Six distinct biotypes of the Asian rice gall midge, Orseolia oryzae (Wood-Mason), have been characterized so far from different parts of India and their geographical distribution has been well mapped and monitored annually through the national gall midge biotype studies. These studies have been showing minor changes in the virulence pattern of the pest population at Warangal in Andhra Pradesh state since 2000. Hence, a sample of the pest population from the site was collected during 2003 and selected subsequently in a greenhouse through 13 successive generations for virulence against diverse sources of plant resistance. This Warangal-derived population (WDP) was tested to record reactions of two sets of differential rice varieties used for biotype detection and known to carry one of the 10 known gall midge-resistance genes. The results revealed that WDP has acquired virulence against CR-MR1523, one of the biotype differential rice varieties, which derived resistance from the source Ptb21 cultivar. Since the virulence pattern noted for WDP was different from that noted for the six characterized biotypes, it is proposed to designate this new biotype, tentatively, as biotype 4M. Only three of the resistance genes, viz. Gm3Gm4 and Gm8 confer resistance against this biotype.

A total of 2256 germplasm accessions, 3000 advanced generation breeding lines and 150 released varieties of rice were screened under artificial infestation in the greenhouse. Among these, 15 new germplasm accessions, 50 breeding lines derived from 16 crosses and 15 released varieties were resistant. Antibiosis was the predominant resistance mechanism; antixenosis affecting oviposition was noted in 33 resistant varieties. Biochemical composition of a set of resistant varieties along with susceptible checks, revealed that nitrogen content of seven test varieties was significantly higher than that of the susceptible checks, while in other six varieties it was lower than the checks. Similarly, eight of the resistant varieties had considerably higher percentage of polyphenolic compounds in basal stem portion, but seven other cultivars showed significantly lower concentration as compared to susceptible checks. Thus, it was apparent that there was no clear trend among the resistant cultivars as a group in relation to quantitative differences of chemical components analysed.

Fourteen differential rice cultivare under four major donor groups were evaluated at 11 field locations in seven Indian states during 13 years against the rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera:Cecidomyiidae). Three basic variations, which qualify to be called biotypes 1,2 and 3 could be identified based on overall reaction patterns against Eswarakora and Siam 29 differential groups. Biotype I cannot damage entries involving either Eswarakora or Siam 29. Biotype 2 is capable of damaging the group of Eswarakora and its derivatives but not able to damage the group of Siam 29. Biotype 3 can damage the Siam 29 group while being incapable of doing so with Eswarakora group.

Results of 7 years' experiments conducted in South China indicated that root-zone application of systemic insecticides effectively controlled nearly all the potential insect pests of rice—the yellow stem-borer, the striped stem-borer, the pink borer, the rice leaf folder, the rice gall midge, the brown planthopper, the greem leafhopper, the rice thrip and the rice weevil. Altogether, 16 compounds have been evaluated for the control of various species. Applications of carbofuran mixed with derivatives of nereistoxin (padan, thiocyclam or dimehypo) in the root-zone were found to be most effective against the major insect pests. The merits and demerits of root-zone applications has been discussed in this paper.

Orseolia oryzae, the rice gall midge, is a major pest of rice in many areas of tropical Asia and is becoming an important pest in Africa. A chronological review of the progress made in various national programmes on varietal resistance, sources of resistance and breeding for resistance is given. Many resistant varieties have been identified and have been utilized in breeding programmes to develop high yielding varieties with multiple resistance to the gall midge and other insect pests and diseases. Mechanisms and inheritance of resistance in rice varieties are discussed. Rice varieties resistant in various countries and sources of resistance used in breeding programmes are listed. Biotype variations in different countries and within the countries are revealed, and a preliminary classification of gall midge biotypes based on varietal reactions is proposed.