**2.2 Test chemicals**

The pesticides test were selected from the common pesticides used in paddy filed of Thailand. Five selected pesticides were malathion 58% w/v (CAS: 121-75-5), chlorpyrifos 40% w/v (CAS:2921-88-2), carbofuran 3 % GR (CAS:1563-66-2), neem extract 40% w/v (CAS:1141-17-6) and glyphosate 36% w/v (CAS:1071-83-6) (Table 1.). Stock solutions were prepared by dissolving the pesticide directly in distill water immediately before to each experiment. Stock solution were added to each of three replication test beakers ( 50 ml total volume) to obtain nominal exposure concentration. Rang in nominal aqueous exposure concentration of chlorpyrifos,malathaion, glyphosate, carbofuran and neem extract on *M. micrura*, were arranged in geometic series between 0.5 -0.0005, 1-50, 500-2500, 3-15 and 50- 250µg/L respectively.
