Anyone who thinks they are too small to make a difference has never met the honey bee! This is so true and aptly highlights the importance of tiny species that have always been overlooked by us. This article highlights the unsung warriors in our biosphere …
Dr Sonika Kushwaha
The planet is presently undergoing dramatic changes caused by human activities. We are living in the era of the Anthropocene, where our activities directly affect all living organisms on Earth whether big or small. Arthropods have existed for more than 400 million years and survived the mass extinctions that took place during the evolution. Insects have been hugely successful in terms of species richness and are the dominant group in terms of both taxonomic diversity and ecological function. Insects play noteworthy roles in the ecology of the world owing to their vast miscellany of form, function and life-style; their considerable biomass; and their interaction with flora and fauna, and the environment.
According to the various scientific studies, insects account for approximately 66% of all known species, constituting more than three-quarters of today’s global biodiversity. There are about one million species of known insects, but only 7% - 10% of these insects have been scientifically described. Many insect species remain unidentified. Insects are important part in the food chain, especially for entomophagous (feeding upon insects) vertebrates such as many mammals, aves, amphibians and reptiles. They play an important role in maintaining community structure and composition both for the fauna and flora; in the case of animals by transmission of diseases, predation and parasitism, and in the case of plants, through phytophagy and by plant propagation through pollination and seed dispersal. From an anthropocentric point of view, insects compete with humans; they consume as much as 10% of the food produced by man and infect one in six humans with a pathogen.
But the losses can be effortlessly looked over when we start considering the reimbursement by these tiny souls. To start with, the moths and butterflies are good bio-indicators in various types of environmental change. Beetles are important predators. They participate in biological control, biological monitoring of pollution from oil, sulfur, herbicides, CO2, insecticides and radioactive phosphorus. Ants are used as soil quality bio-indicators and have a key role in the mending of degraded and reforested areas. This group, which is very sensitive to human impact, is being used as environmental indicators in different ecosystems. Pollinators, especially honeybees (Apis mellifera), are considered reliable biological indicators because they show environment chemical impairment due to high mortality rate and intercept particles suspended in air or flowers. “If the bee disappeared off the face of the earth, man would only have four years left to live -Maurice Maeterlinck, The Life of the Bee.”
Termites are remarkable decomposers in land ecosystems. Their activity increase soil infiltration capacity, leading to water retention and soil productivity. In forests, they play a role in plant origin material and organic soil decomposition and assimilation. In spite of having the highest species in the Animal Taxa all over the world, insects never received the attention that they actually deserve. The tragedy is that these small souls are facing the consequences of human follies. An illustration by Virginia R. Wagner shows a dozen of stressors that are responsible for the change in insect population all over the world.
Interaction disruption: Climate change has been the talk of the century. The unexpected shifts in global climatic phenomena and consequent losses have caught the attention of every person. Insects are adversely being affected by climate change for the reason that environmental factors are having a strong influence on the development, reproduction, and survival of insect pests and their natural enemies. These small creatures have short generation times and high reproductive rates, and hence they are more likely to respond quickly to climate change than plants and vertebrates. Climate change will also result in increased problems with insect transmitted diseases. The monitoring of insect population is providing early warnings of ecological effects attributable to climate change. Insects are revealing how biodiversity and community structure are being affected by climate change. Mountain species and those restricted to high latitudes are most likely to become extinct as a result of climate change. As per the study by Franco and his team, four butterfly species have disappeared from lower latitudes during the past 25 years in the United Kingdom, with climate change being responsible for at least half of the population extinctions.
Nitrification: The use of chemically-reactive nitrogen in fertilizers has brought immense benefits in terms of agriculture productivity and food security. Excess nitrogen pollutes air, soil and water; increases greenhouse gas emissions; and impacts biodiversity and ecosystem functioning. The nitrogen-based fertilizers and products of fossil fuels combustion are nitrifying the planet, challenging the biota adapted to low low-nutrient conditions. These are also detrimental to vegetation, especially lower plants, through direct damage to leaves. The major nitrogen intimidation to soil quality, for both agricultural soils and natural soils, are related to acidification and thereby loss of insect diversity. Soil acidification may lead to a decrease in crop and forest growth and leaching of components negatively affecting the invertebrates. Only limited studies have examined the links between the nitrogen cycle, plant activity, and associated changes in insect diversity. In the case of agricultural fields, it is advisable to apply the 4R concept i.e., the right type of fertilizer at the right rate applied at the right time in the right place.
Fire: Forest fires are considered to be a potential hazard with physical, biological, ecological and environmental consequences. In forest ecosystems, persistent stress significantly alters the community composition, and the trees that grow under high stress support one-tenth the numbers of insects compared with trees that grow under more favorable conditions. Increased levels of tree stress due to forest fires are directly associated with an 8-to-10-fold decline in arthropod species richness and abundance. The forest fires directly reduce the insect population and indirectly the imbalance begins with native vegetation replacement after the forest destruction, which normally has high insect diversity but due to homogeneous plantation ecological balance is fragile and insect diversity reduces. Therefore, the number of harmful insect species gets quite high. The reforestation is usually located in nutrient-poor soils, and at certain times of year the trees are exposed to water stress, becoming highly susceptible to attack by insects. During this period there may be population booms of aggressive and dominant insects.
Global warming: Global warming is a leading stressor for the insects as it pilots faster development of immature stages, and adults emerge much earlier than before. This early adult emergence in turn increases the length of the flight period. Changes in butterfly phenology, early adult emergence and early arrival of migratory aphids have been observed in several places. Global warming and changes in climate are highly influencing the:
•Activity, diversity, and abundance of insects
• Geographical distribution of insects
• Overwintering; development and population dynamics
• Expression of host–plant resistance to insects
• Pest outbreaks and pest invasion
• Synchrony between plants and insect pollinators
• Effectiveness of crop protection technologies
Droughts: Recent increases in drought intensity (i.e., magnitude of reduction in precipitation or soil moisture) are attributed to the atmospheric temperature and changes in precipitation. Changes in drought intensity and frequency have the potential to alter plant defenses and impacts on insects. Drought affects host nutritional quality and habitat susceptibility to colonization by insects. The dry conditions alter feeding behavior of insect by increasing leaf toughness, which is positively associated with plant resistance against foliage-feeding insects. During drought, leaf water content decreases and leaf stiffness and dry matter content amplifies. These changes are associated with reduction in folivore feeding and thereby reproduction.
Pollution: Recent findings suggest that pollutants hinder insect behavior at different stages of the life cycle. For example, they oxidize odors emitted from plants, and in doing so, severely lessen efficient pollination. Intra-specific insect communication by means of sex and aggregation pheromones are also affected by air pollutants, potentially diminishing insect reproductive success, as well as impacting on the ability of natural enemies to locate their prey. The effects of pollutants on flower location and mating are well documented. Recent studies have revealed that, in the Anthropocene, plants can suffer from decreased pollination service, even when insects are present. Whether a plant is pollinated depends heavily on the area in which the plant grows i.e., polluted or green healthy region. Not only do insect numbers decline due to anthropogenic factors, but the remaining insects are hampered in their odour-guided behaviour close to human activities. Oxidative pollutants in the environment can change floral odour plumes and affect their behaviour, resulting pollinating insects have difficulties in locating flowers against a background of vehicle related pollutants, e.g., toluene and xylene, as these activate a similar subset of olfactory sensory neurons as the original floral odour and, therefore, impair the ability of the insect to discriminate among flowers at the neuronal level. The pollutants therefore decrease energetic feeding habits and pollination efficiency. When considering the harmful insects, various anthropogenic effects on mosquito human interactions are predominantly caused by greenhouse gas emissions and urbanization.
Urbanization: Current urbanization and the continuous urban sprawling has resulted in ecological unbalance and loss of traditional agricultural trade of villages. According to UN Department of Economic and Social Affairs, 2018, about 68% of the global population will live in cities by 2050. This uncontrolled and unsustainable increase in urban areas is leading to urban heat islands, cityscapes with increased land temperatures, reduced water sources, and limited vegetation compared with surrounding rural areas. Species that are adapted to urban areas and have a tolerance for high temperatures, such as mosquito species, are currently thriving in cities and broadening their distribution, as well as increasing the association with humans and thereby the risk of disease transmission. Urbanization may further modify insect-host interactions by directly affecting their abilities to detect and locate their hosts.
Introduced species: Due to rapid movement of people and the goods all over the world, new species are arriving habitually to areas where they were absent previously. Introduced species whether plants, animals or pathogens, always prove to be disastrous to the native species. More ever, environmental changes not only support the survival but helps in thriving of insects in the new habitats. As a new resource invasive plants influence the life cycle of native insect herbivores and their natural enemies such as parasitoids and predators leading to host shifts of these herbivores and natural enemies. They influence the spatial and temporal dynamics of native insect (meta) populations and communities, ultimately leading to changes at the landscape level. The dominance of invasive species leads to transformation in the structure of insect communities, by competing and displacing native species to other crops or habitats.
Agricultural intensification: Sufficient food production for a growing human population has become an issue of global concern. It is estimated that by 2050 the global population size will have increased by 46%, requiring increased agricultural production to ensure food security. Insect pests are created through the manipulation of habitats by humans, where crops are selected for larger size, higher yields, nutritious value, and are cultivated in monocultures for maximum production. Monocultures essentially create “biological deserts” where only a limited number of species can survive. In addition, the single crop farming provides a highly favorable environment for the rise in population of certain herbivorous insects. These herbivorous insects in turn have the ability to evolve biotypes that can adapt to new situations, for example, overcoming the effect of toxic materials, such as pesticides, or evade natural or artificial plant resistance.
Deforestation: Deforestation is directly linked to the decline in the population of insects because when trees are cut the insects dwelling on those trees are ultimately destroyed and forests are considered to be the most excellent habitat for living organisms including insects so by cutting the forest causes a serious threat to all form of biodiversity. The rates of pollinators significantly reduce in deforested areas as compared to the forest regions-being between four to ten times lower in deforested habitats. Further the seed production also reduces to half in deforested regions and alters the balance between the relative importance of mutualism and antagonism. It appears that human-caused deforestation may also indirectly deprive insect species of their ability to fly.
Insecticides: The effect of insecticides and other chemicals have been studied since decades giving us alternatives to reduce the harmful effects. The impractical use of pesticides affects the fecundity, fertility and behavioral changes. There is alteration in reproductive stages. The exposure to insecticides causes several changes in the daily activities such as foraging, choice of ovi-position sites, pheromonal communications and other. The pheromonal communications are complex physiological mechanisms that involve hormones and neurohormones, the insecticides act on the endocrine system and effect the production and emission of pheromone by female and male insect. This can be understood by the sublethal doses of insecticides on the beneficial insect, Honey bee, causing changes in development, behavior, morphology, physiology and immune system, affecting the social functions, and decreasing the longevity of individuals.
As students we all study at least one chapter on beneficial and harmful insects during some or other part of our education period. As an irresponsible grown up, we forget about these tiny feathered heroes that support our survival in uncountable ways. We only remember the harmful ones like the mosquitoes and the 2019-2020 locust infestation that was a pest outbreak of desert locusts that threatened the food supply across the regions of East Africa, the Arabian Peninsula, and the Indian subcontinent. Do we really bother to know and accept the causes for such outbreaks? Heavy rains and an increasing number of cyclones, both are a result of the climate crisis, enabled unprecedented breeding and the rapid growth of locust populations. Are we not to be blamed?
The worldwide confront now is to ensure high and quality yields and at the same time ensure that agricultural production is environmentally sustainable. To reach this target we will have to re-evaluate the position of insects in all our ecosystems. Insects are drivers of ecosystem functions and play a key role in agro-ecology, the management of agricultural systems in an ecologically sound and sustainable way by encouraging ecosystem services. To use the existing land more sustainably, insects can endow us with the required solutions. Insects, as most important contributors to ecosystem function on all levels, execute significant functions in all ecosystems. By understanding this simple and basic concept, their value can be realized. With the understanding of ecosystem functions given by insects we can then have room for them by changing the management practices to increase the functional diversity in these systems. We need more scientific studies, opinions and updates on invertebrate declines. These winged creatures do not need the lawns; they need the open green natural spaces. We have started with the butterfly Gardens and beetle banks in many parts of world, but what we actually need is the untouched, natural green and brown spaces that we consider as wasteland.
-With inputs from Dr Akhilesh Kumar, Indian Biodiversity Conservation Society, Jhansi-Uttar Pradesh. All pics used in this article are also by him.