Journal Archive

Pollination studies in cucumber hybrids, viz. Evergreen, NBH-Manu, Damini and Rani, was conducted at research farm of the Department of Plant Pathology and Apiculture Laboratory of the Department of Entomology, CCS Haryana Agricultural University, Hisar (India) during the rainy season, i.e., April to August 2012. The experimental site is situated at 29°10¡˙North latitude and 75°46’ East longitude at an altitude of 215.2 meter above mean sea level. The climate of Hisar region is semi-arid and is characterized by hot and dry winds during summer months and dry and severe cold conditions during winter months.

The maximum and minimum temperature shows wide range of fluctuations during summer, while the temperature below freezing point accompanied by frost may also be recorded during winter months (December- January), which is very common feature of this region. The rainfall is confined mainly to the monsoon months from July to September but light showers cyclonic rains also occur sometimes during winter and spring months.

The soil of the field was sandy-loam with moderate fertility and pH 8.0, indicating slightly alkaline nature of the soil. Based on soil analysis, the soil of the experimental field was low in nitrogen, medium in organic carbon (0.33%), available phosphorus (8kg/ha) and rich in potassium (480kg/ha). Well-decomposed two years old farmyard manure was incorporated into the soil @ 10 t/ha at the time of field preparation. The field was prepared up to fine tilth by giving repeated ploughings with disc harrow followed by planking. The field was first divided into plots of 10m width and 40m length in which the channels of 40cm width and 20cm depth were opened manually with the help of spade at a distance of one meter.

For raising a healthy crop, 50kg nitrogen, 25kg phosphorus and 25kg potash fertilizers were applied per hectare at the time of last ploughing. The seeds of four varieties before sowing were treated with Captan @ 3g/kg of seed and soaked in water over night to hasten germination. Thereafter, the seeds were dried in shade before sowing. The seeds were sown in plots on 25^th March 2011. Per hill, two seeds were sown on the edges of the raised beds keeping a distance of 2m between rows and 50cm between plants. The first irrigation was applied soon after sowing and subsequent irrigations were applied in furrows at an interval of 5~6 days. During vegetative phase, the crop was protected from the attack of red pumpkin beetle by spraying the vines with 0.2% carbryl 50 WP.

A cone type of hand net (30cm) was used to collect insects on the cucumber flowers throughout the blooming period. Sweepings were made at weekly intervals during April to August at two hourly intervals from morning to evening. The collected insects were preserved as dry specimen and got them identified from Insect Identification Service, Division of Entomology, I.A.R.I., New Delhi.

Abundance of different insect visitors of cucumber crop was studied during their blooming period. The total number of different insect visiting on the cucumber flowers of two randomly selected per meter row for five minutes of each hybrid was recorded following the method given by Free (1993). These observations were started when 50% of the plants came into bloom.

Foraging rate of bees was recorded in terms the number of flowers visited per minute following the method given by Free (1993). The total of ten bees of each species were observed for recording time spent by them on flowers of each variety of cucumber and number of flowers visited per minute at two hours interval from 0600 to 1800 h at weekly interval on calm, clear and sunny day during flowering time were counted for 8 days. The number of flowers visited per minute was recorded including the flying time from one flower to another flower.

The loose pollen grains sticking to the body of different bee species were estimated. The bees were captured gently by forceps to avoid shaking of its body from the flowers and its hind legs were amputated following the method given by Kumar (1990). The bees were captured on their peak activity during peak flowering and kept in 70 per cent alcohol in glass vial (9×3cm) after amputating the hind pair of legs very gently. The bees were shaken vigorously to wash out the pollen grains from their body. The total volume of the rinsate was made to 5ml before pollen count. An aliquot, 0.01ml (replicated 5 times) was taken and with the help of a haemocytometer and binocular microscope (15×10 magnification), the number of pollen grains were counted. The total number of pollen grains in the whole rinsate was calculated. Identity of the cucumber pollen grains were accomplished with standard pollen slides. The ten individuals of each bee species were captured for counting the number of loose pollen grains. For the study of pollen grains, insects were captured between 1000 and 1200 h of the day.

Comparative pollination efficiency of different bee species were assessed on the basis of their relative abundance, foraging behaviour parameters such as foraging rate and the amount of loose pollen grains sticking to their bodies. The pollination index was calculated by the following the method suggested by Kumar et al. (2012).

The data pertaining to relative abundance, foraging rate and loose pollen grains were statistically analyzed by using factorial complete randomized design (CRD). Comparative pollination efficiency of different bee species was assessed based on the relative abundance and foraging behaviour.

The abundance of C. sexmaculata (2.79 bees/m²/5 minutes) was highest followed (Table 2) by Halictus sp. (2.69 bees/m²/5 minutes), while A. dorsata was least abundance (0.78 bees/m²/5 minutes). Apis dorsata entrapped maximum number of pollen grains (av. 113690.00 pollen grains) followed by Halictus sp. (av. 47040.00 pollen grains) and C. sexmaculata (av. 43620.00 pollen grains), but the pollination index of Halictus sp. was highest (126537.60) followed by C. sexmaculata (121699.80) and A. dorsata (88678.20). Hence, it was observed that Halictus sp. was the most efficient pollinator followed by C. sexmaculata and A. dorsata on C. sativus flowers under ecological conditions of Hisar (Haryana).

Large number of insects visits the cucumber flowers during the peak flowering period. Free (1993) reported that plants with many flowers attract more floral visitors than those with fewer flowers. In the present investigation, a fluctuation in visits of insect pollinators on different days on cucumber flowers was observed. The visits were low at the time of commencement and cessation of the flowering but these remained high during mid flowering period. This difference might be due to variation in the floral density during the span of blooming on the crop. Kendell and Smith (1975), Schemske (1980) and Dhaliwal and Atwal (1985) also stated that the number of flowers was more at the peak flowering and these were visited by larger number of pollinators and helped maximization of pollination in different crops. Cucumber flowers at Hisar (Haryana) were visited by 12 Hymenopterans, viz. Apis dorsata Fab., Ceratina sexmaculata Smith, Halictus sp., Apis mellifera, Megachile cephalotes Smith, Apis cerana Fabricius, Megachile bicolor Fabricius, Vespa auraria Smith, Vespa orientalis Linnaeus, Polistes hebraeus Fabricius, Eumenes petiolata Fabricius, Eumenes dimidiatipennis Sauss, 6 Lepidopterans, viz. Utethesia pulchella Moore, Lampides boeticus Linnaeus, Parnara sp., Anosia plexippus Linnaeus and two unidentified, 3 Dipterans, viz. Musca sp., Chrysomyia sp. and Eristalis sp., 2 Hemipterans, viz. Nezara graminea Fabricius and Dolycoris indicus Stal and 1 Coleopteran, viz. Epilachna dodecastigma Wiedemar. Among these insects, Halictus sp., C. sexmaculata and A. dorsata were the most frequent visitors. In general, diversity of pollinating insects varies from region to region and locality to locality. McGregor in 1976 stated that insects of many species visited the cucumber flowers and pollinated them. These include bees, wasps, moths, butterflies, beetles, thrips and midges. However, bees were the most efficient and the only dependable pollinators. Kauffeld et al. (1978) listed 37 species, frequenting cucumber blossom in Louisiana (USA). Cervancia and Bergonia (1991) observed that the most common flower visitors of cucumber were Xylocopa chlorine (Cockerell), X. philippinensis Smith, Megachile atrata Smith and Apis dorsata Fabricius in Philippines. Total 24 species of insects were found visiting the cucumber flowers, predominantly Hymenopteran, and among bees, Apis dorsata was the most frequent visitor (Sajjanar et al., 2004). The results of the present investigations and almost similar to those reported by earlier workers (McGregor, 1976; Kauffeld et al., 1978; Cervancia and Bergonia; 1991 and Sajjanar et al., 2004). In the present study, the pollination efficiency of Halictus sp. and C. sexmaculata was much more than the efficiency of A. dorsata on C. sativus bloom under ecological conditions of Hisar (Haryana). This was due to the higher abundance of these bees. However, Stanghellini et al. (1997) observed that honey bees were the best pollinators of cucumber and watermelon followed by bumble bees. Kumar (2002) reported that Melissodes sp. was considered the best pollinator of cucumber followed by Sarcophaga sp. at Hisar.