Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 1998
Publication Date: N/A
Interpretive Summary: Molds that occur on corn can produce toxins that may enter the feed and food supply if not checked. Control of these molds in the field is difficult due to the uncertain and hidden occurrence of damaged ears open to mold spore colonization. Conventional applications of chemical fungicides are costly and impractical. A commercially available bacteria reduces the occurrence of fungi, but delivery of the bacteria has been difficult. In this study a device was used that allowed sap beetles to pick up the bacteria and then carry it to damaged corn. Corn available to sap beetles had much lower levels of mold and toxin compared to ears that excluded the beetles. This control measure is a potentially low cost, environment friendly means of managing mold toxins in corn ears.
Technical Abstract: The ability of sap beetles (Coleoptera: Nitidulidae) to mechanically transmit a strain of Bacillus subtilis to damaged maize (Zea mays L.) and thereby prevent establishment and aflatoxin production by Aspergillus flavus Link ex Fries was examined in laboratory, field cage, and field experiments. A device that attracted and caused the sap beetles to self-inoculate with B. subtilis (autoinoculation) was used in most of the experiments. Laboratory tests with milk stage field corn ears indicated that after one day exposure to sap beetles carrying B. subtilis, colonization by a non-aflatoxigenic, orange mutant strain of A. flavus was reduced from 82% (if the fungus was added first), to 41% (if B. subtilis was added by beetles before the fungus). Field cage studies indicated sap beetles could reduce visible A. flavus (orange mutant) colonization by 97%, when the A. flavus was added to damaged ears four days after beetles were released. The B. subtilis was recovered from all of the damaged kernels inside the cage, but not from any ears outside of the cage. In 1993, field studies with the orange mutant indicated none of the damaged ears that allowed access to sap beetles emerging from B. subtilis containing autoinoculators seven days before inoculation with the orange mutant A. flavus had visible sporulating mold, compared to 92% of ears that did not allow access of beetles but that subsequently had the mold inoculum added. Either sap beetle larvae or frass was found in many of the ears free of A. flavus.