The various types of gourds commonly cultivated in India include ash gourd, Benincasa hispida (Thunberg); bitter gourd, Momordica charantia Linnaeus; bottle gourd, Lagenaria siceraria Standley; Ivy gourd, Coccina grandis (Linnaeus); pointed gourd, Trichosanthes dioida Roxberg; snake gourd, T. anguina Linnaeus; ridge gourd, Luffa acutangula Roxberg; sponge gourd, L. aegyptiaca Milliere; squash gourd, Citrullus lanatus fistulosus Duthie and Fuller; pumpkin, Cucurbita pepo Linnaeus, and red pumpkin, C. maxima Duchesne. Cucurbits are attached by several species of insect pests, among which fruit flies and pumpkin beetles are important.
1. Melon Fruit Fly, Bactrocera Cucurbitae (Coquillett) (Diptera: Tephritidae):
This is the commonest and most destructive fruit-fly of musk melon and other cucurbits throughout India. It is also found in Pakistan, Myanmar, Malaysia, China, Formosa, Japan, East Africa, Australia and the Hawaiian Islands.
In addition to melons it has been found feeding on tomato, chillies, guava, citrus, pear, fig, cauliflower, etc. In north-western India, it is very common on late-sown melons that ripen after the monsoon rains begin. Two other allied species common in India are Dacus ciliatis Loew and Bactrocera dorsalis (Hendel).
Only the maggots cause damage by feeding on near-ripe fruits, riddling them and polluting the pulp. The maggots are legless and appear as headless, dirty-white wriggling creatures, thicker at one end and tapering to a point at the other. A full- grown maggot is 9-10 mm long and 2 mm broad in the middle. The adult flies are reddish brown with lemon-yellow markings on the thorax and have fuscous areas on the outer margins of their wings.
Life-Cycle:
This pest is active throughout the year, but the life cycle is prolonged during winter. The adult flies emerge from pupae in the morning hours and mate at dusk. It takes a few days for the eggs to mature inside the body of a female which starts laying them within 14 days. During winter, the pre-oviposition period is prolonged. They oviposit in comparatively soft fruits avoiding those with hard rind.
The selection of a suitable site and the actual laying of eggs take about 6-8 minutes. A cavity is made by the sharp ovipositor and about a dozen white cylindrical eggs are laid, mostly in the evening hours. After laying the eggs, the female releases a gummy secretion which cements the tissues surrounding the puncture and makes the entrance water proof. The secretion solidifies to form a shiny brown resinous material. The female, on an average, lays 58-95 eggs in 14-54 days.
The eggs hatch in 1-9 days and the maggots bore into the pulp, forming galleries. The attacked fruits decay because of secondary bacterial infection. The larvae are full-grown in 3 days during summer and 3 weeks during winter. The mature larvae come out of the rotten fruits and move away in jumps of 12-20 cm.
These are made possible by folding and unfolding the two ends of the elongated body. After reaching a suitable place, they bury themselves about 5 mm deep in the soil and pupate. The pupae are barrel-shaped, light brown and they transform themselves into winged adults in 6-9 days in the rainy season and 3-4 weeks in the winter. There are several generations in a year.
Pupae are parasitized by Opius fletcheri Silvestri, O. compensatus Silvestri and O. insisus Silv. (Braconidae), Spalangia philippinensis Full, and Pachycepoideus debrius Ashm. (Pteromalidae), Dirhinus giffardi Silvestri and D. Izonensis Rohw. (Chalcididae).
Damage:
The maggots pollute and destroy fruits by feeding on the pulp. The damage caused by this fruit-fly is most serious in melons and after the first shower of the monsoon, the infestation often reaches 100 per cent. Other cucurbitaceous fruits may also be infested up to 50 per cent.
Control:
(i) The regular removal and destruction of the infested fruits helps in the suppression of this pest.
(ii) Frequent raking of the soil under the vine or ploughing the infested field after the crop is harvested can help in killing the pupae.
(iii) Apply the bait spray containing 50 ml of malathion 50 EC + 0.5 kg of gur/sugar in 50 litres of water per ha. When the attack is serious, it should be repeated at weekly intervals,
(iv) Spraying the bait on the lower surface of the leaves of maize plants grown at distance of 8-10 cm as trap crop has been found to be effective as the flies have the habit of resting on such tall plants.
2. Red Pumpkin Beetle, Raphidopalpa Foveicollis (Lucas) (Coleoptera: Chrysomelidae):
The two species, red pumpkin beetle, R. foveicollis and blue pumpkin beetle, R. atripennis Fabricius are common in north-western India, the former being more important. It is widely distributed in Asia, Australia, southern Europe and Africa. It is a serious pest of cucurbitaceous vegetables such as ash gourd (Benincasa hispida), pumpkin (Cucurbita pepo L.), tirida (Citrullus vulgaris var. fistulosus), ghia tori (Luffa aegyptica), cucumber and melon.
Damage is caused by grubs as well as by beetles. The grubs lead a subterranean life and, when full-grown, they measure about 12 mm in length and 3.5 mm across the mesothorax. They are creamy white, with a slightly darker oval shield at the back. The beetles feed on those parts of the plant which are above the ground. They are oblong and 5-8 mm long. Their dorsal body surface is brilliant orange red and ventral surface is black, being clothed in short white hair.
Life-Cycle:
The beetles are found concealed in groups under dry weeds, bushes and plant remains or in the crevices of soil. They resume activity as soon as the season warms up and in their life span of 60-85 days; they lay about 300 oval yellow eggs singly or in batches of 8-9 in moist soil, near the base of the plants.
The eggs hatch in 6-15 days and the grubs remain below the soil surface feeding on roots, underground stems of creepers and on fruits lying in contact with the soil. They are full-grown in 13- 25 days and pupate in thick-walled earthen chambers in the soil, at a depth of about 20-25 cm.
The pupal stage lasts 7-17 days and the beetles, on emergence, begin to feed and breed. The life-cycle is completed in 26-37 days and the pest breeds five times from March to October.
Damage:
The beetles are very destructive to cucurbitaceous vegetables, particularly during March-April when the creepers are very young. The grubs damage the plants by boring into the roots, underground stems and sometime into the fruits touching the soil. The beetles injure the cotyledons, flowers and foliage by biting holes into them. The early sown cucurbits are so severely damaged that they have to be resown.
Control:
(i) After harvesting the infested fields, plough deep to kill the grubs in the soil.
(ii) Sow the crop in November to avoid damage by this pest.
(iii) Apply 7.0 kg of carbofuran 3G per ha 3-4 cm deep in the soil near the base of the plants just after germination and irrigate or spray 375 g of carbaryl 50WP in 250 litres of water per ha.