Virulence of Entomopathogenic Nematodes Steinernema glaseri and Heterorhabditis bacteriophora Poinar (HP88 strain) Against the Black Cutworm, Agrotis ipsilon.

Abstract

Virulence of entomopathogenic nematodes, Steinernema glaseri and Heterorhabditis bacteriophora Poinar (HP88 strain) were studied against 3rd, 4th, 5th and 6th instar larvae of the black cutworm, Agrotis ipsilon. The observed mortality caused by the both tested nematodes at different time intervals was recorded. The establishment of nematodes in a host depends greatly on its ability to manage host defences so, the host haemocyte interaction with entomopathogenic nematodes were observed by encapsulation, nodule formation and phagocytosis processes. Phagocytosis is known to stimulate production of lysosomal enzymes. Acid phosphatase acts as a lysosome marker so; the activity and the pattern of acid phosphatase during the course of infection were recorded. Also, total protein and protein pattern were screened. Results indicated that, the two nematodes had variable significantly effects. S. glaseri recorded a highly significantly affect than H. bacteriophora. In addition, there are relationship between mortality rate and time exposure of S. glaseri and H. bacteriophora against 3rd, 4th, 5th and 6th larval instars of A. ipsilon i.e. the time exposure increased the susceptibility also increased. At the lower concentration, fourth and/or fifth instars were the most susceptible instars to S. glaseri ,while the 3rd and 4th instar larvae were most vulnerable instars to the infection with H. bacteriophora. Results was recorded that, six haemocyte types were identified in A. ipsilon 6th instar larvae: prohaemocytes, plasmatocytes, granulocytes, spherulocytes, oenocytoids, and adipohaemocytes. S. glaseri in A. ipsilon escape encapsulation and overcome host immunity faster than H. bacteriophora which recognized by host haemocytes. Prohemocytes, plasmatocytes or granulocytes are phagocytic cells in A. ipsilon 6th instar larvae. Phagocytosis was expressed in A. ipsilon haemocytes infected with H. bacteriophora at a higher rate compared with S. glaseriinfection. Data demonstrated both S. glaseri and H. bacteriophora induced a significant decrease in total protein contents after 24hrs from infection. While, there was significant increase in acid phosphatase activity after 6 hrs of infected groups of S. glaseri and H. bacteriophora. This increase may be due to phagocytosis processes which recorded in the present study at this time because phagocytosis is known to stimulate production of lysosomal enzymes. There is an acid phosphatise band detected only in H. bacteriophora and S. glaseri samples with Rf 0.86 after 6 and 12hrs from infection. This band may refer to nematodes exudates which contain high amount of this enzyme that the nematodes can easily penetrate and digest host tissues. There is a characterestic band of S. glaseri protein pattern with Mw 47KDa. It was identified as surface coat protein of S. glaseri which play important roles in defeating the host immune system by its antiphagocytic activity.