Stenodiplosis sorghicola; previously, Contarinia sorghicola.
Worldwide. Africa, Asia, North, South and Central America, the Caribbean, Europe, Oceania. It is recorded from Australia, Fiji1, New Caledonia and Papua New Guinea.
Sorghum (grain and forage), and wild grasses, e.g., columbus grass (a natural cross between sorghum and Johnson grass), Johnson grass, Sudan grass.
A major pest; the larvae eat the young seeds in the heads. Moderate infestations leave a few round, full grains amongst undeveloped shrivelled grains. However, when infestations are severe, full grains are absent.
The midge is mosquito-like, orange, 1.5-2 mm long, with clear wings, long antennae, and, for females, a long thin ovipositor (Diagram). The female lays about 100 eggs, usually singly into the flower spikelets, between the lower 'glume' and 'lemma' (see Diagram). Egg-laying occurs just when the spikelets open so that the larvae have the soft developing seed to feed on. About 90% of the eggs are laid within 4 days of head emergence. The female lives for one day; males for a few hours.
Eggs hatch in 2-3 days, and the larvae are white at first, later becoming orange, 2.5 mm long, and spindle shaped. After about 10 days they pupate. The pupae move to the tip of the glumes about 3 days before adult emergence. The life cycle is about 14 days.
Populations of midge build up in successive crops, with late-flowering crops suffering heavy damage.
Not all the larvae pupate, about 2-3% go into a resting stage (called 'diapause') inside a cocoon, and remain there for up to 5 years. The end of diapause depends on temperature and rainfall.
Spread of the midge occurs when grain is moved containing larvae while in the resting stage.
High midge number can destroy susceptible crops. Worldwide, the midge is estimated to destroy about 10-15% of the sorghum grown. Although early planting is considered a good option to manage the midge, often there are difficulties. In any one area, farmers might plant at different times, with different varieties of varying maturity, giving the midge the chance to migrate from one crop to another, with increasing numbers.
It is best to detect the presence of the midge, rather than waiting for shrivelled seeds to show or for the presence of pupal cases on the spikelets after the adults have emerged. During the bloom stage when the head appears, look for midges:
A second method is to use a clear plastic bag placed over the blooming head, tap, remove the bag and count the number of midges. Repeat.
There are several parasitoid wasps: Eupelmus, Tetrastichus and Aprostocetus species. However, the impact of these natural enemies comes late, towards the end of the season, and by then the midge has caused considerable damage. There are general predators, too, but their effect in controlling populations of the midge has not been evaluated.
For many farmers, chemical control will be uneconomic. It is not only expensive, but there is only a short period, at flowering, when it can be done effectively. There is also the problem that the larvae which cause the damage are protected by the glumes. However, if field inspection shows there are more than 1 to 2 midges per head, and pesticides are available, apply a synthetic pyrethroid, e.g., lamba-cyhalthrin or cypermethrin. More than one application will probably be needed.
AUTHOR Grahame Jackson
1Information from Swaine G (1971) Agricultural Zoology in Fiji. Her Majesty's Stationery Office. London; and CABI (2015) Stenodiplosis sorghicola (sorghum midge) Crop Protection Compendium (www.cabi.org/cpc); and from Sorghum midge. Department of Agriculture and Fisheries, Queensland Government. (https://www.daf.qld.gov.au/plants/field-crops-and-pastures/broadacre-field-crops/integrated-pest-management/a-z-insect-pest-list/sorghum-midge). Diagram Mississippi State University Extension. (http://extension.msstate.edu/publications/information-sheets/sorghum-midge-control). Photo 1 Alton N. Sparks, Jr., University of Georgia. Bugwood.org.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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