Rotenone and oxalic acid as alternative acaricidal treatments for Varroa destructor in honeybee colonies

This experiment assessed the efficacy of rotenone and oxalic acid (OA) in an aqueous sugar solution in controlling the honeybee mite Varroa destructor. Colonies were populated with mite-infested brood combs and worker bees. Three rotenone or OA treatments administered during the period with capped brood on 31 July, 14 and 18 August resulted in an average efficacy of 24.10%. In untreated colonies mite mortality averaged 5.40%. No significant differences (P>0.05) were found between the rotenone and OA treatments. Three OA treatments administered on 9, 12 and 18 September resulted in a 77.93% mite mortality. An increase in mite drop (P<0.05) was observed at 2 and 4 days after each treatment. OA applications in broodless colonies resulted in significantly (P<0.001) higher mite mortality rates (98.65% average) than the three treatments of rotenone or OA in colonies with capped brood. The dynamics of mite mortality after each rotenone or OA treatment are discussed in this study.     

The development of beta-carotenemia in dairy cows 1975-1987

On investigation of beta-carotene levels in the blood plasma of 9193 cows in the first and second phases of lactation, and in the eight, ninth months, and to the tenth mid-month of their pregnancy showed the same dynamics in beta-carotinaemia development in all groups, with a wave-like tendency to decrease. The lowest beta-carotene values were recorded during the 1985-1986 winter season and in the following 1986 summer season. Beta-carotene levels also remained low during the subsequent winter and summer feeding season. Different beta-carotene concentrations in the blood plasma were repeatedly found in the phases of lactation reproduction cycle. Increases in the milk production and deteriorated reproduction indicators were recorded in the cows at the time of a steep decrease in beta-carotene concentrations in the blood plasma. The causes of decreasing beta-carotene concentrations in the cow blood plasma are discussed.     

A decrease in blood beta-carotene in dairy cows during late pregnancy period

In four successive seasons of green and winter feeding in the years 1980-1984, beta-carotene concentrations were determined in the plasma of venous blood of 3441 cows in the first phase of lactation, in the other phase of lactation, in the eighth month of pregnancy and in the 9th-9.5th months of pregnancy. The cows in the other phase of lactation had the significantly highest beta-carotene concentrations in the two feeding seasons. In the eighth month of pregnancy there occurs a significant drop that continues also in the 9th-9.5th months of pregnancy. In the first phase of lactation beta-carotene concentrations remained at the level of the values from the 9th-9.5th months of pregnancy. In the period of winter feeding, the mean concentrations of beta-carotene in all groups of cows were deep below the limit value of 7.44 mumol . l-1, which indicated that it was necessary to fortify feeds with vitamin A; in the cows in the 9th-9.5th months of pregnancy and in the cows in the first phase of lactation they were lower than the critical value of 5.58 mumol.l-1, which signaled the disorders of reproduction processes. In the course of the years of investigation beta-carotene concentrations varied in the same manner in all groups of cows in keeping with the vegetation period of the feed, feed kind and quality.(ABSTRACT TRUNCATED AT 250 WORDS)     

Magnesium in the blood and urine of cows during various stages of the reproductive interval being fed summer and winter feed rations

Magnesium concentration was investigated in the blood plasma and urine of 3460 cows in the course of four green-feeding seasons and four winter feeding seasons in 1980 to 1984. A decrease in the magnesium content in blood plasma was found to intensify in the last six weeks of gravidity. In the first stage of lactation the magnesium concentrations of plasma begin to grow to reach a relative maximum in the cows in the second stage of lactation. These regularities apply to both the summer and winter feeding seasons. The magnesium content in urine has a similar pattern. The summer values of the magnesiemia of whole cow populations are significantly higher than the winter values. Tendencies to lower magnesium concentrations generally prevail in both blood plasma and urine; these tendencies are most conspicuous in the cows in the last six weeks to parturition. As a rule, the concentrations of magnesium in urine were lower in summer than in the season of winter feed rations. As for the contents of the blood plasma magnesium of the cow populations as well as individual cows, there are considerable differences between various stages but the trends are the same in all groups. In the green feeding season the range of fluctuation of the magnesiemia values is larger than in the winter feeding season. The same tendency of changes in individual groups was also recorded in the magnesium concentrations in the urine of cows in different stages. However, the direction of the changes did not always correspond to the direction of the changes in the blood plasma. A practical requirement has been derived from the results of the study that magnesium contents should be increased in the feed rations given to high-pregnant cows and cows in the first lactation.     

Resistance of Cucumis sativus cultiv ars to Cladosporium cucumerinum

A set of 249 Cucumis sativus cultivars and lines was tested for resistance to Cladosporium cucumerinum. The cultivars were grouped according to resistance or susceptibility. A clear-cut reaction was observed in 85% of the samples (resistance, 34%; susceptibility, 51%), the rest of the cultivars showing intermediate or heterogeneous reactions. Some results indicate the possibility that physiological races of C. cucumerinum exist.     

Response of Lettuce Cultivars Carrying the Resistance Gene Dm11 to Isolates of Bremia lactucae from Lactuca serriola

Seven Bremia lactucae isolates from Lactuca serriola were tested for pathogenicity on 41 Lactuca sativa cultivars carrying a race specific resistance gene Dm11 which originated from L. serriola. Some of these cultivars also carried other Dm genes. Sporulation was observed in 34 % of the 287 cultivar/isolate combinations, but it was limited in most cases. A compatible response was recorded in 7.3% of cultivar/isolate. Cultivars with Dm 11 alone, or in combination with Dm 2, exhibited a higher decree of susceptibility then those also carrying Dm 3. There were differences in specific virulence among the isolates under study. Nearly all the isolates studied were virulent on newly described resistance genes Dm 15, Dm 16, and Dm 7 +? which originate from L. serriola.     

Evaluation of field resistance of Daucus carota cultivars to Cercospora carotae (carrot leaf spot)

Summary A world collection of 142 cultivars of carrot was tested for resistance to Cercospora carotae in the field. C. carotae infection was observed in all the cultivars. Field resistance was observed in only about 30% of the cultivars, the remainder being highly susceptible.