The following points highlight the three main types of damages caused by pests. The damages are: 1. Damages by Pests with Biting and Chewing Mouth Parts 2. Damages by Pests with Piercing and Sucking Mouth Parts 3. Damages by Pests that are 0Vectors of Pathogens.
1. Damages by Pests with Biting and Chewing Mouth Parts:
They feed by biting pieces of plant material and chewing. It may be adult or larvae of insects.
The type of damage done by them may be generalized as follows:
(a) Loss of photosynthetic tissues; in extreme cases defoliation may result.
(b) Destruction of buds and shoots.
(c) Destruction of flowers, fruits and seeds.
(d) Boring and tunnelling of stems; interruption of sap flow and physical weakening of the stem; stem breakage may result.
(e) Eating or boring of roots and tubers in the soil.
(f) Destruction of seedlings and young plants.
(g) Formation of galls on all or any parts of the plant body.
2. Damages by Pests with Piercing and Sucking Mouth Parts:
These pests have part or all of the mouthparts modified into a piercing proboscis or stylet. Sap is sucked either from the phloem or xylem or from general tissues of foliage, roots or fruits. Within this category there are two basically different types of damage.
(a) Pests without toxic saliva:
These insects and mites remove sap, causing tissue wilt, leaf curl, stunting and in extreme condition causes death of the host plant.
(b) Pests with toxic saliva:
In this case toxic saliva causes a disproportionate amount of damage in relation to insect number. The toxins cause death of the cells and if injected into a young shoot, the entire shoot, distal to the feeding site, may die.
3. Damages by Pests that are Vectors of Pathogens:
These pest are extremely harmful, as a very small number of infective individuals may be responsible for severe outbreak of disease. Disease control by destruction of vectors is very difficult.
These pests are of two types:
(a) Indirect vectors:
This category includes those insects that make feeding punctures, which later becomes infected by aerial spores; this occurs in fruits, tunnelled by fruit fly larvae (Tephritidae) and fruit worms (Lepidoptera).
(b) Direct vectors:
These insects and nematodes are sometimes called ‘biological vectors’. They are responsible for active transmission, as they are often intermediate hosts. The pathogens are plant microbes, which can only be transmitted through vectors.
The Parts of Plant Damaged by Pests:
Pest damage can be categorized according to the parts of the plant body attacked.
These are generally of six categories:
1. Sown Seeds and Seedlings:
The most common pests of this type are bean seed fly maggot, mice and other small rodents which dig up freshly sown seeds. Many birds feed on the seeds sown in the field. Dead heart disease caused by Scirpophaga incertulus.
2. Fruits and Seeds:
Cereal panicles sometimes have only a few grains developed, like sorghum infested with sorghum midge larvae. Some fruits and seeds, including nuts, are bored by weevil larvae, e.g., cotton boll weevil, hazel nut, mango weevil, etc.
3. Flower and Buds:
Blister beetles chew the petals of many plants. Anther eater pollen beetles are also evident.
The leaf margin-notched, irregularly eaten, regularly cut away, leaf-holed, windowed, skeletonized, galled, etc. are the regular activities of different larvae of insects and adult molluscs.
Stem borers are common examples in paddy, jute and vegetable plants.
6. Roots and Tubers:
Roots of economic importance, tubers, etc. are severely attacked by various pests.