From my experiences in Tunisia

The effect of chemical treatments on larval mortality shows that the larval stage L1 of Tuta absoluta is sensitive (100% mortality) to all the chemicals tested. The L2 stage is sensitive to Spinosad, indoxacarb and emactin, whereas Bacillus thuringiensis, martine, and do not cause 50% mortality. The morbidity of stage L3 oscillates between 20% and 80% of

mortality. The L4 stage is more affected by the treatment with Bacillus thuringiensis which can go to 100%.

According to these results, chemical treatments should be directed according to the dominant larval stage in the plants. Indeed, the two larval stages, L1 and L2 of Tuta absoluta generally appear to be the most sensitive to the chemical tested. Thus, treatments must target these stages, to ensure their effectiveness.