Different Types Of Insect Pest Control

Insects as Pest

Insects are considered to be evolved in Ordovician era around 480 million years ago. Availability of flora has made phytotophagous insects more established. Such herbivores insects are adapted to digest the phytochemicals. Food quantity and meteorological conditions affect the spatial distribution of the insects (Hassell at el. 1991). Introduction of commercialized crops to the new parts of the world has enhanced the pest attacks. (Bale et al. 2008) About 50% countries have more than 10% pest insects’ species in common (Bebber et al. 2014). A pest on cotton the Pink bollworm is found in Asia, Australia, America, Europe and all cotton producing nations. Some insects like Mediterranean fruit fly can affect multiple hosts (Alphey & Bonsall 2018). Herbivores insects bite the plant parts and these wounds are susceptible to the infect by the microbes like fungi and oomycete. Furthermore, they act as a vector of these pathogens to plants. (Willsey et al. 2017) About one tenth of the global production is lost due to pest attacks instead of having advance technology.

Management of Insect Pests

Although, insects have their own but limited resistance to the pests and some environmental stress (Christou et al. 2006). But, for a quick relief from the pathogens, various management techniques have been developed which include the utilization of chemicals, genetic alterations in plants, and many other physical traps of insects.

According to Aktar et al. (2009) following risks associated with the chemical pesticides and chemical control of insect pests:

1. Chemical insecticides have multiple chronic or acute impacts on the various physiological functions of humans whether caused by direct or indirect contact.
2. Resistance in insects-A one stage, some insects becomes completely resistant. So quantity of chemical is increased and cost also goes high. The resistance against DDT was initially observed in Diamond black moth. This single pest population is making 4-5 million$ loss in terms of crop damage and control investment. (Alphey & Bonsall 2018)
3. Surface and ground water pollution-The chemicals percolates through the rain water to contaminate the water aquifers. The surface runoff of these chemicals pollute the rivers and streams.
4. Loss of Biodiversity-Chemical pesticides are not target specific and generally tend to have severe negative impacts on non target organisms.

Biological Control of Pest

According to Crump et al. (1999), biological control of a specific pest is done by its natural predator organisms that can be microscopic as well. Organisms like viruses, bacteria, protozoans, nematodes to kill pest insect populations are collectively called as Entomopathogens. Their functions are equal to traditional chemical pesticides but their efficacy and expense are different from agrochemicals. They far outweigh the chemicals in many ways like host specificity, environmentally friendly, and no effect on non-target species (Lacey et al. 2001). As per Cock et al. (2016), in BIOCAT2010 there are 6158 biological control agents (BCAs) are mentioned for pest management in 148 nations. 2007 out of these are established in fields for 588 various pest insects. Nearly 30% of pest insects’ species are successfully targeted by the 10% of the established BCAs. The extensive utilization of chemicals for controlling pest populations came in trend after the World War II. Gradually, these chemicals were proven to be lethal to the environment as they are non-biodegradable and biomagnify at every trophic level in a food chain. There is an inclination in the application for natural enemies for pest insects except poor countries where different biocontrol methods are yet to introduce. (Omkar, B. & Kumar, 2016).

Benefits of Biocontrol:

1. Protection of Biodiversity
2. Low cost- As they have 1:250 cost-benefit ratio (Bale et al. 2008).
3. Freedom from the side effects of chemical pesticides.

Furthermore, biocontrol has several advantages over the traditional approach of chemical pesticides to deal with the pest insects. The biotic agents are host specific that makes no impact on non-target insects. It is recommended that we should let increase the diversity of the insect’s fauna in our gardens, fields as it helps in pollination and pest control. For this, we can maintain the compost quality of soil by mulching. This stuff is eaten by the insects in order to survive.

Biocontrol Agents (Bcas)Arthropods

Aphids are one of the important insect pest and they are becoming insecticide tolerant. Various parasitoid as natural enemies of aphids like wasps (Hymnotopetra), lacewings (Neuroptera) are first choice for the sustainable control of these pest. (Kach et al. 2018)

Nematodes

Symbiotic bacteria are found inside the body of entomopathogenic nematodes. Nematodes can be parasite on the insects and during penetration of the insect body these bacteria are inserted in host insect bodies. Steinerrnematidae and Heterorhabditidae families of nematodes have been successfully applied in fields for pest control. (Szewczyk et al. 2006)

Fungi

From more than 100 genera, almost 1000 species of entomopathogenic fungi have been discovered that have very less impact on non target insects. Necrotrophic fungi are preferred as BCAs that first kill the host and consume them. Such fungal species are reported to attack a multitude of insect orders. (Szewczyk et al.2006) Unlike bacteria and nematodes, fungi can directly penetrate the insect bodies. Thus, it can also target the sucking insects like mosquitoes (Fang et al. 2012). Fungi insecticide are not much effective in high temperature and UV radiation. Because it damages the fungal DNA and uplifts the oxidative stress of the cells. To overcome this problem, fungi are genetically modified to have dark pigments so that they can sustain in these harsh conditions. (Fang et al. 2012)

Baculoviruses

Viruses of family Baculoviridae, with narrow host target range, infect insects. Baculoviruses have double-stranded DNA, and they are pathogenic for arthropods. They are known to infect over 600 insect species worldwide. Immature forms of moths and butterflies are targeted by the Baculoviruses. Nucleo Polyhedral Virus (NPV) and Granuloviruses (GVs) are two genera of Baculoviruses. Once entered in the cells of insects the genetic material of these viruses start to transcript in a sequence and synthesise some essential proteins and proliferate theirs inside the host body. Baculovirus generates its small polyhedral forms in the nucleus which are considered to kill the host by making some toxins like Cathepsin and Chitinase. (Szewczyk et al. 2006). Baculoviruses are 30% cheaper in contrast to chemical insecticide. Moreover, they are applied once per season whereas chemical counterpart needs more than one applications. However, their action time is slow and in early stages, any changes in host cannot be observed. Consequently, recombinant baculovirus are produced which are injected with a specific toxic gene that codes a lethal chemical for specific insects. This reduces the action time of baculovirus. (Szewczyk et al. 2006) To stop the moulting in insects, Autographa californica nuclear polyhedrosis virus (AcNPV) has been discovered. This virus secretes the ecdysteroid which is of insecticidal property (Maeda 1995). Yang et al. (2012) provided that in China, Baculoviruses are being utilized in forests and soybean farms to remove pest insects.

Genetic Control of Insect Pests

Generally, genetically modified organisms are criticized for having bad impacts but they can be really good at controlling pest control as they posses less resistance in contrast to any other method of pest control (Jiang et al. 2008). GMO can be modified to releasing the Cry endotoxins that are lethal to the herbivores insects. Pink bollworm is controlled by introducing the Bt cotton. (Alphey & Bonsall 2018). However, their adoption has been increased through various second and third generation genetically modified crops. Such crops are recorded to have less impact on non target pest species (Christou et al. 2006). GMO can be modified to release certain toxic chemicals like the Cry endotoxins which are lethal to the herbivores insects. Pink bollworm is controlled by introducing the Bt cotton. (Alphey & Bonsall 2018). Various transgenic plants have been inserted with different genes that encode toxin for wide range of pests. (Christou et al. 2006).

Sterile Insect Technique

This method is purely based on the reproductive biology of the insects rather than any chemical. In this, large groups of sterile insects are produced by giving them special treatment. This can be ionizing radiation or the hybridization with the other strains. By such methods, chromosomal material in manipulated for making insect sterile. Afterwards, these insects are introduced in the fields where the wild insect population is present. These sterile reproduce with the wild insects and produces eggs that do not hatch. It is a time taking procedure to completely vanish the pest population from a given area. SIT has successfully implemented to remove the screwworm. (Alphey & Bonsall 2018b)

Gene Silencing

The cotton bollworm, Helicoverpa armigera can not detoxify the gossypol (secondary metabolite) from tobacco but it can do so in cotton. This represents that tobacco has a specific gene that supress the activity of bollworm to detoxify the gossypol (Ishaaya et al. 2012). RNAi (RNA interference, rRNA molecules, and 21–23 nucleotides long) technology has the potential to supress a particular gene. This have been applied successfully in gene silencing in insect pests of agricultural importance. Nematodes have more efficiency of RNAi rather than other insects. Number of hemipteran pests can be controlled by the gene silencing by dsRNA. This dsRNA is introduced inside the body of the insects to degrade the mRNA of the organism. An American agricultural pest, the brown marmorated stink bug has been provided to be controlled by RNAi. However, this method is a molecular work which is done in vivo. There is still on going work to introduce the pest specific dsRNA in crops so that herbivores insect pest can controlled easily. (Ghosh et al. 2017)

Pest Insect’s Control by Light

Nocturnal insects shows positive phototaxis as they can see the UV light. Insects’ posses compound eyes and ocelli as photoreceptors. An omatidium is the unit of compound eye that posses photoreceptor cells. Some traps like yellow illuminating discs are used for controlling them which are based on the insects’ ability to watch light.Some diurnal insects like plant hoppers, leafhoppers, aphids, whiteflies, thrips, and leafminer flies are attracted to artificial sources of lights like UV lamps, Yellow plates, and yellow pan traps at night (Shimoda & Honda 2013). Mulching sheets are used to reflect he light from the surface. This misleads the insects that sun is on the surface. So, they stabilize the horizontal orientation. This affects the flight of the insects (Shimoda & Honda 2013b). Nocturnal insects are deceived by the fluorescent light lamps in night. They assume it as a daytime and consequently, their flying, mating and sucking are suppressed. Nowadays, LED lights are used for these traps as they can produce monochromatic light (UV to Red) and they are cheaper. (Shimoda & Honda 2013c)

Photopesticides

This unique method of controlling pest population has less environmental and toxicological impacts. In this, various photosensitive compounds methylene blue, acridine red, hematoporphyrin dimethyl ether (HPde) are injected in the insect’s body by feeding them a specific diet. Afterwards, they are irradiated with the visible light which activates these compounds and some photochemical reactions take place to make new compounds. These compounds are considered as lethal for the bugs as they cause severe internal damage. However there is ongoing research to find some natural photopesticides at less cost and feeding techniques for target species (Luksiene et al. 2007).

References:

1. Alphey, N & Bonsall, MB. 2018a Genetics-based methods for agricultural insect pest management. Agricultural and Forest Entomology 20, 131-140.
2. Aktar, W, Sengupta, D & Chowdhury, A. 2009 Impact of pesticides use in agriculture: their benefits and hazards. Interdisciplinary toxicology 2, 1-12.
3. Bale, JS, van Lenteren, JC & Bigler, F. 2008 Biological control and sustainable food production. Philos Trans R Soc Lond B Biol Sci 363, 761-776.
4. Bebber, DP, Holmes, T & Gurr, SJ. 2014 The global spread of crop pests and pathogens. Global Ecology and Biogeography 23, 1398-1407.
5. Christou, P, Capell, T, Kohli, A, Gatehouse, JA & Gatehouse, AM. 2006 Recent developments and future prospects in insect pest control in transgenic crops. Trends Plant Sci 11, 302-308.
6. Cock, MJW, Murphy, ST, Kairo, MTK, Thompson, E, Murphy, RJ & Francis, AW. 2016 Trends in the classical biological control of insect pests by insects: an update of the BIOCAT database. BioControl 61, 349-363.
7. Fang, W, Azimzadeh, P & Leger, RJS. 2012 Strain improvement of fungal insecticides for controlling insect pests and vector-borne diseases. Current opinion in microbiology 15, 232-238.
8. Ghosh, SK, Hunter, WB, Park, AL & Gundersen-Rindal, DE. 2017 Double strand RNA delivery system for plant-sap-feeding insects. PLoS One 12, e0171861.