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• Path coefficient analysis of environmental factors influencing flight activity of Apis florea F. and seed yield in carrot (Daucus carota L.)

  87-92.

  D. P. Abrol

  Views:

  118

  Foraging ecology of insect pollinators visiting carrot flowers (Daucus carota L.) was studied in relation to five environmental variables. The dwarf honeybee, Apis florea L., was the most abundant flower visitors and comprised more than 94% of the total flower visiting insects. Commencement of flight activity occurred when a minimum threshold of environmental variables was surpassed while the cessation was governed mainly by decline in values of light intensity and radiation. In between the commencement and cessation, the foraging population correlated significantly and positively with air temperature, light intensity, solar radiation and nectar-sugar concentration and negatively with relative humidity. Path coefficient analysis, however, revealed that direct effect of temperature was high and positive followed by light intensity and solar radiation while the direct effect of relative humidity was high and negative. The direct effect of nectar-sugar concentration was negative and negligible. Evidently, path coefficient analysis gave a more clear picture of effects than did the simple correlation analysis. Apis florea on an average visited 1.14+0.23 and 22.78+2.57 umbels and flowers/min, respectively during different hours of the day. Furthermore, the insect pollinated plots produced significantly more seeds with heavier weights than those isolated from insect visits.

• Character association and genetic gain of nine agronomic traits of F1 populations in onion (Allium cepa L.)

  50-58.

  A. C. Deb

  R. Ara

  Views:

  494

  F₁ populations of half diallel cross were considered for this investigation. Phenotypic component of variation (s²_P) was higher than genotypic (s²_G), interaction ((s²_I) and within error (s²_w) components of variation. Trait bulb weight showed the highest values for s²_P, s²_G, s²_I and s²_w. The noticeable amount of phenotypic, genotypic, interaction and within error covariation was found in the combination of BW×BY, possibly indicating wide scope of selection for this pair of characters. Genotypic correlations were higher than the respective phenotypic correlations. This situation was also marked in the path coefficient analysis. Bulb yield/plot showed highly significant and positive correlation coefficient with other characters both at phenotypic and genotypic levels. When all the nine characters were included in an index, it exhibited the highest genetic gain as percentage. When a combination of two or more characters was studied in a function, the efficacy was higher than that of direct selection for bulb yield. The combination of five, six, seven or eight characters showed higher percentage of expected gain. Due to significantly correlated with BY and having high positive direct effect at phenotypic level characters viz., LL, BW, PH and NLs is considered as primary yield components. Again combinations of these four characters gave the commendable expected genetic gain of 330.7290% may be considered as important selection index for this material.

• Path analysis and correlation coefficient of environmental factors influencing foraging behaviour of four honeybee species pollinating litchi flowers (Litchi chinensis Sonn.)

  77-82.

  D. P. Abrol

  Views:

  120

  Honeybee species Apis dorsata F; A. mellifera L; A. cerana F. and A.florea F. were the most important and efficient pollinators of litchi flowers (Litchi chinensis Sonn.) in India. They constituted more than 65% of the total pollinating insects. The ecological threshold for commencement and cessation of flight activity of each honeybee species varied from one another. In general, 15.5-18.5°C temperature, 600-1700 lx light intensity, 9-20 mW/cm² solar radiation appeared to be the minimum ecological conditions for commencement of flight activity in Apis species. Cessation of activities in all the honeybee species was governed mainly by decline in values of light intensity and solar radiation irrespective of other factors.

  In between commencement and cessation, the activity of all honeybee species followed the same general pattern as temperature (T), light intensity (LI). Solar radiation (SR). Nectar sugar concentration (NSC) and inversely with relative humidity (RH). Path analysis revealed that all the honeybee species differed in their responses to environmental factors prevailing under similar set of conditions depending upon physiological adaptation of each honeybee species. Of all the factors studied; temperature, light intensity and solar radiation were the three important factors whose influence on foraging population was more pronounced.