Columbia-Montour Quarterly Vol. 21: July - September 2026

in diameter. Light green at first, they turn white before hatching. Tomato hornworms ( Manduca quinquemaculata ) have eight V-shaped markings on each side; the horn is at the rear. These species grow to about three inches long. Hornworms strip leaves from tomato vines as they feed. These caterpillars also feed on developing fruit. Rather than boring into the tomato fruit, they feed on the surface, leaving large, open scars. Fruit damage is less common than the loss of leaves. Hornworm damage begins in midsummer and continues throughout the growing season. They are especially attracted to plants under drought stress. Natural parasitism often occurs on hornworm caterpillars when tiny braconid wasps lay eggs inside the hornworms. The larvae feed inside and then pupate on the backs of the hornworms. These pupal cases are small white projections, like rice grains, on the back of the hornworm. If parasitized hornworms are on the plant, feeding has ceased, so allow the caterpillar so that the next generation of beneficial wasps will emerge. If you have not seen this, it is cool and a great teachable moment for the children. Stink bugs (family Pentatomidae) feed on over fifty plants, including native and ornamental trees, shrubs, vines, weeds, and many cultivated crops. Among vegetable crops, stink bugs attack beans, okra pods, ripening tomato and pepper fruit, and stems of melons and asparagus. The brown marmorated stink bug, or BMSB ( Halyomorpha halys ), has become a severe pest of fruit, vegetables, and field crops. Adults are approximately two-thirds of an inch long and are shades of brown on both the upper and lower body surfaces. They have the typical “shield” shape of other stink bugs, almost as wide as they are long. The eggs of the brown marmorated stink bug are often laid on the underside of leaves and are light green. They are elliptical and deposited in a mass of 25 to 30 eggs. This insect is an important agricultural pest.

BROWN MARMORATED STINK BUG

Cultural practices help avoid many insect infestations. Plant tomatoes in well-prepared, fertile, mulched beds and properly watered to promote vigorous growth. Stressed plants tend to attract more insect pests. Handpicking and destroying many pests in a home garden is an effective control measure. In addition, beneficial insects are very effective at controlling pests such as aphids, leafminers, and hornworms. To avoid killing these beneficial insects, use insecticides only when necessary. Always try less toxic alternative sprays first to control insect pests and diseases. •

ABOUT THE AUTHOR: Suann Leighow has been a Penn State Extension Master Gardener of Columbia County since 1995 and gardens in Numidia.

For further reading about various tomato diseases and disorders in the home garden, click the button below to read another article produced by Suann for the Penn State Extension website.