Insect-damaged Kernels Research Articles

Competition of three species of Sitophilus on rice and maize.

Laboratory tests were carried out in order to examine competition among three congeneric species on rice and maize: the granary weevil, Sitophilus granarius, the rice weevil, Sitophilus oryzae and the maize weevil, Sitophilus zeamais. For this purpose, a total of 30 adults were placed in vials that contained 50 g or either rice or maize: 30 adults of S. granarius, 30 adults of S. oryzae, 30 adults of S. zeamais, 15 adults of S. granarius+15 adults of S. oryzae, 15 adults of S. granarius+15 adults of S. zeamais, 15 adults of S. oryzae +15 adults of S. zeamais, and 10 adults of S. granarius+10 adults of S. oryzae+10 adults of S. zeamais. After 62 days at 30°C and 65% relative humidity the number of individuals of each species were counted. Insect damaged kernels (IDK), weight of frass and grain weight were measured. When each species was alone, S. granarius had the lowest numbers of adults in both grains, which did not exceed 34 adults/vial, and S. oryzae numbers were always higher than other species. For S. oryzae and S. zeamais, the numbers of adults were considerably higher on rice than on maize. On rice, S. oryzae numbers ranged between 281 and 563 adults per vial, while for S. zeamais between 137 and 372 adults per vial. At the same time, for both species on maize, adult numbers did not exceed 54 adults per vial. The number of S. oryzae adults were constantly higher than the other species in all combinations tested. Moreover, for rice, IDK in the vials that contained S. oryzae, either alone or in combination with other species, was higher than all the other combinations. Similarly, grain weight was lower in the vials that contained S. oryzae compared to the other species combinations. In general, for S. oryzae and S. zeamais progeny production was increased with the increase of the number of the initial adults that had been placed inside the vials. At the same time, progeny production of all three species was not affected by the presence of another species inside the vial. Given that the coexistence of congeneric species in the same stored product ecosystem is often reported, our results highlight some of the inferences that are necessary in order to predict the potential outcome of competition patterns. Apart from its ecological significance, the prediction of the superior species in mixed species communities, can guide and time any control measures, on a more species-targeted basis.

Field evaluation of the long-lasting treated storage bag, deltamethrin incorporated, (ZeroFly® Storage Bag) as a barrier to insect pest infestation

The deltamethrin incorporated polypropylene (PP) bag, ZeroFly® Storage Bag, is a new technology to reduce postharvest losses caused by stored-product insect pests. Maize was pre-fumigated and used for the following treatments: ZeroFly bags filled with untreated maize, PP bags filled with maize treated with Betallic Super (80 g pirimiphos-methyl and 15 g permethrin per liter as an emulsifiable concentrate (EC)), and PP bags filled with untreated maize (control). The experiment was conducted from February–August 2015, at four sites in different locations of the Middle Belt of Ghana. Moisture content (MC), number of live and dead insects, insect damaged kernels (IDK) and maize weight loss data were collected monthly. ZeroFly bags and Betallic treatment significantly reduced insect damage compared to the control treatment. ZeroFly bags were able to keep IDK levels below 5% for 4 months, but the levels increased to 5.2 and 10.2% by 5 and 6 months of storage, respectively. In the control, IDK increased significantly over time and reached 32% after 6 months. The ZeroFly bag was effective against Sitophilus, Tribolium and Cryptolestes species for 4 months. Mean weight loss of ≤3.68% was recorded in ZeroFly bags during 6 months of storage whereas 11.88% weight loss occurred in the PP bags by 6 months of storage. Based on our results, ZeroFly bags were found to have potential for use in the reduction of postharvest grain losses in bagged grains. Maize may still have been infested during bagging hence ZeroFly bags were effective for storage for only 4 months. However, greater benefits of using ZeroFly bags are realized if insect-free grains or legumes are stored in bags.

Efficacy of methoprene for multi-year protection of stored wheat, brown rice, rough rice and corn

Hard red winter wheat, brown rice, rough rice, and corn were treated with the insect growth regulator (IGR) methoprene at rates of 1.25 and 2.5 ppm, held for 24 months at ambient conditions in buckets on the floor of a grain bin, and sampled every two months. Bioassays were done by exposing 10 mixed-sex adults of Rhyzopertha dominica (F.), the lesser grain borer, and Tribolium castaneum (Herbst), the red flour beetle, on wheat, R. dominica and Sitotroga cerealella (Oliver), the Angoumois grain moth, on brown rice and rough rice, and T. castaneum and S. cerealella on corn. Sample size for all commodities was about 80 g, and these samples were held for 3 months at 27°C-60% r.h. Both rates of the IGR completely suppressed adult progeny development of R. dominica with little resulting feeding damage, sample weight loss, or insect damaged kernels (IDK). Some adult progeny production of S. cerealella and resulting IDK occurred at both rates on rough rice, brown rice, and corn, but was far less than in untreated controls. There was little adult progeny production but some feeding damage caused by larval T. castaneum in the treated wheat and corn but again far less than in untreated control. Allowing continual exposure of parental adults on grains treated with an IGR, rather than exposing those parental adults for a short time period, may give more accurate evaluations of residual efficacy. Results show that methoprene used as a grain protectant will give residual control of stored product beetles for 24 months, but complete control of S. cerealella may require inclusion of a contact insecticide.

Effectiveness of Sulfuryl Fluoride Fumigation for the Control of Phosphine-Resistant Grain Insects Infesting Stored Wheat.

A field experiment was conducted in eight 13.6-MT steel bins containing 6.8 MT each of wheat to assess efficacy of sulfuryl fluoride or SF fumigant to control phosphine-resistant and susceptible Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst). Approximately 400 adults of each type of beetle were added to each bin. Additionally, muslin bags containing immature stages and adults, with their respective diets, were also placed in bins. Four bins were fumigated with SF and others were untreated control bins. The SF dosages in treated bins ranged from 1,196–1,467 mg-h/liter. Mortality of adults in each bag was assessed 5 d postfumigation; diet minus adults was incubated in a jar, and number of adults counted after 8 wk. No significant change occurred in number of insect-damaged kernels in SF-treated bins. In trier samples from SF-treated bins, R. dominica numbers declined from 24 prefumigation to 0 at 3- and 6-wk postfumigation; T. castaneum numbers were unchanged. In WBII traps from SF-treated bins, numbers R. dominica and T. castaneum declined from 25 and 33, respectively, prefumigation to 0 or near 0 at 3- and 6-wk postfumigation. Mortalities of resistant and susceptible adult R. dominica, and adult and large larvae of T. castaneum in SF-treated bags was 100%. For all four types of beetles, adult numbers in jars associated with SF-treated bins were 0 or near 0. Results show SF is effective against all life stages of phosphine-resistant R. dominica and T. castaneum, and can be used for phosphine resistance management.

Real-time 3D visualization and quantitative analysis of internal structure of wheat kernels

Food micro-structure plays a crucial role in determining the properties of its end products. Micro X-ray Computer Tomography (CT) provides an excellent tool to assess the internal components of food products non-destructively. This paper describes the 3D visualization and quantitative analysis of the internal features of Canadian Amber Durum Wheat kernel after damage caused by sprouting and insect infestation with Cryptolestes ferrugineus. Micro X-ray CT images were reconstructed and processed using image processing algorithms. Imaging techniques such as segmentation and thresholding were used to render visualization modules such as volume rendering, geometric reconstruction, skeletonization and absolute permeability experiment simulation. In addition to visualization, morphometric parameters such as porosity, anisotropy and absolute permeability were determined in a selected region of interest of the sprout damaged and insect infested wheat kernel. Our data revealed that sprouting damage is first evident in the middle section of the sprouted wheat kernel, and associated with greater porosity than the insect damaged kernel. Insect damage occurred on the bottom of the wheat kernel. Compared to sprout damaged kernels, insect damaged kernels had similar anisotropy. X-ray micro CT is a powerful tool for the non-invasive investigation of damage, and microstructure organization in biological materials such as single wheat kernels.

Comparison of the processing and quality of tortillas produced from larger grain borer Prostephanus truncatus (Horn.) resistant and susceptible maize genotypes

The aim of this research was to compare the processing and quality of tortillas produced from two kinds of larger grain borer (LGB) Prostephanus truncatus (Horn.) damaged kernels: resistant (IRM) and susceptible (ISM) genotypes. The damaged LGB kernels had significant lower test weight, 1000 kernel weigh and density. The ISM kernels were more negatively affected by insects compared with the IRM counterpart. A significant reduction of 5% in starch was observed in IRM kernels but not in ISM counterparts. Flour acidity and protein increased 8-fold and 5%, respectively parallel to an augmentation of weight grain losses whereas the crude fat content significantly reduced by 29%. Insect damage enhanced the penetration of the hot lime solution into the starchy endosperm. Insect infested kernels which lost 10% and 20% of their weight required 34% and 42% less lime-cooking time compared to sound kernels. The 10% and 20% insect-damaged kernels lost 15 and 23% of their solids during storage and tortilla processing, respectively. Finally, LGB damaged kernels reduced substantially the tortilla quality in terms of color.

Bioactivity of raw diatomaceous earth against Rhyzopertha dominica Fab. (Coleoptera: Bostrichidae): Effects of grain type, dose rate and exposure period

Laboratory experiments were carried out to evaluate the efficacy of raw diatomaceous earth (DE) against R. dominica on Maize: Zea mays (L.), sorghum: Sorghum bicolor (L.) (Moench) and wheat: Triticum aestivum (L). The tests were conducted under ambient laboratory conditions (26-34°C and 27-51% r. h.). Thirty adult insects were bioassayed on 50 g grain sample treated with the DE at five dose rates: 125, 250, 500, 1000 and 1500 ppm. Adult mortality, progeny production and percentage of insect-damaged kernels (IDK) were assessed. On all grain tested mortality increased with higher dose rate and longer exposure period. After 14 days exposure to the highest dose rate, adult mortality was 98.0±0.8, 93.2±1.8 and 99.3±0.75% on maize, sorghum and wheat, respectively. Progeny production was considerably suppressed on treated grains in comparison with the untreated respective controls but significantly influenced by grain type. Similarly, the percentage of IDK decreased with increase in dose rate. At 1500 ppm IDK in maize, sorghum and wheat were 1.2±0.5, 2.8±0.5 and 2.2±0.8 % as compared to 54.1±8.6, 45.1±1.8 and 84.1±1.75% in the untreated control, respectively. To provide effective control of R. dominica using the raw DE, dose rates higher than 1500 ppm are required.

Correlation Between Aflatoxin Contamination and Various USDA Grade Categories of Shelled Almonds

The California almond industry is interested in determining if there is a correlation between aflatoxin contamination and almonds classified into various U.S. Department of Agriculture (USDA) grades. A 12 000 g sample was taken from each of 50 lots of shelled almonds. The almonds in each sample were then partitioned into five USDA grades: high quality (HQ), insect damage (ID), mold damage (MOD), mechanical damage (MED), and other defects (OD). Across all 50 samples, kernels in the HQ grade accounted for 83.7% of the kernel mass and 3.2% of the aflatoxin mass. Conversely, kernels in the remaining four damage grades (ID, MOD, MED, and OD) accounted for 16.3% of the kernel mass and 96.8% of the aflatoxin mass. ID kernels had the highest risk for aflatoxin contamination. Almonds in the ID grade accounted for 76.3% of the total aflatoxin mass and 7.2% of the kernel mass. Regression equations were developed to predict the aflatoxin concentration in each 12 000 g sample by measuring the aflatoxin mass in one or more of the four damage grades. Regression equations demonstrated that aflatoxin mass only in the insect damaged kernels was also an effective way to predict the aflatoxin concentration in each 12 000 g sample.

Field incidence of mycotoxins in commercial popcorn and potential environmental influences

Popcorn ear damage by insects and mycotoxin levels in kernels were monitored in several commercial popcorn fields in central Illinois over a 4-year period. Aflatoxin was rare, but fumonisin and deoxynivalenol (DON) were commonly encountered each year, and occurred at mean levels in fields up to 1.7mg/kg (sample max. 2.77mg/kg) and 1.9mg/kg (sample max. 2.66mg/kg), respectively. Neither fumonisin nor DON levels were significantly correlated with the percent of ears with visibly moldy insect-damaged kernels. Significant correlations were noted for the percent of ears with early caterpillar damage and both fumonisin and DON levels overall for some years and at specific sites in other years. Fumonisin levels were generally more highly correlated with insect damage than DON levels. Insect damaged kernels had 100- to 500-fold or greater levels of fumonisin compared to noninsect-damaged kernels, while DON levels were closer to 10- to 30-fold higher in insect damaged versus nondamaged kernels. A high percentage of DON-contaminated kernels were not insect damaged in 2007 and 2008. In some cases, differing mycotoxin levels for the same hybrid and same year planted at different locations appeared to be due to the prior crop. Higher DON levels in 2008 than other years were most likely associated with higher levels of rainfall and cooler temperatures than average during ear fill. While kernel sorters are reported to remove mycotoxin-contaminated popcorn kernels to acceptible levels, consideration of environmental factors that promote mycotoxins in popcorn should result in more effective control measures in the field.

Control of Rhyzopertha dominica in stored rough rice through a combination of diatomaceous earth and varietal resistance

AbstractAdults of Rhyzopertha dominica (F.), the lesser grain borer, were exposed on four varieties of rough rice with Dobie indices of susceptibility of 1.1 to 1.1 (low), and four varieties with Dobie indices of susceptibility of 3.4 to 3.8 (high). The varieties with low and high Dobie indices were classified as resistant and susceptible, respectively, to R. dominica. The purpose of the study was to evaluate control of R. dominica through the use of diatomaceous earth (DE) in combination with rice varieties that were either susceptible or resistant to R. dominica. The rice was treated with varying rates of the commercial DE Insecto®, up to a maximum of 1 000 mg DE/kg of rice. Adult mortality at each application rate of DE was generally greater on three of four resistant varieties compared to three of four susceptible varieties. Progeny production from the parental generation exposed on the rice was also greater in 3 of the 4 resistant varieties compared to 3 of the 4 susceptible varieties at DE rates of 500 mg/kg or more. Progeny production in rice treated with a maximum rate of 1 000 mg/kg DE ranged from 7‐44 adults on the resistant varieties compared to 75‐155 adults on the susceptible varieties. At DE rates of 500, 750, and 1 000 mg/kg, the percentage of insect‐damaged kernels (IDK) was also greater in 3/4 resistant varieties than in the susceptible varieties. Results show combining the use of DE with varietal resistance of rough rice to R. dominica could be used to limit populations of this insect in stored rice and help prevent economic damage.

Impact of differing population levels of Rhyzopertha dominica (F.) on milling and physicochemical properties of sorghum kernel and flour

The effects of different population levels of Rhyzopertha dominica (F.), the lesser grain borer, on physiochemical properties of sorghum kernels and flour, were investigated through a laboratory study at 27 and 32 °C, and 57% relative humidity. Initial population level and temperature, and their interaction, were significant for the number of F 1 progeny and feeding damage ( P<0.01). A strong positive correlation was also found between initial population size, number of F 1 progeny, percentage of insect-damaged kernels (IDKs) and feeding damage. The impact of R. dominica on the milling quality of sorghum was seen through a reduction in abrasive hardness, milling yield, and kafirin content. Initial population and temperature affected most pasting properties, and overall pasting viscosity increased with initial population, number of F 1 progeny, and percentage of IDK at 32 °C. Results show that R. dominica can potentially impact the milling quality of sorghum and also alter the physicochemical properties of sorghum flour.

Kernel-kernel interactions and behavioral responses of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Laboratory kernel-kernel interaction experiments were carried out to assess the influence of mechanically damaged, insect-damaged, and intact maize kernels (conditioned or not) on the behavior of adult maize weevil, Sitophilus zeamais Motschulsky. S. zeamais adults were much more attracted to insect-damaged or conditioned insect-damaged kernels, than by the other two conditioned kernel categories considered. The intact kernels were more attractive than conditioned mechanically damaged kernels, but without significant difference. The “attractiveness” order of the kernel for S. zeamais adults was: insect damaged>intact>mechanically damaged. When fresh mechanically damaged and stored mechanically damaged kernels as well as fresh insect-damaged and stored insect-damaged kernels were compared, significant differences in the attraction of S. zeamais adults were noted.

Efficacy of diatomaceous earth and methoprene, alone and in combination, against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in rough rice

Combination treatments of diatomaceous earth (DE) (Protect-It ®) and the insect growth regulator (IGR) methoprene (Diacon ® II) were evaluated against Rhyzopertha dominica (F.), the lesser grain borer, on stored rough rice. Application rates of DE and methoprene ranged from 0 to 500 ppm and 0 to 1 ppm, respectively, in 25 treatment combinations. Tests were conducted by exposing 20 adults for 2 weeks at 32 °C and 75% relative humidity on single varieties of long-, short-, and medium-grain rough rice, removing adults, and holding the rice for 8 weeks at the same conditions to collect F 1 progeny. In the absence of methoprene, mortality of exposed adults increased as the concentration of DE increased, but even at the highest rate of 500 ppm, mortality was only 57.5±12% and 58.8±9.7% in long and medium-grain rice, respectively, and 26.3±4.7% in short-grain rice. Mortality of R. dominica exposed on short-grain rice was lower than mortality on long-and medium-grain rice at several combinations with 375 and 500 ppm DE. There was also an unexpected increase in adult mortality with the addition of methoprene so that at 1 ppm methoprene and 500 ppm DE, mortality in long-, medium-, and short-grain rice was 77.5±9.0%, 77.5±10.0%, and 58.5±3.0%, respectively. In the absence of methoprene, progeny produced on long- and short-grain rice ranged from 48.0±21.2 to 87.2±9.0, compared to 16.5±5.5 to 33.5±8.6 progeny produced on medium-grain rice. With the inclusion of methoprene there were few progeny produced in any of the treatment combinations, and the overall average was 0.6±0.3. Similarly, with no methoprene the range of insect-damaged kernels (IDK) was 5.2±2.7 to 12.2±3.1%, but with methoprene the overall average was reduced to 1.8±0.2%. While control of R. dominica was somewhat limited with DE, the differences among rice varieties seems to indicate that the specific type and possibly variety of rough rice may influence mortality and reproduction of R. dominica exposed to DE. With methoprene, progeny production was greatly suppressed regardless of DE concentration, but combining DE with methoprene would give some measure of adult control.

Feasibility of impact-acoustic emissions for detection of damaged wheat kernels

A non-destructive, real time device was developed to detect insect damage, sprout damage, and scab damage in kernels of wheat. Kernels are impacted onto a steel plate and the resulting acoustic signal analyzed to detect damage. The acoustic signal was processed using four different methods: modeling of the signal in the time-domain, computing time-domain signal variances and maximums in short-time windows, analysis of the frequency spectrum magnitudes, and analysis of a derivative spectrum. Features were used as inputs to a stepwise discriminant analysis routine, which selected a small subset of features for accurate classification using a neural network. For a network presented with only insect damaged kernels (IDK) with exit holes and undamaged kernels, 87% of the former and 98% of the latter were correctly classified. It was also possible to distinguish undamaged, IDK, sprout-damaged, and scab-damaged kernels.

Detection of stored-grain insect infestation in wheat transported in railroad hopper-cars.

Levels of insect infestation, insect spatial distribution, and the relationship between the number of insect-damaged kernels (IDK) and the number of insects present in grain samples in three-hopper railcars transporting wheat from country elevators to a mill were studied. Six of eight sampled railcars were infested with more than two species of insects. The most abundant species collected were the lesser grain borer, Rhyzopertha dominica (F.), and rusty grain beetle, Cryptolestes ferrugineus (Stephens), with the larval stage of the two species being the most prevalent (>90%). The spatial distributions of these two species within the grain mass were typically clumped in railcar compartments containing >0.4 insect/2.75-kg sample of wheat, and these foci of high-infestation levels varied in compartments within the railcars and among the sampled railcars. There were no significant correlations between IDK and insect density for any of the different stage-specific insect populations that were collected in the grain samples. Mean numbers of immatures and IDK differed among railcars and compartments within railcars, but not among grain depths. Number of insects in the first discharge sample was not correlated with mean numbers of insects in the entire compartment. This indicates that each compartment of a railcar should be sampled to determine level of insect infestation but that sampling at different depths within a compartment is less important.

Detection of Stored-Grain Insect Infestation in Wheat Transported in Railroad Hopper-Cars

Levels of insect infestation, insect spatial distribution, and the relationship between the number of insect-damaged kernels (IDK) and the number of insects present in grain samples in three-hopper railcars transporting wheat from country elevators to a mill were studied. Six of eight sampled railcars were infested with more than two species of insects. The most abundant species collected were the lesser grain borer, Rhyzopertha dominica (F.), and rusty grain beetle, Cryptolestes ferrugineus (Stephens), with the larval stage of the two species being the most prevalent (<90%). The spatial distributions of these two species within the grain mass were typically clumped in railcar compartments containing <0.4 insect/2.75-kg sample of wheat, and these foci of high-infestation levels varied in compartments within the railcars and among the sampled railcars. There were no significant correlations between IDK and insect density for any of the different stage-specific insect populations that were collected in the grain samples. Mean numbers of immatures and IDK differed among railcars and compartments within railcars, but not among grain depths. Number of insects in the first discharge sample was not correlated with mean numbers of insects in the entire compartment. This indicates that each compartment of a railcar should be sampled to determine level of insect infestation but that sampling at different depths within a compartment is less important.

Biotic and abiotic factors limiting efficacy of Bt corn in indirectly reducing mycotoxin levels in commercial fields.

Incidence of insect damage, and association of insect damage with mycotoxigenic corn ear molds and mycotoxins was examined in commercial fields of Bt and non-Bt hybrids of different backgrounds in Illinois in 1998 and 1999. Nearly 50% Helicoverpa zea (Boddie) infestation sometimes occurred in Bt hybrids that express high levels of the protein in silks and kernels. Damage by European corn borer, Ostrinia nubilalis Hübner, was uncommon, even in non-Bt ears. Levels of total fumonisins were generally less (15- to 1.8-fold) in Bt versus non-Bt hybrids at the same site, with some significant differences. There were several instances where there were no significant differences in fumonisin levels between low/no Bt kernel hybrids and Bt hybrids that produced high levels of the protein in the kernel and silk tissue. However, significant correlations were often noted between numbers of insect-damaged kernels and total fumonisin levels, especially in 1998, suggesting in these cases that reducing insect damage was still reducing fumonisin levels. There was variability between the correlation coefficient for numbers of insect damaged kernels and fumonisin levels at different sites for the same year, different hybrids at the same site, and the same hybrid for different years. Although reductions in fumonisins in Bt hybrids were more limited than reported in the past, planting the Bt hybrids still appears to be a useful method for indirectly reducing mycotoxins in corn ears.

Augmentative releases of parasitoid wasps in stored wheat reduces insect fragments in flour

Field studies were conducted to assess the effectiveness of the parasitoid wasp, Theocolax elegans, for reducing insect fragments in flour by suppressing populations of Rhyzopertha dominica in six bins, each containing 27 tonnes of wheat. Beetles were released into all the six bins at monthly intervals for 3 months. Parasitoid wasps were released into three of the bins, 21 days after the first beetle release. Wheat samples from the bins were milled to determine the effects of parasitoid releases on insect fragment counts in flour. In the first year of the study, after 198 days of storage, insect fragment counts were 9.4 and 31 per 50 g flour in the treatment and control bins. However, because of high variability, the means were not significantly different. New grain was used in the second year of the study, and higher numbers of beetles were released. After 131 days of storage, fragment counts averaged 56 and 487/50 g in the treatment and control bins, a reduction in the former of 89%. In the second year of the study, insect myosin in the treatment and control bins averaged 0.27 and 3.23 ng/well, a percentage reduction in the treated bin of 92%. The number of insect damaged kernels (IDK) was significantly lower in the treatment than in the control bins in both years of the study. In the first year, IDK was 6 and 15 IDK/100 g wheat in the treatment and control bins respectively, a reduction in the former of 61%. In the second year, IDK was 12 and 148 IDK/100 g wheat, in the treatment and control bins respectively, a reduction of 92%. This study showed that augmentative releases of parasitoid wasps into bins of stored wheat reduced damage to wheat kernels and the number of insect fragments in flour.

Nitrogen and environmental factors influencing macadamia quality

Applications of nitrogen fertiliser in macadamia orchards remain high, despite indications that optimum yields and quality are obtained at a lower rate. This 6-year study examined the effect on quality of 230, 690 and 1150 g nitrogen/tree . year, applied in April (floral initiation), in April and June (inflorescence development), in April, June and November (rapid nut growth and premature nut drop), in April, June, November and January (nut maturation/oil accumulation) or monthly. Higher rates of nitrogen increased kernel recovery by 1% in 5 years out of 6. In 1 year only, 4 or more split applications of the medium and high rates of nitrogen increased kernel recovery by up to 1.6%. These increases were insufficient to compensate for depressed yields (17% lower) at high nitrogen. In good years, when yields were above average, kernel recovery tended to be high and in years with poor yields, kernel recovery tended to be low except when nuts were small. Moderate summer—early autumn rainfall of about 100 mm/month was associated with high kernel recovery whereas very heavy rainfall (&gt;200 mm/month) during this period was detrimental. The percentage of first grade kernels was influenced most by season but was negatively correlated with the rate of nitrogen. Impurities, including immature, deformed, mouldy and insect-damaged kernels, were lowest at low rates of nitrogen and highest during wet harvest seasons. Time of nitrogen application had no significant effect on yield, kernel recovery, the percentage of first-grade kernels or impurities. For sustained high yield and quality, 355 g nitrogen, or 0.8 kg urea/tree.year, applied in April—June is indicated. Agronomic and economic advantages of reducing rates of nitrogen applied to macadamia orchards are enhanced by increasingly important environmental considerations. Multiple regression analyses indicated that the rate, strategy and timing of nitrogen application, rainfall, temperature, flushing and litterfall were correlated with kernel recovery and first-grade kernels but more work is needed to elucidate the significance of these factors.

Pirimiphos-Methyl and Thiabendazole Impact on the Quality of On-Farm Stored Shelled Corn

A study was conducted to examine the ability of Actellic® (pirimiphos-methyl, ICI Americas, Wilmington, DE), an organophosphorous insecticide, and Mertect® 340-F (thiabendazole, Merck and Co., Inc., Rahway, NJ), a benzimidazole fungicide, to preserve the quality of shelled corn stored for an extended duration in metal grain bins. Treatments included application of pirimiphos-methyl, thiabendazole, pirimiphos-methyl and thiabendazole combined, and untreated control. Corn samples of 0.3 liter were taken bi-monthly with a deep-bin cup probe and kept frozen until processed. Quality parameters examined included total insect contaminants (numbers of insects and insect fragments), numbers of insect-damaged kernels, percent fines, and numbers of kernels with visible fungal growth. Suppression of insects and fungi by Actellic or Mertect was evident, but the overall quality of the corn was not consistently improved by their application.