Watermelon: Insect, Mite and Nematode Pests Management

Red pumpkin beetle

• Egg: Eggs are brownish-yellow in colour, elongated, laid singly or in batches in moist soil near rhizosphere. Incubation period is 5-8 days after which tiny larvae hatch out and enter the soil.
• Larva: Grubs grow by feeding on the debris and on roots and stems of plants. There are four larval instars and larvae must enter the soil each time before to moult. Larval period is 18-25 days, which is spent mostly in soil. Fully grown grubs are 10-12 mm in length.
• Pupa: Pupation also takes place in the soil in a waterproof cocoon up to a depth of 25 cm. Adults emerge and make their way out of the soil.
• Adult: Adults are small bright reddish beetles, 4-7 mm long, active beetles, flying from plant to plants and feeding on leaves. Hibernation takes place in adult stage from November to March in northern India, usually in debris or under stones or other hiding places. Longevity of adult is more than a month. Fecundity is 150-300 eggs per female.

• Seedlings may be completely destroyed by adult feeding.
• Older plants have foliage riddled with holes or completely defoliated, and the floral parts, including anthers are nibbled.
• Feeding by larvae causes rotting and withering of the roots and stems.
• The surface of young fruit may show feeding marks caused by the adults and the undersurface of fruits where they touch the soil surface may have indications of larval tunnels in the surface.

• Parasitoids: Braconid wasp, Celatoria cetosa (tachinid fly)
• Predators: Pennsylvania leatherwing beetle, ground beetle, spider, earwig etc.

Fruit fly

• Egg: The egg is elliptical, pure white and about 2 mm long. It is almost flat on the ventral surface, and more convex on the dorsal. Eggs are often somewhat longitudinally curved.
• Larva: The maggot is cylindrical cigar shaped. It has anterior mouth hooks, ventral fusiform areas and a flattened caudal end. Last instar larvae range from 7.5 to 11.8 mm in length.
• Pupa: The puparium ranges in color from dull red or brownish yellow to dull white, and is about 5 to 6 mm in length. Pupation takes place in soil.
• Adult: The adult melon fly is 6 to 8 mm in length. Distinctive characteristics include its wing pattern, its long third antennal segment, the reddish yellow dorsum of the thorax with light yellow markings, and the yellowish head with black spots. Total life cycle completes 14-34 days depending on weather conditions.

• Newly hatched maggots bore into the fruit pulp by forming serpentine galleries and contaminating them with its frassy excreta and providing entry points for saprophytic fungi and bacteria resulting rotting of fruits.
• Due to feeding, there is pre-mature dropping of fruits and make them unfit for consumption.
• Formations of galls are also rarely seen on stems.

• Parasitoid: Opius fletcheri
• Predators: Ants, dragon fly, spider, robber fly

Thrips

• Egg: Eggs are microscopic and white or yellow in colour. Eggs are inserted one by one by the gravid females in the plant tissue. Only one end of the egg will be near the surface of the tissue to allow the immature to emerge. Adults prefer to lay their eggs in leaf, cotyledon, or flower tissues.
• Nymph: Nymphs are tiny, small and pale yellow to brownish colour. Nymphs are similar to adults except wing and are smaller in size.
• Adult: The adult are slender, pale yellow to dark brown in colour and measures up to 1.5-2mm. Adults have fully developed fringe things. There are several overlapping in generations of this pests in a year.

• Thrips have a very peculiar feeding behavior as they are typical xylem-feeder.
• They start the feeding by rasping the leaf surface with their mouth parts to release the liquids from the plant cells and suck the plant juice.
• The plant loses more water than normal through the damaged tissues and plant pathogens penetrate the injured plant cells easily.

• Parasitoid: Ceranisus menes
• Predators: Predatory mite, predatory thrips, Oligota spp., Orius spp. (pirate bug), mirid bug.

White fly

It is polyphagous pest and occurs almost throughout the country.

• Egg: Eggs are stalked, sub-elliptical and light yellow to light brown in colour. Gravid female lays eggs singly on under side of the leaves. Incubation period varies 3-7 days during summer season.
• Nymph: Nymphs are louse like, pale yellow coloured and clustered together underside of the leaves.
• Adult: Adults are winged, tiny (1-1.5 mm long), yellowish body covered with white waxy powder. Several overlapping generations are completed in a year.

• Affected plant loses its vitality due to sap sucking by both nymph and adult whiteflies resulting yellowing, downward curling and finally drying of leaves.
• Normal photosynthesis is restricted due to growth of black sooty mould on the honeydew excreted by the whitefly.

• Parasitoids: Encarsia formosa, Eretmocerus spp., Chrysocharis pentheus
• Predators: Dicyphus hesperus, lacewing, ladybird beetle, big-eyed bugs (Geocoris sp), mirid bug, spider, reduviid bug, robber fly, dragon fly, Orius spp.

Aphid

• Egg: Eggs are very tiny, shiny-black, and are found in the crevices of bud, stems, and barks of the plant. Aphids usually do not lay eggs in warm parts of the world.
• Nymph: Nymphs look like the wingless adults but are smaller. They become adults within 7 to 10 days.
• Adult: Adults are small, 1 to 4 mm long, soft-bodied insects with two long antennae that resemble horns. Most aphids have two short cornicles (siphunculi) protruding from 5th or 6th abdominal segment of the body. They complete their life cycle 9-21 days depending upon weather conditions.

• Infesting tender shoots and under surface of the leaves.
• Curling and crinkling of leaves
• Stunted growth
• Development of black sooty mould due to the excretion of honeydew

• Parasitoids: Aphidius colemani, Aphelinus sp
• Predators: Red ant, robber fly, big-eyed bug (Geocoris sp), earwig, ground beetle, cecidomyiid fly, dragon fly, praying mantis, lacewing, ladybird beetle, spider etc.

Leaf eating caterpillar

• Egg: A female can lay upto 350 eggs, mostly singly or some time in groups on the lower surface of the leaves. Incubation period is 306 days.
• Larva: Elongate bright green caterpillar with two narrow longitudinal white stripes dorsally.
• Pupa: The pupa color is dull red or brownish yellow to dull white, and is about 5 to 6 mm in length. Pupation takes place in the silken cocoon formed in the leaf fold.
• Adult: The wingspan is about 30 mm. Adults have translucent whitish wings with broad dark brown borders. The body is whitish below, and brown on top of head and thorax as well as the end of the abdomen. There is a tuft of light brown "hairs" on the tip of the abdomen, vestigial in the male but well-developed in the female.

• Larva folds the leaves and scrapes the green matter. As a result the leaves get dried up.
• It can also feed on ovaries of flower; sometimes bore into young developing fruits.

• Parasitoids: Trichogramma spp., Apanteles taragamae, A. machaeralis, Bracon hebetor, Phanerotoma hendecasisella, Chelonus sp., Campoletis chlorideae, Goniozus sensorius, Elasmus brevicornis, Xanthopimpla punctata, Brachymeria lasus, B. margaroniae etc.
• Predators: Reduviid, predatory bird, wasps, ground beetle, spiders, ants, earwig etc.

Serpentine leaf miner

• Egg: Eggs are minute in size and orange yellow in colour. The egg hatches in 3-5 days.
• Larva: Apodous maggot feeds on chlorophyll mining in between epidermal layers. Full grown maggot measures 3 mm. Larval duration is about 7-9 days.
• Pupa: Pupation is in soil. Some pupae are found in leaves. Pupation takes place inside a thin loose mesh of silken cocoon. Pupal period is about 5-7 days.
• Adult: It is a pale yellowish fly, measuring 1.5 mm in length. The female fly punctures upper surface of leaf to lay eggs singly Total life cycle takes 3 weeks.

• Leaves with silvery serpentine mines
• Drying and dropping of pre-matured leaves in severe cases

• Warm weather conditions are favourable for multiplication.

• Parasitoids: Gronotoma micromorpha (larva and pupa), Diglyphus sp (larva), Halticoptera circulus and Opius sp (pupal) Chrysocharis sp, Neochrysocharis formosa.
• Predators: Lacewings, ladybird beetle, spiders, red ants, dragonfly, robber fly, praying mantis etc.

Red spider mite

• Egg: Eggs reddish, spherical, provided with a small filament. Incubation period is 2-4 days, before hatching becomes light orange colour.
• Nymph: Upon hatching, it will pass through a larval stage and two nymphal stages before becoming adult. Developmental stages include six legged larva, protonymph and deutonymph.
• Adult: Adult female elliptical in shape, bright crimson anteriorly and dark pruplish brown posteriorly. Mites spin a web of silken threads on the leaf. Each developmental stage is followed by a quiescent stage and life cycle completed in 10-14 days.

• Spider mites usually extract the cell contents from the leaves using their long, needle- like mouthparts. This results in reduced chlorophyll content in the leaves, leading to the formation of white or yellow speckles on the leaves.
• In severe infestations, leaves completely desiccate and drop off.
• The mites also produce webbing on the leaf surfaces in severe conditions.
• Under high population densities, the mites move to using strands of silk to form a ball like mass, which will be blown by winds to new leaves or plants, in a process known as "ballooning".

• Predators: Anthocorid bugs (Orius spp.), mirid bugs, syrphid/hover flies, green lacewings (Mallada basalis and Chrysoperla sp.), predatory mites (Amblyseius alstoniae, A. womersleyi, A. fallacies and Phytoseiulus persimilis), predatory coccinellids (Stethorus punctillum), staphylinid beetle (Oligota spp.), predatory cecidomyiid fly (Anthrocnodax occidentalis), predatory gall midge (Feltiella minuta), predatory thrips etc.

Root-knot nematode

• Most species of plant parasitic nematodes have a relatively simple life cycle consisting of the egg, four larval stages and the adult male and female. They are microscopic in size.
• Development of the first stage larvae occurs within the egg where the first moult occurs. Second stage larvae hatch from eggs to find and infect plant roots or in some cases foliar tissues.
• Under suitable environmental conditions, the eggs hatch and new larvae emerge to complete the life cycle within 4 to 8 weeks depending on temperature.
• Nematode development is generally most rapid within an optimal soil temperature range of 70 to 80°F.

• Infected plants in patches in the field.
• Formation of galls on host root system is the primary symptom.
• Roots branch profusely starting from the gall tissue causing a ‘beard root’ symptom.
• Infected roots become knobby and knotty.
• In severely infected plants the root system is reduced and the rootlets are almost completely absent. The roots are seriously hampered in their function of uptake and transport of water and nutrients.
• Plants wilt during the hot part of day, especially under dry conditions and are often stunted.
• Seedlings infected in nursery do not normally survive transplanting and those surviving have reduced flowering and fruit production.
• Nematode infection predisposes plants to fungal and bacterial root pathogens.

• Primary: Egg masses survive in infected plant debris and soil or collateral and other hosts like Solonaceous, Malvaceous and Leguminaceous plants act as sources of inoculum
• Secondary: Autonomous second stage juveniles that may also be water dispersed

• Loamy light soils

IPM for Watermelon

To know the IPM practices for Watermelon, click here.

Source: NIPHM and Directorate of Plant Protection, Quarantine & Storage