The virus-vector relationship of the tomato leafcurl virus (TLCV) and its vector,Bemisia tabaci gennadius (Hemiptera: aleyrodidae)

Basic studies carried out in India showed that the incubation period of TLCV in plants varied from 8 days in August to 90 days in winter. The acquisition threshold for the whitefly,Bemisia tabaci Gen., was 31 min; it resulted in 3% transmission. An acquisition access of 24 h for a female whitefly on a TLCV source resulted in 30% transmission. A minimum feeding period of 32 min was required by a viruliferous whitefly to cause infection on tomato test plants; this gave 4% transmission. With inoculation access of 24 h on tomato test plants, the transmission rose to 24%. Starving the vector for 1 h pre-acquisition or 1 h pre-inoculation resulted in higher levels of transmission of TLCV: 36 and 40%, respectively, compared with 20% for non-starved whiteflies. Extending the fasting period beyond 1 h resulted in a reduced transmission level. The whiteflies could acquire the virus from the cotyledonary leaves of an infected tomato plant, with a resultant 28% transmission; but infection did not occur when the whiteflies had an inoculation access to such leaves. Higher transmission rates were obtained when the younger leaves on tomato plants were used for acquisition and inoculation. Transmission was 8 and 38% when five whiteflies per plant were allowed 24 h of acquisition access to 11- and 2-month-old virus sources, respectively. After an acquisition access of 24 h to a TLCV source, male and female whiteflies retained their infectivity for 5 and 53 days, respectively. Nymphs can acquire and transmit the virus. When ten whiteflies of each sex were given 24 h of acquisition and of inoculation access, the subsequent transmission rate of males and females was 56 and 86%, respectively. This virus is not transovarially transmitted. Whitefly colonies raised on brinjal were more efficient (70 and 84% transmission in two experiments) than those raised on chilli, cotton, cowpea, tobacco or tomato.     

Variation of canine and feline frontal-plane QRS axes with lead choice and augmentation ratio

The intraindividual variability in mean electric axis referable to choice of ECG leads and augmentation ratio was investigated by means of a digital computer program. Although, in theory, the choice of leads for determining the QRS axis should make no difference, the maximum intraindividual variation in axis angle was about 50 degrees for canine and feline subjects. The angle conputed for the lead combinations I and III and I and aVF will usually fall within 5 to 10 degrees of the mean of all lead combinations, but larger variations are seen at time. The application of an "augmentation ratio" for the augmented unipolar leads was most helpful when it was individually computed. Further methods of lead-vector improvement are discussed.     

Alternative complement pathway in bovine serum: lysis of human erythrocytes.

The hemolysis of unsensitized human erythrocytes by fresh bovine serums was investigated. Lysis occurred in ethylene glycol bis-amino tetraacetate buffers and with serums depleted of Clq. Serums extensively absorbed with packed human erythrocytes at 0 C effectively lysed human erythrocytes, but optimal lytic capacity required target cells "sensitized" with a heat-stable serum factor. Lysis did not occur with serums absorbed with zymosan at 17 C or heat inactivated at 50 C. These results indicate that human erythrocytes can activate the alternative pathway of complement in bovine serums. Lysis can proceed in the apparent absence of antibodies, although their presence may enhance the reaction.     

Gastrointestinal colonization by salmonellae and pathogenic Escherichia coli in monoxenic and holoxenic chicks and poults

Chicks monocolonized by either salmonellae or pathogenic strains of Escherichia coli had persistent and undiminished colonization of all levels of the gastrointestinal tract and frequently had bacteremia during test periods ranging to 35 days. Poults monocolonized by salmonellae or Arizona hinshawii 7:"1,7,8 developed a similar pattern of colonization. Conventionally reared chicks and poults had rather variable colonization by these pathogens, and it was most persistent in the ceca. Groups treated with a native protective microflora were infrequently colonized. Differences in colonization are explainable by lack of competing bacteria in the monocolonized group and by various degrees of protection provided by microflora colonizing the other groups.