Susceptibility of the German cockroach, Blattella germanica to entomopathogenic fungi using two different methods

In human residences, cockroaches can contribute to increases in allergic processes since they are agents of induction and exacerbation of asthma disease and act as mechanical vectors as natural reservoir of pathogens. Cockroaches are controlled primarily by synthetic organic insecticides. An alternative to chemical methods is the use of entomopathogenic fungi.
Native strains of entomopathogenic fungi were evaluated for control of adults and nymphs (III) of B. germanica, there were used Metarhizium anisopliae (Metschnikoff) Sorokin, and Beauveria bassiana (Bals. Criv.) Vuill. from the culture collection of entomopathogenic fungi of CEPAVE and ARSEF collection Ithaca, NY USA.
The insects were exposed to conidia of M. anisopliae or B. bassiana by two methods. By direct contact, the conidial suspension of 1x10⁹ spores per milliliter was applied in Petri dishes with filter paper and cockroaches were exposed for 24 h. By bait, it was prepared with dog food mixed with 1% medium water agar. One ml of the conidial suspension was added to 4 ml of bait, and 4 ml of this mixture was applied on the bottom of 35 mm sterilized Petri dishes. Cockroaches were exposed to these baits for 72 h. Control insects were treated with Tween 80 (0.01%), under the same conditions in both treatments. The treated cockroaches were placed in plastic containers, were fed with dog food and tap water. The bioassay was conducted at 25 ± 2ºC and 70 ± 5% RH. Mortality was controlled daily for 20 day, and dead cockroaches were removed and placed into sterile Petri dishes. The fungal infectivity was confirmed through monitoring emergence of hyphae up to 8 days post treatment. Adults and nymphs of B. germanica were susceptible to M. anisopliae and B. bassiana infection by direct contact between 60 – 90 % and 40 – 60 % mortality respectively. By baits the susceptibility was weak and mortality was very low from 10 to 40 %.