Impacts of pyriproxyfen, flufenoxuron and acetone extract of Melia azedarach fruits on the haemogram of the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae)

The black cutworm, Agrotis ipsilon, is a serious agricultural insect pest worldwide. In Egypt it has acquired resistance against most of the applied conventional pesticides. Therefore, the present study aimed to investigate the effect of pyriproxyfen, flufenoxuron, and acetone extract of Melia azedarach fruits on the total haemocyte count (THC), percentage of haemocyte viability and percentage of each type of haemocyte (differential haemocyte count; DHC) in A. ipsilon last instars. For this purpose newly molted 4th instars were treated with the LC50 of these compounds based on the leaf-dip method. THC was conducted with Neubauer haemocytometer. Flufenoxuron significantly increased both the THC and their viability compared to the untreated control. There are five types of haemocytes in A. ipsilon larvae: prohaemocytes, plasmatocytes, granulocytes, spherulocytes and oenocytoids. Both pyriproxyfen and flufenoxuron significantly increased the number of granulocytes and oenocytoids compared to the control. Also, granulocytes were significantly increased in larvae treated with acetone extract of M. azedarach fruits. On the contrary, this extract significantly decreased the number of spherulocytes and oenocytoids compared to the control. Plasmatocytes were significantly decreased in pyriproxyfen–treated larvae. In conclusion, flufenoxuron and acetone extract of M. azedarach fruits may stimulate the cellular immune system of A. ipsilon larvae via increasing the number of phagocytic granulocytes, in addition to increasing the haemocyte viability with flufenoxuron. On the other hand, pyriproxyfen may act as immunosuppressant to A. ipsilon where it suppresses the number of phagocytic plasmatocytes although this compound had no significant effect on haemocyte viability.

Keywords:

Agrotis ipsilon , Total haemocyte count , Differential haemocyte count , Juvenile hormone analogs , Chitin synthesis inhibitors , Plant extracts