Insect Pests and Crop Losses 2 Smriti Sharma, Rubaljot Kooner, and Ramesh Arora
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Insect Pests and Crop Losses 2 Smriti Sharma, Rubaljot Kooner, and Ramesh Arora Abstract The world population has been galloping upwards at an unprecedented rate dur- ing the last 50 years. So far, the modern agricultural technology has enabled us to largely keep pace with the increasing human population through increased productivity of major crops. But in addition to causing environmental deteriora- tion, it has also resulted in increasing losses by pests, pathogens and weeds. There is however a paucity of reliable data on the extent of food losses caused by these biotic agents, especially in the developing countries. The limited data avail- able indicate that arthropods may be destroying an estimated 18–20% of the annual crop production worldwide estimated at a value of more than US$470 bil- lion. Further, the losses are considerably higher in the developing tropics of Asia and Africa, where most of the future increase in world population is expected during the next 50 years. There is an urgent need to precisely estimate the extent of food loss and waste at different stages from the agricultural fields to human consumption with emphasis on the developing countries. This is the necessary first step towards development of safe, economical and sustainable methods of pest management, as well as food security, for the future. Keywords Crop losses • Insect pests • Global losses • Food security • Potential food loss S. Sharma (*) • R. Kooner Department of Entomology, Punjab Agricultural University, Ludhiana 141004, India e-mail: [email protected]; [email protected] R. Arora Department of Entomology & Zoology, Eternal University, Baru Sahib, Himachal Pradesh 173101, India e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 45 R. Arora, S. Sandhu (eds.), Breeding Insect Resistant Crops for Sustainable Agriculture, DOI 10.1007/978-981-10-6056-4_2 46 S. Sharma et al. 2.1 Introduction In natural ecosystems, phytophagous insects coexist in a complex relationship with plant communities. Different species of plant-feeding insects must search out their host plants from the mixed vegetation. In this search, they face the dangers of anni- hilation by various abiotic and biotic agents. Therefore, the damage caused by insects is quite limited in the natural ecosystems. In contrast, the natural regulating factors play only a limited role in agroecosystem, and insect pest outbreaks are quite frequent. Further, rapidly increasing human population during the last century has necessitated intensification of agriculture, which has resulted in aggravation of pest problems and increasing pest-associated losses (Pimental 1977; Bramble 1989; Arora and Dhaliwal 1996; Dhaliwal and Arora 2006). Despite great advances in agricultural productivity and economic well-being in much of the world over the past 50 years, food insecurity continues to be a serious issue for large sections of the human population. The world population has been galloping upwards rather rapidly in the recent past. While it took more than a mil- lion years for humans to reach the first billion mark in 1804, it reached a level of 7 billion in another 207 years by 2011 (Anonymous 2011). During the last 50 years, the human population has jumped from 3.5 billion to more than 7.4 billion. There has thus been more growth in human population in the last 50 years than during the entire period of more than a million years that humans have inhabited the Earth. Interestingly, the greatest episode of population growth in human history was accompanied by an increase in the per capita food supply, especially during the first half of this period. This was made possible by the ‘green revolution’, which resulted in a quantum jump in the productivity of major cereal crops in Asia and to a lesser extent other parts of the world from the late 1960s onwards. It thus helped to avert mass famines but may also have contributed to the population explosion. During the last five decades, intensive agriculture utilizing green revolution tech- nologies has caused tremendous damage to the natural resources that sustain it. Fresh water, quality soil, energy and biodiversity are all being depleted, degraded and/or polluted (International Food Policy Research Institute 2016). The rate of increase in productivity of major cereal crops has also declined significantly. Consequently, the per capita availability of food grains has been declining of late. Thus, intensive high-input technologies may not be able to meet the human needs for food, feed and fibre in future. As per various estimates, around 1 billion people in the world are undernour- ished and/or living without adequate energy. Further, the human population contin- ues to grow at a rapid rate and is likely to reach 9.1 billion by 2050. Even more alarming is the fact that future increases in population will be largely concentrated in the developing countries of Asia and Africa, many of which are already battling severe food shortages. It has been estimated that world food production will need to rise by 70%, and production in developing countries will need to double to meet the food needs of the world by 2050 (Anonymous 2015a). This must be achieved in the face of energy shortages, growing depletion of underground aquifers, continuing 2 Insect Pests and Crop Losses 47 loss of farmland to urbanization and increased drought and flooding due to climate change (Schuster and Torero 2016). In the face of increasing demand for food, it is ironic that at least one-third of the potential agricultural production is lost due to damage by animal pests and diseases (Oerke et al. 1994). Reduction in pre-harvest pest-associated losses is one of the important means of increasing agricultural production. Minimizing pest-associated losses will take us a step closer to achieving the recently adopted global Sustainable Development Goals (SDGs) of ending poverty, hunger and all forms of malnutrition (Anonymous 2016). However, precise estimates of the extent of losses caused by insect and non-insect pests in important crops are not available for most of the developing countries (Culliney 2014). The losses have been reported to vary widely in different crops as well as across different regions of the world (Oerke et al. 1994; Oerke 2006). This chapter attempts a brief overview of the extent of field losses caused by insect pests in important crops. 2.2 Types of Crop Losses Insects are the most ubiquitous, diverse and abundant group of animals on planet Earth. These tiny but versatile creatures are the major competitors with humans for the resources generated by agriculture (Oerke and Dehne 2004). The damage caused by these organisms is one of the most important factors in the reduced productivity of any crop plant species (Metcalf 1996; Pimentel 1976). FAO/WHO (2014) have defined pest as ‘any species, strain or biotype of plant, animal or pathogenic agent injurious to plants and plant products, materials or environments and includes vec- tors of parasites or pathogens of humans and animal disease and animals causing public health nuisance’. Crop losses are usually defined as the reduction in either quantity or quality of yield (Zadoks and Schein 1979), and these may be caused by abiotic and biotic fac- tors, leading to the reduction in crop productivity and lower actual yield than the attainable yield of crops. Losses can occur at any stage of crop production in the field (preharvest) or even during storage (postharvest) (Oerke 2006). Direct yield losses caused by pathogens, animals and weeds are altogether responsible for 20–40% loss of global agricultural productivity (Teng 1987; Oerke et al. 1994; Oerke 2006). Although crop protection aims to avoid or prevent crop losses or to reduce them to an economically acceptable level, the availability of quantitative data on damage caused by these pests is limited (Oerke 2006). The ultimate effect of the attack by pest organisms on a crop is commonly expressed as the effect on yield, the quantity of harvestable economic product which is typically given as weight of product per unit area, such as kilograms or tonnes per hectare. Still, several ways of categorizing yield have been proposed (Nutter et al. 1993). The theoretical yield potential is the yield obtained, when crops are grown under optimal environmental conditions using all available production and pest con- trol technologies to maximize the yield. The attainable yield is defined as the site- specific technical maximum, depending on abiotic growth conditions, which in 48 S. Sharma et al. general is well below the yield potential. This is a theoretical yield level that cannot be realized under practical growth conditions. The actual yield is the site-specific yield obtained, when crops are grown using practical cultivation and plant protec- tion practices at the farm level (Oerke et al. 1994). Crop losses may also be expressed in absolute terms (kg/ha, financial loss/ha) or in relative terms (per cent loss). Quantitative losses are expressed as loss in productivity leading to a smaller yield per unit area, while qualitative losses are defined as loss in content of important ingredients or reduced market quality. Two loss rates must be differentiated: the potential loss and the actual loss. The potential loss from pests includes the losses without physical, biological and chemical crop protection com- pared with yields with similar intensity of crop production in a no-loss scenario. Actual losses comprise the crop losses sustained despite the crop protection practices employed, and under such conditions, the efficacy of crop protection practices is cal- culated as the percentage of potential loss prevented (Oerke 2006). The loss rate may be expressed as the proportion of attainable yield, but sometimes the proportion of the actual yield is calculated. The economic relevance of crop losses may be assessed by comparing the costs of control options with the potential income from the crop losses prevented due to pest control.