Exercise: Insect Pests of Leafy Vegetables
Amaranthus
1. Amaranthus stem weevil, Hypolixus truncatulus (Curculionidae: Coleoptera):
- Damage: Adult females bite circular holes in the stems, lay eggs singly in each hole and cover the hole with black coloured secretion. Newly emerged grubs bite their way into the stem and feed on the pith making irregular zig-zag tunnels which are filled with excreta. The affected stems become weak and often split longitudinally due to excessive transpiration and evaporation. The plants desiccate and ultimately dry up completely. Adults feed on tender leaves and stems but the loss caused by them is negligible.
- Eggs: Eggs are smooth, oval, about 1 mm long and pale yellow in colour.
- Larvae: Grubs are stout, curved, legless, white in colour and about 13-17 mm long.
- Pupae: Pupae are about 9 mm long and pale yellowish brown in colour.
- Adults: Adult weevils are ash-grey in colour, 10-15 mm long having elbowed antennae and brown elytra.
2. Amaranthus leaf caterpillars:
i) Hymenia recurvalis
- Damage: Damage is caused by caterpillars by feeding initially on epidermis and palisade tissues of leaves, later they web the leaves together with silvery silken threads secreted by them and feed within. Gradually these webbed leaves become completely devoid of chlorophyll and dry up.
- Eggs: Eggs are spherical in shape and snow white in colour.
- Larvae: Caterpillars are greenish in colour with white lines and black crescents on thorax below the lateral line. Full grown larva measures 17-20 mm in length.
- Pupae: Pupae are 10-14 mm long and brownish in colour.
- Adults: Adults are black coloured, slender bodied moths about 10 mm long and having thin long filiform antennae. Both pairs of wings are dark fuscous in colour having broad white fuscia in the middle and outer margins are fringed with short hairs. Wing expanse is 15-20 mm.
ii) Eretmocera impactella (Heliodinidae: Lepidoptera):
- Larvae: Full grown caterpillars are 9-12 mm long, cylindrical, brownish yellow to brownish grey in colour with a broad submedian dark stripe and black tubercles bearing several divergent longitudinal hairs.
- Pupae: Pupae are about 6 mm long and uniformly brown in colour.
- Adults: Moths have cuprous head and thorax and yellow abdomen with second, third and terminal segments cuprous in colour. Fore wings are also cuprous with yellow spots, hind wings are pale in colour. Wing expanse is 14-18 mm.
INSECT PESTS OF SPINACH
Spinach blue beetle, Altica caerulescens (Alticidae: Coleoptera)
- Damage: Freshly emerged grubs scrap and feed on chlorophyll containing tissues, later they mine inside the leaves and feed on the mesophyll tissue and pupate there in. Adults nibble the leaf margins causing very little damage.
- Larvae: Grubs are 5-10 mm long, dark brown in colour.
- Pupae: Pupae are 12-15 mm long and brown in colour when freshly formed and turns blackish brown later on.
- Adults: Adults are 5-7 mm long steel blue in colour with hind femora strongly thickened which enable the beetles in jumping movements.
POLYPHAGOUS PESTS:
1. Locusts:
- Desert locust, Schistocerca gregaria (Acrididae: Orthoptera)
- Bombay locust, Patanga succincta (Acrididae: Orthoptera)
- Migratory locust, Locusta migratoria (Acrididae: Orthoptera)
- Damage: Locusts are harmful in both the adult and nymphal stage (hopper stage). They are gregarious and voracious feeders and eat up the entire vegetation except a few plant species viz., neem, dharek dhatura etc. They move in swarms and consume all the green vegetation and can cause a famine.
- Eggs: Eggs are laid in soil in egg pods. Each female can lay up to 11 egg pods, each pod containing up to 120 eggs. Before egg laying each female with the help of its ovipositor, bores a 5-10 cm deep hole into the loose soil. The ground used for laying eggs is easily recognized by numerous holes which are of the diameter of an ordinary led pencil. The eggs resemble the grains of rice.
- Nymphs: Newly emerged hoppers are light yellow but soon they turn black (Gregarious brood). They march in swarms and feed voraciously on all kind of vegetation.
2. Termites:
- Termites are commonly known as white ants are widely distributed in tropical and subtropical regions of the world. They are social insects and live in colonies in under ground nests. They make small earthen mounds or earthen passages which are visible above the ground. In a single colony these are several workers, lot of soldiers, one queen, a king and a good number of complementary or the colonizing forms of true but immature males and females.
Different castes:
- a) Reproductive castes:
- Colonizing individuals: These are winged individuals of both sexes and are produced in large number during the rainy season.
- Queen: This is the only perfectly developed female in the colony and lay eggs. Each queen can lay up to 70000-80000 eggs in 24 hours. There is only one queen in the colony which lives for 5-10 years
- King: A king develops from an unfertilized egg and becomes fully developed by consuming a superior diet. He is the father of the colony and is a constant companion of the queen living with her in the royal chamber
- Complementary castes: They are short winged or wingless creatures of both sexes and lead a subterranean life.
- b) Sterile castes:
- Workers: They develop from fertilized eggs but remain stunted as they feed on ordinary food. Numerically they are the most abundant in a colony. In size they are smaller than the soldiers. Their mandibles are well developed and used for gnawing of the wood. Except reproduction and defense, all other duties are performed by the workers.
- Soldiers: They develop from unfertilized eggs but remain comparatively under developed. They can be easily recognized by the large head and strongly chitinised sickle shaped mandibles. In a colony two types of soldiers can be distinguished:
- Mandibulate type: They are with large and powerful jaws, but without frontal rostrum. They defend the colony by direct fighting with the intruders.
- Nasute type: They have median frontal rostrum, but the jaws are small or vestigial. They defend the colony by repelling the intruders by spraying an obnoxious smelling fluid through the rostrum.
 3. Hairy caterpillars:
4. Cutworms:
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