Borers in Horticultural Crops

Borer insects belong mainly to two orders viz., Coleoptera and Lepidoptera. Family wise description of borers:

 

COLEOPTERAN BORERS 

                                                                                                         

Buprestidae: They are metallic coloured wood boring beetles. The adults are 3-100 mm in length. They are coppery, green, blue or black. Many are attracted to dead or dying trees, logs and slash. Other lives on the foliage of the trees and shrubs. The grubs bore under the bark or into the wood. They attack living trees, newly cut, dying logs and branches. Adult female lay eggs in crevices in the bark. The galleries in the bark are often winding and filled with frass. The galleries in the wood are oval in cross section. The grubs are commonly called as “Flat headed borers”.

 

Cerambycidae: These are commonly called as longicorn beetles. Body is elongate, cylindrical with long antennae and brightly coloured. They vary from 3-60 mm in length. Most of the brightly coloured adults feed on flowers. Many, usually not brightly coloured ones are nocturnal in habit and during day time are found under the bark or resting on trees or logs. When picked up, they make squeaking sound. Most of Cerambycids are wood boring in the larval stage and are destructive to shade, forest, ornamental and fruit trees. The adult female lay eggs in the crevices in the bark and larvae bore into the wood. The larval tunnels in the wood are circular in cross section. They may attack living trees, freshly cut logs, weakened or drying trees. The larvae are elongate, cylindrical, whitish and almost legless. The larvae are also called as “Round headed borers”.                   

 

Curculionidae: (Weevils or snout beetles): All the members of this family are plant feeders. When adults are disturbed they characteristically draw their legs and antennae, fall to ground and remain motionless. In case of Banana rhizome weevil, Cosmopolites sordidus, adult makes wounds on the rhizome and also causes injury by egg laying into the rhizome. Grubs make tunnels and feed on the inner content. Not all in the family are borers.

 

Scolytidae: These are commonly called as shot hole borers or ambrosia beetles as they cultivate fungi in the tunneled nest and feed on them. Adult female lay eggs inside the gallery on the branch. Both adults and grubs damage. Adults cause damage to branches and main stem by making small tiny or pin holes. Fine powder like material comes out from such bored holes. In later stages, a gum oozes out from the damaged parts. Incidence is favoured by water stress, water logging and old age of the plant.

 

LEPIDOPTERAN BORERS   

                                   

Carposinidae: The moths in this group are relatively broad with raised scale tufts on the front wings. The larvae bore into the fruits, plant shoots and the gummy enlargement of fruit trees. The infested fruits eventually drop and larvae pupate in the soil.

 

Cossidae: These are commonly called as carpenter moths or leopard moths. The adults are medium sized and heavy bodied; wings are usually spotted or mottled. These moths require two to three years to complete their life cycle. They bore and feed on the internal content at the larval stage and cause wilting of branches. The bored holes are plugged with excretory pellets.   

                 

Crambidae: The moths are pale brown with white hind wings. Adult female lays scale like eggs in batches, each batch containing 9-11 eggs in two rows on the leaf sheath. A single female can lay about 350-400 eggs. Larva is white bodied with dark spots and a brown head, it pupates in the bored holes or leaf sheath. The larva bores  into fruits, stem and the hole is plugged with excreta.

 

Gelechidae:  The moths are small, dark brown. Female lays eggs (100-150 eggs) singly on the under surface of the leaves or on the exposed tubers. The yellowish caterpillar with brown head pupates in silken cocoon among trash, clods of earth. Hibernation takes place in the larval or pupal stage.

 

Gracillariidae: This is a large group of small to minute moths with lanceolate wings. The adult moth is white with broad, irregular, bronze bands on the front wings. The adult moths at rest elevate the anterior part of the body, with the wing tips touching the surface on which the moth rests. The larvae are flattened, with only rudiments of legs and with an enlarged prothorax. The larva pupates in a delicate cocoon inside the bored hole.

 

Lycaenidae: These are commonly called as blues, coppers or harvesters. These are small delicate and brightly coloured butterflies and some are quite common. The lycaenid larvae are light pinkish smooth bodied and measures 2 mm in length are flattened and slug like, many secretes honey dew which attracts ants and some live in the ant nests. The chrysalides are fairly smooth and are attached by the cremester with a silken girdle about the middle of the body. The adults are rapid fliers. In pomegranate and aonla, Deudorix isocrates acts as a fruit borer where the larvae bore into the fruits and grow by feeding on the internal content. The entry holes are not visible on fruit, internal feeding causes rotting of fruits.   

    

Metarbellidae: These are commonly called bark eating caterpillars and attack the  main stem or branches of the plant. The adult moth is medium, brown coloured with pale forewings. Adult female lays eggs in cracks of loose bark. The larvae measure 4-5 cm, pale brown with reddish brown head, they pupate in the tunnel. Initially the larvae scrape on the bark portion and later bore into the stem and feed on the inner content of the branch. Entry holes are plugged with excretory pellets. During day time they hide at the entry holes.

 

Noctuidae: This is the largest family in the order. These are small to medium moths with somewhat narrowed forewings and broadened hind wings.  The female lays eggs on the tender shoots, on the leaves. The larvae vary in colour and most of them have five pairs of prolegs. Majority feeds on the foliage but some may act as borers. The larvae bore into the tender shoots, fruits and feed inside leading to drying and wilting of tender shoots and the fruits.   

      

Phycitidae: The moth has greyish brown fore wings with transverse lines in the middle and white hind wings. The larvae are yellowish with red head, pupates in silken cocoon in the bored holes. The larva bores into the stem at leaf or branch axil and covers the hole with excreta and frass.

 

Pterophoridae: The moths are small, slender, usually gray or brownish. The wing splits into two or three feather like divisions. The front wing has two divisions and hind wing has three. At rest front and hind wings are folded close together and are held horizontally at right angle to the body. They are leaf rollers, stem borers. 

                             

Pyraustidae: The moths have brownish and red markings on the whitish fore wings. The female lays about 250-300 eggs, singly on tender shoots and developing fruits. The larvae are pinkish with sparsely distributed hairs on the body with brownish head. The larva measures about 16-20 mm long. It pupates in a tough greyish cocoon on the plant. The larva bores into the tender shoots in early stage, in the later stage it bores into the flower buds and developing fruits causing shedding of buds and making the fruits unfit for consumption and marketing.     

  

Tortricidae: This is one of the largest families  in the microlepdoptera. The moths are small, usually grey, tan or brown and often have dark bands or mottled areas in the wings. The front wings are square. At rest the wings are held roof like over the body. The larvae vary in habit, they bore into the various parts of the plants.