Insect Morphology: An Overview

• Insects are abundant and successful terrestrial animals; estimated to be 75% of all described species.
• Small body size helps insects hide easily and survive with small amounts of food.
• Insects have varied feeding habits, including plant feeders, carnivores, decaying matter feeders, and parasites.
• Insects are regarded as serious competitors for food, fiber, and shelter.

General Morphology

• Insects are segmented with bodies covered by a cuticle, which serves as an exoskeleton.
• The insect body comprises three regions: head, thorax, and abdomen.
• The head bears sense organs (antennae, eyes) and mouthparts.
• Antennae are variable in form and are used for feeling, smelling, and sometimes defense.
• Adult insects have two sets of eyes: compound eyes and simple eyes (ocelli).
• Compound eyes are composed of hexagonal facets, each seeing a fragment of the environment, creating a mosaic-like image.
• Simple eyes distinguish dark from light and are common in lower insects and larvae.
• The thorax is next to the head and consists of the prothorax, mesothorax, and metathorax.
• Adult insects have a pair of jointed legs on each of the three thorax segments.
• Each leg has six parts: coxa, trochanter, femur, tibia, tarsus, and pretarsus, varying in size and length depending on function.
• Mole crickets have legs with broad, short segments for digging.
• Praying mantises have legs with long, spiny segments for catching prey.
• Most insects have two pairs of wings, one on the mesothorax and one on the metathorax.
• The abdomen is the third region, composed of segments with posterior parts modified for mating and reproduction.
• Abdominal segments are connected by a membrane, allowing expansion during feeding and egg production.
• Valuable parts for insect identification include antennae, mouthparts, wings, and sometimes legs.

Insect Antennae

• Insects have a pair of antennae for smelling and sensing environment elements like air, temperature, and sounds.
• Antennae are composed of three major parts: scape, pedicel, and flagellum or clavola, and vary in shape.

Insect Mouthparts

• Mouthparts are organs involved with feeding and ingestion, consisting of labrum, mandibles, maxillae, labium, and hypopharynx.
• Mouthparts can be simplified into two basic types: biting-chewing and piercing-sucking.
• Biting-chewing mouthparts are for feeding on solid foods where powerful mandibles are used.
• Piercing-sucking mouthparts are adapted for feeding on fluids.
• Modifications of mouthparts for liquids include sponging (housefly), siphoning (butterfly), piercing-rasping (thrips), and chewing-lapping (honeybee).
• Biting-chewing insects tear off plant or insect tissues, resulting in holes, broken twigs, and shredded plant parts.
• Examples include grasshoppers and beetles, where young and adult stages share the same food.
• In fruit flies, corn borers, and leaf folders, the larval stages are most destructive, while adults do not feed on plants.
• Piercing-sucking insects modify mandibles into sharp stylets to stab and puncture plant tissues, sucking liquids and injecting saliva.
• Damage caused by piercing-sucking results in wrinkled/crumpled leaves, stunted growth, sooty molds, and yellowing due to fluid depletion.
• Pests with piercing-sucking mouthparts include aphids, leafhoppers, whiteflies, scale insects, and true bugs.
• Knowing the type of mouthparts helps in selecting the appropriate pesticide.
• Stomach poisons are used for biting-chewing pests, while systemic insecticides are used for piercing-sucking pests.

Insect Wings

• Insects generally have two pairs of wings on the thorax for flight.
• These wings are often called forewings and hindwings but some insects lack the hindwings.
• Insect wings enable insects to protect themselves from predators and find a mate.
• Some insect wings, especially the forewings, are modified for the protection of the hindwings when not in use.

Insect Legs

• Most insects have three pairs of legs used for walking.
• Each pair of legs is connected to the thorax and has 5 part: coxa, trochanter, femur, tibia, and tarsus.
• Legs are modified based on the insects structure and specific function.
• Caterpillars have soft fleshy legs with many tiny hooks or barbs on one or more abdominal segments.

Internal Anatomy

• Most internal organs, including circulatory, digestive/excretory, reproductive, and nervous systems, are in the abdomen.
• The circulatory system is open; instead of blood, they have hemolymph.
• The digestive system has three parts: foregut, midgut, and hindgut.
• The nervous system has three subsystems: central, visceral, and peripheral.
• The main function of female reproductive organs produce eggs, while the male's function is to produce and store sperms.
• Insects lack lungs and air enters through spiracles.

Growth Development and Types of Metamorphosis

• Most insects reproduce bisexually by laying eggs.
• Eggs hatch into larvae that undergo molts, increasing in size with each molt.
• Change in form during development is called metamorphosis.
• Adults break pupal case and emerge in winged form.
• Complete metamorphosis (holometabolous) involves significant changes between instars.
• Incomplete metamorphosis involves little change between instars other than size and coloration.

Reproduction and Population Growth

• Insects are adaptive with high fecundity, rate, and short life cycle, leading to large populations.
• Reproduction continues if not checked by parasitoids, predators, or weather disturbances.
• Stresses affect population depending on abiotic (temperature, humidity, light) and biotic (host, biodiversity, enemies, diet) factors.
• Abiotic stress affects ovulation, fecundity, development, survival, and genetic responses.
• Biotic stresses affect reproduction, multiplication, emergence, and migration.

Insect Orders with Pest Species

• Eight insect orders are associated with agricultural production and two are associated with animal production.
• Some are warehouse contaminants or cause annoyance/damage to humans.

Lepidoptera

• Moths, butterflies, and skippers are winged adults.
• Adults have no mandibles and use soft, coiled mouthparts to siphon nectar and plant exudates.
• Adults reproduce by laying eggs, becoming larvae or caterpillars.
• Caterpillars are plant feeders, defoliating crops.

Coleoptera

• Beetles and weevils comprise 40% of all insects and 30% of all animals.
• Adults have modified forewings, forming hardened elytra.
• Adults and larvae have chewing mouthparts, making them destructive to crops.
• Some beetles are beneficial, controlling pests like aphids and whiteflies.

Orthoptera

• Grasshoppers, crickets, locusts, and katydids are solitary or gregarious.
• They can walk and jump. For escape or flight.
• Nymphs and adults have mandibles to chew leaves or other insects.
• Some are destructive to crops.
• Short-horned grasshoppers/locusts are foliage feeders but hot weather/dry spells trigger migratory locusts.

Isoptera

• Termites or white ants live in social family units.
• Castes include reproductive kings/queens, wingless sterile soldiers, and workers.
• Antennae are moniliform, and wings are membranous.

Hemiptera

• Members of this group have piercing-sucking mouthparts; development is incomplete.
• Main suborders: Sternorrhyncha, Cicadomorpha, Fulgoromorpha, Coleorrhyncha, and Heteroptera.
• Sternorrhyncha includes aphids, mealybugs, and scale insects and the sucking mouthparts are short with most being plant feeders
• Also produce honeydew that may result in sooty molds when infestations are heavy.
• Some members have wings, others only males
• Cicadomorpha contains species with organs for sound production, most members are xylem feeders
• Fulgoromorpha members produce honeydew, all members are plant juice suckers
• Coleorrhyncha is not present in the Philippines
• The suborder Heteroptera consists of true bugs and is characterized by a distinct forewing

Thysanoptera

• Thrips are small, slender with piercing-sucking mouthparts.
• They attack new shoots/flushes, resulting in bronzing and drying.
• Some members are plant feeders and the vectors of plant pathogens.

Diptera

• Includes mosquitoes, midges, sand flies, blow flies, houseflies, syrphids, and fruit flies.
• Easy to recognize because they have one pair of wings
• Some are pests to crops while mosquito females drink blood.
• Mosquitoes transmit human and animal diseases.
• Some members are beneficial.

Major Insect Pests in Rice Production:

• A wide range of insect pests attack rice at different growth stages and seasons; harvested rice is also prone to attack.
• Important rice pests: a) whorl maggot, b) brown planthopper, c) green leafhopper, d) stem borers, e) leaffolder, and f) rice bug.
• Rice seedling maggots' adults are grey, larvae feed at the center of the plant and mine the edges, bores white feeding marks.
• Brown planthoppers are small, are at the bottom of the plant and suck plant sap, leaves the plant drying, results in hop per burn, has vectors.
• Green leafhoppers: they suck the sap from the upper part of the plant and transmit a yellow dwarf virus.
• Stemborers: there are four important type of stemborers: Striped stemborer, Yellow stemborer, White stemborer, and Pink stemborer.
• Leaffolder: The leave fold leaving the edges to spin a web, leaves looks scraped, The larva eats around 4 leaves before turning into pupo.
• Rice bugs: Suck liquid from withing the grain and leaving it empty, panicle show white and empty grain, and end up in either empty grains or broken grains

Corn Production

• Corn: the most important insect pests attacking corn are corn seedling maggot, corn semi-looper, corn borer, corn earworm, cutworm, true armyworm and pink stem borer.
• Corn seedling maggot: serious insect pest that attack the seedling, result in leaf curling. The egg turn dark and hatch into maggots.
• Corn borer: can find at whorls, the stem is where the holes start, they weaken the corn, and may cause death. The eggs hatch pinkish larvae-pinkish.
• Corn earworm: it has a bread host range and can feed on other crops such as tomato, beans, sorghum, cotton and tobacco
• Fall armyworm: It a defoliate ear, flower and seed feeder

Vegetables:

• Vegetables: the most important insects are chewing, shredded leaves; plants lack sap and results in lower yield.
• tomato is attacked by tomato fruitworm, it lays its eggs under the leaves. The insect bore the leaves and fall into the soil and pupates.
• Crucifers important leafy vegetables can be damaged causing the loss of 20-80% insects on the plant.
• Diamondback moth, cutworm, cabbage worm, earworm, and aphid.

Legumes

• Legumes attract the Beanfly that infests leaves, leaffolders feed up the leaves, the black bean aphids feed the leaves as well and cause severe curling.

Onions and Garlic

• Onion Garlic is infected with Thrips who feed on leaves and dry them. This happens more often in January-March

Banana

• The corm weevil, scarring beetles and banana aphis attach this plants by scarring them rendering them unfit

Mango

• the insects that attach this fruit are is the mango hoppers, the twig borers, the mango fruit fly, and the mango pulp weevil.

Medical, Veterinary and Structural Pests

• Medical can have different species of Ant pest that cause many problems.
• Cockroaches: Can be considered pests because of their odor and filthy habits. The Search of dirt in places where kitchens, food storage is present
• Flies: Are a nuisance and and carry many diseases.
• Mosquitoes: act as various vectors and cause diseases.
• Termites: wood destroyers.

Management Approaches

• There are ways and methods in a way of controlling or managing insect Pests. Control meaning The pest is meant to be eliminated or eradicated Completely . Management: the pest's population has to be at an accepted and manageable levels.
• in the urban setting the best to get rid of the pest.
• integrated Pest Management (IPM) the is the key to combine at least two methods to ensure an effective results.
• Cultural Control Methods: The agricultural operations that take part in crop. Crop rotation- Planting of crop that different from family and or group
• Industrial Setting practices is called FIFO that help with pest infestation Sanitation is the way to eliminate to maintain cleanliness
• Mechanical methods Use of vacuum cleaner
• Traps
• Handpicking
• Screen nets to injury
• Biological control: utilization of other living organisms -Bacillus thuringiensis: the source of Dipel or Thuricide which are the commercial formulations of the bacterium's endotoxin that kills the larvae.
• Conservation Biological Control
• Classical Biological Control
• Augmentation Biological Control
• Chemical Control Method
• Synthetic
• Natural
• Genetic Control Method
• Propagation Regulatory or legal Method: eradicate by law Physical: fire and sound(the house cannot be on fire only pest)