Flower shedding in summer mungbean, Vigna radiata (L.) Wilczek, is a common feature caused by thrips, Megalurothrips distalis (Karny). Eleven insecticides were tested in field trials for the control of thrips during the period 1982 to 1984. All the treatments were significantly better in controlling the thrips, reducing flower shedding, increasing the pod numbers and grain yield, in comparison with the control. Increases in yield compared with the control during trials ranged from 85 to 89% (1982), 26 to 96% (1983) and 5 to 194% (1984). Dimethoate gave the highest increases in yield and profit followed by monocrotophos and endosulfan.
Sesamum phyllody is a serious disease of sesame (Sesamum orientate L.). The disease is mainly spread by the leaf-hopper vector Orosius albicinctus Distant (Ghauri, 1966). The biology and bionomics of the hopper was worked out by Bindra & Singh (1970). The relative fecundity-cum-fertility and longevity of the hopper on the diseased and healthy plants were studied to supplement the existing information.
MATERIALS AND METHODSFifteen pairs, each comprising a male and a female, from each of viruliferous and non-viruliferous stocks of the leaf-hopper (Orosius albicinctus Distant) •were released, one pair on a healthy potted plant of sesame, under glass chimneys. The hoppers were transferred successively to the other plants at 8-to 12-day intervals. The nymphs hatched out were counted and removed daily. The total number of nymphs produced per female, in each case, was taken as its fecundity-cum-fertility. The dates of deaths of the male and female parent-hoppers were recorded in all cases.
RESULTS AND DISCUSSIONIt is evident from Table 1 that the mean life span of the viruliferous adult hoppers (43-9 days) * Present address: Ahmadu Bello University, Zaria, Nigeria.was significantly longer than that of the nonviruliferous adults (30-5 days). The mean life span of 47-6 days of the viruliferous male hoppers was significantly longer than the 29-6 days for the nonviruliferous males, whereas the difference in the longevity of the viruliferous and non-viruliferous female hoppers was not significant. Sahambi (1966), did not observe a significant difference between the mean life spans of the viruliferous and nonviruliferous adults of this leaf-hopper. However, the observations of Maramorosch & Jensen (1963), revealing longer survival of the leaf-hopper (Dalbulus maidis De Long and Walcott) on asters, Callistephus chinensis, infected with yellow virus and the present findings rather indicate beneficial effects of the respective viruses on the life spans of the leaf-hoppers Dalbulus maidis (De long and Walcott) and Orosius albidnclus Distant. The difference between the mean rates of fecunditycum-fertility of the viruliferous and non-viruliferous female hoppers was not significant. Sahambi (1966) also reported that the difference between the fecundity-cum-fertility of viruliferous and nonviruliferous female hoppers of the same species (Orosius albicinctus Distant) was not significant.
SUMMARYThe comparative rate of development of Orosius albicinctus Distant was studied on different host plants, sesame, sannhemp, radish, purslane, lucerne, chicory, Indian rape, sugar beet and black gram. The duration of the egg stage was the shortest (7·1 days) on sesame and was prolonged to 12·0 days on chicory. The nymphal duration was again minimal (11·9 days) on sesame and was prolonged to 15·4 days on chicory. The nymphal survival was also more on sesame than on the other hosts. Thus, among all the host plants tested sesame was found to be the best suited host for this leaf-hopper.
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