The effect of Bacillus thuringiensis subsp. Kurstaki. on Colorado potato beetle larvae. Leptinotarsa decemlineata (say) (Coleoptera: Chrysomelidae) and role of henna as a synergist in increasing of its efficiency

In this study the susceptibility of larval instars of Colorado potato beetle to Bacillus thuringiensis subsp. Kurstaki (ber) alone and in combination with henna was investigated. For this reason the larvae were reared on potato leaves in laboratory. Different larval instars were separated by measuring the diameter of head capsules. The experiments were conducted on 1 st, 2 nd, 3 rd, and 4th instar group and values were 220.384, 465.538, 1283.797 and 3488.562 ppm, respectively. To evaluate the synergistic effect of henna in respectively. To evalute the synergistic effect of henna in combination with B. thuringiensis certain concentration of henna (3000, 4000 and 5000 ppm) was added to the known concentration of B. t. (500 ppm) for 3 rd instar larvae. The results revealed that there is a striking synergistic effect of this material on increasing efficiency of this strain. The larval mortality for mixture of B. t. (500 ppm) with henna (5000 ppm) after six days was 85%, however it was 22.5% and 5% for B. thuringiensis and henna alone, respectively.