Sweetpotato hornworm is not usually a serious pest , although severe outbreaks have been reported in Vietnam. Yield losses can occur if heavy defoliation takes place when the crop is young.

A. convolvuli occurs worldwide, but is prevalent in Africa, Asia, Australia, the Pacific and Southern Europe.

The larva is a large voracious caterpillar that is capable of defoliating the plant. It feeds on the leaf blade causing large irregular holes or may start feeding on the leaf edges eventually  eating the entire leaf blade, leaving only the petiole.  They are initially found at the shoot tip, preferring young leaves, but will eat all leaves if population is high. They are extremely sluggish, moving only enough to reach a new leaf after one has been consumed. Frass can be found near the infested plant part.

Morphology

Egg. The greenish spherical eggs measure 1 to 2 mm in diameter.

Larva. The larvae are variable in colour from green to brown, occasionally yellow and are distinctly patterned. They have a distinctive posterior horn and reach 95 mm in length.

Pupa. The reddish brown pupae are characterized by their prominent proboscis or "trunk" which is curved downward. The body surface is glossy.  Pupae are found in the soil under the plants.

Adult. The adults are  large greyish brown hawkmoths  with black lines on the wings and pink markings on the abdomen.  Wingspan is 8-12 cm.

Biology and Ecology

The female lays spherical eggs singly on either surface of the leaves or stem. Egg hatching takes place 4 days after oviposition. The larvae have five larval instars from 13 to 25 days with an average of 2 to 6 days per instar. In the early stages, larvae nibble holes through the leaf, little food is consumed hence growth is slow. In the second and third instar, the ground colour deepens further, and pale yellow lateral stripes appear. By the fourth instar larvae consume more food, both by day and night, and growth becomes more rapid. They change their colour to green, brown and, occasionally, yellow. When fully grown, most larvae only emerge at night to eat.  Pupation takes place in the soil. Pupal period is 5 to 26 days. The total life cycle ranges from 22 to 60 days.

Host range

Apart from sweetpotato, it also attacks eggplant, grapes, legumes, pepper, tomato and taro.

Management

Plowing the field to expose the pupae reduces infestation. Handpicking of the larvae may be quite effective in small areas. Light trapping can be used to monitor the population of the adults.

Biological Control

Among its important  egg parasites are Trichogramma spp. while Sycanus sp., a large reduviid, and tachinid flies feed on the larvae.

Pesticide use is not recommended as it disrupts the action of the egg and larval parasites.

References

Amalin, D.M. and Vasquez, E.A. 1993. A handbook on Philippine sweetpotato pests and their natural enemies.  International Potato Center  (CIP), Los Baños, Philippines. 82 p.

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.

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

Shepard, B.M., Carner, G.R., Barrion, A.T., Ooi, P.A.C. and van de Berg, H. 1999. Insects and their natural enemies associated with vegetables and soybean in Southeast Asia. 108 p.

Vasquez, E.A. and Sajise, C.E. 1990. Pests of sweetpotato: Insects, mites and diseases. Philippine Root Crop Information Service, Philippine Root Crop Center. 65 p. 

Contributed by: Erlinda Vasquez and Vilma Amante

Taxonomy

Economic importance

Geographical distribution

Damage

Morphology

Biology and ecology

Host range

Management

References

Sweetpotato hornworm feeding on leaf (E. Vasquez).

Young hornworm caterpillars produce roundish to irregular-shaped holes.

The caterpillars vary considerably in colour and markings (CIP, J. O'Sullivan).

Pupa showing prominent curved proboscis.

Adult hornworm or hawkmoth.