Aspergillus flavus presence in silks and insects from developing and mature corn ears

To determine the origin of the inoculum responsible for Aspergillus flavus infection of maize before harvest, silks and insects from developing and ripe ears of 2 maize hybrids grown at 6 sites in the USA were examined for presence of the fungus. Incidence in the silks varied with the hybrid, the site and the degree of ripeness. A. flavus occurred in at least 1 silk sample from each site and was found more frequently on silks from ripe ears than on those from unripe ears. From 1200 ears, 3442 insects were collected. Distinct interactions were observed between the number and type of insects and the site, hybrid and sampling time. A. flavus was detected in surface-sterilised insects from 5 of the 6 sites. Some 60% of the insects collected were Coleoptera and of these, 3.1% of the larvae and 2.8% of the adults contained A. flavus; some 18% were stored grain pests (Sitophilus oryzae (L.), angoumois grain moth [Sitotroga cerealella (Ol.)], confused flour beetle [Tribolium confusum Duv.], sawtoothed grain beetle [Oryzaephilus surinamensis (L.)] and square-necked grain beetle [Cathartus quadricollis (Guer.)]) and A. flavus was present in 1.7% of these. It was also present in 2% of Ostrinia nubilalis (Hb.) and Heliothis zea (Boddie) (4% of the total number of insects), and in 2.8% of the other insects taken (including Diptera, Hemiptera, Neuroptera and Psocoptera). Dissemination of the fungus was not related to the activities of a specific insect. Some 52% of A. flavus isolates from maize and 32% of those from insects produced aflatoxin in a qualitative test.<new para>ADDITIONAL ABSTRACT:<new para>Data are presented from six states in the USA showing that insect infestation of mature corn ears and the incidence of Aspergillus flavus on the silks of those ears was generally lower in a hybrid with tight, heavy ear husks than in a hybrid with lighter, more open ear husks.