Insect Pests of Vegetable, Tuber and Spice Crops

Exercise: Insect Pests of Potato

1. Potato tuber moth (PTM), Phthorimaea operculella (Gelechiidae: Lepidoptera):

• Damage: Damage is caused by larvae which mine the leaves or bore into the petiole and terminal shoots causing wilting. After tuberization, the larvae enter into the tubers and feed on them. In stores, the larvae bore into the stored tubers through minute holes which become blackish within 3-4 days due to accumulation of fecal matter near the entrance hole. Larvae tunnel into the pulp which ultimately becomes unfit for use as seed or for human consumption. The infested tubers are further exposed to microbial infection which leads to rotting. The extent of damage to stored tubers varies from 30 - 70 per cent in plateau regions, 18 - 84 per cent in North-eastern hill region and 25 – 50 per cent in Himachal Pradesh.
• Eggs: The eggs are oval and measure less than 1mm in diameter.
• Larvae: Newly emerged larvae are gray yellowish white with brown head. Full grown caterpillars come out of the tubers/ foliage and pupate in silken cocoons either in dried leaves, soils, over the stored tubers or in cracks and crevices in the store.

2. White grubs (Scarabaeidae: Coleoptera)

Important species of white grubs are given sub-family wise as under
Melolonthinae:

1. Brahmina coriacea
2. B. crinicollis
3. B. flavoserica
4. Melolontha indica
5. Holotrichia longipennis
6. H. repitita
7. H. rustica
8. H. serrata
9. H. conferata
10. H. excise
11. H. nototiocollis

Rutelinae:

12. Anomala dimidiata
13. A. polita
14. A. rugosa
15. A. rufivenrtis
16. A. communis
17. A. nathani

Dynastinae:

18. Xylotrupes gideon
19. Phyllognathus dionysius

• Damage: Both grubs and adults are damaging. Grubs feed on under ground plant parts of various crops. Potato grown during summer as rainfed under long day conditions as is practice in hill regions is prone to attack by these grubs. Initially young grubs feed on fibrous roots or mother tubers but after tuber formation, older second and third instar grubs feed on under ground potato tubers by making large, shallow and circular holes into them thus rendering the tubers unfit for consumption or marketing. They live concealed while feeding on tubers and plants continue to grow normally without showing any injury on aerial parts of the plant. Because of this concealed damage, white grubs generally remain unnoticed during crop growth and at the time of harvest a large number of tubers are found infested/ damaged. Some times up to 80 per cent of the crop may be lost. White grubs are also found to feed on the roots of horticultural/ forest nurseries and some ornamental plants. Such plants show varying degree of wilting, yellowing, browning and drying/ dying. White grubs are serious pests of turf grass too and cause serious damage to lawns all over the world.
• Adult beetles commonly known as Chafer beetles, June beetles, Scarabaeid beetles and Monsoon beetles emerge with the first monsoon shower and feed on the foliage of many fruit trees, forest trees, ornamental plants, wild shrubs, etc.
• Eggs: Freshly laid eggs are creamy white which turns dirty white before hatching.
• Larvae: Full grown larvae are 35-38 mm in length, creamy white ‘C’ shaped grubs with brown head. They construct earthen cells before entering into pupal stage during April – May. Pupal period ranges from 12-20 days.

 

The other important pests of potato are:

• Hadda beetles: Discussed under the insect pests of egg plant
• Cutworms: Discussed under the insect pests of cole crops
• Tomato fruit borer: Discussed under the insect pests of tomato
• Aphids: Myzus persicae and Aphis gossypii
• Leaf hoppers, Amrasca biguttula biguttula
• Whitefly, Bemisia tabaci
• Phytophagous mites
• Green potato bug