Metarhizium Anisopliae Metch. Sorrokin as a Potential Microbial Control Agent Against the German Cockroach, Blattella Germanica (L.) (Dictyoptera:Blattellidae)

The German cockroach, Blatella germanica (L) is an important urban insect pest in many parts the world. In Malaysia, It is abundant in hotels and food preparative outlets. Several methods are being used to control this pest and the most common method is using chemical insecticides. The use of chemical for controlling cockroaches , however, has incurred a serious drawback. The cockroach population in many parts of the world developed resistant to chemical insecticides. Thus alternative methods for controlling are warranted. One of these methods is the use of biological agents such as entomopathogenic fungus, Metarhizium anisopliae. In this study eleven indigenous isolates of M. anisopliae were evaluated for their pathogenicity to adult male of German cockroach. Monoconidial cultures of the isolates were obtained from soil and insect cadaver that were collected from various localities in Malaysia and were maintained on Potatoes Dextrose Agar+Yeast (PDAY).The result from the screening test shows that from eleven isolates tested, HSAH gave the best result with 87.5% mortality after 13 days inoculation and LT50 values of 6.78 days. Although not significantly different, there was a tendency for mortality on nymphs to be higher than mortality on adult males and females. Further bioassay on four selected isolates, HSAH, Mam, Ckrk, LPR3, shows that the infectivity of the fungus varied with the isolates and dosages to which the cockroaches were exposed. The ED50 values ranged from 2.73 x 109 to 3.15 x 1011 at day 4 after inoculation and 4.19 x 103 to 1.22 x 106 at day 14 after inoculation, the LT50 values ranged from 12.37 to 16.45. The result evidently shows that HSAH isolate was the prominent isolate. Using HSAH isolate to control a cockroach colony, the result shows that highest mortality of 78.5 % was achieved when a colony of 50 insects were used and with dosage of 10:90. The same level of mortality i.e 78.5 % could not be achieved by a colony of 100 insects when applied with a dosage of 10:90. Apparently with a bigger cockroach colony, a higher dosage of fungus was required to kill B. germanica

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