Insect feeding mechanism

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 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.

3. introduction Certain types of feeding behaviours are exhibited by insects. Insects go through a series of behavioural activities which leads to the acceptance and rejection 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 range of 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 and are called 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) Some insects grow fungi on specially prepared substrates as in termites and ants. All the Macrotermitidae ( Isoptera) are fungus- growers and they produce a ‘ comb’ of chewed food on which the fungal hyphae grow and produce conidia. Some fungi such as Xylaria , produce fruiting bodies when the nest is deserted by the termites. The fungus 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 prepare specific substrates.

6. Predaceous insects Several species of predaceous insects catch their prey by either sitting or waiting for it to come their way or by actively pursuing it. Praying mantis ( mantodea) as it has a very mobile head, the movement of the prey can be followed 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 are used for grasping prey.

7. Parasitic insects In the majority of internal parasites, the parent insect oviposits in a suitable host. Smell and contact chemoreception are involved in this. The parent oviposits or larviposits in places frequented by the host so that the larvae make their own way on to the host. In strepsiptera and meloid beetles, both produce large number of larvae known as triungulins , such type 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 are found on the antennae. TARSI - In moths and butterflies ( lepidoptera) , flies ( siphonaptera ) taste organs are located on the tarsi. OLFACTORY SENSILLA - These enable insects to smell and are present in the antennae. COMPOUND EYES - Ocelli and compound eyes supply insect vision. In dragonfly ( odonata) and mantis ( mantodea) compound eyes consists of individual light receptive units called ommatidia. These are around 10,000 in dragonfly which help in capturing prey.

9. Sensilla on the mouthparts Most of the sensilla on the mouthparts are chemoreceptors. Mechanoreceptors and olfactory sensilla are also 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 and tooth- like. Chemoreceptors on the dorsal and ventral walls of the cibarium, often called as epipharyngeal and hypopharyngeal sensilla. Orthoptera and Blattodea have large number of 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 varies considerably. Species amongst Homoptera and sawflies , are restricted to one particular plant species and are regarded as monophagous. Insects such as Pieris, only feed on particular and limited range of plants, these are called oligophagous. Insects feeding on wide range of plants , but they even show food preferences are called polyphagous. Ex – Schistocerca . Selection is based on physical factors and secondary chemical substances such as glycosides , 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 and antennae 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 or mechanical 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 and begins to feed. Lice are extremely host – specific. Spider wasps ( pompilidae) capture only spiders for provisioning their nest.

14. Significance of food preferences There are a wide variety of insects rearing on abnormal food substances. Food preferences are often of considerable significance. Melanopus , ( grasshopper) fails to survive on some food plants, but on its preferred food, hedge mustard, development and survival are good. Mosquitoes can survive solely on nectar, but many species require a blood meal if they are to produce eggs, such species are called 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 mechanical resistance. As the stylets penetrate the tissue saliva flows from the tip to the mouth as seen in homoptera. The stylets are then removed from 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 moved into 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 Several species of insects such as Platymeris , inject venom while 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 and odonata 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 exceeds the 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 are very variable. In caterpillars it is of 15-30 minutes and in grasshoppers it is of 1-2 hours. Adult female mosquitoes take a blood meal once every few days in relation to oogenesis. Larval Rhodnius feeds only once in each larval stage. Grasshopper nymphs take more 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 or in 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.