to establish a range of levels of disease. At weekly intervals leaf numbers were determined as well as vertical canopy profiles of senescent and lesion covered leaf and stem area. P. infestans reduced appearance of new leaves on the main stem only at the highest level of disease. The cultivars differed more in rate of primary infection of healthy leaves than in the subsequent increase in percentage lesion coverage of the infected leaves. Differences between cultivars in stem lesion coverage resembled the differences for leaf lesions, but in every cultivar stem lesions were most prominent in the top of the canopy, contrary to leaf lesions.P. infestans stimulated leaf senescence similarly in the different cultivars.  相似文献   

4.
Nine Alternaria species have been reported to be associated with sunflower leaf blight worldwide, and A. helianthi has been recognized as the most prevalent and damaging species. However, the population structure of Alternaria species causing leaf blight of sunflower in China had not been examined thoroughly prior to this study. During 2010 to 2013, a total of 272 Alternaria isolates were obtained from infected sunflower leaves in 11 provinces, autonomous regions, and municipalities of China. Based on morphological traits and sequence analyses of the internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) and the partial coding sequences of the histone 3 gene, 227 (83.5 %) isolates were identified as belonging to Alternaria tenuissima, the remainder 45 isolates were grouped to A. alternata (16.5 %). Compared with the ITS regions of rDNA, sequence analyses of the partial coding sequences of histone 3 gene displayed a critical role in discrimination of the small-spored Alternaria species. Phylogenetic analysis of the partial coding sequence of histone 3 gene clearly divided the representative Alternaria isolates into two main clades, A. tenuissima and A. alternata. The pathogenicity of A. tenuissima and A. alternata on detached leaves of sunflower cv. Gankui No.2 did not significantly differ between the two species or among isolates from different geographical origins. Our results indicate that the population structure of Alternaria species associated with sunflower leaf blight differed from that reported previously in China since A. helianthi was not found in this study. In addition, this is the first report about A. tenuissima causing leaf blight on sunflower in China.  相似文献   

5.
Various immature stages of male and female California red scale,Aonidiella aurantii (Maskell) (Homoptera: Diaspididae), were treated with avermectin B1 (MK-936) at concentrations ranging from 10 to 100 ppm. Treatments at 10 ppm completely arrested crawler development and 20 and 100 ppm caused 100% mortality of 48-h and 7-day-old male and female 1st instar nymphs, respectively. The development of the 2nd instar was slightly affected by MK-936 at up to 40 ppm. Sublethal doses of the chemical applied to immature stages caused no dramatic reduction in the fecundity of the subsequent, mature females. MK-936 applied to male prepupal and pupal stages and mated females did not prevent male emergence, nor did it affect the ability of males to copulate and inseminate female scales, or the female fecundity. The development and adult emergence of treatedAphytis holoxanthus DeBach (Hymenoptera: Aphelinidae) larvae and pupae parasitizingChrysomphalus aonidum L. scales were not influenced by a 9 ppm MK-936 treatment; leaves sprayed with this concentration had residual toxicity onA. holoxanthus adults for only 24 h post-treatment. Feeding byChilocorus bipustulatus L. (Coleoptera: Coc-cinellidae) on 0.9 ppm MK-936-treated Florida red scales resulted in 100% mortality of 2nd instars and induced sterility in the females.  相似文献   

6.
Egg hatch of two nitidulids,Carpophilus hemipterus L. andUrophorus humeralis F., was affected by the chitin synthesis inhibitor triflumuron (Alsystin; BAY SIR 8514)via the adult stage of the beetle. This occurred by exposure to treated diets, by a brief dip of the adults in aqueous dilutions of the toxicant, or by contact with a treated plastic netting cage. Exposure of adults ofC. hemipterus for 24 h to 0.0125%, 0.00125%, 0.00025% or 0.000125% and ofU. humeralis to 0.0125% a.i.-treated diets completely prevented hatch of eggs laid during the subsequent 48 h on an untreated diet. Although at first sterile eggs were obtained with adults of either nitidulid species transferred to an untreated diet after 24 h exposure to the 0.0125%-treated diet, egg viability gradually recovered. The speed of recovery and the course of mortality of larvae that hatched from eggs laid by treated adults, indicated thatC. hemipterus was more susceptible thanU. humeralis to triflumuron. DippingC. hemipterus adults — males or females — in 0.0125% a.i. triflumuron also resulted in complete prevention of egg hatch. Similar results were obtained by a 1-h contact of adults with treated cages. Triflumuron had no direct ovicidal activity against the two species at the concentrations used but was very effective against larvae of both species. At 0.0125% a.i., 3-5-mm-long larvae ofU. humeralis were more tolerant than newly hatched larvae and than 3-5-mm-long larvae ofC. hemipterus. Application of 0.0125% a.i. triflumuron in a date palm grove did not prevent fruit infestation by nitidulid adults but, due to prevention of egg hatch, almost no larval development was observed.  相似文献   

7.
Insecticides commonly used in cotton fields in Israel against lepidopterous pests were tested against eggs, as well as against 2nd-instar larvae and adults raised from eggs ofSpodoptera littoralis (Boisduval) collected in cotton fields in the Bet She’an Valley. Methomyl, chlorpyrifos, methidathion, monocrotophos, ethyl parathion, and methyl parathion were effective against eggs even at low doses, profenofos and phosfolan were less active, and azinphos-methyl was ineffective. The doses needed for 90% kill (LD 90 ) of the 2nd-instar larvae were 8.5, 35, 280, 1300 and 3400 g a.i./1000 m 2 for chlorpyrifos, methomyl, profenofos, methyl parathion and ethyl parathion, respectively; monocrotophos was inactive against 2nd-instar larvae even at relatively high doses. The LD 90 of adults was reached with 16, 32, 1700 and 6100 ga.i./l000 m2 of chlorpyrifos, methomyl, ethyl parathion and profenofos, respectively. Only chlorpyrifos and methomyl gave successful control of all three stages of the insect tested, at doses close to those generally used with aerial applications.  相似文献   

8.
Application of various fungicides to cotton plots (Gossypium barbadense cv. Pima) affected byAlternaria macrospora resulted in a yield increase from 3955 kg/ha in unsprayed plots to 5207 kg/ha in plots treated with fentin acetate. Pathogen, host and disease parameters were estimated by a key of grades in the field and by precise measurements of detached plants. Measurements included the number of spores present in the field and numbers and/or areas of healthy, lesioned and shed leaves and bolls. No significant differences were found between the number of healthy bolls on variously treated plants and the number of lesioned bolls on the same plants. Disease incidence was relatively low in treated plots, with no significant difference between treatments and no correlation with the size of the pathogen population or the yield level in variously treated plots. The low proportion of lesioned leaves resulted from their tendency to shed and from the emergence of new leaves, which masked the damage. Rate of shedding was correlated with the respective yield and with the size of the pathogen population in the same plot. Leaf shedding was induced by lesions occupying an average of 1 to 3% of the leaf area. Shedding was affected by leaf position on the plant, being most frequent for the lowest leaves despite their being the least lesioned, and least frequent for the upper leaves even though these were the most lesioned.  相似文献   

9.
The vector competence of Frankliniella occidentalis for Chrysanthemum stem necrosis virus (CSNV) was evaluated. Three vector strains with distinct competences for Tomato spotted wilt virus (TSWV) transmission were investigated, including an artificially selected strain (TsH) that has a particularly high competence (>90 %). Newly hatched larvae of F. occidentalis were given an acquisition access period of 5 days on CSNV-infected D. stramonium leaves, and reared to maturity. Their transmission efficiencies were examined using a leaf disk assay using Petunia x hybrida leaves. Following the leaf disk assay, the virus accumulation in the vectors was examined via a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) of their bodies. The results showed that the CSNV acquisition and transmission efficiency of the TsH strain did not differ from those of the others, indicating that the competence of F. occidentalis as a vector for CSNV is not related to that for TSWV. The CSNV transmission and acquisition efficiencies of two F. intonsa strains (Hiroshima and Fukuoka) were also evaluated. In Hiroshima strain, 35 % of adults were viruliferous, but only two transmitters (3 %) were observed. In Fukuoka strain, 6 % were viruliferous, and no transmitters were observed. These results indicate that F. intonsa cannot be a major vector for CSNV. The accumulation of CSNV in the adults of F. occidentalis and F. intonsa evaluated using DAS-ELISA showed a significant difference in ELISA values among transmitter, viruliferous non-transmitter, and non-viruliferous individuals. These results clearly demonstrated that only transmitters that accumulated a threshold quantity of virus can transmit CSNV to plants.  相似文献   

10.
A quick and easy method for estimating the number of surviving nymphs of the tobacco whitefly (TWF),Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), after spray applications was developed in the laboratory. The method is based on the number of honeydew droplets ejected by TWF immatures during 30 minutes. Since the nymphs ofB. tabaci feed on the lower leaf surfaces, the honeydew excreted falls downward. In this study infested cotton leaves were placed with their lower side up, forcing the nymphs to eject the honeydew droplet upwards. Inverted plastic petri dish covers were placed over infested cotton leaves and after 30 minutes the droplets deposited on the inner side of each cover were counted and the average number of droplets per nymph was calculated. To estimate the number of live nymphs on an infested cotton leaf, the number of droplets ejected during 30 minutes was divided by the average number of droplets per nymph (factor of 1.23).  相似文献   

11.
This study was carried out to determine the antimicrobial activity of essential oil derived from leaves of eucalyptus (Eucalyptus globulus) against Phytophthora colocasiae, the causal agent of taro leaf blight (TLB). Essential oil was obtained by Clevenger-type water distillation. The major compounds in this essential oil were identified using gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC/MS). Antimicrobial activity of the essential oil was tested in vitro against mycelial growth, sporangia and zoospores germination of P. colocasiae. Additionally, in situ tests were conducted on detached healthy taro leaves discs and evaluating necrosis symptoms of TLB were assessed. Results of the chemical composition of the essential oil analysis showed that, 1.8-cineole (26.4 %), α-pinene (14.1 %) and p-cymene (10.2 %) are the most abundant compounds. In addition, four components could be identified in noticeable amounts (18.1 % in the total): regulator G1/G2 and its derivatives as well as flavesone, a regulator G3 derivative. G is a generic term for a family of 2,3-dioxabicyclo[4,4,0] decane system growth regulators. Here, G-regulators and derivatives are described for the first time in E. globulus. Antimicrobial activity of the essential oil was recorded with total inhibition of mycelia growth and sporangia germination at 0.625 mg/ml, while the complete inhibition of zoospores germination was recorded at 0.156 mg/ml. In situ results showed that essential oil completely inhibited the appearance of disease symptoms, necrosis development and sporulation at 3.5 mg/ml. These results demonstrated that, the essential oil of Eucalyptus globulus has high ability to inhibit the development of P. colocasiae, and might be used for controlling TLB.  相似文献   

12.
Six fungicides were evaluated under laboratory and field conditions for control of Phytophthora leaf blight of taro,Coloeasia esculenta, incited byPhytophthora colocasiae. Inin vitro tests Deraosan 65W was the most effective in inhibiting the mycelial growth of the test pathogen followed by Difolatan 80W, Fytolan (copper oxychloride), Apron 35F, Topsin-M 50W and Dithane Z-78 75W. Excellent control was obtained with Demosan 65W and Difolatan 80W, good control with Apron 35F, fair control with Fytolan, and poor control with Topsin-M 50W and Dithane Z-78 75W. Results ofin vivo tests were correlated with those of thein vitro tests. Roguing of infected leaves did not eradicate the pathogen but can only delay epiphytotics.  相似文献   

13.
Diflubenzuron was tested for its efficacy against the eggs and larvae ofEarias insulana Boisd. in laboratory experiments. The toxicity obtained on dipping the eggs was only moderate and, moreover, the results were highly inconsistent. The mortality of larvae on an artificial diet into which the wettable powder had been incorporated, was relatively high.  相似文献   

14.
Stemphylium lycopersici (Enjoji) W. Yamam was initially described from tomato and has been reported to infect different hosts worldwide. Sequence analyses of the internal transcribed spacer (ITS) regions 1 and 2, including 5.8S rDNA (ITS-5.8S rDNA) and glyceraldehyde-3-phosphate dehydrogenase (gpd) gene, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR), as well as virulence studies were conducted to analyze 46?S. lycopersici isolates. Stemphylium lycopersici isolates used in this study were obtained from diseased tomato (Solanum lycopersicum L.), eggplant (Solanum melongena L.), pepper (Capsicum annuum L.) and lettuce (Lactuca sativa L.) from major vegetable growing regions of Malaysia, including the three states of Pahang, Johor and Selangor between 2011 and 2012. Phylogenetic analysis of a combined dataset of the ITS-5.8S rDNA and gpd regions indicated that all isolates were clustered in the sub-cluster that comprised S. lycopersici, and were distinguished from other Stemphylium species. Cluster analyses using the UPGMA method for both RAPD and ISSR markers grouped S. lycopersici isolates into three main clusters with similarity index values of 67 and 68 %. The genetic diversity data confirmed that isolates of S. lycopersici are in concordance to host plants, and not geographical origin of the isolates. All S. lycopersici isolates were pathogenic on their original host plants and showed leaf spot symptoms; however, virulence variability was observed among the isolates. In cross-inoculation assays, the representative isolates were able to cause leaf spot symptoms on eggplant, pepper, lettuce and tomato, but not on cabbage.  相似文献   

15.
Ulvan is an algal polysaccharide known for its ability to induce resistance to plant diseases such as the Glomerella leaf spot of apple caused by Colletotrichum gloeosporiodes. This study was aimed at investigating microscopically, in tests in vitro and in vivo, whether ulvan interferes in the development of pre-infective structures of C. gloeosporioides. Conidial germination and appressoria formation were monitored hourly on agar and cellophane, and at 48 h on water- and ulvan-treated susceptible as well as resistant apple leaves. Amendment of agar with ulvan (10 mg ml?1) enhanced the germination and resulted in longer germ tubes at 7 h of incubation. On cellophane it significantly delayed appressoria formation up to 8 h, but later after 14 h increased the number of appressoria per conidium. Spraying of susceptible leaves with ulvan 6 days before inoculation decreased disease severity by 50%. This was associated with inhibition of appressoria formation and stimulus in growth of germ tubes, without interfering with conidial germination, when compared with both water-treated control and resistant plants. Appressorium formation occurred preferentially on anticlinal walls of epidermal cells and its location was not influenced by host resistance or by ulvan treatment. This study suggests a new mode of action for ulvan interfering with appressorium formation that could protect apple plants against C. gloeosporioides infection.  相似文献   

16.
Cotton leaf curl virus (CLCuV) (Geminiviridae : Begomovirus), the causative agent of leaf curl disease in cotton plants (Gossypium hirsutum), is exclusively transmitted by whitefly species Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). CLCuV transmission occurs in Sriganganagar (Rajasthan), an area endemic with cotton leaf curl disease. The relationships between plant viruses, their herbivore vectors and host plants can be beneficial, neutral, or antagonistic, depending on the species involved. To further understand these relationships, fecundity and life history parameters of an indigenous non- b (Asia II genetic group) biotype whitefly, B. tabaci, were compared on 10, 25, and 40 days post-inoculation (DPI), in CLCuV-infected and healthy cotton plants to determine the effect of virus on its vector. The development time of the immature stages of whiteflies was significantly reduced on CLCuV-infected plants. The development time of the immature stages did not change with severity of symptoms at 25 and 40 DPI (45- and 60-d-old plants). Cotton leaf curl virus infection increased percent egg viability of B. tabaci. Whiteflies deposited significantly fewer eggs on virus-infected plants than on healthy plants. Whiteflies had better egg viability on younger plants than older plants, whereas plant age did not affect the fecundity. Male and female whiteflies had shorter longevity on CLCuV-infected plants than on healthy plants.  相似文献   

17.
In mosaic-diseased plants ofHippeastrum hybridum two viruses were found. One virus with a normal length of 706 nm caused local lesions onHyoscyamus niger test plants and mosaic symptoms in the leaves ofH. hybridum. This virus was identified with theHippeastrum mosaic virus (HMV) (*/*∶*/*∶E/E∶S/*) and had a dilution end point between 10?3 and 10?4, a thermal inactivation point between 55–60°C and a longevity at room temperature of 28–32 hours. The second virus had a normal length between 584 and 611 nm depending on the method used. It caused local lesions onGomphrena globosa andChenopodium quinoa leaves, and after inoculation ofH. hybridum was found to be present without showing symptoms. It was readily purified from inoculated leaf tissue ofC. quinoa andNicotiana clevelandii by differential centrifugation and ofH. hybridum by density-gradient centrifugation. Purified virus had an absorption minimum at 242 nm, a maximum at 262 nm and a 260/280 absorption ratio of 1.19. The dilution end point was between 10?3 and 10?4, the thermal inactivation point between 70 and 80°C and the longevity in vitro at room temperature 28–32 hours. Although no direct comparisons have been made with other members of the potexvirus group, the virus seems to be a new one now namedHippeastrum latent virus. Both viruses were not seed-borne.  相似文献   

18.
Ethyl [2-(4-phenoxyphenoxy)ethyl] carbamate (RO 13-5223) at a dietary concentration of 100 mg kg-1 synergized the toxicity of thetrans- andcis-isomers of permethrin and cypermethrin in inhibiting the growth (measured as gain in larval weight) ofTribolium castaneum andMusca domestica vicina. With both species the synergism factor forcis-cypermethrin with 100 mg kg-1 synergist was 1.5- to twofold for RO 13-5223 and about fourfold for piperonyl butoxide. Synergism was more pronounced with first instar than with fourth instarT. castaneum larvae. Methoprene was not a pyrethroid synergist withT. castaneum larvae, so the synergistic effect of RO 13-5223 appears to depend on its structural features and not its insect-growth-regulator activity. Joint application of RO 13-5223 and pyrethroids resulted in a dual effect on bothT. castaneum andM. domestica: increased inhibition of larval growth due to pyrethroid synergism, and progeny suppression — expressed by larval and pupal mortality — due to RO 13-5223 juvenilizing activity.  相似文献   

19.
The potency of diflubenzuron is much greater in inhibiting growth and development of 1st instar larvae ofTribolium castaneum than of 4th instar larvae, as expressed by death at the apolytic stage and retardation of larval development. A dose-dependent decrease in the activity of trehalase, invertase and amylase was obtainedin vivo with the increase in diflubenzuron concentration. At 5 ppm dietary concentration, a reduction of 37 and 27% in invertase and trehalase activity, respectively, was obtained in 4th instar larvae fed for 3 days on treated diet. The amylase activity was affected to a lesser extent. The observed disturbances of trehalase activity might hamper the supply of glucose needed for chitin build-up and those of invertase and amylase activity might affect feeding. Diflubenzuron does not inhibit these enzymesin vitro; hence, thein vivo effect seems to result from general disturbances in carbohydrate metabolism.  相似文献   

20.
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