In nectars

The iridoid monoterpenes, catalpal and catalposide occur in nectar in flowers of Catalpa speciosa (Bignoniaceae) and are toxic to many non-coadapted insects which attempt to rob nectar. The bees which normally pollinate this plant are relatively insensitive to the effects of these compounds (88). 

All these examples focus on the temporal aspect of nectar induction. In addition, extrafloral nectaries are also especially suited for the study of spatial dynamics following induction. This aspect can be easily assessed because of the discrete distribution of nectaries, the possibility of non-destructive sampling, as well as the ease of nectar collection. With respect to the spatial pattern of induction, Wackers et al. (2001) showed that the impact of herbivory on extrafloral nectar induction is primarily localized (i.e., restricted to the damaged leaf). This local increase in nectar production can help in actively guiding ants to the site of attack. In addition, a weaker systemic response was found. This systemic induction was restricted to the younger leaves. 

This and other recies of lilacs develop large numbers of ike-like inflorescences in the early ringtime before the leaves have developed. These flowers are rich in nectar and fragrance and are pollinated by inseds. 

Amino acids are the most abundant of the other nutrients present in nectar. The relative proportions of amino acids versus sugars, and the acidity of nectar can change during the day. This may influence the timing of flower visits by specific nectar-seeking visitors, but the significance of these daily changes is not fully understood. 

RAGUSO, R.A., WILLIS, M.A., Synergy between visual and olfactory cues in nectar feeding by naive hawkmoths, Manduca sexta. Anim. Behav., 2002, 64, 685-695. 

The average and the range of Cs and activities found in nectar honey (meadow nectar, bush-tree, and mixed honey) that was collected between 1990 and 1996 in Croatia are presented in Table 10.3. Previously documented trends showed year to year reductions in the activity levels of Cs in bush-tree and meadow nectar honey types [19,37]. This finding was confirmed by following the Cs activity in nectar honey types up to 1996. Ten years after the serious cesium contamination event of the Chernobyl accident, Cs activity in nectar honey types has become very low, frequently below the instrument detection limit. On the basis of data presented in Table 10.3, it is evident that for each successive year, Cs activity in nectar... 

Spectrophotometry as a Tool for Dosage Sugars in Nectar of Crops Pollinated by Honeybees... 

The study of sugar from floral nectary is important for identification if a rise or decrease in quantity or nectar quality. The plant may secret a little bit of nectar, but with high sugar concentration, or unlike, secret more quantities, but with low sugar concentration. These differences in nectar may vary depend on pollinator visitation. However, the frequency of honeybees that visit flowers may contribute for rising nectar production like change the sugar proportion. 

Other factors that must be considered are secreted sugars sucrose, glucose and fructose. The quantities of them may vary depending on variety and type of vegetal. Honeybees have preference for nectar with more sucrose concentration. Sugars present in nectar are related with honey quality that will be produced by honeybees and, finally will be commercialized. 

There are several enzymatic methods for determination of the three principal sugars individually present in nectar - fructose, glucose, and sucrose, and in biological samples like plasma, blood, and urine. A lot of these methods are commercialized in kits and can be used successfully for rapid determination of the sugar from natural products samples. These kits are precise and sensitive, which enable rapid analysis and reliable results. 

Fig. 5. Total sugar and glucose contents in nectar of siratro flowers along two-day period reprinted from Toledo et al. (2005) with permission.

Analysis of sugar composition in nectar can be used for detecting variation between flowers or nectaries from different taxonomic varieties, and consequently generate differences in type and frequency of visitation of pollinators. Alves et al. (2010) studied the total sugar concentration in soybean nectar Glycine max L. Merrill) var. Codetec 207 by spectrophotometry, using the general method for carbohydrates determination by phenol-sulphuric technique (Dubois et al., 1956). 

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