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AND SYED A2ELAN S A. HASSAN

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Fig, 4: Progress curues oj mińds relaiivegrowth rutę exposed to 0. 3-0.5 ppm ojNO_r

▲ conlrol, ♦ mińds and cocoa shoots fumigated simultaneously; 0 mińds fed on post fumigated shoots. I heplots were

ojmean ualues with 95% confidencelimits.

Fig. 5:Progress curues oj mean cumulaliue weight of mińds exposed to 0.030 + 0.035 ppm ofSO, + NO_y ▲ eon troi, ■ mińds and cocoa shoots fumigated Simultaneously; • mińds fed on post fu migated shoots. I he plots were of mean values with 95% confidence limits.

control). As observations progressed, the diffe-rencesin RGRbetween the treatments became less marked and no statistical differences in RGR were found at the last measurement. Comparison bet-ween treatments revealed that FIL was the most sensitive in termsof growth stimulation by NO ,.

Fig. 5 represents the progress curves of mean cumulative weights of nymphs subjected to SO_t, and N0₂ mixtures. The results clearly indicate that from day 3 to day 6 significant differences were found between FIL and NFIL treatments. The

NFIFL regimeshowed no significant differences in adultemergence limes between the treatments.

The plot of RGR (Fig. 6) showed similar pat* terns for NFIFL and NFIL. For the FILregime, the RGR was significan tly higher for the First four days and then becamecomparable with the NFIFL and NFILvalues. ItappearsthatfumigationofSO_kłand NO., in combination enhances growth performance of the nymphs feeding on fumigated leaves (FI L) and also inereases, albeit slightly, the growth of NFIFL. The inerease in growth ranged from 20 to 30% despite the fact that the level of S0₉ and N0₉ applied were very much lower compared to the previous individual treatments.

DISCUSSION

Previous studies (Hughes etal 1981; Chappelka etal 1988; Dohmen etal 1984) havedemonstrated that there is a large rnterspecific difference in response to atmospheric pollution among insect species with respect to growth and performance; somespeciesare resistant toelevated S0₉, NO_t>or ozonelevels_tothersaresensitive toacertaindegree. whilst the growth ofothersisapparentlystimulated. The results of this study show that cocoa mirid nymphs respond differently when exposed to different types and concentrations of pollutants. For treatments with SO_t), no significant difference in mean weights were observed between treatments.

10

PERTANIKAYOL. I4NO.I. 1991