eChapters

Introduction

Agricultural pests cause considerable yield losses throughout the world. In ancient times, farmers had to manage pest problem to safeguard their basic needs, and as a response, the farmers use to practice and develop cultural and mechanical pest control strategies based on their field experience. Over a period of time, these practices have become a part of their production management system. Pest management practices began to change in later stages of the 18^th century. Introduction of pesticides in agricultural ecosystems 1950’s contributed substantially in raising agricultural productivity and they become an integral component of intensive agricultural ecosystems. At the same time, environmentalists raised their concerns on deleterious effects of pesticides on environment, human health and non-target organisms. Excessive use and abuse of pesticides leads to the problems like resistance, resurgence and residues (Beaument, 1993). One of the deleterious effects of over use of pesticides is the death of effective predator and parasitoids. This ultimately leads to the imbalance in the agroecosystem. Concerns about the negative effects of pesticides led to research and promotion of alternative pest control practices – Integrated Pest Control or simply IPC. This new concept called Integrated Pest Control (IPC) and later Integrated Pest Management (IPM) was stimulated by symposia organized by the Food and Agriculture Organization (FAO) of the United Nations in 1966 and the International Organization for Biological Control (IOBC) in 1967. IPM made a paradigm shift in the philosophy of pest control, from pest eradication to pest management. Instead of single tactic control, emphasis was placed on the use of a combination of available tactics in a compatible manner keep the pest below economic injury levels. Consequently, a more integrated approach of pest control was advocated considering the natural mortality factors. IPM is a complex system approach that comprises judicious use of cultural, physical, mechanical, biological, host plant resistance, regulatory and chemical methods.

Introduction

The guava fruit is a good source of vitamin C, pectin, calcium and phosphorus. The fruit is used for the preparation of processed products like jams, jellies and beverages. Guava jelly puree is very popular for its attractive purplish-red colour, pleasant taste and aroma. The puree can be used in juice, cakes, puddings, sauces, ice-cream, jam and jelly. Fruits can be preserved by canning as halves or quarters, with or without seed core (shells). Good quality salad can be prepared from the shell of ripe fruits. Their cultivation in India about 1.32 lakh ha area with production is 17.12 lakh tonnes. Biointensive pest management is use to major emphasis on conservation and enhancement of natural enemies and utilization of all compatible methods for achieving effective economical and safe pest control. These methods are the most appropriate in horticulture and in protected cultivation. The major aim of Biointensive pest management is to provide guidelines and options for the effecting management of pests and beneficial organisms in an ecological context. It will help to reduce the dependence on chemical pesticides and ecological deterioration. Biointensive pest management includes bio-pesticides derived from microbes, parasitoides, predators, botanicals and all conventional non-chemical methods or use of need based. Large number of insect pests has been reported to occur on guava at various growth stages. More than 80 species of insects and mites have recorded on affecting the growth and production. About three species of fruit flies, Bactrocera dorsalis, B. Cucurbitae and B. Zonata found to attack guava fruits, B. Dorsalis being the dominant. Maximum activity of fruit flies is observed during August to December reaching its peak during September. Two species of bark eating caterpillars, Indarbela quadrinota and I. Tetraonis are commonly found in the region. Sucking pests included Mealy scale, Chloropulvinaria psidii, Mealy bugs Ferrisia virgata, Plannococcus citri, Tea mosquito bugs, Helopeltis antonii, aphid, jassids etc (Azad Thakur et al., 2009). The major pests of guava that are economically damage on this crop given below:

Introduction

Papaya is a tropical tree fruit crop that cannot tolerate freezing temperatures. It has commercial importance because of its high nutritive and medicinal value. Papaya cultivation had its origin in South Mexico and Costa Rica. Total annual world production is estimated at 6 million tonnes of fruits. India leads the world in papaya production with an annual output of about 3 million tonnes. Other leading producers are Brazil, Mexico, Nigeria, Indonesia, China, Peru, Thailand and Philippines. Papaya fruit are borne on peduncles attached to the main trunk of the papaya tree and are clustered, starting a few feet above the ground and extending up to a foot below the top of the plant adequate water is essential to the uninterrupted growth and production of papaya fruit. There is number of factors which affect quality and quantity of papaya production. Out of insect pest is one of the important factors to reduction of papaya fruit production. List of insect pests of papaya given as below:

Pomegranate (Punica granatum L.) also known Anar in Hindi it is belonging to the Punicaceae family, it is grown in tropical and sub-tropical regions. Originated in Indo-Burma region Iran and is extensively cultivated in the Mediterranean region since ages (Sheikh and Manjula, 2009). Pomegranate is used as table purpose, making juice, jam, jelly and paste. The fruit peel, tree stem and leaves and root bark are good source of secondary metabolites such as tannins, dyes and alkaloids (Mirdehghan and Rahemi, 2007). The edible part of the fruit is the seeds having a fleshy covering and called arils.

India is major pomegranate producing country in the world. In India main pomegranate producing states are Maharashtra, Karnataka, Gujrat, Andhra Pradesh, Madhya Pradesh, Tamil Nadu and Rajasthan. Maharashtra is leading state of pomegranate production in India. The prominent pockets where pomegranate cultivated area are concentrated are Solapur, Nashik, Sangli, Satara and ahemednagar districts of Western region of Maharashtra.

Indian total pomegranate crop covers 0.24 Mha and production is 2.87 MT in India (Anonymous 2017). The export of pomegranate from India is only 0.04 MT it is very low. Pomegranate is majorly exported to UAE (43%), Bangladesh (16%) and European Countries (14%) A few tons also go to Saudi Arabia, Russia, Thailand, Nepal, Kuwait etc.

Introduction

Banana (Musa sp; family: Musaceae) is the second most important fruit crop in India next to mango. Its year round availability, affordability, varietal range, taste, nutritive and medicinal value makes it the favorite fruit among all classes of people. It has also good export potential. Banana evolved in the humid tropical regions of South East Asia with India as one of its center of origin. Modern edible varieties have evolved from the two species – Musa acuminata and Musa balbisiana and their natural hybrids, originally found in the rain forests of S.E. Asia. During the seventh century AD its cultivation spread to Egypt and Africa. Banana and plantains are grown in about 120 countries. Total annual world production is estimated at 86 million tonnes of fruits. India leads the world in banana production with an annual output of about 14.2 million tonnes. Other leading producers are Brazil, Eucador, China, Phillipines, Indonesia, Costarica, Mexico, Thailand and Colombia. In India banana ranks first in production and third in area among fruit crops. It accounts for 13% of the total area and 33% of the production of fruits. Production is highest in Maharashtra (3924.1 thousand tones) followed by Tamil Nadu (3543.8 thousand tonnes). Within India, Maharashtra has the highest productivity of 65.70 metric tones /ha. against national average of 30.5 tonnes/ha. The other major banana producing states are Karnataka, Gujarat, Andhra Pradesh and Assam.

Introduction

A symposium organized by the Food and Agricultural Organization (FAO) in 1966 and International Organization of Biological Control (IOBC) in 1967, felt the need for the development of a new concept called “Integrated control” which was later replaced by “Integrated Pest Management”. The origin of IPM was necessary after the serious failure of the chemical age which started in the 1940’s. The pesticides were used as the only tactic to completely annihilate the pests from the crop ecosystem, which did miraculously decreased the pests and increased the production of the crop extensively, but they failed to realize the balance of life, by nature and by virtue of the selection pressure pests started developing resistance against all kind of pesticides being dumped on them.While the pests were getting resistant, the dumped pesticides were accumulating in the environment and biomagnifying inside the bodies of animal (WHO, 1990; Alewu & Nosiri, 2011; Eskenazi et al., 1999). The indiscriminate use of pesticides led to the significant health hazard to the humans (WHO, 1990; Alewu & Nosiri, 2011; Sanborn et al., 2007; Mnifet al; 2011; Semchuk et al., 1992; Goad et al., 2004; McKinlay et al., 2008; Gasnier et al., 2009; Lin et al., 2015; Waddell et al., 2001), reproductive malfunction in male (Jamal et al., 2015), nervous system (Jaga and Dharmani, 2003; Rosenstock et al., 1991; Wesseling et al., 2002; Eskenazi et al., 2006), cardiovascular system (Hung et al., 2015) and ultimately death (WHO, 1990; Gunnell et al., 2007). From the lessons acquired of the hazards, the concept of IPM proposed the concept of “pest eradication” was replaced with “pest management”. There are more than 64 definitions of IPM but the most accepted one came from FAO (1967) which defined IPM as “a system in context with associated environment and the population dynamics of pest species, utilizes all suitable techniques and methods in as compatible manner as possible and maintains the pest populations at level below those causing economic injury”. IPM decreased the pest pressure of the crop and increased the productivity of the crop and income of the farmers. IPM is a complex approach that advocates the integration of several components such as physical, mechanical, biological, legal, ecological and chemical tactics, in a compatible manner in a complete ecological set up, so that natural mortality has a role in checking the pest population building up above economic injury level (EIL).

Introduction

Litchi (Litchi chinensis Sonn), like most fruit tree crops, is usually attacked by two or three key pests, several secondary pests and a large number of occasional pests in localized areas where it is grown. Litchi is an important subtropical evergreen fruit crop belongs to family Sapindaceae. It is known as queen of the fruit due to its attractive deep pink/red colours and flavoured juicy aril (Singh et al., 2012).

Insect pest attacks on litchi, in China there are 193 species of litchi pests in two classes, 11 orders, and 57 families. In India, nearly 42 insects and mite species reported to attacking on trees and fruits of litchi at different stages of growth (Singh et al., 2012). The majority belong to the Lepidoptera and Coleoptera, followed by the Homoptera and Hemiptera. However, only about three or four key pests including fruit and flower borers, sucking bugs, stem borers and erinose mites which require regular control, and the species involved vary between orchards. Secondary pests viz., fruit-piercing moths, defoliators etc generally occur at sub-economic levels, but can become serious pests as a result of changes in cultural practices and litchi cultivars or because of indiscriminate use of insecticides against a key pest. Recently, litchi fruit borer and litchi leaf roller have acquired the status of major pests and now, litchi looper, litchi bug and bag worm are emerging pests of litchi (Choudhary et al., 2013; Singh et al., 2014). Occasional or incidental pests also can cause economic damage only in localized areas at certain times; the great majority of pests reported here fall within this last category.

Biointensive IPM incorporates ecological and economic factors into agricultural system design and decision making while addressing public concerns about environmental quality and food safety. It provides suitable guidelines and options for the effective management of pests and beneficial organisms in an ecological context in a holistic self-sustaining manner. The flexibility and environmental compatibility of the Biointensive IPM strategy make it useful in all types of cropping systems particularly in an agro-biodiversity rich ecosystem.

Introduction

Horticulture is the science and art of propagation, production, utilization, improvement, harvesting and marketing of crops such as fruits, vegetables, ornamental plants, spices & condiments, medicinal & aromatic plants, plantation crops, postharvest technology etc. The term is derived from the Latin word hortus mean garden and cultura means to cultivate. These crops are diverse which includes annuals to perennials, edible to ornamentals, temperate to tropical, humid to desert, etc. Horticultural plants help to sustain and enrich people by providing nutritious food, medicines, enhances the beauty of surroundings, besides reducing carbon footprint. They also serves as raw material for various industries, such as processing, pharmaceutical, perfumery and cosmetics, chemical, confectionery, oils and paints, etc.

Importance of Horticultural Crops

The horticulture crops are a source of variability in farm produce as well as human diets. The comparative production per unit area of horticultural crops is much higher than field crops. They are not only a source of nutrients, vitamins, minerals, flavour, aroma and dietary fibres, but also contains health benefiting compounds and medicines. Ornamental horticulture have aesthetic value and protects the environment. These crops are also useful for cultivation in wasteland, poor quality soil, slopy, uneven or undulating lands. Mango and cashew nut are cultivated on a large scale in hilly and hill back areas. Such crops are of high value, labour intensive and generate employment throughout the year. Further they have national and international demand and are a good source of foreign exchange.

10.1 Introduction

Biomass fuels are a potential source of renewable energy. One of the major barriers to their widespread use is that biomass has a lower energy content than traditional fossils fuels, which means that more fuel is required to get the same amount of energy. When combined — low energy content with low density -the volume of biomass handled increases enormously. Compaction or densification is one way to increase the energy density and overcome handling difficulties.

Densification means compaction of loose material or to increase density of loose biomass so that its volumetric efficiency can be increased. Densification essentially involves two parts; the compaction under pressure of loose material to reduce its volume and to agglomerate the material so that the product remains in the compressed state. The resulting solid may be a briquette, a pellet and a cube. It will be briquettes if roughly, it has a diameter greater than 30 mm. Smaller sizes are normally termed pellets though the distinction is arbitrary. The process of producing pellets is also different from the typical briquetting processes. The densified product can be developed in the cubical shapes as well.

If the material is compacted with low to moderate pressure (0.2-5 MPa), then the space between particles is reduced. Further, increasing the pressure will, at a certain stage particular to each material, collapse the cell walls of the cellulose constituent, thus approaching the physical, or dry mass and more, density of the material. The pressure required to achieve such high densities are typically 100 MPa plus. This process of compaction is entirely depending on to the pressure exerted on the material and its physical characteristics including its moisture content.

9.1 Introduction

The rapid growth of industrialization and population significantly affect on the demand of ethanol as an alternate fuel. Generally, conventional crops like sugarcane and corn become unable to meet the demand of bioethanol, due to their primary role in food and feed. Therefore, lignocellulosic biomass from agriculture waste is attractive precursor for bioethanol production. Biomass is renewable organic material, abundant and cost effective. Ethanol production from agriculture waste has been projected an economically attractive option for industrial sector. However, sugar and starch derived ethanol have a more theoretical yield as compared to lignocelluloses, theses sources are insufficient for bioethanol production. The major agricultural wastes including rice straw, corn straw, wheat straw and sugarcane bagasse etc. can subsequently used for ethanol production. Rice straw has a highest worldwide potential for bioethanol production (205 giga liter) followed by wheat straw (104 giga liter), corn straw (58.6 giga liter), and finally for sugarcane bagasse (51.3 giga liter)¹.

A bio fuels is environmentally friendly options for power generation. Most of the fossil fuels are biological in nature. These are plant forms that, typically, remove carbon dioxide from the atmosphere and give up the same amount when burnt. The bio fuels are therefore considered to be “CO₂ neutral”, not adding to the carbon dioxide level in the atmosphere. The type of bio fuel used will depend on a number of factor, chief amongst them being the available feedstock and the energy that can be used locally.

India import 70% of the oil it uses, and the country has been hard by the increasing price of oil, uncertainty and environmental hazards that are concerned with the consumption of fossil fuels. In this context, bio fuels constitute a suitable alternative source of energy for India. There are two examples of bio fuels are Ethanol and Bio diesel (Renewable Diesel)

Ethanol can be made from biomass material containing sugar, starches, or cellulose (starch and cellulose are complex from of sugar)

8.1 Introduction

Rising petroleum prices, increasing threat to the environment from exhaust emissions and global warming have generated an intense international interest in developing alternative non-petroleum fuels for engines. The use of vegetable oil in internal combustion engines is not a recent innovation. Rudolf Diesel (18581913), creator of the diesel cycle engines, used peanut vegetable oil to demonstrate its invention in Paris in 1900. In 1912, Diesel said, “The use of vegetable oils as engine fuel may seem negligible today. Nevertheless, such oils may become, in the passing years, as important as oil and coal tar presently.” Nowadays, it is known that oil is a finite resource and that its price tends to increase exponentially, as its reserves have being decreasing¹.

India ranks sixth in the world in total energy consumption and needs to accelerate the development of the sector to meet its growth aspirations. The country, though rich in coal and abundantly endowed with renewable energy in the form of solar, wind, hydro and bio-energy has very small hydrocarbon reserves (0.4 % of the world’s reserve). India, like many other developing countries, is a net importer of energy, more than 25 percent of primary energy needs being met through imports mainly in the form of crude oil and natural gas. The rising oil import bill has been the focus of serious concerns due to the pressure it has placed on scarce foreign exchange resources and is also largely responsible for energy supply shortages. The sub-optimal consumption of commercial energy adversely affects the productive sectors, which in turn hampers economic growth².

7.1 Introduction

Biomass gasification is age old technology originated in 1800 century for lighting and cooking purposes (Sansaniwal et al., 2017). Biomass typically contents biopolymers such as cellulose, hemicellulose and lignin in addition to the presence of average composition of C₆H₁₀O₅ which depends upon physical characteristics of biomass¹. Oxygen is required for combustion of every fuel. For complete combustion of biomass stoichiometric air to fuel ratio required varies from 6:1 to 6.5:1 with CO₂ and H₂O as end product.

Biomass gasification is an efficient and environmentally friendly way to produce energy². Gasification process is nothing but it is a conversion of solid fuel into gaseous fuel for wide applications. This whole process completed at elevated temperature range of 800-1300 ^oC with series of chemical reaction that is why it come under thermo chemical conversion³. Thermo chemical processes are most commonly employed for converting biomass into higher heating value fuels⁴. Major thermal conversion route is include direct combustion to provide heat, liquid fuel and other elements to generate process heat for thermal and electricity generation is summaries in Fig. 7.1.

6.1 Introduction

Torrefaction is a thermophilic process of biomass conversion into a solid, friable, homogenous coal-like material, which has better fuel characteristics than the original biomass. Torrefaction involves the heating of biomass material in the absence of air at 250 to 300°C temperature. Torrefaction produces high-grade hydrophobic nature solid biofuels from various streams of woody biomass or agro residues.Torrefied biomass has high energy density then the original biomass which make torrefied biomass as renewable alternate source for power generation in coal power plant. Torrefied biomass being hydrophobic in nature can be stored easily for longer duration with negligible biological degradation. At 250-300°C temperature volatilization has been taking place and around 30% mass of the biomass is reduced as compared to original untorrefied biomass with net energy loss of approximately around 10%.The end product is a predictable, homogeneous, hydrophobic, high value solid biofuel with far higher energy density and calorific value than the original biomass feedstock. During the torrefaction process a combustible gas is released, which can also utilised to provide heat to the process. The process diagram of torrefaction process is shown in Fig. 6.1.

5.1 Introduction

Today, energy distribution and environmental issues have developed into international threats. Demand for alternative fuels increases every day due to rapid population growth, rising living standards, and economical sustainability. With its massive population, India has become the fourth largest energy consumer country in the world after the United States, China, and Russia. Because most nations use fossil fuels to fulfill their energy demands, they create negative impacts on the environment including raising global temperatures, pollution, acid rain, and other effects. As such, the quest for alternative fuels derived from renewable resources has captured significant attention throughout the world¹. Biomass as a renewable energy sources is an important asset for achieving economic development is due to the availability of biomass at a low cost, a good conversion efficiency, the addition of jobs, and an increase in the biodiversity^2,3. Typically, biomass is composed of cellulose (40-50%), hemicelluloses (25-35%), and lignin (15-30%). Large amount of resources for biomass are available such as woody biomass, crop residues and their by-products, food processing waste, municipal solid waste, aquatic plant etc.

In the present context, pyrolysis process has been received a remarkable identity as a potential method for the conversion of any organic biomass into valuable energy rich products due to its simple in operation and also required a reasonable cost for conversion process. Pyrolysis is the thermal decomposition of any organic material at a specific temperature in absence of air/oxygen; the process ends with three resulting products, namely liquid (bio-oil), solid (biochar), and syngases⁴. Recently, biooil produced through pyrolysis process and further it up grading has been attracted a significant attention due to its major use as biofuel and as a precursor material for making chemicals⁵. The pyrolysis process also classified in three different types as per its operating conditions; slow, fast and flash pyrolysis.

4.1 Introduction

Biomass is referred to as an indirect source of solar energy and considered a source of stored chemical energy. Biomass is renewable organic material derived from plants and animals serving as sources of energy. Biomass produced from agricultural sector is big challenges for all over the world due to its improver disposal. Mitigating greenhouse gas emissions and ensuring adequate global food supplies represent two of the last decade’s mostdifficult challenges.Although global food production has benefitted from chemical fertilizers, environmental problems have emerged as a result of their use. Additionally, overuse of fertilizers can result in hardened soil, decreased soil fertility, polluted air and water, and the release of greenhouse gases. There is an urgent need to find an alternative to chemical fertilizers that, ideally, can be sourced in abundant amounts, promotes global food production, enhances CO₂ capture , and does not affect soil health or damage the environment¹. To sustain agricultural productivity, it is crucial to maintain adequate levels of organic matter in the soil to preserve its physical, chemical, and biological integrity. Biochar, a pyrogenic black carbon, may play an important role in improving soil health, resulting in higher crop yield and absorbing atmospheric carbon dioxide. Biochar is the most auspicious straw management measures and have highest carbon abatement and economic profit².

Biochar is produced by heating biomass at high temperatures (300 – 600 °C) in a closed reactor containing no to partial levels of air. Under these conditions, biomass undergoes thermo-chemical conversion into biochar. Because of its numerous potentials uses in agriculture, energy, and the environment, much attention has been given to biochar in both political and academic areas. Biochar can be used in a variety of applications such as energy production, agriculture, carbon sequestration, waste water treatment, and bio-refinery; additionally, biochar provides an alternative strategy for managing organic waste. These advantages have renewed the interest of agricultural researchers in producing biochar from bio-residues and using the product as a soil amendment.

3.1 Introduction

Nature has a provision for destroying and disposing off wastes and dead plants and animals. This decay or decomposition is carried out by tiny micro-organisms called bacteria. Making of farm-yard manure (FYM) and compost is also through decomposition of organic matter (OM). When a heap of vegetable or animal waste and weeds etc., die or decompose at the bottom of backwater or shallow lagoons, bubbles can be noticed rising to the surface of water. Sometimes these bubbles burn with dancing flame at dusk. This phenomenon has puzzled man for a long time. It was only during the past hundred years that Scientists unlocked this secret as the decomposition process. The gas thus produced was and is still called “Marsh Gas.” The technology of harnessing this gas under artificially created conditions is known as Biogas Technology.

2.1 Introduction

Biomass store solar energy in the chemical form and it is most precious and versatile resources on earth. Biomass, unlike fossil fuels, is a renewable energy resource that is available where the climatic conditions are favorable for plant growth and production¹. The term biomass is used for all organic materials which are combustible in nature, mainly plant and animal origin present in land and aquatic environments. Biomass is considered carbon neutral, because the amount of carbon it can release is equivalent to the amount it absorbed during its life time. There is no net increase of carbon to the environment in the long term when combusting the lignocellulosic materials. Therefore, we can say that biomass is a renewable source of energy and can play vital role in responding to concerns over the protection of the environment and the security of energy supply^2,3.

Biomass energy accounts for about 15% of the world’s primary energy consumption and about 38% of the primary energy consumption in developing countries⁴. Furthermore, biomass often accounts for more than 90% of the total rural energy supplies in developing countries⁵. It is the main source to meet out domestic energy in developing countries⁶. The efficient use of fuel wood is much more eco-friendly than the use of efficient and conventional fuels like kerosene and liquefy petroleum gas (LPG). LPG emits 15 times more CO₂ per kg than wood, and kerosene emits nearly 10 times as much. CO₂ is the prominent candidate for global. It is commonly assumed that biomass fuel cycles based on renewable in nature and greenhouse-gas (GHG) neutral because the combusted carbon in the form of CO₂ is soon taken up by re-growing vegetation⁷.

1.1 General

The term “biomass” generally refers to renewable organic matter generated by plants through photosynthesis. Materials having organic combustible matter is also referred under biomass.Biomass is an important fuel source in our overall energy scenario. Biomass is produced through chemical storage of solar energy in plants and other organic matter as a result of photosynthesis. During this process conversion of solar energy in sugar and starch, which are energy rich compounds takes place. The chemical reaction of photosynthesis can be written as:

6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂ + 636kcal

It indicates that the storage of 636 kcal is associated with the transfer of 72 gm carbon into organic matter. Biomass can be directly utilized as fuel or can be converted through different routes into useful forms of fuel. In fact, biomass is a source of five useful agents, which start with ‘F’ like food, fodder, fuel, fiber and fertilizer. Further, biomass has many advantages like.

(1) It is widely available

(2) Its technology for production and conversion is well understood.

(3) It is suitable for small or large applications

(4) Its production and utilisation requires only low light intensity and low temperature (5 to 35°C)

(5) It incorporates advantage of storage and transportation

(6) Comparatively, it is associated with low or negligible pollution.

3.1 Tomato

Tomato (Lycopersicon esculentum) is an important vegetable crop. Its 2n= 24.

Floral biology

Flowers are borne in small forked racemose cyme. Anthesis starts at 6.30 a.m. and continues up to 11.00 a.m. Anther dehiscence is longitudinal. It occurs 1-2 days after opening of corolla. The stamen sheds its pollen when the style grows up through anther tube, thus self-pollination occurs. When the stigma protrudes above the anther tube, chances of cross pollination through bees increases. The optimum temperature for pollination is around 21°C.