FLOWERING , NECTAR PRODUCTION AND INSECTS VISITS IN TWO CULTIVARS OF CUCURBITA MAXIMA DUCH

The study was conducted on experimental plots in the conditions of Lublin. In the years 1998–2000 fl owering, nectar secretion and insect visitation of male and female fl owers of two winter squash (Cucurbita maxima Duch.) cultivars: ‘Ambar’ and ‘Amazonka’, were studied. The plants fl owered from July to October. The fl ower life span was within the range of 7–10 hours. Female fl owers of cv. Ambar were marked by the most abundant nectar secretion (129 mg). The nectar sugar content can be estimated as average (25%–35%). Winter squash nectar contained 84% of sucrose as well as 8–9% of fructose and 7%–8% of glucose. Flowers of the studied taxa were frequently foraged by the honey bee (66%–98% of total insects) and bumblebees (1%–30%).


INTRODUCTION
Plants from the Cucurbitaceae family have been long cultivated and used by man in many ways.They are introduced into cultivation more and more readily due to their dietetic fruit.They are also appreciated as melliferous plants.Their apicultural value is associated with the prolonged time of fl owering and the supply of nectar over a long period of time (D e m i a n o w i c z , 1953; M a u r i z i o and G r a f l , 1969).Squash fl owers produce the largest amount of nectar among plants grown in our climatic conditions.One female fl ower can produce 400 mg of nectar (L i p i ń s k i , 1982; B a n as z a k , 1987).
The aim of the study was to compare the abundance of fl owering and the amount of nectar secreted by fl owers of two winter squash cultivars.The total sugar concentration and content of sucrose, fructose and glucose in nectar were also determined.The intensity of visitation of both sex fl owers by pollinating insects was observed.

MATERIALS AND METHODS
The study was conducted in the years 1998-2000 on experimental plots in Al.Warszawska street in Lublin (51 o 14 ' N and 22 o 32 ' E), on loess-based grey-brown podzolic soil.
Winter squash (Cucurbita maxima Duch.) plants belonging to two cultivars: Ambar and Amazonka, were seeded after 15 May and observations were made throughout the whole period of fl owering.
The observations covered the date and duration of fl owering, average fl ower life span, abundance of fl owering, including the proportion between the number of male and female fl owers, number of insect visits and time of insect visitation in fl owers on specifi ed dates in the years 1999-2000.The number of insects was recorded between 5.00 and 17.00, and results were given at 0.5-hour intervals.Nectar production was investigated using the pipette method, sampling at a time the amount of nectar from the whole fl ower life span (D e m i a n ow i c z et al. 1960).The percentage nectar sugar content was determined using the Abbe refractometer.Based on the average weight of nectar sugars and abundance of fl owering, sugar yield was calculated for the two studied taxa which was then translated into the so-called honey yield.In 2000, at the Puławy-based Division of Apiculture of the Institute of Pomology and Floriculture, the nectar sugar content was determined using gas chromatography in accordance with the harmonised methods of the European Honey Commission (B o g d a n o v et al. 1997).

Duration of fl owering
Observations of fl owering carried out in the years 1998-2000 demonstrated that, depending on the year and cultivar, the start of winter squash fl owering fell on different decades of July, and even the fi rst decade of August.The end of fl owering was noted from the second decade of September till the fi rst decade of October.The average duration of fl owering for winter squash was from 72 days (cv.Amazonka) up to 80 days (cv.Ambar) (Tab.1).

Flower blooming and fl ower life span
In their fi nal development stage, swollen fl ower buds of winter squash changed their colour from light green to yellow.After the bud reached the size of at least 2 cm, 5.5 days (female fl owers) up to 10 days (male fl owers) elapsed until the open fl ower stage (Figs 1, 2).
Changes leading to fl ower opening in most of the investigated plants started between 2.30 and 3.00.At this time, anther dehiscence and pollen release in the bud were also observed.The fl ower bud loosening was associated with the appearance of small slits visible at 1/3 height of the corolla length until the corolla petals took a position almost perpendicular to the fl ower axis.For both taxa, on the average, ½ hour elapsed from the loosening of petals at the bud apex to corolla opening.The duration of the open fl ower stage and hours of corolla opening and closing differed, depending on fl ower sex, cultivar and weather conditions in the particular year and month.In 1999 male fl owers opened ½ hour before female fl owers, whereas in 1998 the opening of fl owers of both sexes was almost simultaneous.Winter squash fl owers opened between 4.30 and 6.30.The duration of the open fl ower stage from corolla opening until corolla closing for winter squash was from 7 up to 10.5 hours.Winter squash fl owers closed between 13.00 and 17.00.The process of fl ower closing lasted about 1 hour (Fig. 4).

Abundance of fl owering
Intensively smelling fl owers of Cucurbita maxima Duch.cv.Ambar and cv.Amazonka have a fi ve-lobed, radial, yellow corolla with rounded lobes and the corolla diameter of 10 cm (Fig. 3).
When investigating the abundance of fl owering, changes in the proportion of the number of male to female fl owers were found in different growing periods.Generally, the number of male fl owers exceeded the number of female fl owers (5-20 times).On the average, winter squash cv.Ambar produced twice more male fl owers (162) than cv.Amazonka (77).But the average number of female fl owers of both cultivars was similar (Ambar -10, and Amazonka -11).The percentage share of male fl owers on the cv.Ambar plant was 94% and of female fl owers 6%, whereas for cv.Ambar it was 88% and 12%, respectively (Tab.1).

Nectar secretion
Nectar secretion in fl owers started soon after fl ower opening, that is, already in the fi rst hour of anthesis.
The average weight of nectar calculated for 10 fl owers indicates that female fl owers of winter squash cv.Ambar were marked by the most abundant nectar production -1 289.7 mg of nectar.Both winter squash cultivars are characterised by the production of a larger amount of nectar in female than in male fl owers (Tab.2).The higher three-year average of nectar sugar concentration was noted in the case of male (34.91%) and female (32.04%) fl owers of winter squash cv.Ambar.Cv.Amazonka exhibited similar percentage nectar sugar content in female fl owers (32.23%) and a smaller one in male fl owers (24.86%).The amount of sugars in nectar secreted by fl owers, that is, their sugar yield, is a measure of the abundance of plant nectar production.The three-year averages of sugar weight in nectar from 10 fl owers were the highest in female fl owers of winter squash cv.Ambar (393.3 mg).The lowest average values of nectar sugar weight were noted in male fl owers of winter squash cv.Amazonka (133.8 mg) (Tab.2).The studied taxa were characterised by a larger nectar sugar weight in female than in male fl owers.Female fl owers of both winter squash cultivars produced about twice more nectar sugar than male fl owers.Honey yield of winter squash.cv.Ambar was over 2.5 times higher than in the case of cv.Amazonka (Tab.2).
Winter squash was characterised by a high percentage content of sucrose in the investigated amount of nectar, 25.6 -27.8%, what made up a large percentage share of this sugar in total sugar content determined as 100% (83-84%).Monosaccharides were found in winter squash nectar in much smaller amounts, fructose in the range of 2.5-3.1% and glucose 2.4-2.5% (Tab.3).
Bees started their fl ower visitation between 7.00 and 7.30.The peak time of mass appearance of bees was between 8.00 and 12.30.The largest number of visits in one fl ower was noted in winter squash cv.Amazonka (141.5).A larger number of bee visits in male than in female fl owers was observed over their whole life span (Fig. 5).

DISCUSSION
The sequence of blooming of winter squash fl owers of particular sexes is different, depending on the vegetation year.Many authors (D e m i a n o w i c z , 1953; L i p i ń s k i , 1982; F a j k o w s k a , 1985; D or o f e e v et al. 1990; N e p i and P a c i n i , 1993; M as i e r o w s k a and W i e n , 2000) report that male fl owers appear on the plant from 2 up to 8 days earlier than female fl owers.The variation in these results can be explained by the correlation of the sex of fl owers produ-   It the present study, it was demonstrated that more male than female fl owers developed on plants of the studied taxa throughout the whole period of fl owering.The proportion of male to female fl owers in winter squash cv.Ambar was 16.6, whereas in cv.Amazonka it was 7.2.The advantage in the number of male compared to female fl owers was also noted by F a j k o w s k a (1985) and B a t t a g l i n i (1968) who observed 10 staminate fl owers per one pistillate fl ower on a squash plant.Similar results were obtained by N e p i and P a c i n i (1993) who found that 7.9 times more male than female fl owers were produced in summer squash (Cucurbita pepo).They add that this proportion may slightly change during vegetation.
In the taxa investigated in my study, the average number of female fl owers, produced by one plant over the whole growing period (winter squash cv.Ambar -9.7; cv.Amazonka -10.7) much exceeded the number given for summer squash by N e p i and P a c i n i (1993), which was 4.5.In summer squash, M a s i er o w s k a and W i e n (2000) noted the number of female fl owers within the range of 7.1 -13.5 in summer squash.
My observations show that fl owers of both winter squash cultivars were characterised by a short life span which was about 9 hours.Depending on the species and weather conditions as well as the time of the growing period, fl owers opened between 4.00 and 6.00 and closed between 10.00 and 17. M a u r i z i o and G r a f l (1969) reported that winter squash fl owers produced 201 mg of nectar with the nectar sugar concentration at the level of 20%.The study presented in the present paper shows smaller amounts of nectar secreted by winter squash fl owers: 132.2 mg (cv.Amazonka) -181.0 mg (cv.Ambar), but with higher sugar content of 24.9%-34.9%.My study proves that higher nectar secretion takes place in fema- 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00However, in the present study female fl owers of winter squash cv.Amazonka produced nectar with a higher sugar concentration than male fl owers.But K a z i e v a and S e i b o v a (1965) report that pistillate fl owers secret more nectar with a higher percentage sugar content.

Cultivars
D e m i a n o w i c z (1953) reports that squash nectar contains the largest amount of sucrose.According to Z a u r a l o v and P a v l i n o v a (1975) squash nectar is composed in 85% of sucrose, 6% glucose, 5% fructose and 3% oligosaccharides.Qualitative and quantitative analysis of nectar of two winter squash cultivars presented in the present study showed a similar percentage content of sucrose (83%-84%) and much larger amounts of glucose (8%) and fructose (9%).But no presence of oligosaccharides was found.
Winter squash fl owers were mainly visited by bees and bumblebees, to a smaller extent by fl ies, beetles as well as ants.Bees accounted for 66%-98% of total insects.Numerous authors claim that the Cucurbitaceae are visited and pollinated primarily by bees (Ve r d i e v a and I s m a i l o v a , 1960; W o l f e nb a r g e r , 1962).B a n a s z a k (1987) reports that in the process of pollination of the Cucurbitaceae, apart from the honey bee, the large earth bumblebee and small garden bumblebee may be of some signifi cance.Within America, squash fl owers are visited by the honey bee, however, wild bees perform the main role in pollination and fruit set.Wild bee species belonging to Peponapsis and Xenoglossa collect eagerly not only nectar but also pollen of the Cucurbitaceae (M a u r i z i o and G r a f l , 1969; F r e e , 1970; W i l l i s and K e v a n , 1995).
My observations demonstrate that bees started foraging soon after the complete opening of winter squash fl owers: 7.00 -7.30.Other authors give different hours of visitation of Cucurbitaceae fl owers by bees.L i p i ń s k i (1982) also states that bees start visitation of fl owers after their opening.S a n d u l e a c (1959) noticed that squash fl owers were pollinated by insects between 6.00 and 12.00.According to A t w a l (1970) insect visits took place between 7.00 and 10.30.
In the conditions of Lublin, the peak time of mass appearance of bees was between 8.00 and 12.30.S a nd u l e a c (1959) gives a shorter time range: 8.00-9.00,relevant to three species: Cucurbita maxima, C. pepo and C. moschata.N e p i et al. (1996) demonstrated that the maximum frequency of insect visits in summer squash fl owers also lasted an hour, but it started as early as 7.00.The presented time differences are undoubtedly associated with different climatic conditions relating to the observations made.
The observations of the present paper's author showed that, in the case of the winter squash cultivars studied, a larger number of bee visits related to male fl owers, 16.1 -141.5 (on the average, 65.3), than female fl owers, 14.4 -82.9 (on the average, 49.2).The observations were carried out throughout the whole fl ower life span.Ve r d i e v a and I s m a i l o v a (1960) confi rm that honey bees are more prone to visit better visible male fl owers growing on long stalks.But S a n d u l e a c (1959) observed in winter squash 22.8 visits in the female fl ower and 16.1 in the male fl ower between 8.00 and 9.00, which was the peak time of bee foraging.
00.Many authors (Mc G r e g o r , 1976; L i p i ń s k i , 1982; B a n a s z a k , 1987; D o r o f e e v et al. 1990; P h i l i p p e , 1991; N e p i and P a c i n i , 1993; N e p i et al. 1996) confi rm the short duration of the open fl ower stage in squash.Similar hours of fl ower opening were noted by: N e p i et al. (1996) 5.00 -6.00; M a s i e r o w s k a and W i e n (2000) 5.00, and slightly later hours by D o r o f e e v et al. (1990) 6.00 -8.00.The opening of fl owers of both sexes lasted about 1/2 hour and closing about 1 hour.It is consistent with the description of the process of closing and opening of summer squash fl owers contained in the paper by N e p i and P a c i n i (1993).

Fig. 4 .
Fig. 4. Life span of male and female fl owers of two cultivars of winter squash in 1998-1999 years.
Characteristic of nectar producted in two cultivar Cucurbita maxima fl owers.Period and abundance of fl owering two cultivars Cucurbita maxima.le fl owers.F a h n (1949) and N e p i et al. (1996) also claim that pistillate fl owers secret more nectar than staminate fl owers.