Insects in small groups do little harm while others on a larger scale can ruin tomato plants. You’ll need to take action to get rid of the latter. Before you can embark on a bug-killing mission, you’ll need to know exactly what kind of insects you have.
Identify the Tomato Bugs
Identify the tomato fruitworm and pinworm, which mine holes into the fruits and buds. The tomato fruitworm has a 1 ½- to 1 ¾-inch-long, yellowish-green or cream-colored body with three pairs of legs and five pairs of “prolegs” behind its head. The tomato pinworm is much smaller and is yellowish-gray when young and yellow, green or gray and purple-spotted as an adult.
Spot leafminer holes-- each mine is slightly larger at one end. The vegetable leafminer has a pointed head, and is up to 1/10 inch long and colorless to bright-yellow.
Identify the potato beetle. It has a yellowish-brown, oval body that’s up to a half inch long with five black stripes on each wing cover and black spots behind the head. You’ll find the potato beetle feeding on the leaves and terminal growth of your tomato plants.
Spot the silverleaf and greenhouse whiteflies. Their tiny moth-like bodies are slightly yellow. They suck on the tomato plant sap, causing stunted growth, yellowing and dropping leaves and fruit failure.
Look for grayish-brown or black fat grubs on the leaves or ground to identify cutworms--up to two inches long with three pairs of legs near the head and five pairs of prolegs. The Southern potato wireworm is slender, about a half-inch long, and white, cream or yellowish-gray with reddish-orange on its head. Both feed on the tomato plant's roots.
Spot the cabbage looper, which eats the tomato plant’s leaf tissues but leaves the leaf veins. The cabbage looper is a one-inch-long green caterpillar with white stripes, three pairs of legs and three sets of prolegs.
Find the hornworm feeding on the tomato plant leaves, stripping them from the vines. The hornworm is three and a half inches long, green to reddish-brown, with V-shaped marks on each side of its body, a red or black horn on its hind end and black round spiracles along the side of its body.
Look for aphids feeding in groups on your tomato plants. The green peach aphid is pale-yellow to green, 1/10 of an inch long, and may be winged or wingless. The potato aphid is solid pink, light green with a dark stripe, or mottled green and pink, is up to 0.14 inches long and has slender, long antennae-like cornicles.
Identify the stink bug by its 2/3- to ¾-inch-long, green or brown, shield-shaped body. You’ll find the stink bugs sucking the sap out of the buds, causing them to drop and the tomatoes to grow deformed.
Treating the Bug Infestation
Apply an insecticidal soap to the foliage of your tomato plants to get rid of stink bugs, green peach and potato aphids, as well as the silverleaf and greenhouse whiteflies.
Spray your tomato plants with a methomyl-based insecticide, no more than once every three days, to kill cutworms, cabbage loopers, tomato fruitworms and tomato pinworms. Spray your tomato plants with pyrethrin to get rid of flea beetles, aphids, potato beetles and blister beetles.
Apply a microbial insecticide, such as spinosad, to your tomato plants to get rid of leafminers or cabbage loopers. Apply imidacloprid at a rate of seven to 10 ½ fluid ounces per acre once every 21 days to eradicate Southern potato wireworms.
Apply the naturally-occurring bacteria Bacillus thuringiensis to get rid of hornworms, cabbage looopers, tomato fruitworms and tobacco budworms.
Spray your tomato plants with a narrow-range oil, neem oil or pyrethrin combined with piperonyl butoxide to kill Western flower thrips.