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Sorghum head bug, Calocoris angustahlS Leth. (Hemiptera: Miridae) is an important insect pest of sorghum in the semi-arid tropics. A technique to screen for resistance to head bugs under fieid conditions was tested. Planting infester rows of susceptible cultivars (CSH 1 or CSH 5), 20 days before the test material or pianting early (4~5 days) fiowering lines (IS 802, IS 13429 and IS 24439) along with the test material, split planting oftest material at IS-day intervals, grouping test material according to maturity, and use of sprinkler irrigation to maintain high humidity, were found effective in increasing the efficiency of screening and selecting for resistance to head bUgs. A head cage technique to screen for resistance under no-cboice conditions has also been developed. Panicles Infested with 10 pairs of bugs at pre-and half-anthesis, result in maximum population build-Up and grain damage under headcage. This technique Is useful for confirming the resistance observed under field conditions. Under natural Infestation, five genotypes harboured relatively lower head bug numbers than the susceptible checks, but only three (IS 17610, IS 17618 and IS 17645) maintained their level of resistance under the headcage. Seed gemiBation was > 70% In these genotypes compared to < 10% in CSH 1 and CSH 5.

Four mi rid head bugs, Calacoris anguslalus Leth., Creontiades pailidus R am b., Eurystylus bdlevoyei Put. and Reut., and Campylomma'.sp., infest sorghum at IC R I SAT Centre in India. C. anguslalus is the predominant species, followed by Campylomma'.sp., C. pailidus and E. bdlevoyei. T he incidence o f C. anguslalus is higher in crops grown on Vertisols than on Alfisols, and maximum numbers are recorded in panicles at the milk stage. Females oi'C. anguslalus lay eggs inside the glumes before amhesis, whereas the other species insert their eggs in the grain at the milk stage. T he life cycle is completed in 15-20. ! 7-23, 14-16 and 16-17 days by C. anguslalus, C. pailidus. E. bdlevoyei. and Campylomma sp., respectively. T he maximum numbers o f C. anguslalus, C. pailidus and E. bdlevoyd were recorded during Septem ber-O ctobcr, whereas Campylomma sp. tended to be most active during M arch-June. Lower minimum temperature (< 1 8°G) and relative humidity (r.h.) (< 3 0 " ») were associated witli a decline in C. anguslalus density during Novem ber-January, while higher temperatures (> 32°C i and lower r.h. (< 30"«j restricted its numbers during M arch-June. During the rainy season, rainfall, temperature and r.h. were generally positively associated with populations ol'C. anguslalus, C. pailidus and E. bdlevoyd. However, there were some exceptions in some years. During the post-rainy season, higher temperatures (> 32°C) and moisture deficit had a negative association with numbers oi'C. anguslalus, C. pailidus and E. bdlevoyd. However, these factors were positively associated with numbers o f Campylomma. Weather parameter means for the same week and two preceding weeks showed a greater effect on C. anguslalus populations. K e y w o r d s : (,'atocon.\ a n g m la lu s; Creontiades pa ilid u s: Etirvsl\ii<.\ b d le v o y d ; C a m p rk m m a ; b i o lo g y ; p o p u la t i o n d y n a m i c s ; Erythcm dus hd upellidis; p a r a s ito id

A i i s t k a c t .Avoidable losses and economic injury levels (ElLs) were computed for the sorghum head bug. Calocoris amjustatus Leth., on three cuitivars during three rainy seasons {1985-1987) at IGRISAT. Grain yield in plots i)rotected with 2-5 insecticide sprays (carbaryl at 500 g a.i./ha) between the half-anthe^is and the dough stage was significantly higher than in untreated plots, with cost benefit ratios > 1. Plots that were not protected aL half-ail thesis and/or complete-an thesis, and at milk and dough siages, suffered a significant loss in yield. Bug damage spoiled the grain quality in terms of germination, 1000-grain mass, grain hardness and percentage floaters. Three io four sprays between coniplete-aiuhesis and the dough stage prevented a significant reduction in grain quality. Mead bug density at hall-ainhesis. eomplete-anthesis, milk and dough stages was significantly and negatively associated with grain yield. Bug density at different siages explained -hi 94% of the variance in yield. Direct effects of bug numbers at the milk stage and the indirect elici ts of head bug density at other stages through the milk stage contributed towards maximum reduction in yield. M aximum avoidable losses were recorded in cultivar I CSV 1 (88-6%), followed by GSIf 1 (69-9%). and CSII 5 {:>3-9% in lf)H(i and 554)% in 1987). Loss in grain yield/ha due to one insect/panicle at hall-anthesis and that based on natural increase,-were 548 tind 232 kg in CSII 5 (hiring 1986 and 1987, respectively. 251 kg in IC.SV I, and 77 kg in CSH 1. EILs based on a cost-benefit ratio of 1 :! ranged from 1-3 1-4 insects/panicle for CSH I. 0-4 for I CSV 1, and O-I-(M) and 0-2-0-! for CSH 5 during 1986 and 1987, respectively. Simple cost estimates for insecticide sprays and the resultant saving in grain yield are a useful tool for decision-making in pest management.

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