**Abstract**

Survival and reproduction of several wild plants and crops is mostly by insects pollinator, their recognition and importance have been increased in this climatic changing scenario, which affects the various aspects of their life cycle. According to an estimate, approximately 30,000 species of bees are known in entomology, and about 190 species of bees have been reported to be associated with pollination. There can be an established link between seed production and pollinator diversity, for the plants with a generalist pollination system. The increasing of human habitation affects insect pollinators in various ways, i.e. of habitat destruction, results in low availability of food sources, nesting, oviposition, resting, and mating sites. Pollinator availability restraints the geographical distribution of plant species, i.e. to develop an ecological niche of certain plant species. Failure of pollinator- plant interaction mutualism results in lower seed production and sometimes extirpation of plant population has been recorded. The declining pollinators' population strengthens existing plant-pollinator interaction or allows new pant pollinator interaction to form. Maintaining the commercial and wild pollinator populations and preventing future shortages of pollination services, therefore, is extremely significant.

**Keywords:** agro-ecosystem, ecology, plant-pollinator interaction, pollinator, pollination, sustainable

#### **1. Introduction**

Plant and pollinator interaction results in the pollination of various plants that are *self*-*incompatible*. These pollinating agents are important for the existence and reproduction of about 87.5 percent of wild species of plants [1, 2]. Pollinators are important to increase agriculture production and in ecosystem functions to increase plant genetic diversity [3, 4]. The total annual economic value of crop pollination around the world has been estimated at about €153 billion [5]. Klein et al. [4], surveyed that more than 87 of the world's leading food crops, representing 35 percent of global food production, depends upon animal pollinators, pollination by insect directly contributed about \$20 billion and that of honey bee contribution was \$14.6 billion in 2000 in the U.S [6]. The total economic value of insect pollination of

Chinese fruits and vegetables recorded about52.2 billion US dollars in 2008, which represented 25.5% of the total production value of the 44 crops produced in China [7]. The area among the pollinator-dependent crops has increased up to 300% during the last 50 years, both in temperate and tropical crops [8, 9]. Pollination is an essential prerequisite to seed and fruit development; it is a pivotal, keystone process and insects provide an important function in both natural and managed ecosystems [10, 11]. The mutual relationship has been found between insect pollinators and flowering plants, that in return nectar and pollen are major food rewards for pollinators.

Robbins et al. [12] reported that most accepted estimates indicate honeybees' account for at least 80% of all insect pollination. For decades the consequences of insect pollination have been documented in treaties by Free [13], McGregor [14], and Pesson and Louveaux [15]. In apiculture the most important species, *Apis mellifera* L. has been reported as the single most important pollinator [13, 14]. The pollinating potential of a single honeybee colony becomes evident when it is recognized that its bees make up to 4 million trips per year and that during each trip an average of 100 flowers are visited [16].

#### **2. Pollinators diversity in agro-ecosystem**

An enormous number of the world's insect diversity visits flowers for nutrition, but all are not efficient pollinators. Among crop foods, fibers, edible oils, medicines, and other valuable products, a significant production occurs due to the vital role of insects and other animal pollinators. In all types of ecosystems, bees are recognized as the most valuable pollinators, but their precise roles in pollination are not well documented. According to estimation, approximately 30,000 species of bees are known in entomology, and about 190 species of bees have been reported to be associated with pollination in North America. Some of the other noteworthy contributors in pollination are; alkali bee (*Nomia melanderi* Cockerell) found as solitary bees to pollinator in alfalfa and alfalfa leaf cutting bee (*Megachile rotundata* Fabr.) also play its role in the pollination of this crop [17–20]. Through artificial mud nesting tunnels, orchard bees (*Osmia* spp.) can be managed in the field for pollination, as orchard bees are far much better for apple pollination than honeybees [21]. Another, bumblebees (*Bombus* spp.) are pollinators of red clover (*Trifolium pratense* L.) and cranberries (*Vaccinium macrocarpon* Ait.), but difficult to manage in field conditions [22]. Carpenter bees (*Xylocopa* spp.) are the outstanding pollinators of vine crops, especially of passion fruit (*Passifloraedulis* Sims), giant granadilla (*P. quadrangularis* L.), kiwi-fruit (*Actinidia deliciosa* (A.Chev.) C.F. Liang & A.E. Ferguson), various gourds, and winged beans (*Psophocarpus tetragonolobus* (L.)) but there is not much available data on these pollinators.

The interdependency of plants and pollinators vary in their degree, some plants species depend primarily on a single species of pollinator, which in turn has restricted sources of pollen or nectar. One example of a closely dependent association is the interaction between plant Yucca (Agavaceae) and its pollinators, yucca moth (*Tegeticula* spp.), having a mutualism estimated to be more than 40 million years old [23]. Squash crops i.e. pumpkins and gourds are pollinated by specialized squash bees, *Peponapis* spp. and *Xenoglossa* spp., and are more manageable, they nest in underground burrows and become active at dawn, visiting cucurbit flowers until about midday when unisexual flowers close [24, 25]. There are many other pollinator native bees, which include sunflower bees (*Eumegachile pugnata* (Say) [26], blueberry bees (*Habropoda laboriosa* (Fabr.)) [27], and *Osmia ribiflloris* Michener (**Table 1**) [28–30]. Oil palm weevil, *Elaeidobius kamerunicus* as the most

#### *Pollinators: Their Relevance in Conservation and Sustainable Agro-Ecosystem DOI: http://dx.doi.org/10.5772/intechopen.100531*

valuable in terms of the economic importance of this crop at the world trade level [31]. Non-biting midges, *Forcipomyia* spp., a specialty pollinator among the cocoa (*Theobromacacao* L.) crop, which breeds in rotting vegetation in its plantation [32] are a few of specific examples of pollination to produce the economic plants/crops that are in need of human beings.

Among the herbivorous insects, the interaction of butterflies and moths is found during both its larval and adult stages and the latter is involved in pollination (**Table 2**). Some of these are *Heliconius* butterfly [41, 42]; yucca moth [43], obligatory mutualisms are exceptional in order Lepidoptera of pollinators. Moths from the families Geometridae, Noctuidae, and Sphingidae are among the most studied moths to be known as pollinators, their pollinating activity takes place at night in many plants such as cacti, orchids, trees [44–47]. Many had also identified and reported thrips on flowers and they noticed that thrips feed on pollen so that they


#### **Table 1.**

*Bees and specific plant fauna they visit and pollinate.*


#### **Table 2.**

*Beetles, butterflies, and moths with specific plant fauna they visit and pollinate.*

can be effective pollinators or minor or secondary pollinators of a wide variety of plants in agro-ecosystem or nature [48–52].

### **3. Pollinators and plant interaction**

In an ecosystem, the interaction between the organisms favors co-evolution and it gradually helps to evolve together for some betterment or for existence in nature. Those plants having a generalist pollination system, have a link between pollinator diversity and seed production can also be established [53]. Pollination biology (**Figure 1**) draws attention to both evolutionary and ecological approaches i.e. the link between pollinator behavior and plant mating patterns, generalization, and specialization in a pollination system [24, 54, 55].

There are many reasons for which pollinators visit flowers, including feeding, pollen collection, warmth in some cases, oils and resins, as well as for shelter and mating rendezvous sites [56]. These plant and pollinator interactions as mutualisms sustain not only plant diversity, but also the diversity of an estimated 350,000 animal species, including insects, birds, and mammals [57–59]. Ratto et al. [60] reported an average 63% loss of fruit or seed production when vertebrate pollinators are excluded from the flowering plants' ecology they visit. These results often reported experimentally that selective exclusion of a single group of an effective pollinators from plant-pollinator interaction can result in the failure of plants to produce fruits or seeds.

Diversity of pollinators in habitat can compete for floral resources [61], the declining pollinators population strengthens existing plant-pollinator interaction or allow new plant-pollinator interaction to form [62, 63]. The diverse pollen feeding behavior by bee species is due to digestibility and nutritional content requirement fulfillment [64]. There are specialized flower plant-pollinator relationships like certain solitary bees species [65], reduction of these flower plants from habitat often results in the elimination of their specialist plant-pollinator populations. Viana et al. [66] evaluated more than 250 studies that showed the impact of landscape and pollinators interactions. The forage bees' ability to assess the nutritional value of pollen sources before establishing plant-pollinator interaction is valuable [67, 68]. A recent study by Armbruster [69] on pollination ecology mainly emphasizes three aspects, first ecological (pollination involving one or few kinds of plant and animals), second phenotypic (having specialized flowers or morphologies) and third is evolutionary (showing transitions towards increased specialization).

#### **Figure 1.**

*Conceptual representation of the interplay between ecology and evolution in the study of plant-pollinator interactions.*
