Forty forage sorghum genotypes, including 30 hybrids, 5 inbred forage varieties and 3 resistant and 2 susceptible checks were screened for resistance to the sorghum shootfly, Atherigona soccata (Rondani) (Diptera: Muscidae) and the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) under natural infestation in July-September 1996 and 1997. Six sorghum genotypes including two forage sorghum hybrids, HH 1 and NFSH 10659, three resistant check entries, IS 2205, IS 5469 and IS 18551 and inbred forage variety HC 171 showed multiple resistance to both the shootfly and the stemborer. The forage sorghum hybrid HH 1 also gave the highest green fodder yield. It is therefore suggested that this cultivar may be used in breeding programmes as a donor parent for developing sorghum cultivars resistant to A. soccata and C. partellus, or used directly for general cultivation.

Several insect pests are associated with the sorghum crop, but essentially a few are considered key pests. These include shootfly, several species of stem borers, sorghum midge and a complex of head bugs. Other insect pests which are occasionally devastating and sporadic include leaf feeders and defoliators (Lepidoptera of various genera, locusts, grasshoppers, aphids, beetles, etc.) and also several species of head worms and head beetles. A list of 101 insect pests of sorghum occurring in Africa is presented.

The shootfly, Atherigona soccata Rondani, is a major seedling pest of sorghum in many areas of tropical Asia, Africa and Mediterranean Europe. A chronological review of the progress made in various programmes on the screening techniques (natural and artificial) with artificial diets, sources, stability and mechanisms of resistance, bases (physico-morphological and biochemical factors) of resistance, inheritance and breeding for resistance is made. Many resistant varieties have been identified and sources of resistance utilized in breeding programmes to transfer resistance in high yielding background are listed. In addition, the glossy and trichome traits identified is sorghum cultivars are also reported. Glossy leaf surface and trichomes are frequently associated with shootfly resistance.

A number of resistance sources have been identified against two major pests of sorghum, viz the sorghum shootfly, Atherigona soccata Rondani, and the stem-borer, Chilo partellus (Swinhoe). These identified sources of resistance were generally tall, late maturing and poor yielders. Two of these identified sources of resistance, viz. BP 53 and M 35-I, have been utilized in the breeding programme, by crossing with dwarf exotic types, which are highly susceptible to both the pests, but are agronomically desirable varieties. The crosses thus obtained were screened for their reaction to the two pests. An extensive screening programme was carried out under heavy levels of shootfly and stem-borer infestation from 1968 to 1980, which resulted in the identification of nine advanced generation derivatives possessing moderate to high levels of resistance to both shootfly and stem-borer as well as desirable agronomic characters.

The derivatives with M 35-I, as one of the parents showed more resistance to shootfly as compared to derivatives with BP 53, as one of the parents. However, in the case of resistance to stem-borer, the reverse was true.

Insect pests are major yield reducers in sorghum under traditional farming practices in Africa. The use of resistant varieties in an integrated pest management scheme provides the most cost effective and practical means of sorghum insect control. Corneous grain sorghums are more weevil resistant than their softer endosperm counterparts. A wide range of sources of resistance to shootfiy, stem-borer and greenbug are known. Breeding for resistance to sorghum insects has been practised with varying degrees of success. Greenbug resistance breeding in sorghum has been successful in the U.S.A. Stem-borers are perhaps the most serious group of sorghum insects in Eastern Africa and further efforts are needed in breeding for resistance to these pests. In an effective pest resistance breeding work, the breeder and the entomologist must work as a team to make the fastest possible progress. Where several pests are of concern in an area, genotypes with multiple resistance in good agronomic backgrounds are needed.

Sorghum shootfly, Atherigona soccata, oviposition and infestation on eight resistant sorghum cultivars (IS nos: 2122,2123, 2205, 2291, 4660, 5092, 5480 and 18551) and two susceptible cultivars (Serena and CSH-1), were studied under field conditions (natural infestation). The eight resistant cultivars and CSH-1 were also tested for preference for oviposition in a two-choice situation in the screenhouse. The eight resistant cultivars received considerably less shootfly eggs and showed fewer “dead hearts” than the susceptible cultivars. The results indicate that non-preference for oviposition is an important mechanism for resistance to shootfly in eight test cultivars. There was also evidence for a certain degree of antibiosis in IS 2291.

The behaviour of shootfly resistance is examined over the Fl, F2, F3 and advanced generations. The Fl is almost intermediate between two parents with an added heterotic advantage of a lower ‘dead-heart’ percentage. Resistance shows partial dominance under low to moderate shootfly infestation but this relationship may shift under heavy infestation conditions.

The resistance is polygenic in nature and governed by additive genes. In the absence of host immunity, gradual accumulation of favourable genes is possible by line breeding from R × I and I × I crosses by selecting 1 SD below the population mean. Selection for multiple characters limits the genetic advance for shootfly resistance—resulting in 0- 5% selection intensity and relatively less resistant but high yielding desirable progenies. Multilocation tests enable the selection of varieties stable for shootfly resistance.

The sorghum shootfly was first recorded as a pest in the central rainlands, causing losses of up to 25% in local varieties and 25–62.5% in introduced varieties. The pest has also been recorded in the Northern, Khartoum and Equatorial provinces.

In the Sudan, more than one species of Atherigona attack cereals, Atherigona soccata being the most dominant species. Sorghum plants attacked by the shootfly flower and ripen at different times.

A study of the biology of the shootfly showed that the incubation period of the egg was 2–3 days, the pupation period was 6–8 days and the duration from egg to adult was 17 days. The closer the eggs were laid to the leaf blade, the better the chances of the shootfly causing ‘dead-heart’ symptoms. The mortality of the first-instar larva was highest in the first 24 hr. The incidence of the shootfly coincided with rainfall and lower temperatures.

In a selection programme, Combine Kafir 60 had the lowest infestation level, compared to Sudan Grass, Abu Sabein and Feterita Gadarif varieties.

Movement, feeding behaviour and growth of larvae of the sorghum shootfly, Atheriyona saccata, were studied under controlled conditions on a susceptible sorghum variety, CSH-1. The time of hatching coincided with the presence of moisture on the leaf, a condition favourable to movement of the larvae to the base of the leaf. Cutting of the central shoot at its base by the larva caused the symptom referred to as ‘dead heart’. The three larval instars are described and changes in the cephalopharyngeal skeleton discussed.

Movement of the larva to the base is not due to positive geotaxis. Larvae in plants placed horizontally to the ground did not develop normally and a high mortality resulted. The larvae are strongly cannibalistic inside the host-plant but not outside of it. The first-instar larvae do not migrate from one plant to another, but the third instars may do so if the source of food is exhausted.