150 



At the beginning of the experiment, there were significant differ- 

 ences between larval population means in the treatment blocks, but the 

 control block had the lowest mean of all blocks (Figure 30). 



By the second sampling period, only blocks treated with dimethoate 

 and CGA 72662 (0.05%) at 1.92 1/9.12 m 2 had larval population means 

 that were significantly greater than that of the control block (Table 

 32, Figure 30). There were no significant differences between the 

 larval population means of blocks treated with dichlorvos at 3.S5 1/ 

 9.12 m 2 and Ravap, and the larval population mean of the control block. 

 Larval means of all other blocks were significantly lower than the 

 control block. 



By the end of the third sampling period, fly resurgence had begun 

 in the blocks treated with dimethoate, dichlorvos at 1.92 1/9.12 m 2 , 

 and Ravap, and the larval population means were all significantly 

 greater than the larval population mean of the control group (Figure 30). 

 Larval means of all other treatment blocks were significantly lower than 

 the control block population. Larval populations in the blocks treated 

 with both rates of CGA 72662 were reduced to zero. 



At the and of the fourth sampling period, populations in blocks 

 treated with dimethoate and dichlorvos at 1.92 1/9.12 m 2 continued to 

 resurge, and resurgence also began in the block treated with dichlorvos 

 at 3-84 1/9.12 m 2 (Figure 30). Sampling was discontinued in these 

 blocks. The block treated with Ravap shewed a decrease in larval popu- 

 lation, but by the end of the fifth sampling period, the population was 

 considered too numerous to count. Therefore, the larval population 

 counted during the fourth sampling period was the last recorded count 

 and sampling in the Ravap-treated block also ceased. 



