Other sweetpotato weevils

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Scientific name: Cylas puncticollis (Boheman) and C. brunneus (Fabricius)










Economic importance

These weevils are serious pests in the  sweetpotato  growing areas of Africa.

Geographical distribution

C. puncticollis and C. brunneus are confined to Africa. They often occur simultaneously and might both emerge from one infested storage root.


Damage symptoms are similar to those of the common sweetpotato weevil Cylas formicarius. Adult sweetpotato weevils feed on the epidermis of vines and leaves, but damage is hardly noticeable. Adults also feed on the external surfaces of storage roots, causing round feeding punctures. The developing larvae of the weevil tunnel in the vines and storage roots, causing significant damage. Frass is deposited in the tunnels. In response to damage, storage roots produce toxic terpenes, which cause a greenish discolouration, an off-taste and distinct odour. Depending on the marketing and food security situation, the storage root is considered a total loss or the affected part is cut off and the remaining part used as food. Larval feeding inside the vines causes malformation, thickening, drying and cracking of the affected vine.


Egg.  The eggs of both species are shiny white and roundish.

Larva. The legless larvae are white and curved and have an orange head capsule. The last instar larvae of C. puncticollis are distinguishably larger than those of C. brunneus.

Pupa. The pupae are white, with that of C. puncticollis being the larger in size.

Adult. Adult Cylas spp. are elongated and ant-like. C. puncticollis is completely black while C. brunneus is not uniform in its colour. Most specimen are bicoloured like C. formicarius, while others are black like C. puncticollis.  Average-sized adults of C. brunneus  are smaller than adults of C. puncticollis, which are 7 mm long.

Biology and ecology

Cylas spp. are found in almost all zones of sweetpotato production in Africa, and are considered a severe constraint in relatively dry agro-ecological zones and/or during dry growing seasons.

All sweetpotato weevil species have a similar life history. The adult female lays eggs singly in cavities excavated in vines or in storage roots, preferring the latter. The egg cavity is sealed with a protective, grey faecal plug. The developing larvae tunnel in the vine base or storage root. Pupation takes place within the larval tunnels. A few days after exclusion, the adult emerges from the vine or storage root. Because the female cannot dig, it finds storage roots in which to lay the eggs by entering through soil cracks.

Adults of all species may be conveniently sexed by the shape of the distal antennal segment, which is filiform (thread-like, cylindrical) in males and club-like in females.

At 27oC C. puncticollis has a total developmental period of 20-28 days, whereas C. brunneus takes 32-41 days. Adults of the first species live an average of 140 days, whereas the latter dies after about 92 days. Both C. puncticollis  and C. brunneus females lay around 100 eggs in their lifetime.

Host range

The insects prefer sweetpotato. Cylas spp. can complete all their life stages on several wild Ipomoea spp.

Detection and inspection

Detection of infestation is difficult, as adults are most active by night. Early detection of the pest can be done by checking for swollen vine bases and infested exposed roots. When damage has been detected, several plants could be dug up to establish an idea of the damage level to the roots. This could lead to the decision for an early harvest. The species-specific pheromones of the Cylas species that are released by female weevils and attract males have been identified.


When sweetpotato weevil populations are high, no single control method provides adequate protection. The integration of different techniques, with emphasis on the prevention of infestation, provides sustainable protection. 

Cultural control

Cultural control practices have proved to be effective against the sweetpotato weevil and should be the main basis of control. The local growing conditions and the use of the crop (commercial or for own consumption) will indicate which practices should be applied. Cultural practices include:

  • Use of uninfested planting material, especially vine tips.
  • Crop rotation.
  • Removal of volunteer plants and crop debris (sanitation).
  • Timely planting and prompt harvesting to avoid a dry period.
  • Planting away from weevil-infested fields, and/or using a barrier crop.
  • Hilling-up of soil around the base of plants and filling of soil cracks.
  • Removal of alternate, wild hosts.
  • Flooding the field for 24 hours after completing a harvest.
  • Applying sufficient irrigation to prevent or reduce soil cracking.

Chemical control

Dipping planting material in a solution of an insecticide (such as carbofuran or diazinon) for 30 minutes prior to planting can control sweetpotato weevils for the first few months of the growing season. Spraying insecticides after planting is not (cost)-effective.

Host resistance

Varieties with immunity or a high level of resistance are not available. Some varieties have low levels of resistance. Others escape weevil damage because their storage roots are produced deep in the soil or because they mature quickly and can be harvested early.

Sex pheromones

Several good and simple trap designs have been produced making use of locally available materials. Mass-trapping of the Cylas species with their specific sex pheromones will reduce the numbers of males, but the beneficial effect on infestation rate and yield is limited. The availability and price of pheromones will restrict the number of users.

Biological control

Promising biological control agents for sweetpotato appear to be the fungi Beauveria bassiana and Metarrhizium anisopliae and the nematodes Heterorhabditis spp. and Steinernema spp. The fungi attack and kill adult weevils, whereas the nematodes kill the larvae. A solution of B. bassiana could be used as a pre-planting dip.

Ants, spiders, carabids, and earwigs are important generalist predators that attack weevils. The ants Pheidole megacephala and Tetramorius guineese are used as biological control agents in Cuba.


Ames, T., Smit, N.E.J.M., Braun, A.R., O’Sullivan, J.N., and Skoglund, L.G. 1996. Sweetpotato: Major pests diseases, and nutritional disorders. International Potato Center (CIP). Lima, Perú. 152 p.

Gonzales, S.S. 1925. The sweetpotato weevil (Cylas formicarius Fabr.), Philippine Agriculturist  14:257-281.

PANS. 1978. Pest Control in Tropical Root Crop. Manual No. 4. Centre for Overseas Pest Research.London.  235pp.  

Smit, N.E.J.M. 1997. Integrated Pest Management for sweetpotato in Eastern Africa. PhD thesis Agricultural University Wageningen, 151 p.

Smit, N.E.J.M. and van Huis, A. 1998. Biology of the African Sweetpotato Weevil Species Cylas puncticollis (Boheman) and C. brunneus (Fabricius) (Coleoptera: Apionidae). Insect Science and its Application, 18: 93-100.

Smit, N.E.J.M., Downham, M.C.A., Laboke, P.O., Hall, D.R. and  Odongo, B. 2001. Mass-trapping male Cylas spp. with sex pheromones: a potential IPM component in sweetpotato production in Uganda? Crop Protection 20:643-651.

Wolfe, G.W. 1991. The origin and dispersal of the pest species of Cylas with a key to the pest species groups of the world, pp. 13-44. In: Sweetpotato Pest Management, A Global Perspective (Edited by R.K. Jansson and K.V. Raman). Westview Press, Boulder, USA.



Contributed by: Nicole Smit


Economic importance

Geographical distribution



Biology and ecology

Detection and inspection



C. formicarius fact sheet

Larval tunnels and storage root flesh discolouration (N. Smit).

Larvae of C. puncticollis on stem tunnels ( IIBC).

Adults and pupae of C. puncticollis ( N. Smit).

Adult C. puncticolis

( IIBC).