Hornworms in sweetpotatoes

In the past couple of weeks, we have observed this individual feeding on sweet potato plants in the Simcoe area.

Sweet potato producers who used to grow tobacco will likely recognize this as a hornworm, however it is not the same species as the more common tobacco or tomato hornworm.  This is likely a sweetpotato hornworm.

Sweetpotato hornworms can vary in colour from green to brown, and can be distinguished by slanted, dark lines running along the side of their bodies, dark horns at the end of the abodomen and three dark stripes along the side of their heads.  In contrast, tobacco and tomato hornworms have white markings on their sides (diagonal for tobacco, and V-shaped for tomato), and do not have dark stripes on their heads.   The larvae are behemoths, with mature caterpillars more than 90 mm long – considerably more than their tobacc0-eating cousins. Sweetpotato and morning glory plants are supposed to be the main host of this insect, however it may feed on some other crops or weeds.

Sweetpotato hornworms are common in more tropical regions. Although this is the first time I have seen one on sweet potatoes, other reports say that the odd moth can stray as far north as Canada.  While the larvae can eat large amounts of foliage and are occasional pests of sweet potatoes in tropical regions, they are unlikely to pose a significant issue in Ontario.

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