David K. Weaver

Fungal colonists of maize grain conditioned at constant temperatures and humidities

Abstract Fungal colonization of shelled maize (Pioneer 3320) harvested from a field near Furman, South Carolina, in 1992 was determined after 348 and 751 days of continuous storage at each of seven temperatures (10, 15, 20, 25, 30, 35, or 40°C) and four constant relative humidities, giving equilibrium grain moisture contents ranging from 9.4% to 17.5% m.c. in 28 grain conditioning environments. Twenty fungal species infected surface sterilized seeds and were recorded from these conditioned grain treatments, including species commonly found in preharvest maize [e.g. Acremonium zeae , Aspergillus flavus , Fusarium moniliforme (syn. F. verticillioides ), Penicillium pinophilum (syn. P. funiculosum ), etc.]. Eupenicillium cinnamopurpureum and Monascus ruber were recorded only from conditioned grain treatments. Eurotium chevalieri colonized 50–96% of the kernels from grain conditioning treatments with the highest moisture content for each incubation temperature. Grain samples with >33% E. chevalieri infection had a decreased occurrence of F. moniliforme and A. zeae , and no kernels from these samples germinated. No fungi colonized more than 50% of the kernels conditioned at 30–40°C and 9.4–14.2% m.c. The results of this study indicate that individual patterns of fungal colonization during grain conditioning were a function of the survival rates for preharvest fungal colonists and their potential replacement by E. chevalieri .

Aggregation pheromone ofCarpophilus dimidiatus (F.) (Coleoptera: Nitidulidae) and responses toCarpophilus pheromones in South Carolina

The major component of the male-produced aggregation pheromone ofCarpophilus dimidiatus (F.) is (3E, 5E, 7E, 9E)-6,8-diethyl-4-methyl-3,5,7,9-dodecatetraene. It attracts beetles of both sexes in the field and is synergized by odors from fermenting bread dough; mean trap catches for the tetraene alone, tetraene plus dough, dough alone, and control were 24.5, 48.3, 0.02, and 0.00, respectively. In the laboratory, individual males produced 0.58 µg±0.35 µg (SD) of the tetraene per day, but males in groups of 10–50 produced <2% as much per beetle. A second male-specific compound, (3E, 5E, 7E, 9E)-5,7-diethyl-9-methyl-3,5,7,9-tridecatetraene, was also identified fromC. dimidiatus and is about 5% as abundant as the major pheromone component.Carpophilus flight activity was monitored for one year in South Carolina corn fields with the pheromones forC. dimidiatus, C. freemani Dobson,C. mutilatus Erichson,C. hemipterus (L.),C. lugubris Murray, andC. obsoletus Erichson, all in combination with bread dough. The first four of these species accounted for 18, 70, 5.7, and 0.03%, respectively, of the totalCarpophilus trapped, but noC. lugubris orC. obsoletus were captured. Captures ofC. freemani were as high as 11,400/trap/week. Species specificity for the first four pheromones was high, except that a synthetic impurity in theC. dimidiatus pheromone was somewhat attractive toC. freemani andC. mutilatus. Three other species captured.C. antiques Melsheimer,C. marginellus Motschulsky, andC. humeralis (F.), accounted for 0.005, 5.0, and 1.3% of the total catch, respectively.C. antiquus was attracted primarily to the pheromone ofC. dimidiatus, butC. marginellus andC. humeralis responded to most of the test pheromones. There were two major periods ofCarpophilus flight activity: February through June and September through November.

Phenology and spatial pattern of Typhaea stercorea (Coleoptera: Mycetophagidae) infesting stored grain: estimation by pitfall trapping.

Abstract The hairy fungus beetle, Typhaea stercorea (L.), occurs frequently in stored grain, often in large numbers. Populations infesting stored barley in Minnesota, corn in South Carolina, and wheat in Florida were sampled by means of grain probe traps. Spatial distribution of the species was examined by contour analysis of trap catch. In South Carolina, corn was sampled at 2 locations over 2 storage seasons, and temperature, moisture content, and malathion residues were measured. These data were used to examine phenology as well as spatial distribution, and showed peak trap catch shortly after harvest in the fall, and in the spring. This pattern followed seasonal changes in grain temperature, but there was no apparent relationship of trap catch to either grain moisture content or malathion residue. The populations of T. stercorea were not distributed randomly, but were largely concentrated in 1 or very few aggregations associated with the “spoutline,” a region high in foreign material and broken grain that forms near the center of a bin as it is loaded. However, the spatial patterns were dynamic, even on a very small time scale (week to week). Numbers of insects in aggregations rose and fell, the areas involved expanded and contracted, the centers shifted, and secondary centers appeared and disappeared. These changes were apparently in response to changing patterns of grain temperature and moisture content. Secondary centers of aggregation often formed in warmer grain along bin walls.

Toxicity of terpenes secreted by the predator Xylocoris flavipes (Reuter) to Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.)

Abstract Four terpene alcohols, linalool, geraniol, α-terpineol, and nerol, which are compounds produced by Xylocoris flavipes (Reuter), were tested for toxicity against adults of Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.) using a Petri dish assay. Dose-response studies were conducted for each compound singly and in a combination that mimicked the concentrations of these volatiles in exocrine secretions of X. flavipes . Linalool and α-terpineol were toxic to T. castaneum in a dose-dependent fashion, but geraniol and nerol were not toxic during the 24 h bioassay. The mixture of the four compounds was several times less toxic than linalool and α-terpineol for T. castaneum , even when exposed to large amounts. All four terpene alcohols and the mixture were toxic to O. surinamensis , with α-terpineol proving most toxic and linalool the least toxic. Toxic effects of linalool and α-terpineol against O. surinamensis occurred within very narrow ranges, suggesting the possibility of a threshold concentration. Variation in toxicity among similar compounds and between insect species for the same compounds should be examined in studies that assess terpenoids for toxicity against stored-product insects.

Suitability of the maize weevil and angoumois grain moth as hosts for the parasitoids Anisopteromalus calandrae and Pteromalus cerealellae

Two parasitoids, Pteromalus cerealellae (Ashmead) and Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), were compared for their ability to parasitize two important internally‐developing insect pests of stored maize (Zea mays L.). Parasitism by P. cerealellae was greater on Angoumois grain moth, Sitotroga cerealella (Olivier), than on maize weevil, Sitophilus zeamais Motschulsky, in no‐choice experiments. Anisopteromalus calandrae parasitized more maize weevils than did P. cerealellae. The former parasitoid parasitized only a few Angoumois grain moths successfully in maize, but parasitized many in wheat if the hosts were younger than 3 weeks old. Thus, both host age and type of grain affect suitability for parasitism. The effects of parental host (species on which the female developed) and experimental host (species exposed to parasitism) on parasitism rate of P. cerealellae were tested in a host‐switching experiment. Parasitism by parasitoids reared on maize weevils was 23% lower than that of parasitoids reared on Angoumois grain moth. This effect was independent of which host the filial generation of parasitoids was tested on. However, the experimental host species had a much greater effect on parasitoid fecundity than the parental host species. Female progeny had smaller body sizes when emerging from maize weevil than from Angoumois grain moth, which may explain the parental host effect on fecundity. There was also a slight intergenerational effect of host species on parasitoid body size.