DISPERSAL OF FORMULATIONS OF FUSARIUM-OXYSPORUM F SP. ERYTHROXYLI ANDFUSARIUM-OXYSPORUM F SP. MELONIS BY ANTS

A natural epidemic of Fusarium wilt on coca (Erythroxylum coca) in Per u prompted the suggestion of possibly using the pathogen Fusarium oxys porum f. sp. erythroxyli as a mycoherbicide against this narcotic plan t. During field trials conducted in Kauai, HI, to test the pathogenici ty of the coca wilt pathogen, ants were observed removing formulations from test plots. While removal of formulations by ants was considered detrimental with respect to conducting field tests, ant removal was c onsidered potentially beneficial in disseminating the mycoherbicide. T hus, research was initiated to assess the ability of formulation addit ives to alter the preference of ants for the formulated mycoherbicide. In Hawaii, preference of indigenous ants for removing formulations wa s tested using three different food bases (rice, rice plus canola oil, and wheat flour [gluten]). Similar tests were conducted at Beltsville , MD, using F. oxysporum f. sp. melonis, in which the formulation base d on wheat flour was replaced by a formulation based on canola meal. F ormulations based on wheat were preferred by ants in both locations; u p to 90% of the wheat plus rice flour granules (C-6) and the wheat glu ten plus kaolin granules (pesta) were removed within 24 h, while only 20% of those containing rice without oils were taken. However, when ei ther canola, sunflower (Maryland only), or olive oil was added to the rice formulation, up to 90% of the granules were taken. The formulatio n based on canola meal was less attractive to ants, as only 65% of the granules were removed within a period of 24 h. Ants showed no prefere nce with respect to presence or absence of fungal biomass. To alter th e attractiveness of the C-6 formulation to ants, C-6 was amended with three natural products. Canna and tansy leaves were added to C-6 at a ratio of 1:5 (wt/wt), while chili powder was added at 1:25 or 1:2.5 (w t/wt). Canna, tansy, and the higher rate of chili powder significantly reduced the number of C-6 granules removed by ants. Canna and tansy l eaves affected neither germination nor sporulation of the mycoherbicid e, while the high concentration of chili powder reduced viability of p ropagules in the formulation. More F. oxysporum f. sp. erythroxyli-typ e colonies were recovered from inside ant nests (9 cm depth) than from nest surfaces, indicating that ants may distribute the mycoherbicide in the soil profile. Ants passively carried propagules of F. oxysporum f. sp. erythroxyli outside their bodies, as well as either very close ly adhering to the outside or within their bodies.