The ppt covers Introduction Feeding habits in –, Phytophagous insects, Mycetophagous insects, Predaceous insects, Parasitic mode of nutrition ,Sensory organs associated with feeding, Sensilla on the mouthparts, Food selection by phytophagous insects, Prey specificity and selection by predators Host- finding by blood- sucking and parasitic insects Significance of food preferences Ingestion by phytophagous, blood-sucking, predaceous and, venomous insects, Regulation of feeding, timing associated and food- storage in insects.

1. INSECT FEEDING
MECHANISM

2. synopsis
 Introduction
 Feeding habits in –
 Phytophagous insects
 Mycetophagous insects
 Predaceous insects
 Parasitic modeof nutrition
 Sensory organs associated with feeding
 Sensilla on the mouthparts
 Food selection by phytophagous insects
 Prey specificity and selection by predators
 Host- finding by blood- sucking and parasitic insects
 Significance of food preferences
 Ingestion by phytophagous, blood-sucking, predaceous and venomous insects
 Regulation offeeding, timing associated and food- storage in insects.

3. introduction
 Certain types of feeding behaviours areexhibited by insects.
 Insects go through a series of behavioural activities which leads to the
acceptance andrejection of food.
 This behaviour enables the insect to monitor the chemicals on the surface of
the plant and also the odour of the plants.
 Mouthparts assist in feeding which comprises of unpaired labrum in the front,
median hypopharynx, a pair of mandibles and maxillae laterally, labium
forming the lower lip.
 These component parts allow insects to exploit a wide rangeof food sources.

4. Feeding habits
phytophagous insects ( plant- feeders )
 Phytophagous insects are typically plant- feeding insects with
biting mouthparts.
 They bite off fragments of food and pass them back to the mouth
with the aid of the maxillae.
 Some insects may obtain the food from cell- sap or from
distributive vessels andarecalled fluid- feeders.
 Grasshoppers ( orthoptera) guide the food into the mouth by
holding it between the forelegs.
 Aphids intake food by tapping the phloem.

5. Mycetophagous ( insects- growing fungus)
 Someinsects grow fungi on specially preparedsubstrates asin termites and ants.
 All the Macrotermitidae ( Isoptera) are fungus- growers and they produce a ‘ comb’
of chewed food on which the fungal hyphae grow andproduce conidia.
 Some fungi such as Xylaria , produce fruiting bodies when the nest is deserted by
the termites.
 Thefungus is eaten in small amounts by the workers and is fed to some of the larvae.
 The wood boring insects also have constant association with particular fungi
although they do not preparespecific substrates.

6. Predaceous insects
 Several species of predaceous insects catch their prey by either sitting or
waiting for it to cometheir way or by actively pursuing it.
 Praying mantis ( mantodea) as it has a very mobile head, the movement of
the prey can befollowed without the whole mantis moving.
 Eyes are large and wide- apart enabling the mantis to judge the distance of
the prey accurately.
 Front legs of mantis are raptorial and armed with spines, so when the prey is
caught, it is held by rapid movement of the forelegs and brought back to the
mouth.
 Some dragon fly larvae wait for their prey, lying concealed in the mud and
seizing the prey with the labial mask.
 Labial mask is the modification in which pre and post- mentum are elongated
and palps areused for grasping prey.

7. Parasitic insects
 In the majority of internal parasites, the parent insect oviposits in a suitable
host.
 Smell andcontact chemoreception areinvolved in this.
 The parent oviposits or larviposits in places frequented by the host so that the
larvaemake their own way on to the host.
 In strepsiptera and meloid beetles, both produce large number of larvae
known as triungulins , suchtype of feeding behaviour is seen.

8. Sensory organs associated with feeding
 Chemical senses include the use of certain chemoreceptors, related to taste and
smell which affect feeding and parasite- host relationships.
 ANTENNAE - Taste is usually located on the mouthparts , but in some insects
such as bees and wasps (hymenoptera ), taste organs arefound onthe antennae.
 TARSI - In moths and butterflies ( lepidoptera) , flies ( siphonaptera ) taste organs
arelocated on the tarsi.
 OLFACTORY SENSILLA - These enable insects to smell and are present in the
antennae.
 COMPOUND EYES - Ocelliand compound eyes supply insect vision.
 In dragonfly ( odonata) and mantis ( mantodea) compound eyes consists of
individual light receptive units called ommatidia.
 These arearound 10,000 in dragonfly which help in capturing prey.

9. Sensilla on the mouthparts
 Most of the sensilla on the mouthparts arechemoreceptors.
 Mechanoreceptors and olfactory sensilla arealso present on the palps.
 Chordotonal organs which probably function as pressure receptors, are
present at the tips of the mandibular cusps and also in the lacinea, which is
heavily sclerotized andtooth- like.
 Chemoreceptors on the dorsal and ventral walls of the cibarium, often called
asepipharyngeal and hypopharyngeal sensilla.
 Orthoptera andBlattodea havelarge numberof sensilla in groups.
 Gryllus, has 3000 sensilla on each maxillary palp.
 Fluid- feeding insects have chemoreceptors at the tip of the labium on the
palps.
 In piercing and sucking insects ( hemiptera) cibarial sensilla come in contact
with the food as it is ingested.
 In blood- sucking insects, labial sensilla come into direct – contact with the
blood.

10. Finding and recognising food material
food selection by phytophagous insects-
 Degree of specificity of insects to particular plants variesconsiderably.
 Species amongst Homoptera and sawflies , are restricted to one particular
plant species and are regardedas monophagous.
 Insects such as Pieris, only feed on particular and limited range of plants,
these arecalled oligophagous.
 Insects feeding on wide range of plants , but they even show food preferences
arecalled polyphagous. Ex –Schistocerca.
 Selection is based on physical factors and secondary chemical substances
such asglycosides ,alkaloids and essential oils.
 Orthoptera selects the softest and moistest grass.
 Lepidoptera only feeds on cruciferae and other plants which contain mustard
oils.

11. prey specificity and selection by predators
 Majority of predators and hunters have well- developed eyes since vision gives
a rapid response to moving prey.
 Tiger beetles hunt on the ground and have long legs which increase their speed,
and prognathus mouthparts with large mandibles.
 Wasp , Philanthus, is prey – specific as it only hunts bees , the finding of prey is
olfactory.
 Dytiscus, ( coleoptera ) responds to chemical stimuli in water rather than
sighting prey.
 In dragonflies ( odonata) , mechanoreceptors present on tarsi andantennae are
used for finding prey.
 Coccinellids ( coleoptera) larvae preying on aphids only respond to the prey on
contact.

12. Host- finding & preferences of blood- sucking insects
 Blood- sucking insects are called sanguivorous . Perception of a host at a distance
may arise from visual , olfactory ormechanical stimulation.
 Several species of free- living blood sucking insects such as mosquitoes and tse-
tse flies bite a wide range of hosts, although most are restricted to mammals and
birds.
 Fleas (siphonaptera) bite unusual hosts.
 Pediculus ( lice) on the other hand ,spends the entire life on one host, extremely
host –specific.

13. Host- finding by parasitic insects
 Species parasitic on other animals usually locate a host by its scent, for many
species which feed on blood of birds and mammals.
 Temperature and humidity gradients are important in determining the precise
location at which insect aligns to host andbegins to feed.
 Lice areextremely host – specific.
 Spider wasps ( pompilidae) captureonly spiders for provisioning their nest.

14. Significance of food preferences
 Therearea wide variety of insects rearingon abnormal food substances.
 Food preferencesare often of considerable significance.
 Melanopus , ( grasshopper) fails to survive on some food plants, but on its
preferred food, hedge mustard, development andsurvival aregood.
 Mosquitoes can survive solely on nectar, but many species require a blood
meal if they areto produce eggs,such species arecalled anautogenous.
 Others which can produce eggs on a diet of nectar alone are called
autogenous.

15. Feeding and ingestion
phytophagous insects
 Phytophagous insects insert their mouthparts into the plant tissue using the
protractor and retractor muscles of the stylets in the head aided by clasping
action of labium.
 In the course of penetration through the leaf epidermis it encounters
mechanicalresistance.
 As the stylets penetrate the tissue saliva flows from the tip to the mouth as
seen in homoptera.
 Thestylets arethen removedfrom the plant tissue using cibarial sensilla.

16. Ingestion in blood- sucking insects
 In the blood- sucking species they penetrate the host tissue before starting to
feed.
 Proboscis is movedinto feeding position through the host.
 In mosquitoes and triatromine bugs, the stylets are pushed into the tissues
and the labium folds up.
 In tsetse and stable flies, rasping movement of the prestomal teeth tear into
the tissues.
 In nectar- feeding bees, the glossa is repeatedly extended into the nectar
while galea and labial palps remain motionless.

17. Feeding in predaceous insects-
 In predaceous insects , such as mantids and dragonfly the postmentum and
prementum are both elongate and the labial palps are claw- like structures set
distally on the prementum.
 Labial mask is folded beneath the head, if a prey comes within range, the
labial mask is extended and the prey caught by labial palps.
 Adult dragonflies are active aerial hunters pursuing other insects in flight.
 Their thoracic segments are rotated forwards ventrally, bringing legs into an
anterior position which facilitates grasping.

18. Venomous insects
 Severalspecies of insects such asPlatymeris , inject venomwhile feeding.
 Venoms are produced in the salivary glands which are enlarged and have a
muscular coat.
 It is forcibly injected by a salivary pump in the haemolymph.
 Venoms are non- specific being toxic to a wide range of insects and the action
stops the nervous system.
 Larval neuroptera, diptera andodonata use venoms.
 Hymenoptera paralyze their prey by injecting the venom through the sting,
which is a modified ovipositor.

19. Regulation and control of feeding
 Most insects eat discrete meals separated by relatively long – periods of non-
feeding.
 In some blood- sucking insects such as ,Rhodnius, the quantity of blood
ingested exceedsthe weight of the insect,
 Hemiptera such as aphids and leafhoppers ,that are phytophagous do not
have meals or have prolonged meals feeding continuously because of very
low concentrations of nutrients in their food.

20. Timing associated with feeding
 Intervals between meals arevery variable.
 In caterpillars it is of 15-30 minutes andin grasshoppers it is of 1-2hours.
 Adult female mosquitoes take a blood meal once every few days in relation to
oogenesis.
 Larval Rhodnius feeds only oncein eachlarval stage.
 Grasshopper nymphs takemore food during light than in dark periods.

21. Food- storage in insects
 In great variety of insects , internal stores of food are built up in their fat
bodies orin the crop.
 Many solitary hymenoptera build cells and provision then for use of their
larvae.
 Female wasp continues to bring food to the nest until larvae is fully grown,
this is called mass provisioning.
 Nectar- feeding insects fill the crop and blood- sucking insects when feeding
on blood , fill the midgut.