Insect biology The science that deals with insect’s individual developmental history. It is divided into the study of reproduction, embryology, post embryology and adult

Stage: hatching from egg to the adult. Larval stage or nymph stage Stage: hatching from egg to the adult. Characteristics: feeding and increasing volume

Primitive nymph Apterygota: anamorphosis or epimorphosis More appendages at the sides of abdomen: flipping organ

The same typical nymph Pterygota Paurometamorphosis Nymph and adult are different : wings and reproductive organ Nymph and adult are same: figure, internal and external organs, as well as habit and habitation

atypical larva Larvae of complete metamorphosis Larvae are different to adults in figure, internal and external organs, as well as habit and habitation Wings develop in the larva No wings outside the larva No compound eyes Pupa stage

Types of atypical larva protopod larvae Oligosegmented protopod larvae Polysemented protopod larvae potypod larvae campodeiform larvae eruciform larva oligopod larvae carabiform larva Scarabaeform larva elateriform larva platyform larvae apodous larvae eucephalous larvae hemicephalous larvae acephalous larvae

Protopod larvae Parasitic hymenopteran insects Little yolk Thin chorion or no chorion Larvae hatche at the early stage of embryo development Some larval insects do not segment in their abdomen Thoracic legs are simple protuberance Nervous and respiratory systems do not develop Mouthparts are undergrown Absorb host’s nutriment through their integument

Potypod larvae: Except for thoracic legs, the larvae have pairs of abdominal legs

campodeiform larvae Campodeiform larvae have a flattened body with long legs, usually with filaments on the end of the abdomen. Larvae of some Megaloptera, Neuroptera, and Trichoptera are typical examples. megaloptera larva

eruciform larva Eruciform larvae are cylindrical; they have a well-formed head, thoracic legs, and abdominal prolegs. Larvae of Lepidoptera and sawflies are typical examples. Lepidopteran larva

oligopod larvae Coleoptera/ Trichoptera/ some of Neuroptera Thoracic legs are developed No abdominal legs

Carabiform larvae Carabiform larvae are similar to the campodeiform type, but the legs are shorter and filaments are lacking on the end of the body. They receive their name from the larvae of carabid beetles. Chrysomelid beetle larvae are of the same type.

Scarabaeform larva Scarabaeiform larvae are C-shaped, have a welldeveloped head, and usually possess thoracic legs but lack prolegs. The type is named after larvae of scarabaeid beetles Larvae of sweetpotato weevil

Elateriform larvae Elateriform larvae are cylindrical, smooth, and relatively tough-skinned larvae with short legs. They are named after larvae of click beetles Larvae in the beetle family Tenebrionidae also have this appearance. tenebrio molitor click beetle

Platyform larvae Platyform larvae are broad and flat with legs short or absent. This type is not common, but examples are found among larvae of some syrphid flies, certain caterpillars, and blister beetles. syrphid flies

apodous larvae Devoid of legs and prolegs. Vermiform larvae Diptera /Anoplura/ some of Hymenoptera and Coleoptera Root Maggots

eucephalous larvae hemicephalous larvae acephalous larvae

It seems a still stage: Complete metamorphosis Pupation It seems a still stage: Complete metamorphosis Prepupa Decomposition of old organs Generation of new organs

Insect Pupae Classes based on whether the appendages are free or adhere to the body.

Surface Anatomy of Pupa (ventral view)

Types of insect Pupae Pupal Type Common Name Description Examples Obtect Chrysalis Developing appendages (antennae, wings, legs, etc.) held tightly against the body by a shell-like casing.   Often found enclosed within a silken cocoon. Butterflies and moths Exarate None All developing appendages free and visible externally Beetles, Lacewings Coarctate Puparium Body encased within the hard exoskeleton of the next-to-last larval instar Flies

Obtect

Exarate

Coarctate Encased in hardened cuticle of next to last larval instar – puparium Diptera

This is the coarctate type with the puparium removed – note pupa itself is exarate

Protection of pupa

Main variation of pupal stage External variation: integument, antenna, eyes, mouthparts, legs, wings and genital organs Internal variation: histolysis and histogenesis

Emergence Definition incomplete metamorphosis complete metamorphosis

Monarch Butterfly emergence

Emergence

Sexual dimorphism Females and males are different: sex glands and outside genital organs Other different sides: Individual size, type of figure, variation of coloration

Sexual dimorphism of tumble beetle

Female Male

Strepsiptera

Monarch butterfly Monarch male Monarch female

Polymorphism Individual size, type of figure, variation of coloration are different in the same sex in one species. Adults, eggs, larvae, pupae.

Life of adults The last stage of insect. Sex is ripe in this stage and the insects have generative ability. Flying ability and sensory apparatus are developed.

The larval form of this moth (a) does not have wings or eyes, two important adaptations that the adult form (b) has.

replenish nutrient Some insects mate, blow and die soon after they emergence Most insects need replenish nutrient： Orthoptera ,Hemiptera and other incomplete metamorphosis insects all the blood-absorb insects

Mating Sex pheromone Sound

Life history Generation : leave from mother’s body- generate their own offspring. Voltism: generation numbers in one year. univoltine bivoltine polyvoltine partvoltine

Univoltine Univoltine cycles refers to insects with a single generation each year – most of the population is at the same growth stage at any one time. praying mantids, silk moth

Multivoltine cycles Multivoltine cycles refers to more than one generation per year – more generations per year means more overlap between generations houseflies, thrips, aphids

Partvoltine The lifecycle takes more than one year to complete 17 year Cicada takes 17 years to complete cycle

Dormancy Dormancy is a seasonally recurring period in the insects lifecycle when growth development and reproduction are suppressed. if it occurs in summer it is aestivation if it occurs in winter it is hibernation – most common in temperate climates

Hibernation Many insects die when winter approaches. But many others live through the cold by hibernating in the egg, larval, or pupal stage. A number of adult insects, including houseflies, mosquitoes, ladybugs, and some moths and butterflies, also hibernate. They spend the winter in barns, cellars, attics, caves, holes in trees, burrows in the ground, or other protected places.

Diapause in Insects A genetically determined state of suppressed development (cf. quiescence, an immediate response to adverse weather) Neurohormonally controlled, but can be triggered by environmental cues A strategy for withstanding adverse environmental conditions (extreme cold, prolonged dry season)

Two types of diapause Obligate – genetically programmed, all individuals in population enter diapause irrespective of environment; univoltine species. Facultative – ‘decision’ during a sensitive developmental point, cued by the environment. Most reliable environmental indicator for predicting onset of winter is daylength (i.e. critical photoperiod induces diapause). Bivoltine or multivoline species.

Diapause can occur in any lifestage, but is species-specific Egg: silkworm, red-backed cutworm; often maternally determined, i.e. photoperiod to which adults are exposed. Long day – eggs will diapause; short day – no diapause. Larval: spruce budworm (2nd instar)

Pupal: many lepidopterans (best studied), some lacewings Adult: diapause = delay in reproduction; e.g. milkweed bug, allows dispersal of young adults; results from a lack of JH (i.e. CA are inactive)

Alternation of generations Multivoltine sp. where succeeding generations are different in mode of reproduction or morphology are said to have alternating generations Aphids: in a simple aphid life cycle: winter is spent in egg stage in spring all hatch as wingless females

stem mothers reproduce parthenogenetically and produce more females by midsummer winged (alate) and wingless females are produced – winged disperse in late summer and fall winged males and wingless females are produced mating occurs in this sexual generation and eggs are produced for overwintering

Aphid Alternation of generations

Habits and behavior Habits : species or population Behavior : sense and reaction---insect ethology

Biological clock-insect clock Diurnal insect Nocturnal insect Crepuscular insect

Feeding habits According to food nature： phytophagous / herbivorous sarcophagous / carnivorous saprophagous omnivorous

Herbivorous

carnivorous

Feeding habits according to the food spectrum Polyphagous : many species of different families Ologophagous：some species of one family monophagous：only one species

An orientated movement of an organism.

Insect taxis Act of orienting towards some external stimulus or combination of stimuli. Spatial orientation, aided by different sensory modalities, is described by the corresponding term light (phototaxis) smell (chemotaxis) sound (phonotaxis) gravity (geotaxis)

If orientation is towards the source, it is called a positive taxis, and away from the source a negative taxis. In such instances individuals move in a directed fashion along a particular stimulus gradient until they reach a perceived optimal range.

Mosquitoes are attracted by perspiration, warmth, body odor, carbon dioxide, and light. Humans vary in their body chemistry and this is why some people are more prone to being bitten than others

Insect Mimicry Katydids mimicry to a wide variety of environments. Can you find the katydid in each picture?

Insect Mimicry Mimicry = Resemblance of an organism (the mimic) in color, pattern, form, behavior, or a combination of these to another organism or object (the model). The taking on by an animal of the look of another sort of animal or thing for the purpose of: keeping itself safe (traditional sense) enhancing predation

Three components: Model - species or object being mimicked. Mimic - looks and acts like another species or object by resembling the models Dupe- the deceived predator or prey.

Kinds of Mimicry Aggressive mimicry Müllerian mimicry Batesian mimicry

Aggressive mimicry The development of an appearance of things around it that keeps the mimic from being seen by prey animals. Aggressive mimics resemble the background or signals that it is something else to aid in capturing prey. Goal of aggressive mimicry is to enhance predation; not to avoid being eaten

examples: Malaysian preying mantids Resemble flowers. Pollinating insects come to the flowers. Captured and consumed. Female fireflies of the genus Photuris Photuris females mimic the signal of other firefly species. Responding male firefly is captured and eaten.

Müllerian mimicry Unrelated species that are distasteful or otherwise protected come to resemble each other. All are mimics and all are models.

Müllerian mimics advertise their dangerousness by: APO somatic (warning) coloration Sound - buzzing Behavior - aggressive flight Examples Lady beetles Honey bees and drone bees (automimicry)

Batesian mimicry A harmless mimic resembles an unpalatable, dangerous, or otherwise protected model. False advertising: Auditory mimicry fly wing-beat sound which is very much like the buzzing of a bee Visual mimicry - mimic the color and shape of bees Behavioral mimicry - aggressive flight behavior Example: Monarch Butterfly - a distasteful model for the harmless Viceroy butterfly

Hawk Moth Mimicry This moth caterpillar defends itself by mimicing a snake.

Insect mimicry

Caterpillars that Match Their Environments Caterpillars of the moth Nemoria arizonaria differ in shape depending on their diet. Caterpillars that hatch in the spring resemble the oak flowers on which they feed.

Caterpillars that Match Their Environments Caterpillars that hatch in the summer eat leaves and resemble oak twigs. Experiments have demonstrated that chemicals in the leaves control the switch that determines whether caterpillars will mimic flowers or twigs.

Protective coloration

Protective Coloration in Insects Insects are not always able to defend themselves, and so many of them have developed ways for blending into their surroundings. Some insects hide in plain sight, their bodies resembling non- living or inedible objects such as bark, thorns, buds, twigs, leaves, or bird droppings.

That's right, the caterpillar of the viceroy butterfly looks just like a bird dropping and easily gets passed up by an animal looking for a meal. Other insects, such as the stick insects are shaped like twigs or leaves. stick insect

The dead-leaf butterfly of India is also another example of this type of protective coloration and camouflage. When they fold their wings over the back, the undersides of the wings look just like dead leaves - complete with stem, leaf veins, and shiny spots that look like holes nibbled by leaf-feeding insects.

Many night-flying moths are colored and marked so that they "disappear" when they sit on a rock or tree trunk during the daylight hours. Some insects create a disguise for themselves by covering their bodies with plant parts, stones, dirt, cast skins, and other inedible "junk".

Insects may have another reason to use camouflage: to improve their chances for sneaking up on their prey. For example, some mantids are shaped and/or colored like flower petals or leaves and go unnoticed by plant-inhabiting insects.

Some insects are brightly colored and can't help but be noticed by other animals. These insects are also using their coloration as protection, but in a very different way.

Some insects (such as orange-and-black monarch butterflies and milkweed bugs and red-and-black ladybird beetles and milkweed beetles) are using their bright colors to warn other animals that they are distasteful and should not be eaten. Other insects (such as black-and-yellow bees and wasps) are telling other animals to stay away because they can defend themselves by stinging.

Warning color

many numbers of one species aggregate in one place Aggregation many numbers of one species aggregate in one place Temporary : potato ladybird Permanent : flying grasshopper

Why Insects Aggregate: environmental conditions aggregation as a mating strategy aggregation as a defensive strategy chemical cues in aggregation

Black Slug Cup Moth Scientific Name: Doratifera casta The caterpillars of this species feed communally and aggregate on the leaf surface. Once the surface layer of the leaf has been consumed, the caterpillars spread out onto other leaves, each inhabiting a single leaf.

Ladybirds- hibernation or mating

Aphids

Aggregation termite ( a social insect)

Migration Active travel between distant locations.

Introduction to Movement One of the most prevalent features of insects; Earth is canned by millions of insects flying on air currents, who encounter suitable and unsuitable habitats Understanding movement critical for characterizing population dynamics

Types a) emigration - movement out of an area b) immigration - movement into an area Movement is sometimes more important than natality or mortality Normal behavioral/physiological movements often modified by weather Can result in substantial mortality (e.g., over water, glaciers, etc.)

The most common insects that migrate are Monarch (Danaus plexippus) butterflies. Every fall, North American monarch butterflies gather in great clouds and fly south to spend the winter in tropical or subtropical areas. That is a distance of over 3,000 kilometres! In spring, they drift northward again, laying eggs as they go.

Their offspring, after becoming adults, continue the northward journey. Painted ladies and several other species of butterflies also migrate with the seasons, as do some species of moths.

Many other insects also make long migratory flights. The most famous are probably the locusts. They often travel in swarms so huge that they black out the sun. Scientists do not know why locusts migrate, except that they do so after building up an enormous population.

Locusts do not migrate because they are hungry. In fact, they may leave a land of plenty and not stop to feed during most of their long flight. But after they settle down, they destroy every bit of plant life.

Biological and Ecological Significance of Migration Important Adaptive Characteristic Use wind flow to relocate and colonize favorable habitats Dispersal mechanism Transport insects beyond the boundaries of their old reproductive site

Strongly Influences Population Dynamics Migrations often responsible for tremendous outbreaks May change genetic makeup of population Prevalence As research continues, more insects are added to the migrant list

Evolutionary Aspects Two-way migrants (obvious advantages, habitat exploitation) What about one-way migrants? a) if no remigration, then genetic dead end b) remigration is not well understood (may be more common) c) migration may facilitate incremental habitat gains

Dispersal Travel of Individuals, which (1) as an ecological process affects distribution of individuals; (2) as a genetic process affecting geographic differentiation and variation.

Adaption