Interactions of Metarhizium anisoplae and tree-based mulches in repellence and mycoses against Coptotermes formosanus (Isoptera: Rhinotermitidae)

The use of mulch in urban landscapes has increased in the United States for the past decade. Tree-based organic mulches can supply Coptotermes formosanus Shiraki with food, moisture, and shelter. The current research contributes to mulch management technology in termite control. A choice test arena was designed to determine the repellence and mortality caused by commercial mulches treated with different concentrations of the fungus Metarhizium anisopliae (Metschnikoff) against C. formosanus. Each of six tree-based mulches (pine bark, pine straw, bald cypress, eucalyptus, water oak, and melaleuca) was coated with six conidial concentrations ranging from 1 x 10(3) to 1 x 10(8) conidia/ml. The foragers of C. formosanus were repelled significantly by the fungal-treated mulch substrates; the proportion of termites on fungal-treated mulch was usually <20% during the 28-d test. By day 28, >99% of the termites were killed in test arenas containing a chamber with mulch treated with 10(7) or 10(8) conidia/ml. M. anisopliae significantly reduced mulch consumption by 34-71%. Mulch consumption by the termites was negatively correlated with fungal concentration, and the type of mulch also affected consumption. The differences in termite foraging activities, mortality, and food consumption among mulches were usually confounded by differences in fungal concentrations of M. anisopliae. The results indicate that repellence and virulence of M. anisopliae conidia should significantly reduce the suitability of these six mulches as a habitat for C. formosanus.