Uninfested Grain Research Articles

EVALUATION OF THE PROTEIN QUALITY OF BEANS, CORN, AND WHEAT GRAINS INFESTED BY INSECT PESTS

Insect infestation of grains causes several types of damage, including reduced grain weight, heat damage and consequent deterioration, diminished market value, and decreased nutritional value due to grain consumption by insects. The goal of this study was to compare the digestibility, chemical score, protein digestibility corrected amino acid score (PDCAAS), protein efficiency ratio (PER), and net protein ratio (NPR) of infested and uninfested grain flours. This study found that infested grain flours had higher nitrogen contents than uninfested grain flours. The presence of insects did not alter the digestibility of the analyzed grains. However, insects decreased the PER and NPR for beans but not corn and wheat. Similarly, there was a greater reduction in the levels of essential amino acids for beans than for corn and wheat. Insect infestation reduces the nutritional quality of grains, although the type of insect and the grain quality determine the extent of this reduction

Stored-grain insect population commingling densities in wheat and corn from pilot-scale bucket elevator boots

Grain elevator boot and pit areas facilitate the commingling of insects with the grain moving through the elevator leg. A removable boot was developed to facilitate residual grain removal and preservation in the boot and to quantify the commingling magnitude as a function of stored-product insect density. This study included two species that develop inside kernels, Rhyzopertha dominica and Sitophilus oryzae, and three species that develop outside kernels, Tribolium castaneum, Oryzaephilus surinamensis and Cryptolestes ferrugineus. The removable boots were loaded with infested residual grain and remained undisturbed for 0, 8, 16, or 24 weeks (wk). After each time point, uninfested grain was transferred through the infested boot. The adult beetles that commingled with the clean grain were sifted and counted. Further, the commingled lots were examined after 8 wk for adult progeny. The insect densities in the infested bucket elevator leg boots affected the insect densities transferred through the elevator leg to other locations. The insect density in clean wheat or corn transferred over infested boots was 1 insect/kg immediately after transfer, but this density doubled in 8 wk. More internally developing insects were collected by the elevator buckets when the clean grain flowed over the infested grain compared with the externally developing insects. β-Cyfluthrin application as a residual insecticide reduced the insect densities in the elevator boot, which consequently reduced the insect transfer to clean grain. Cleaning the bucket elevator boot area and applying residual insecticide monthly should minimize clean grain contamination.

First Report of Limonomyces roseipellis Causing Pink Patch on Bermudagrass in South China.

Hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) is widely used on golf course putting greens in southern China. In September 2011, circular pink patches ranging from 10 to 20 cm in diameter were observed on putting greens established with cv. 'Tifgreen' on a golf course in Haikou, Hainan Province. There were approximately 50 pink patches on a putting green. Infected leaves were covered with pink, gelatinous fungal mycelium, which resulted in the production of chlorotic lesions. Lesions expanded, became water-soaked, and leaves died basipetally. A pink fungus, characterized by the presence of clamp connections, was consistently isolated from leaves of infected plants on a potato dextrose agar amended with 0.01% gentamicin sulfate. Based on morphological characteristics, the fungus was preliminary identified as Limonomyces roseipellis Stalpers & Loerakker, the causal agent of pink patch of turfgrass (2,3). To verify the identity, the internal transcribed spacer (ITS) of rDNA was amplified and sequenced using primers ITS1 and ITS4. Comparison with sequences in the GenBank database revealed that the ITS sequence (Accession No. KC193592) showed 98% homology with the sequence of L. roseipellis (EU622846). For pathogenicity tests, inoculum was prepared by culturing the fungus on an autoclaved mixture of 100 g of rye grain and 20 ml water for 3 weeks at 25°C. Six-week-old C. dactylon plants in 10-cm pots were inoculated by placing 2 g of infested grain in the center of the turf canopy, or 2 g sterilized, uninfested grain as a control, with four replications of each treatment. After inoculation, pots were covered with translucent plastic bags and placed in a greenhouse at 24 ± 2°C with a 12-h photoperiod (1). After 3 weeks, more than 70% of leaves in the infested pots showed symptoms identical to those observed under natural conditions while control plants remained asymptomatic. The fungus was reisolated from symptomatic plants. To our knowledge, this is the first report of L. roseipellis causing pink patch on hybrid bermudagrass in China.

Effect of insect infestation on the organoleptic characteristics of stored cereals

Two major pests of stored cereals in tropical and subtropical regions of Asia and Africa, Rhizopertha dominica Fabricius and Trogoderma granarium Everts, were used in experiments to investigate the effect of insect infestation on organoleptic characteristics of stored cereals. Infestations were achieved by releasing the two insect species either singly or in mixed populations in samples of wheat, maize and sorghum. These releases resulted in infestation levels of 25, 50 and 75%. ‘Chapatis’ made from infested and uninfested grain flours were evaluated for colour, taste, texture, aroma and appearance by a panel of semi-trained judges. There were no significant differences in the scores for colour, appearance, aroma and texture at all infestation levels for all three cereal grains and the scores also did not differ significantly from uninfested grains. However, at 50 and 75% infestation levels, scores for the taste of chapatis of three cereal grains were significantly ( P < 0.05) lower than uninfested grains. Bitter taste also resulted in poor overall acceptability of chapatis prepared from flours infested at the 50 and 75% levels.

Maize Weevil Control, 1987

Abstract In Test 1, 19 treatments were applied to uninfested grain of‘Across 8363 QPM’ maize (11% moisture) in December 1986. Each treatment consisted of 1.0 kg of grain, divided into 4 replicate batches of 250 g each in pint glass jars (lids ventilated with screen apertures). They were held at 25 ± 1°C and 60-80% RH. Each replicate jar was infested with 50 ± 2 newly emerged, unsexed weevils 10 DAT, and mortality was recorded after a 7-d exposure period. The treatments with high initial mortality were reinfested with 50 ± 2 weevils/jar 3 months after treatment. Treatments giving only partial or no control were maintained with only the initial infestation. Effective treatments were again reinfested at 6 and 9 months after treatment to check on persistence of control. Between intervals, seeds were moved to Poza Rica, Mexico (a humid lowland tropical area), to simulate field conditions. Eleven months after treatment, the percentage of germination (in greenhouse flats, 4-cm soil cover) was determined to assess possible phytotoxic effects on seed and reduction in germination as a result of weevil damage to grain. In Test 2, to simulate the situation of field infested grain, weevils were allowed to feed and lay eggs on 20 kg of‘Across 8363 QPM’ maize grain (12.5% moisture) for 14 d. Then, the same 19 treatments used in Test 1 (1.0 kg grain/treatment split into 4 replicates) were made. At 40 DAT, the number of adult weevils emerged in each treatment was recorded.

Hermetic storage of pearl millet, Pennisetum americanum (L.) Leeke; laboratory studies

The effect of airtight storage of pearl millet, Pennisetum americanum (L.) Leeke, on intergranular atmosphere, insects, mold infection, grain viability and moisture content (m.c.) was investigated in the laboratory. Six hermetically sealed 19-1 cans were used to store millet of three moisture contents (9.9, 12.8 and 15.6%) for 76 days at 27 ± 1°C. One can of grain of each m.c. was infested with 150 adult Sitophilus oryzae L./kg; the others remained uninfested. Carbon dioxide concentrations increased and oxygen concentrations decreased in all cans infested with insects, and in uninfested grain of 15.6% m.c. The changes in atmospheric concentrations were slower in the uninfested grain than in the infested 15.6% m.c. grain. No live insects were found in any treatment, percentages of mold-infested kernels were not significantly different among treatments, and m.c. did not change due to treatment or time. Kernel viability decreased significantly only in the 15.6% m.c. gram. All grain appeared normal; but the 15.6% m.c. grain had a slightly sour odor.

The effect of three species of mites upon fungal growth on wheat.

Every week, for 20 weeks, the growth of naturally occurring grain storage fungi on wheat infested with the three commonest British grain storage mites, Acarus siro, Glycyphagus destructor and Tyrophagus longior, was compared with that on uninfested wheat. The number of colonies of the Aspergillus glaucus group per gram were always less on grain infested with mites than on uninfested grain. Penicillium spp. were also less numerous on grain which was infested with A. siro but did not appear to be affected by the other mites. In contrast, two fungi which are pathogenic to mites, Aspergillus restrictus and Wallemia sebi, were more abundant in the presence of certain mites. The former was associated with G. destructor, the latter with G. destructor and A. siro. The three species of mites either feed on the A. glaucus group and Penicillium spp., or inhibit them by an unknown secretion. Pathogenic fungi are probably avoided. Mites are therefore an important variable in studies on fungal growth during grain drying and storage.

Insect Populations in Wheat, Corn, and Oats Stored on the Farm

One or more live, stored-product insect species were found in 25.1% of the wheat, 56.4% of the oats, and 79.7% of the corn samples obtained from over 8,000 farm storages across 27 states. The average number of insects per 1,000 g in the infested samples was 26 for com, 39 for oats, and 105 for wheat. Insects of the genus Cryptolestes were the predominant pests in wheat and com, and Oryzaephilus surinamenis (L.) was the principal insect in oats. Rhyzopertha dominica (F.) was found throughout much of the grain-producing areas, including the northern states, but Sitotroga cerealella (Olivier) was only rarely detected in farm-stored grain. Plodia interpunctella (Hubner) occurred in 27.6% of the com, but was only an infrequent pest in wheat and was not detected in oats. Insect species that prefer high moisture or feed on molds were found in 28.8% of the corn samples. The incidence of insects generally increased with increased grain moisture, and average test weights per bushel were lower in infested grain than in uninfested grain. The incidence of insects and the composition of insect populations within each commodity did not vary significantly with the length of time the grain had been in storage.

CONTROL OF TYROGLYPHOID MITES IN STORED GRAIN BY THE PREDATORY MITE CHEYLETUS ERUDITUS (SCHRANK).

The authors deal with the problem of mite infestation of stored grain in Czechoslovakia, where more than 10% of the grain is infested by Acarus siro L. and Glycyphagus destructor (Schr.). The methods of mite control hitherto used (fumigants CH3Br, HCN, and ALP) were poor and of short duration. Accordingly, the authors investigated the possibility of biological control using the predacious mite Cheyletus eruditus (Schr.). Some observations showed spontaneous biological control, culminating in the complete eradication of the grain mites. The investigation covered eight grain storages. Details are given of the characteristic course of observations in one grain store, and the results of seven other stores are summarized. In three other stores was studied the influence of cleanliness and moisture contents of grain on the development of mites. The authors found that the mites multiplied on uncleaned wheat (16% moisture content), on cleaned wheat (16% moisture content), and on dry, uncleaned wheat (14% moisture content) in the ratio of 100:10:1.Further details are given about two semioperational trials following the introduction of the predacious mite Cheyletus eruditus (Schr.). These trials were generally successful with the complete eradication of harmful mites.The authors report successful results on the introduction of the predacious mite into uninfested grain destined for long-term storage. They discuss 28 experiments with its artificial introduction (25 successful in biological control) and the course of an operational trial which showed good results as well. Experiences and results from semioperational and operational trials form the basis of a set of technological principles as a guide to practice. It is recommended that the predacious mite be collected from natural biotopes where complete eradication of harmful mites has already been completed. For successful results, the authors recommend artificial introduction in spring or autumn (temperature 5–10 °C) on the surface of grain in the proportion 1:100 to 1:1000 (Cheyletus eruditus Schr.: Acarus siro L. + Glycyphagus destructor Schr.).

A study of the heating of stored grain caused by insects

SUMMARYThe rates of increase of temperature and of population density are calculated for an insulated culture of granary weevils, assuming a Malthusian rate of increase, and basing heat production on respiration rates. This is done first by a step method, but it is shown that the increase in population density can be related to rise in temperature, irrespective of the original density, which makes a short‐cut method possible.The calculations are then modified for the situation in which the culture is embedded in and loses heat by conduction to a bulk of uninfested grain. The spread of heat by conduction is slow; spread by convection is not considered. At I m. from a hot pocket with a steady heat output, the rise of temperature at equilibrium will be less than half the rise at the margin of the hot pocket and only 15% of this rise will be achieved in 4 weeks. The numbers of insects needed to raise the temperature of an infested pocket in a grain bulk are much larger than those required for an insulated culture. The extra time required to reach a temperature is that needed to build up a sufficient population in the original environmental conditions.It is argued that hot pockets increase in size because of the movement of insects induced by high temperatures and by overcrowding, rather than because of spread of heat by conduction. Convection currents cause upward, but not lateral, extension of hot pockets. If sufficient insects are to develop to produce enough heat to cause high temperatures the expansion of a hot spot is necessary, so that small cages of insects cannot be used to induce heating experimentally.Warehouse observations are described to support these predictions. Heating of home‐produced grain in Britain is caused chiefly through storing either grain which is damp and therefore heats, or dried grain which has been insufficiently cooled. Either produces an ideal environment for any stored‐grain insect species.Stored grain should be inspected both to find insects and to measure its temperature and moisture content. Any warehouse containing grain at temperatures above 22° C. and insects should be examined monthly.