Incidence Of Whiteflies Research Articles

Pumpkin (Cucurbita maxima and C. pepo), a new host of Beet pseudo yellows virus in California.

In the summer of 2002, pumpkin plants (Cucurbita pepo L. and C. maxima Duchesne) with extensive leaf chlorosis similar to those observed in crinivirus infections were found in fields at two locations in Monterey County, California. Leaves of diseased plants were observed to have large populations of the greenhouse whitefly (Trialeurodes vaporariorum) present. Double-stranded RNA was extracted from symptomatic leaves of these plants and tested by northern hybridization for numerous criniviruses. A positive signal was identified exclusively with probes against the HSP70h gene of Beet pseudo yellows virus (BPYV) and confirmed by reverse transcription-polymerase chain reaction (RT-PCR) amplification of a 335-nucleotide section of the BPYV minor coat protein (CPm) gene (3). Similar symptoms were observed in additional fields in 2003, and BPYV was again confirmed. In addition, the CPm RT-PCR product was cloned into a TOPO pCR2 vector (Invitrogen, Carlsbad, CA) and sequenced. BLAST analysis of the cloned CPm RT-PCR product sequence corresponded to the published sequence of the CPm gene of BPYV (98%) (3) and Cucumber yellows virus (CuYV), a recently sequenced crinivirus considered to be a strain of BPYV (97%) (2). Incidence of BPYV in pumpkin appears to be variable and probably corresponds to the incidence of viruliferous whiteflies. On the basis of foliar symptoms, BPYV incidence varied from less than 50% in these fields in 2002 to nearly 100% infection of a large commercial field in 2003. BPYV is transmitted semipersistently by the greenhouse whitefly and has an extensive host range (1). The virus causes economic losses worldwide for greenhouse vegetable production and is becoming an increasing problem for field crops in areas of high greenhouse whitefly incidence (3). The impact of BPYV on pumpkin production remains to be determined; however, grower data suggests an increased incidence of fruit abortion and a substantial decrease in fruit weight. To our knowledge, this is the first report of BPYV infecting pumpkin.

Influence of intercropping system on insect pests and viral diseases of tomato, Lycopersicon esculentum Mill.

Studies to assess the effects of intercropping in tomato under irrigated and rainfed conditions for the management of key pests at Regional Research Station, Paiyur, TamilNadu. Agricultural University, TamilNadu during 1998-2000. Experiments were conducted in a factorial randomized block design using intercrops viz, clusterbean, green gram and mustard and two rounds. of spraying with NSKE 5% and monocrotophos 0.07%, once on 30th day after transplanting and second at the time of maximum flowering and fruit set. The results revealed that tomato intercropped with mustard at 2:1 ratio had recorded reduced incidence of whitefly and thrips population and fruit borer damage as well in two different field studies. Natural incidence of tomato spotted wilt virus (TSWV) and leaf curl virus (LCV) diseases. were noticed on the rainfed tomato crop raised during August-September, 1999 planting season. The incidence of TSWV and LCV diseases were less under intercropped tomatoes than sole crop tomato and this was significantly low on the mustard intercropped plots. Nearly 30% of plants were lost due to these diseases in the tomato sole crop plots and this loss in plant population was nearly 45-60% more than the mustard intercropped plots. The combined yield of undamaged and damaged fruits was 16.319 t ha and 16.028 t ha for the sole tomato and mustard intercropped tomato under irrigated condition. However, under rainfed condition due to the severe incidence of viral diseases, an yield of 5.832 tha was recorded in sole crop while it was 8.527 t ha in mustard intercropped plots. The undamaged fruit yield recorded was 15.00 and 7.810 tha for the mustard intercropped plots, whereas it was 13.386 and 4.833 t ha for sole crop tomato under irrigated and rainfed conditions respectively. The mustard intercropping had given an additional net return of Rs.7080 and Rs.12400 because of reduced pest infestation under irrigated and rainfed conditions respectively.

Evaluation of Insecticides and Agril Polyester Cover against Whitefly (Bemisia Tabaci Gennadius) in Tomato Crops

Field experiments were conducted on tomato crops over a two year period to evaluate the efficacy of six insecticides, viz., triazophos, phosphamidon, dimethoate, buprofezin and Aflix (endosulfan + dimethoate) each at 0.05% and Repelin (plant insecticide) at 1% concentration along With a cultural treatment by covering the plants with Agril (a polyester material ) for the control of whitefly, Bemisia tabaci. The insecticides were applied eight times at weekly interval immediately after transplantation. The whitefly eggs, nymphal population counts and the per cent incidence of tomato leaf curl virus (TLCV) were recorded every week for eight weeks in all the treatments including untreated control. The incidence of whitefly was more severe in the second year (i.e, 1992-93) as compared to the previous season. Among the various treatments, the Agril cover, a newly introduced cultural practice, recorded the least incidence of whitefly and of TLCV. The average of counts of eggs were 0.0 and 5.47 and of nymphs 0.54 and 0.58 per 10 leaflets and TLCV were 4.32% and 4.76% in Agril cover treatment during the first and second year, respectively. Among the insecticides tested only Aflix recorded less incidence of the pest, being 3.46 and 30.4 eggs per 10 leaflets and 0.94 and 5.34 nymphs per 10 leaflets during the two years of study, respectively. The other treatments were less effective in reducing pest and disease incidence. The crop under Agril-cover recorded the maximum yield of 34.57 and 26.15 t/ha of tomatoes as compared to 16.48 and 10.82 t/ha in control during the first and second year, respectively.

MONITORING OF COTTON WHITEFLY, Bemisia Tabaci GENN. WITH STICKY TRAPS

Rectangular yellow sticky trap was most effective for monitoring the adult whitefly, Bemisia tabaci Genn. in cotton. Stick-gum (poly-isobutane) and castor oil were effective in trapping the attracted adults. increasing the trap height was effective with the plant growth. The traps facing the sky and placed horizontally either inside or adjacent to the cotton field attracted more whiteflies. It was established that yellow sticky traps can be used for predicting the incidence of whitefly. A positive correlation was observed between trap catches and number of eggs in the field.

Studies in sampling technique

(i) The incidence of white-fly is highly variable and the maximum variation occurs in leaves. The variations between the clumps and the canes if and when they exist are of a much lesser magnitude. Therefore, increase in the number of leaves alone in a sample is pre-eminently effective in the reduction of error of an estimate. (ii) In a field where the infestation is either high or fairly high (puparia per square inch of the affected area more than 5.00), Nested sampling has to be adopted so as to ensure the equitable representation of clumps, canes and leaves in a sample. In such a field, 10–13 per cent, of the 3 ft. units should first be selected and then Nested sampling done in each unit in that particular form of the alternatives, which gives the larger number of leaves in the sample, namely 2 clumps × 2 canes × 5 leaves per unit or 20 affected leaves equitably representing the clumps and canes in a unit as far as possible or 18–20 per cent, of affected leaves (i.e., about one in every five) equitably representing the clumps and canes in a unit. (iii) In a plot of low or mild infestation, Nested sampling is not essential. Only the leaves as a whole may be subjected to random selection, other requirements being the same as mentioned under number (ii) above. (iv) For a required error percentage, a medium infested field (puparia, 2.00–5.51 per square inch) requires a smaller sample size than that needed in a plot of high infestation or of an infestation which is fairly high. A difference in the sample size in the number of leaves by even about 75% gave the same efficiency. This suggested inherent homogeneity in variation occurring in mild form of infestation. (v) If in each leaf, 10 random inch units (about 25% of the total inch units) be taken instead of enumerating the whole leaf, the estimate of the incidence will be fairly reliable with a very slight additional error; but for practical consideration and working convenience, the complete enumeration of a leaf may be preferred to counting puparia in 10 random inch-units.