Agrius convolvuli (convolvulus hawkmoth)

The phytophagous larvae are mainly nocturnal and generally eat the younger leaves of hosts, often stripping growing shoots. During major infestations, whole plants may be defoliated. Larvae are often present in such enormous numbers that a distinct odour can be perceived in the fields of sweet potato attacked (Dietz, 1915).

Insecticidal sprays applied at the first signs of larval damage are usually very effective (Hill, 1983). Before the introduction of organic pesticides, water-filled ditches were utilized to prevent the migration of larvae from field to field (Franssen, 1934).Telenomus australicum is an important parasitoid of Chilo spp. on rice in India. As A. convolvuli is also a good host for this egg parasitoid, and Clerodendrum fragrans, a known wild host plant of this sphingid, already grows along the borders of many rice fields, it is suggested that this shrub should be left, or even planted, to facilitate the maintenance of wild reservoirs of the parasitoid (Sudha Nagarkatti, 1973).Different fertilizer regimes can also be used as a form of control. In Nigeria, five and six different levels of potassium fertilizers with constant levels of nitrogen and phosphorus were applied to sweet potato at 6 weeks after planting in 1987 and 1988, respectively. The unfertilized control plots had the least damage. They were less attractive than the fertilized plots due to poor vegetative development; however, varying the levels of potassium applied did not have any significant effect on the damage caused by A. convolvuli (Anioke et al., 1993).

Larvae of this species can reach alarming numbers under certain conditions, where they may completely strip entire fields of all leaves, before moving en masse to new fields. The damage done to sweet potato depends largely on the stage at which the plant is attacked (Dietz, 1915). If the young plants are healthy and growing well the damage is not too great, because sweet potato has remarkable powers of recovery. However, damage to the leaves delays harvest in Indonesia and increases the likelihood of attack by the sweet-potato beetle Cylas (Kalshoven, 1981). Defoliation of fields of Vigna usually results in complete loss of the crop (Dietz, 1915; Kalshoven, 1981; Hill, 1983; Aherkar et al., 1993).