Yearlong association of Apis dorsata and Apis florea with flowering plants : planted forest vs . agricultural landscape

Honey bees play a vital role in crop production and in preserving the wild habitats. They have coevolved with native flora and sometimes this coevolution results in specialized relationships. Because of their diverse nesting strategies and specific host plant biochemical relationships, honey bees are regarded as the most suitable social insect for the monitoring of environmental processes (Nathan et al., 1999). There are three native honey bee species in Pakistan i.e. the wild bee or rock bee, Apis dorsata (Fabricius, 1793); the little bee or dwarf bee A. florea (Fabricius, 1787) and domesticated bee, A. cerana (Fabricius, 1793) whereas, the exotic Italian bee, Apis mellifera (Linnaeus, 1758) has been successfully domesticated since 1977. Apis cerana occurs in Northern and Western hills and foot-hills in some parts of KPK, Punjab, Baluchistan and Kashmir, while the A. dorsata and A. Abstract The yearlong association of two native honey bee species (Apis dorsata and A. florea) with 49 plant species was recorded in a planted forest and adjacent agricultural landscape at Multan, Pakistan. The study resulted in 588 interactions of A. dorsata with 40 plant species and 454 interactions of A. florea on 38 plant species. The most visited plants species by A. dorsata included Helianthus annuus, Citrus reticulata, Trifolium alexandrinum, Moringa oleifera and Calotropis procera, while the most visited plant species by A. florea included C. procera, Mangifera indica, T. alexandrinum, Coriandrum sativum and H. annuus. The peak abundance of bees and floral resources (i.e. number of plant species in flowering and abundance of floral units) was recorded during early March to late May followed by a gradual decline until December. Monthly abundance of both bee species was positively related to the floral resources, negatively related to relative humidity while it was not significantly related to temperature. The current study may serve as a baseline to track the degradation in ecosystem service of cross pollination and making new conservation strategies at local scale while future research should focus on tempospatial variations in foraging preferences, floral constancy and effect of foraging competition on crop pollination in different ecological regions of Pakistan. Sociobiology An international journal on social insects


Introduction
Honey bees play a vital role in crop production and in preserving the wild habitats.They have coevolved with native flora and sometimes this coevolution results in specialized relationships.Because of their diverse nesting strategies and specific host plant biochemical relationships, honey bees are regarded as the most suitable social insect for the monitoring of environmental processes (Nathan et al., 1999).
There are three native honey bee species in Pakistan i.e. the wild bee or rock bee, Apis dorsata (Fabricius, 1793); the little bee or dwarf bee A. florea (Fabricius, 1787) and florea occur in the foot hills and plains of Pakistan.Although Asia is not rich in bee diversity compared with some other biogeographical regions e.g.Neotropics (Michener, 1979) however, social bees (Apis sp.) -in terms of their abundance play a critical role in maintaining the vital ecological process of cross pollination (Momose et al., 1998;Roubik et al., 2005;Devy & Davidar, 2006).
Both, A. dorsta and A. florea tend to migrate locally in response to the availability of floral resources and have the ability to increase rapidly in number in response to flowering events (Itioka et al., 2001).Honey bees require carbohydrates, proteins, fats, minerals, vitamins, and water for the maintenance, growth and development of their colonies (Loper & Berdel, 1980).These elements are sourced by flowering plants in shape of pollen and nectar.However, the foraging activity of honey bees is greatly influenced by the weather conditions and availability of nectar and floral resources (Neupane & Thapa, 2005).
A sharp decline in number of honey bee combs has been reported during last two decades in neighboring India (Sihag, 2014) however, for Pakistan, there is no study in hand based on systematic observations.The decline is probably due to the increase in pesticide usage and destruction of natural habitats (Kremen et al., 2002).Khan et al. (2002) reported the direct annual loss of 9.91 million rupees on account of a loss of 5661 MT of honey while net annual loss of 6.55 million rupees in sunflower production in the selected nine districts of the cotton zone of Punjab, Pakistan.
The associations between plant diversity, social bee abundance, honey production and local livelihoods have poorly been documented for Pakistan.The flora visited by honeybees remains scarce in most parts of the beekeeping areas for a fairly long period during the year (Ahmad, 1984;Aziz, 2015).Moreover, the strong turnover in quality and quantity of floral resources are known to influence the behavior and foraging strategy of pollinator species (Subbareddi & Reddi, 1994;Murugan et al., 1997).
Site list of floral host plants, their temporal dynamics in providing floral resources and ways they interact with honey bees temporally, serve as baseline studies without which it is difficult to track the degradation in ecosystem service of cross pollination and making new conservation strategies (Mark et al., 2002).Several preferred plant species for managed honey bees (A.mellifera) have been documented from Himalayan foothills and northern Pakistan (Noor et al., 2009;Partap, 1997) however no such data is available for the plain areas of Southern Punjab.The purpose of this study was to enlist the floral host plants and identify the Apis most loving plant species for the first time from southern part of Punjab, Pakistan.Moreover, we hypothesized that seasonal population fluctuations of Apis is influenced by abiotic (relative humidity and temperature) and biotic (number of plant species in flowering and total floral abundance) factors.

Materials and Methods
The study was conducted in a planted forest of 20 hectares and an adjacent agricultural farm at Bahauddin Zakariya University campus Multan (30.255°N; 71.513°E; 114±6 meter above sea level), Pakistan from January to December, 2008.The planted forest is comprised of trees/ shrubs of the species Prosopis juliflora, Moringa oleifera, Eucalyptus camaldulensis, Tamarix aphylla, Albizia procera, Ziziphus jujuba, Dalbergia sissoo, Capparis decidua, Leucaena leucocephala and Acacia nilotica.Besides planted trees, there also grows a variety of natural vegetation including annual wild plants and perennial shrubs (Table 1).Some seasonal crops and fruit trees are grown in adjacent agricultural landscape including Helianthus annuus, Trifolium alexandrinum, Coriandrum sativum, Momordica charantia, Brassica campestris, Daucus carota, Allium cepa, Citrus reticulata, Grewia sub inaequalis and mangifera indica.Climate of the area is sub-tropical with a long hot summer and short cold winter.The mean daily maximum and minimum temperatures are in the range of 30 to 35°C and 15 to 20°C, respectively with the mean monthly summer rainfall of ca.18mm.The highest temperature (45 to 51°C) is recorded in May and June while the lowest (3 to 0°C) is recorded in January (Khan et al., 2010).
A variety of annual wild plants and perennial shrubs naturally grow in the forest.There were eight hives of A. dorsata while the number of hives of A. florea was uncertain as they are smaller in size and mostly build combs in thick vegetation.As different plant species had different type of inflorescences, we defined the floral units for each plant species separately and each time recorded observations on those floral units.Floral abundance was estimated by randomly tagging 15 plants of each plant species and counting total floral units at every two weeks interval.
During each census, we performed random walks in forest and selected15 plants of each plant species at their flowering stage.For agricultural crops, 15 plants were selected randomly from the margins of the field.Each plant was observed for 60 seconds in its floral units for any visit of honey bees.In this way there was a total of 15 minutes of observation per plant species in one census.Only those plant species were selected which were in the phase of flowering.
For each plant we counted the number of visiting individuals of both Apis species by visual observation.Visiting bees other than Apis species were also recorded during the census.The census of each flowering plant species was carried out at two weeks interval throughout the flowering period.The observations were taken on clear sunny days, while rainy or cloudy days were avoided.
To avoid the phenomenon of floral constancy i.e. bees tend to visit single plant species even in the presence of many other flowering plant species in that particular area (Gruter et al., 2011), we selected wild plants of a particular species at a considerable distance from each other (>50m).
We used rank-abundance plot with fitted curve as a way to visualize the overall visitation pattern of bees on 36 plant species (Magurran, 2004).Frequency distribution test was applied to identify various classes of plant species based on abundance of Apis bees.We used linear regression analysis to explore the relationship between abundance of bees and abiotic (relative humidity and temperature) and biotic (number of plant species in flowering and total floral abundance) factors.

Results
A total of 72 flowering plant species in 30 families were observed for recording the visitation of A. dorsata and A. florea.The total sampling efforts of 121 hours yielded 1049 interactions of both bee species (constituting 44.36% of total native bee visits) on 49 plant species in 26 families (Table1).Twenty three plant species in 18 families were not visited by any of the two Apis species (Table 2).A total of 588 individuals of A. dorsata were recorded on 40 plant species in 21 families while 454 individuals of A. florea were recorded on 38 plant species in 19 families.Eleven plant species were exclusively visited by A. dorsata while 13 by A. florea.Twenty five plant species were visited by both the bees (Table 1).
The rank abundance curve shows only a few plant species with higher bee abundance while many plant species showed lower bee abundance (Fig 1).The frequency distribution test identified five classes of plant species based on visitation frequency of both bee species.Calotropis procera (class 1) was visited by the maximum number (129) of bees followed by Helianthus annuus, Trifolium alexandrinum (class 2) and Citrus reticulata and C. sativum (class 3).Class 4 included ten plant species while class 5 included 34 plant species (Table 1).Monthly abundance of both bee species was positively related to the floral resources i.e. number of plant species in flowering (y = 10.43x-15.81,R² = 0.338, P = 0.047) and abundance of floral units (y = 0.029x -31.76,R² = 0.382, P = 0.032).The monthly abundance of bees had a significant negative relationship (y = -5.674x+ 474.9, R² = 0.409 P = 0.025) with relative humidity while no relationship was verified with temperature.availability of food in general while livelihoods of local communities in specific (Devy & Davidar, 2006).
Therefore, in order to maintain honeybee populations, it is important to ensure the conservation and management of sufficient forage resources within agricultural and surrounding natural landscapes (Zhang et al., 2007).These resources include both suitable nesting habitat and sufficient floral resources i.e. nectar and pollen (Kremenet al., 2007).In various parts of India, A. dorsata, A. cerana, A. florea and A. mellifera are the most effective pollinators (Chandel et al., 2004).Apid bees probably play an important role in pollinating crop plants in India, although quantitative data are lacking (Potts et al., 2003).
Twenty five plant species were visited by both Apis species.There was evidence of ecological niche overlapping among them i.e. value of Pianka's index was 0.66 (simulated indices mean = 0.66, simulated indices variance = 0.000, P (observed >expected) = 0.122) at alpha 0.05.Different floral nectar compositions are preferred by different species (Abrol, 2011).For example, A. florea prefers flowers having low caloric rewards (Sihag & Rathi, 1992) whereas A.dorsata prefers flowers with high caloric rewards.Similarly, in our studies, A. dorsata did not visit two of the most preferred host plants of A. florea i.e.M. indica; C. sativum which contain low nectar rewards.
Twenty three plant species were not visited by both of the Apis species.However, some of these plant species have already been reported as good source of pollen and nectar for A. mellifera i.e.Sisymbrium irio, Cucumis prophetarum, Medicago sativa (Taha, 2015).Besides this, there seems no specific reason of avoiding some other very good sources of nectar and pollenin this study like Mangifera indica, Conyzacan adensis, Cajanus cajan, Abutilon indicum and Torilis japonica etc.This might be due to the marked behavior of floral constancy among bees (Amaya-Marquez, 2009).Floral constancy is the behavior of restricting visits largely to a single floral type (Waser, 1986) yet little is known about the reasons and thereby no any general theory is in place that can explain all kinds of floral constancy (Amaya-Marquez, 2009).This constraint suggests taking into account rather a large geographical area when attempting quantification of floral host plants of bees in order to avoid this behavior.

Discussion
In this study, we recorded 1049 visits of both Apis species which constituted 44.36% of the total pollinating bee visits.This high abundance of honey bees signifies the importance of semi-natural habitats (i.e.forest in our case) in maintaining the viable population of pollinators (Johannsmeier & Mostert, 2001).Moreover, the size and quality of seminatural habitats have been reported to impact significantly on the bee abundance in adjacent agricultural landscapes (Liow et al., 2001).Since insect pollination contributes 75% of total global crop pollination while honey bees constitute 70-80% of insect pollination (Klein et al., 2007), loss of honey bees therefore can significantly impact the biodiversity and The seasonal dynamics revealed the peak activity of both Apis bees during early March to late May (summer months) while almost no activity was recorded from November to January (winter months).This could be due to the availability of high foraging resources in summer months compared to the winter months as it is clear from the significant positive relationship of monthly bee abundance with the floral resources (number of plant species in flowering and availability of floral units) in our data.Hussein et al. (1992) also reported the maximum honeybee foraging activities during the summer months (July to September) and minimum in winter months (November to January).Whereas, it has also been studied that A. dorsata migrates locally in response to the availability of floral resources and its abundance showed positive relationship with the floral resources (Itioka et al., 2001;Sihag, 2014).
The monthly bee abundance was also found to have significant negative relationship with relative humidity while it had no relationship with the temperature.The previous studies have also reported a decreased daily activity of honey bees on the days characterized by maximum temperature and highest humidity (Nargis et al., 2001;Kumar et al., 2002;Mordago et al., 2002).High humidity, heavy rain fall, wind and low temperature had negative influence on sunflower inflorescences visits.
Knowledge of the honeybee flora of an area is a basic tool for the development and sustainability of apiculture as well as commercial agricultural crop pollination (Dimou et al., 2006).The availability of adequate forage resources positively impact the honeybee colony health and beekeeping profitability leading to improved crop pollination (van Engelsdorp & Meixner, 2010).The current study may serve as a baseline to track the degradation in ecosystem service of cross pollination and making new conservation strategies at local scale while future research should focus on tempo-spatial variations in foraging preferences, floral constancy and effect of foraging competition on crop pollination in different ecological regions of Pakistan.

Fig 1 .
Fig 1. Rank abundance curve based on population of A. dorsata and A. florea on 49 plant species at Bahauddin Zakariya University Campus, Multan, Pakistan during January to December, 2008.

Fig 2 .
Fig 2. Monthly abundance of A. dorsata and A. florea at Bahauddin Zakariya University Campus, Multan, Pakistan during January to December, 2008.

Fig 3 .
Fig 3. Availability of floral resources (number of flowering plant species and floral abundance) at Bahauddin Zakariya University Campus, Multan, Pakistan during January to December, 2008.

Fig 4 .
Fig 4. Average monthly temperature and relative humidity at Bahauddin Zakariya University Campus, Multan, Pakistan during January to December, 2008.

Table 1 .
Monthly abundance of bees, on 49 plant species at Bahauddin Zakariya University Campus, Multan Pakistan during January toDecember, 2008.

period Flower color A. dorsata A. florea Total Class boundary Lower- Upper (contribution to ᵡ² )
The plant species most visited by A. dorsata included H. annuus, C. reticulata, T. alexandrium, Moringa oleifera and C. procera, while the most visited plant species by A. florea included C. procera, M. indica, T. alexandrium, Coriandrum sativum and H. annuus (Table1).

Table 2 .
Plant species which were not visited by A. dorsata and A. florea during January to December, 2008.