Wheat Triticum aestivum L. is grown on broad range of climatic conditions because of edible grains, cereal crop and stable food of about 2 Billion peoples worldwide. Additionally, it is the rich source of carbohydrates (55–60%), vegetable proteins and contributed 50–60% daily dietary requirement in Pakistan. Globally, wheat crops is grown over 90% area of total cultivated area; facing devastating biotic and abiotic factors. The estimated economic losses in wheat quantity and quality are about 4 thousands per tonne per year including physical crop losses and handling. Economic losses of about 80–90 million USD in Pakistan are recorded due to inadequate production and handling losses. Wheat agro-ecosystem of the world colonizes many herbivore insects which are abundant and causing significant losses. The feeding style of the insects made them dispersive from one habitat to another imposing significant crop loss. Areas of maximum wheat production are encountered with either insect which chew the vegetative as well as reproductive part or stem and root feeders. This chapter provides the pest’s taxonomic rank, distribution across the globe, biology and damage of chewing and sucking insect pest of wheat. It is very important to study biology of the pest in accordance with crop cycle to forecast which insect stage is economically important, what the proper time to manage pest is and what type of control is necessary to manage crop pest. The chapter will provide management strategies well suited to pest stage and environment.
- Wheat crop
- economic losses
- insect pests
Wheat is undoubtedly one of the major cereal crop, staple food and rich portion of daily intake for much of world’s population. With annual global production over 770 MT from 220 M hectares, it is a grain of life. The cultivation of wheat started about 10,000 years ago as part of the Neolithic revolution which state a transition from hunting and gathering of food to settle agriculture. Earlier cultivated forms of wheat were diploid (einkorn) and tetraploid (emmer) with known initial origin of the south-eastern part of Turkey. Hexaploid bread wheat that is currently widely adapted in about 95% area of world.
Though wheat was one of pesticide free crop in major areas of the world, however the things are not the same now. Today, all crop production practices are being highly challenged by biotic and abiotic stresses. Biotic stresses especially insect pests and diseases cause devastating damage in terms of yield and quality. On average pests cause 20–37% yield losses worldwide which is translating to approximately $70 billion annually.
Wheat is damaged by sucking and chewingtypes of pests. The list of insect pests damaging different stages of wheat crop varies from region to region, however the complete list of insect pests is around 100. It is therefore important to understand biology of insect pest simultaneously with the crop biology to understand when, where and what chemical should be used to control specific insect/pest more effectively. In this review, we have outlined major insects of wheat along with their biology and control strategies to minimize grain yield losses.
2. Chewing insects’ pests of wheat
2.1 Wheat termite
Microtermes obesiHolm. (Termitidae: Blattodea)
Wheat termites belong to order (Earlier Isoptera) Blattodea consisting of 9 families exists worldwide. The families of termites were further classified as monogeneric families including Mastotermitidae (holotype
Termites found all over the world except the Antarctic region. Termites distributed to Tropical, subtropical and temperate regions Worldwide. Termite’s diversity is found to be very high in the South American region compared to North America and Europe. Out of 3000 known species of termites are extremely abundant if African region. In Asia the main distribution is restricted to China, India, Pakistan, Sri Lanka and Veitnam totaling 435 species.
Termites undergo a developmental process as in case of other insect species known as incomplete metamorphosis with egg, nymph and adult stages . Nymphs are small entities resembling adults, molts as they grow converted into adult stage. A nymph usually undergoes 3 molts . During the summer months after monsoon, fertile reproductive caste of termites leaves its colony for nuptial flight. After successful fertilization the queen increased in size from 9 to 11 cm and laid around 70,000 kidney shaped eggs that will hatch in nearly 30–90 days. Usually in full reproductive colonies 80–90% individuals belong to the workers caste and 10% Soldier caste . After sometimes they are produced into full adults with wings and reproductive or fertile females which can fly for nuptial flight to repeat cycle for new colony .
Under field conditions, the termites (
2.3 Wheat armyworm
Mythimna separataWalk. (Noctuidae: Lepidoptera)
Many synonyms of this name were used in the literature are
The wheat armyworm is present in various wheat growing agro-ecosystems from Asia to Australian continent between 45 north and 45 south Latitude and 60 east to far 170 West Longitude. It is found in 27 countries including China, Japan, Pakistan, and India also in Pacific islands from tropics to temperate climatic regions .
The fertile females lay maximum eggs from 500 to 900, spherical and milky white in color to approximately 2000 eggs. The eggs are laid in clusters on or underside the young seedlings or in soil. The eggs will hatch in 2–7 days after that larva emerges and lasts long for 14–22 days. The mature larva possesses green to pink color having greenish to brownish black stripes on the entire body length . Pupation is usually done in soil but can be done under dry leaves or fresh stubbles or fresh tillers as well. The pupae are shiny brownish yellow in color and last upto13 days. Thus, the whole span lasts in about 35–40 days which may repeat multiple times in each year.
During the young vegetative stage of wheat plant, the damage is more prominent with extensive defoliation. Young larvae may feed at lemma and palea of young grain as well as male part anther of mature flowers. The larvae cut the young seedlings so often the damage is restricted to a single part of the field. During the grain formation stage, the larvae feed upon the panicles from the basal part of the plant causing it to bend downwards and sometimes the plant may fall down.
2.4 Wheat shoot fly
Atherigona naqviSteylskal (Muscidae: Diptera)
The taxonomic classification was described by Steyskal in 1966. In Asia, it was first reported in wheat agro-ecosystem by . However, in the subcontinent, 5 different species from genus
The damage is usually done by the immature larvae of all instars. After the emergence of young seedlings, usually 3–4-week-old young seedlings are targeted by the maggots. After hatching, maggots feed the young growing tissues of the plant resulting in drying of central shoot by chewing the central phloem tube produce white dry seedling known as dead hearts. Dead hearts due to dryness can be pulled easily. Sever infestations resulted in bushy appearance of young tillers.
2.5 Surface grasshopper or cutworm
Adults are much larger than nymphs, have well developed mandibles and wings too. Sexual dimorphism is present as a female has four ovipositors to lay eggs and is usually bulky than males whereas males are smaller and rounded .
2.6 Pink stem borer
2.6.1 Taxonomy and nomenclature
Francis Walker in 1856 described
2.6.2 Worldwide distribution
According to CABI [35, 36], the current distribution of
Life span of
Pink stem borer
2.7 Shield bug
2.7.1 Taxonomy and nomenclature
Shield bug of wheat is also known as Sunn pest. A total of fourteen species has been reported so far, three of them are considered economically important;
2.7.2 Worldwide distribution
Sunn pest has a cosmopolitan distribution in
The eggs of the
Adults are elongated and elliptical, and their color varies from grayish to brown, to red or black . In this concern, Color of the
2.8 Loreyi Leafworm
2.8.1 Taxonomy and nomenclature
Current accepted scientific name ofLoreyi Leafworm
2.8.2 Worldwide distribution
Loreyi leafwormis a major pest of graminous crops including wheat and maize . Up till now,
2.9 Black cutworm
2.9.1 Taxonomy and nomenclature
Ochsenheimer proposed the genus
2.9.2 Worldwide distribution
Black cutworm is also scattered worldwide and causes a huge loss of crop yield. They are distributed in
Black cutworm has a broad has range and feeds on all crops and pasture plants. Newly emerged crop seedlings are attacked by the full-grown larvae migrated from summer and autumn weeds. Species of the
3. Management of chewing insect pests of wheat
Seed is the basic building block of a crop. As seed is healthy insect and disease free more the yield is obtained. Insects are small creatures but are highly reproductive in nature so that they compete with humans for resources. Controlling of insects at appropriate time is the key point to obtained higher and healthy yields.
3.1 Seed treatment
Seed treatment is one of most important control measures which reduce the chances of insect’s pests attack because eggs of some insects are glued to seeds and spores of different seed born diseases are attached so that seed treatment is necessary to control the insect’s population at its initial stages. Different Insecticides were used to treat seeds against different insects’ pests. Fall army worm
A quarantine pest is “a pest of potential economic importance to that piece of land where it is present but not widely distributed and controlled or the endangered zone where pest does not presentyet. Chewing insect pests requires quarantine measures. Different chewing pests which were not reported or not widely distributed to wheat zone of Pakistan. Arecent exampleof it is fall armyworm that were 1st reported in Nigeria in west Africa in 2016 and within a short duration of time it was reported in 44 countries of Africa. In 2018 it was 1st reported in India [85, 86] that moved to Bangladesh, China, Sri lanka, Thailand, Myanmar . Suitable and perfect environmental conditions for fall armyworm reproduction and wide range of host plants availability in Pakistan. corn and wheat zones are endangered, and several articles were published in newspapers. The international maize and wheat improvement center (CIMMYT) have cautioned Pakistan to make efforts against fall armyworm a potential threat to maize and wheat in Pakistan.
World Trade Organization agreement on the application of sanitary and phytosanitary measures and the international plant protection convention of the food and agriculture organization of united nations and convention for biological diversity all these organizations highly recommended that prevention is the most effective control of invasive species within a minimum cost. It shows better and cost-effective results where it is adopted. The IPCC released a summary of international standards and phytosanitary measureswhich includes all sanctions and guidelines for whole trade processes. Economically harmful species of plants and plants product are black-listed and banned from entering in the whole continent in Europe. The most cost-effective control against invasive species of insect pests is to inspect the incoming consignments with sanitary and phytosanitary inspections at borders this is the last weapon of defense which can be used against invasive species otherwise their control is very difficult.
3.3 Biological control
Biological control plays an important role in wheat crop pest management. Negligible use of insecticidesprovides conducive environment for biological agents to flourish and reproduce. Biological control is the most effective control method when using with other compatible controlling techniques for example in IPM we use biological control as an effective component of crop pest management with other controlling practiceslike cultural control and planting resistive varieties against insects’ pests. On the other hand, we use selective insecticides against pests when other controlling method failsdue to some biotic or A-biotic factors to keep the population below ETL.
3.3.1 Biological control managers
Biological control managers of insects are divided intopredators, parasites and pathogens.
Predators are lions they kill and eat their host within few minutes for example Convergent lady beetles.
Parasites are internal and external or attack to specific life stages of pests. The most important parasites belong to parasitic Hymenoptera puncture the parasites eggs with their sharp ovipositor and lay single egg eggs hatched in 6 to 7 days and larvae feeds on these eggs. Some parasitoids lay eggs directly larvae after hatching parasitoid larvae feed on internal parts of parasite and emerge dead larvae and their mummies left and found in the fields.
3.4 Physical control
physical control is also possible in some insects like larvae of some insects identified and picked from plants individually it is also done with modified method by
3.5 MST and RIDL
Release of sterile male to reduce the population of an insect pest is a molecular approach and it is also practically performed against different pests like lepidopterans and dipterans. Male sterile techniques are used against chewing pests of wheat is a good approach to reduce the population without affecting our biological fauna.
RIDL is defined as release of insect with dominant lethal gene this technique was used against different pests like fruit flies and this control is also use against different dipterans. RIDL approaches as an insect having a dominant gene surviveand cause lethality in conditions when mating with a female. The survivors refer to a carrier of set of genes and strategies having bisex lethal, flightless females and non-sex specific late-acting lethal systems.
3.6 Legislative control
Wheat legislative control adds as timely sowing of wheat crop with good practices, recommended density of plants,
3.7 Push pull strategies
A behavior manipulation strategy known as Push Pull technique, which is widely used against different insect pests. The term Push pull coined by Australians to control the pests without use of hazardous insecticides. This strategy used against different pests to reduce their abundance. Australians use this strategy against different Helicoverpa species in cotton. Push pull technique combining with other control methods like natural enemies gives good results .
Genetically modified organisms are used to kill insect pests and also genetically modified verities of different crops used to control the pests without using of any chemicals. Bt corn and Bt cotton is one of most popular strategies which are currently use against pests .
4. Sucking insect pests of wheat
4.1 Chinch bug
Chinch word in Spanish means Pest. The family lygaeidae genus Blissus which contain chinch bug species, yet the taxonomy of the genus is poorly understood. Chinch bug, though native of tropical America but extended its range to the world. It subdivided into two species
There are five nymphal instars with 5, 6, 5, 4, and 6 intervals during each instar when reared at 29°C, under field conditions, the development time may be extended. The normal development time is 30–40 days in normal and may be extended in 60 days. Identification of nymph in early stages, head and thorax are brown, legs are yellowish. These colors are darker as the mature nymph, so the mature nymphs are blackish in color. There are yellowish and whitish colors on the first two segments of abdomen. Wing pads become visible in 3rd instars. Nymphs prefer sheltered locations to feed and aggregate on the stem near the main stem of the plant .
Adults are blackish in color; wings nearly attain the end of abdomen and are white in color with blackish spots found near the center. Measurements of adults are 3.5 to 4.5 mm in length.
Host of chinch bugs consist solely of family gramineae, but also include other grasses and plants. Chinch bug is a plant feeding insect, causing reddish color at the site of feeding and death of the plant. Plant growth can be stunted, or dead by a large number fed on plants. The losses by chinch bug were estimated at 19 million dollars in 1989 .
4.2 Wheat aphid
Aphids evolved in Carboniferous period about 280–300 million year ago [95, 96] Many species of aphid attack on wheat crop, three major aphids pest are
Order: Hemiptera. Suborder: Sternorrhyncha, Family: Aphididae, Genus: Myzus, Sitobion and Schizaphis, Species:
Aphids biology is quite complicated than other insects. In single colony, aphid adults are present in wing form or wingless form. Aphids characters in life cycle is continuous asexual production and of larvae by live birth, parthenogenesis and viviparity respectively. In parthenogenesis, embryos arise from cells without reduction of chromosomal and individuals, so all females are genetically identical to their parents. Sexual reproduction occurs in autumn, female of autumn season oviparous results in the production of overwintering eggs. In the following growth season of plant eggs hatch and produce a series of parthenogenetic generations [100, 101].
4.3 Green stink bug
The development of life stages of this species has been described by Jones in 1918. Females lay eggs in clusters; each cluster contains 60–90 eggs . Fresh eggs are cream in color, and become dark after one day, eggs hatch in 3 days . First instars of
4.4.1 Taxonomy and nomenclature
Haplothrips was first described by Amyot & Serville in 1843. Synonyms of the
Eggs of Haplothrips are cylindrical, rounded from posterior, tapered anterior end, which looks like a knoblike process. Eggs measure 433-500 μ length and 137-150 μ width. Nymphs at the time of egg hatching are microscopic, transparent and amber in color. Color changes from amber to pink after considerable feeding. The length of the first instar before eclosion measures 1100 μ in length. The color of the second instar nymph is glowing red except for the appendages which are dark brownish to black. Second instar mature nymph measures about the same length as that of the adult. The pre pupal stage of the
5. Management of sucking insect pest of wheat
5.1 Cultural methods
Cultural control comprises the modification of regular farm operations that destroy the insects or prevent them from causing injury. This control is to adjust the time of sowing, plowing, irrigation, harvesting and improved farm management. The opinion regarding aphids shows that it damages the wheat badly that is sown earlier and if the cool weather remains until March .  reported that the crop sown earlier was least affected and the wheat crop can be set aside by doing modification in sowing dates. The early sowing of the wheat crop is the best way to minimize the risk of aphid attack . The abundance of
Intercropping with different crops can increase the natural enemy population in a wheat field for many reasons. The intercrop plants may release chemicals to attract natural enemies and their early establishment in the field. Intercropping with non-host plants seemed to be favorable for the parasitoid’s population . The ryegrass strips in wheat fields and wheat– oilseed rape intercropping is used to enhance the number of natural enemies. The population density of ladybeetle and ratio of ladybeetle to
5.2 Seed treatment
Seed treatment is environment friendly and economical with excellent control. The systematic and relatively low rate of the application makes it user-friendly for seed dressing and it protects from sucking insect pests by eliminating the repeated needs for sprays. Seed treatment by using neonicotinoid insecticides against piercing-sucking insects, such as aphids is very effective.  reported that when imidacloprid in combination with tebuconazole is used as seed treatment against
5.3 Biological control methods
Natural Biological control is the action of predators, parasitoids, pathogens and plant extracts in maintaining pest density. The natural enemies may help to reduce the sucking pest population from reaching the economic injury level in the Wheat. The aphid parasitoids in Pakistan have been reported by [128, 129]. In Pakistan,
In wheat, sucking pest populations are effectively restricted by adults and larvae of ladybird beetles, lacewing larvae and larvae of hoverflies. Predators are the parasitoids due to their broader host range and can feed on both egg and larvae stage of pests and also . Coccinellids are the most abundant predator on wheat and cotton for the controlling of the aphid population .
There are several botanicals derived from plant oils extracted from leaf and seeds have been used to control aphids in Pakistan.
5.4 Host plant resistance
Plants can resist invading insects and diseases. The plants with this ability can be attributed to their morphological and chemical characteristics. Moreover, resistant plants can change their physiology in case of invasion and compensate for the damage caused by the pests. Planting resistant cultivars is a simple and effective method to reduce its damage.  proved that Galaxy 2013 gives higher yield and can tolerate aphid damage. Wheat genotypes can play a vital role to suppress the aphid population, Sarsabz, Kiran-96 and Khirman varieties were shown to be resistant . Results proved that 6309–2103 shows resistance among other varieties and has the lowest Aphids population density . Shafaq-06 is more susceptible and 9114 is relatively more resistant wheat varieties lines against the aphid population .