INSECTS: THE INDISPENSABLE REGULATORS OF AGROECOSYSTEMS

 

    Derived from a Latin word, ‘insectum’  meaning ‘to cut into’, insects (Class: Hexapoda under Phylum Arthropoda of the Animal Kingdom) are the most diverse and abundant organisms on Earth consisting of 3 pairs of jointed legs, body divided into 3 segments namely Head, Thorax, and abdomen, respiring through trachea and possessing a chitin rich exoskeleton called cuticle. Out of about 1.35 million identified species of living organisms around the world, about 925,000 of species are identified to be insects i.e. about 70% of the total number of species of organisms on Earth but it is estimated that 5 to 7 times as many are yet to be discovered. It is estimated that at any instant of time there are over 10 quintillion (10 × 10¹⁸) insects on Earth. ( EO Wilson quoted on Howstuffworks, 2019).

   Being the most diverse, abundant and dominant species among the living organisms, an ecosystem cannot be considered complete without insects. Entomology is rooted in nearly all human cultures from prehistoric times, primarily in the context of agriculture. In terrestrial ecosystems insects play key ecological roles in diverse ecological processes such as nutrient cycling, seed dispersal, bioturbation [(Fincher, Monson and Burton, 1981), (De Groot, Wilson and Boumans, 2002), (Nichols et al., 2008)], pollination [(Gabriel and Tscharntke, 2006), (Slade et al., 2016)], and pest control [(Landis, Wratten and Gurr, 2000), (Brewer and Elliot, 2004), (Bell et al., 2008), (Lonsdorf et al., 2009)]. In conventional agriculture, production practices focus on few preferred species and their specific requirements, yet the potential services of many other species are ignored. (Hoehn et al., 2008)

   The insect-plant relationship is the dominant biotic interaction. (Samways, 1993) and approximately 50% of the insect species are herbivorous, with most herbivorous species feeding on plants in one or a few related plant families  (Schoonhoven, Van Loon and Dicke, 2005). The amount of damage sustained is quite small as plants appear to have broad‐spectrum physical and chemical defenses against insect herbivores and pathogens (Giron et al., 2018). Herbivorous species damage 18% of the world agricultural production ( Losey and Vaughan, 2006). Being the indispensable and vital regulators of an agroecosystem, insects are responsible for different types of functions and activities aiding in improving the resiliency and ultimately sustainability of the agroecosystem. Since crop production is almost impossible without the ecosystem services provided by the insects, some of the major ecosystem regulating activities performed by different types of insects in the agroecosystems are discussed below:

 

Pollination: Insects are regarded as excellent pollinators. 80% of the total pollination activities are performed by insects whereas about 80% of the total insect pollination is contributed by bees. Some other major pollinator insects are Beetles, Butterflies and Flies. Insects therefore contribute to plant population and diversity directly and animals directly through pollination. (Jankielsohn, 2018)

 

Bio-controlling activities: Some insects remain at the higher trophic levels and feed on other insects esp. phytophagous insects as a predators or parasitoids of such insects and help in controlling their population in the agroecosystem. For eg. Lady bird beetles feed on Aphids and mealy bugs, Praying Mantis feed on crickets and grasshoppers, etc.

Trichogramma parasitoid wasps attack Lepidopteran eggs and feed them from inside out.

   On the other hand, not all phytophagous insects are pests of agricultural crops due to their host-specific nature which facilitates in controlling weeds from the agricultural fields and reducing competition with the main crops increasing the yield. For eg. Mexican Beetles feed on Parthenium, Octotoma scabripennis feed on Lantana camara, etc.

 

Nutrient Recycling: Some of the insects feed on dead and decaying plants, animals and animal excreta and help in recycling of nutrients in the soil. For eg. Dung beetles feed on dung (eg. Cattle dung) and contribute to the soil health by increasing the Nitrogen, Phosphorus, Potassium, Calcium, and magnesium content of the soil (Macfadyen et al., 2015) and to the environment as well by reducing GHG emissions by 7 to 12%. (Nichols et al., 2008). Beetle larvae, flies, ants and termites clean up dead plant matter and break it down for further decomposition by microbes. Ants and termites, the soil macrofauna in dry and hot regions, play an important role in the increase of mineral nitrogen in the soil. (Evans et al., 2011).

 

   These were the major ecosystem services provided by insects in the agroecosystem leading towards increased production and sustainability. Insects as vital members of an agroecosystems and acting as regulators and contributors to the ecosystem function on all levels, perform critical activities for the provision of ecosystem services. Thus, keeping this fact in mind, agricultural ecosystems should be managed in such a way that the beneficial insects performing vital ecosystem service activities and the harmful insects affecting the production and sustainability of the agroecosystem are regarded as a fundamental part of the management strategies.

 

References:

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