Sweet potato weevil







Cylas formicarius

Straight – snouted weevils


The adults are ant-like beetles with bright orange/red thorax, antennae and legs. They have the typical long rostrum (snout) of weevils which is very slightly curved. Their body, legs and head are long and thin. The elytra (wing covers) are dark metallic blue/black. They are able to fly, but don’t seem to travel far during the day, being more active at night. The females are larger than the males. The larvae look like typical beetle grubs.

Adult size: 5-7 mm

Out and about

All stages will be around throughout the year if there is a suitable food source. Found around the world in tropical regions. In Australia it is found in Queensland and parts of far north New South Wales.

Reproduction and Life cycle

Eggs are sometimes laid in the root or stem, but generally where the stem and root join. The female lays a single egg in a cavity she creates, which she then seals over with faeces. They are very difficult to see. Two to four eggs are laid per day with seventy-five to one hundred eggs laid over her life span of about one month. The complete life cycle is 1-2 months but can be slightly less in warmer months. There can be five to eight generations per year. The adults will over winter until the weather warms up. After hatching the larvae burrow into the root or stem. The larvae are a typical beetle grub (7.5 mm-8 mm). When the weather is warmer, larval growth will be quicker. The larvae pupate in the tuber.

To deter

To control

-Seed potatoes need to be certified weevil free- cuttings may be a better option for propagating -Rotation of crops important so that crops will not be replanted within 3 years -The female likes to lay eggs where stem meets tuber – mound around base so that this area is covered -Mulch – keeps soil moist and thereby stopping the soil from cracking which would allow the female to get to the root to lay her eggs -Clean up weeds especially any in the morning glory family-host plants (Convolvulaceae) -Clean up any tubers left around -Pheromone traps are available which will help monitor the presence of the weevil -Neem drench over soil or neem pellets in soil may help to deter the larvae. Spraying the foliage may keep the adults in check, reducing the number of eggs being laid. -Plant summer savory as a companion plant- confuses adult weevil and may repel them The host plants for the weevil is the Convolvulaceae family, or morning glory family, which have funnel -shaped flowers and are usually vines.

Plants to repel

Plants to attract


Wasps / Ants / Brown earwigs
Why they are a Pest
This weevil is considered a very serious pest, with heavy infestations causing the vine leaves to yellow. The larvae cause damage to tubers by chewing tunnels which then fill with faeces as the larvae grow. These tunnels also allow pathogens to enter the tuber as well as causing tubers to rot. This results in the tubers being riddled with cavities, spongy and dark coloured. The tubers tend to be bitter tasting even if damage appears minor. Adult weevils feed on the underside of leaves but do not do very much damage. The adult will pretend to be dead if threatened. Sweet potato is the only vegetable crop affected by these weevils with infestations more severe during dry conditions.