Population growth of the khapra beetle,Trogoderma granarium Everts (Coleoptera: Dermestidae) on different commodities

We evaluated the population growth of the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) on different grains, cracked wheat containment categories and amylaceous materials by conducting three series of laboratory bioassays. In the first series, peeled barley, whole (raw) barley, peeled oats, whole (raw) oats, peeled rice, rough rice, rye, triticale and hard wheat were tested. In the second series, six cracked wheat containment categories were tested: wheat containing intact kernels only (0% cracked kernels), wheat containing 5% cracked kernels and 95% intact kernels, wheat containing 10% cracked kernels and 90% intact kernels, wheat containing 25% cracked kernels and 75% intact kernels, wheat containing 50% cracked kernels and 50% intact kernels and wheat containing 100% cracked kernels. In the third series, the following amylaceous commodities were tested: hard wheat (intact kernels), whole oat flakes, maize flour, whole barley flour, pasta, white soft wheat flour, whole soft wheat flour, white hard wheat flour, whole hard wheat flour, whole rye flour and semolina. Significantly more dead adults were found on wheat than on peeled barley, maize, whole oats, rough rice and rye. Significantly more larvae alive were found on wheat and triticale, than on the other grains, with the exception of oats, both whole and peeled. The increase of the percentage of cracked wheat kernels increased population growth, except in the case of 10% cracked wheat kernels. In vials that contained 100% cracked wheat kernels, 584.1 individuals per vial were found, which was 3.7 times more than the respective number of larvae alive in vials with intact wheat kernels only. Significantly more dead adults were found on whole barley flour than on the other commodities. More than 1213 larvae per vial were recorded on whole barley flour, which was 1.3–15 times higher than the other commodities. The lowest number of larvae alive was found on pasta, followed by the white soft wheat flour. The findings of the present work show that some commodities are more prone to spread T. granarium than others, a fact which should be seriously taken into account in international trade of grains and related amylaceous products.     

Developmental and reproductive biology of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) on seven commodities

This study examines the effect of semolina, cracked wheat, maize flour, cracked maize, whole oat flakes, whole barley flour and cracked barley on the developmental and reproductive biology of the saw-toothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). The pest completed its development at all tested commodities except semolina and cracked wheat, while females did not produce eggs on maize flour and cracked barley. The developmental time of larvae was significantly longer when O. surinamensis fed on whole oat flakes (20.3 days) and whole barley flour (19.2 days) compared with maize flour (16.6 days) or cracked maize (17.2 days). The developmental duration of larvae fed on cracked barley (18.3 days) did not differ significantly when fed on cracked maize or whole barley flour, but it was significantly longer compared to maize flour and significantly shorter compared to whole oat flakes. The tested commodities did not affect the pupal development, which ranged between 4.6 and 4.7 days. The highest fecundity was recorded when O. surinamensis fed on cracked maize (4.8 eggs/female) and whole oat flakes (0.3 eggs/female). The tested commodities also affected the risk of death of O. surinamensis and its mean survival time. The shortest survival time was recorded on cracked wheat (11.1 days) while the longest was on cracked maize and whole oat flakes (37.8 and 42.2 days, respectively). The calculation of demographic parameters was feasible only on cracked maize. The net reproductive rate, the intrinsic rate of increase, the finite rate of increase and the mean generation time were 1.48 females/female, 0.01 females/female/day, 1.01 and 37.1 days, respectively. These results may be useful for improving the knowledge on the biology of this species and its potential spread.     

Life history of Trogoderma granarium Everts (Coleoptera: Dermestidae) on peeled barley,peeled oats and triticale

The life history of the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), was investigated on cracked peeled barley, cracked peeled oats and cracked triticale. The results suggest that the biological and demographic parameters of T. granarium are affected by the tested commodities. The developmental time of total immature period of T. granarium was significantly lower on barley (35.06 days) than on oats (42.87 days) and triticale (43.58 days). Mean longevities of adult females were 7.00, 7.89 and 8.24 days, and for adult males were 5.79, 6.05 and 5.49 days when T. granarium fed on barley, oats and triticale, respectively. The highest fecundity recorded when T. granarium fed on barley (39.0 eggs/female) or triticale (35.2 eggs/female), but it was significantly lower when this species fed on oats (25.4 eggs/female). While the net reproductive rate did not differ significantly when T. granarium fed on barley (14.6 females/female), oats 10.2 (females/female) and triticale (11.0 females/female), the mean generation time was significantly lower when fed on barley (40.5 days) than on oats (48.7 days) and triticale (46.1 days). The intrinsic rate of increase of T. granarium did not differ significantly when fed on barley and triticale (0.066 and 0.052 females/female/day, respectively), but it was significantly lower when fed on oats (0.047 females/female/day). The biological and demographic parameters of T. granarium may be incorporated in population models that evaluate the population dynamics aiming to the optimization of management strategies against this noxious species.     

Influence of different non-grain commodities on the population growth of Trogoderma granarium Everts (Coleoptera: Dermestidae)

We investigated the population growth of the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) on seven groups of commercially available non-grain commodities. Six powdered spices were used in the first group of experiments: black pepper, clove, nutmeg, allspice, cinnamon and turmeric. The second group of the tested commodities included seven animal products: powdered cow milk, powdered pork zelatin, sheeps’ wool, goat’s skin, ducks’ feathers, dry dog food and dry cat food. The third group of commodities was consisted of six herbs: oregano, spearmint, basil, coriander, laurel and marjoram. The fourth group of commodities contained ten pulses: chickpeas, lentil, split peas, black-eyed peas, beans, soybean flour and whole kernels, lima beans, mung bean, and broad beans. The fifth group comprised six dried fruits: Corinthian currants, sultanas, banana chips, melons, apricots and figs. The sixth group was consisted of five non-grain commodities: cottonseed cake, tobacco, black tea, Turk kahvesi and potato flour. The seventh group included seven nuts: sunflower seeds, pumpkin seeds, pistachios, roasted chickpeas (yellow), almonds, hazelnuts and walnuts. Finally, six cracked containment categories (0% cracked kernels, 5% cracked kernels and 95% intact kernels, 10% cracked kernels and 90% intact kernels, 25% cracked kernels and 75% intact kernels, 50% cracked kernels and 50% intact kernels and 100% cracked kernels) from five pulses were tested: chickpeas, black-eyed peas, mung bean, soybean and split peas. The highest progeny production (3.01 individuals per vial) was recorded on powdered cow milk. On pistachios, split peas, sunflower seeds, soybean flour, pumpkin seeds, walnuts, almonds and coriander, T. granarium built high population densities rapidly, while on roasted chickpeas, cottonseed cake, hazelnuts, chickpeas, dog food and lentils, its population growth was much less. Broad beans, melons, figs, lima beans, beans, Corinthian currants, pork zelatin and potato flour were less suitable diets for the development of this species. On black pepper, clove, nutmeg, allspice, cinnamon, turmeric, sheeps’ wool, goat’s skin, ducks’ feathers, cat food, sultanas, banana chips, apricots, tobacco, black tea, Turk kahvesi, oregano, spearmint, basil, laurel and marjoram, no progeny production was recorded. The proportion of 100% cracked black-eyed peas or mung beans was more suitable for the population growth of T. granarium. Also, the percentages of 50% cracked chickpeas or 10% cracked soybeans enhanced the development of the species, in comparison with the whole kernels of each pulse. Our study indicated that several non-grain commodities are beneficial for the population growth of T. granarium, a fact that should be seriously taken into account in international trade, as this pest may utilize them as “vehicles” of expansion.     

Effects of developmental stage,cold acclimation and diet on the cold tolerance of three species of Cryptolestes (Coleoptera: Laemophloeidae)

Flat grain beetles (Coleoptera: Laemophloeidae) are common stored-product insect pests in Canada, infesting cereals in grain bins, equipment and end products in flour mills. We studied the cold tolerance of the three most common flat grain beetles: Cryptolestes ferrugineus, Cryptolestes turcicus and Cryptolestes pusillus, by measuring the survival at −10 °C and supercooling point (SCP) for different life stages (egg, young larva, old larva, pupa and adult) reared on flour mixed with brewer’s yeast. Probit analysis was used to estimate the lethal time for 50 and 95% mortality. This was done with non-acclimated individuals (only held at 30 °C) or cold-acclimated individuals (held at 18, 10 and 5 °C, for 1 week/temperature). In general, adults were the most cold-hardy stage for each of the species. Acclimated insects were anywhere from no increase in cold tolerance to 14-fold more cold-tolerant than the corresponding non-acclimated stage and species. Cryptolestes ferrugineus was most cold-tolerant species (58 d at −10 °C to reach 95% mortality for acclimated adult), C. turcicus was the next most cold-tolerant, (39 d) and C. pusillus was the least cold-tolerant (11 d). The cold tolerance of adults reared on three diets was measured both for acclimated and non-acclimated insects. The adults reared on grain diet (whole wheat kernels, cracked wheat kernels and wheat germ (90:5:5 mass ratio) were the most cold-tolerant, adults reared on white-wheat flour and brewer’s yeast diet (95:5 mass ratio) had the next highest cold tolerance followed by the adults reared on 100% white-wheat flour. Supercooling point (SCP) of insects ranged from −20.6 to −26.7 °C. In general, acclimated insects had slightly lower SCP than non-acclimated insects.     

Insecticidal activity of three diatomaceous earths on lesser grain borer,Rhyzopertha dominica F., and their effects on wheat,barley, rye,oats and triticale grain properties

This study aimed to evaluate insecticidal activity of three diatomaceous earths DEs, two originated from Serbia (DE S-1 and DE S-2) and one commercial formulation (Protect-It, Hedley Technologies Ltd. Canada) applied at rates of 0.5, 1.0 and 1.5 g/kg (500, 1000 and 1500 ppm) on Rhyzopertha dominica in wheat, barley, rye, oats and triticale grains and their effects on mass of kernels and several properties: adherence, hectolitre mass, moisture, protein and ash contents. Mortality of R. dominica adults increased with exposure duration and DEs rates. In all tested grains after the longest exposure period (21 days), 1.0 and 1.5 g/kg rates of Protect-It, and 1.5 g/kg rate of DE S-1 and DE S-2 (in barley) caused 95–100% mortality. Offspring reduction of ≥95% was recorded after the application of 1.0 and 1.5 g/kg of Protect-It and 1.5 g/kg of DE S-1. The lowest weight of damaged grain was found after applying 1.0 and 1.5 g/kg of DEs to all grain types, and the highest in rye and wheat treated with 0.5 g/kg DE S-1 and DE S-2, respectively. The highest DEs adherence of 83–95% was detected in wheat, and 87–92% in oats, and the lowest of 71–77% in rye and 59–73% in triticale. All DEs significantly reduced hectolitre mass of all grains, especially Protect-It, 3.6–8.8%. No negative effects of DEs were detected on moisture contents, and the contents of proteins and ashes in the grains. The changes were due to the activity of R. dominica.     

Sorption of ethanedinitrile in fumigated commodities and its impact on efficacy for Rhyzopertha dominica (Coleoptera: Bostrichidae) and Lasioderma serricorne, (Coleoptera: Anobiidae) control

The present study evaluated sorption and desorption of ethanedinitrile (EDN) by different agricultural commodities at 2.6 and 4.8 mg/L during a 24 h fumigation period at 25 Cº. This study also investigated the impact of EDN sorption on the toxic efficacy against the lesser grain borer, Rhyzopertha dominica, and the cigarette beetle, Lasioderma serricorne. Results showed that decrease in the free-headspace concentration of EDN was high in all tested commodities. The concentrations of EDN declined by average levels of 99.8, 98.9, 98.5, 96.2 and 84.3% of the initial applied doses for wheat flour, wheat kernels, pinto beans, corn and tobacco leaves, respectively, at both doses by the end of the 24 h exposure periods. The relationship between the decrease in the free-headspace of EDN concentration over time followed the first order kinetics equation which was described as Ct = 1.77e^−0.183t, Ct = 0.22e^−0.215t, Ct = 2.03e^−0.169t, Ct = 2.59e^−0.136t, Ct = 2.17e^−0.071 at 2.6 mg/L and Ct = 3.32e^−0.179t, Ct = 0.41e^−0.222t, Ct = 3.55e-^0.165t, Ct = 4.42e^0.14t, Ct = 3.87e^0.071t at 4.8 mg/L for wheat kernels, wheat flour, pinto beans, corn and tobacco leaves, respectively. Moreover, we found that sorption of EDN (mg EDN/kg of commodity) by wheat flour, wheat kernels, pinto beans, corn and tobacco leaves was 12.84, 12.57, 12.66, 12.17 and 37.52 mg/kg at 2.6 mg/L, and 23.73, 22.74, 23.33, 22.73 and 69.37 mg/kg at 4.8 mg/L indicating that more than 99.0, 97.0, 98.0, 96.0 and 90.0% of the initial applied doses were sorbed, respectively. Desorption of EDN from the treated commodities after 1 h aeration and during 1 week of observation was very low, ranging from less than 0.016 mg/L for pinto beans to 0.002 mg/L for wheat flour at day 1. Results also showed that sorption of EDN by wheat kernels or wheat flour led to reductions in the insecticidal activity against L. serricorne and R. dominica mixed life stages cultures.     

Synergistic effects of insect-resistant maize and Teretrius nigrescens on the reduction of grain losses caused by Prostephanus truncatus (Horn.)

Prostephanus truncatus is a pest that causes serious losses in stored maize (Zea mays L.) especially in developing countries. This research was conducted to investigate the use of post-harvest insect resistance maize in combination with biological control of P. truncatus by the predator Teretrius nigrescens to reduce maize storage losses. We studied the population dynamics of P. truncatus with and without a predator in combination with susceptible maize and resistant maize to insects under laboratory conditions. This study confirms that P84c3 is a resistant variety against P. truncatus. Maize resistant kernels had a reduction of 30% losses in comparison with susceptible kernels. Significant and favorable interactions were observed between P84c3 maize and presence of T. nigrescens. A dramatic reduction of 80% in progeny number, 81% grain weight loss, and 75% frass production caused by P. truncatus was observed when the predator was used in combination with P84c3. Resistant maize reduced the prey development time and consequently the insect density allowing the predator to control more effectively the population. Prey/predator proportion on resistant maize was significantly higher in comparison with susceptible kernels; thus, giving a more effective pest population control by the predator. These results demonstrated that the combination of post-harvest insect resistance maize with the predator T. nigrescens reduces grain maize losses by P. truncatus.     

Influence of maize kernel state and type on life history of Plodia interpunctella (Lepidoptera: Pyralidae)

The objective of this study was to investigate the influence of different mechanical states (whole, broken and ground kernels) and types (dent, semi-flint and flint) of maize kernels on life history parameters of Plodia interpunctella (Hübner), the Indian meal moth. These parameters included larval development and its dynamics, adult emergence, mean development duration (MDD) and fecundity. Since the larvae are the developmental stage that causes the most damage on maize, additional data on larval development helps identify conditions that promote development. The results of our study indicate that broken maize kernels are the most suitable for P. interpunctella development, where the most successful larval development, the highest number of emerged adults, the shortest MDD and the highest total fecundity were recorded. On the contrary, whole kernels were the least suitable and the most resistant to infestation by P. interpunctella. The type of kernel also significantly affects P. interpunctella developmental parameters. Females reared on flint kernels (the hardest kernel type tested in our study) laid the largest total number of eggs, which implies that kernel hardness, i.e. the type of kernel should be an important parameter when choosing maize hybrids for cultivation and for storage. Our study warrants further investigation of maize types and their susceptibility to P. interpunctella.     

Susceptibility of commercial oat cultivars to Cryptolestes pusillus and Oryzaephilus surinamensis

Susceptibility to two storage insect pests [(Cryptolestes pusillus (Schönherr) and Oryzaephilus surinamensis (L.)] of eight commercial oat cultivars from the United States was determined in laboratory studies. Duration of insect development was shorter and number of progeny produced was greater on cracked than on whole oats. Simulations based on data from the study showed that insect populations would reach the threshold level for treatment in 2-3 months of storage at 30°C on cracked oats. Insect population development was slowest on the hulless cultivar Paul when the oat kernels were cracked. Simulations also indicated that all cultivars of whole oats tested could be stored for at least 1 yr at 30°C without reaching the threshold for treatment when infested with these two species of insects, and insect populations would decrease over time on the cultivars Don, Jerry, Milton, NewDak, Otana, and Valley. Analyses of oat grain quality characteristics, including kernel weight, groat hardness, and groat composition, provided little insight into the mechanism of observed differences in insect development among cultivars. Hardness of the kernels (as indicated by % broken groats after dehulling) may be related to near immunity to these two species of insects in whole Otana. Steaming whole oats to inactivate hydrolytic enzymes in the trichomes of the pericarp did not increase susceptibility to these two species of insects, suggesting that enzymes in the trichomes were not responsible for insect population development being slower on whole oats than on cracked oats. Although we were unable to identify the factors that determined relative susceptibility in this study, the results will be useful for selecting commercial oat cultivars for planting that will be less susceptible to insect pests in storage and suggest that the economics of cleaning oats before storage to reduce insect population growth should be investigated.     

Is the calculation of the gluten content by multiplying the prolamin content by a factor of 2 valid?

Presently, the only essential therapy of celiac disease (CD) is the permanent strict withdrawal of gluten from the diet. With respect to gluten containing foods from wheat, rye, barley, and oats, CD patients have to consume surrogates that must be gluten-free according to the “Codex Alimentarius Standard for Gluten-Free Foods”. The recent “Draft Revised Standard” proposes a gluten threshold of 20 mg per kg gluten-free product. For gluten quantitation, the alcohol-soluble prolamins should be extracted and analyzed by an immunochemical method; the amount of gluten is calculated by multiplying the prolamin content by the factor of 2. To investigate, whether this calculation is valid in any case of contamination of gluten-free products by wheat, rye, barley, and oats, wholemeal or white flours from common wheat, spelt, durum wheat, kamut, emmer, einkorn, rye, barley and oats were analyzed for the ratio of prolamins to glutenins (PROL/GLUT) by a combination of extraction and reversed-phase HPLC procedures. Additionally, different industrial wheat starches were analyzed for their prolamin and total gluten content using different extraction and concentration steps followed by gel permeation HPLC. The results for the cereal flours revealed that the ratio PROL/GLUT was generally higher than 1.0 as proposed by the “Draft Revised Standard” and strongly influenced by cereal species and variety. Common wheat showed the lowest ratio (1.5–3.1), followed by oats and spelt (1.7–3.3), barley (1.4–5.0), durum wheat and kamut (3.1–3.4), emmer (3.5–7.6), rye (6.3–8.2), and einkorn (4.0–13.9). In any case, the gluten content of gluten-free products contaminated with CD activating cereals was generally overestimated, when the prolamin content was multiplied by the factor of 2. In extreme cases, e.g., contamination with rye, the overestimation amounted to 72–79%. Completely different PROL/GLUT ratios were found in ten commercial wheat starches ranging from 0.2 to 4.9. Obviously, the quality of wheat cultivars used for starch production and/or different process parameters, e.g., washing steps, influenced the composition of gluten proteins adherent to starch granules. For wheat starch, the calculation of the gluten content by 2 × PROL may either lead to underestimation (−71% at most) or overestimation (+66% at most). In conclusion, this calculation is invalid; therefore, a future task will be the development of immunoassays with antibodies against all types of storage proteins from wheat, rye, barley, and oats.     

Environmental factors influencing the development and rate of increase of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) on stored maize

Temperature, relative humidity (r.h.), food density, and maize (corn) cultivar (CV) influenced oviposition, development and intrinsic rate of increase of Prostephanus truncatus (Horn). The lower and upper limits for complete development were 25 and 32°C at 40% r.h.; 18 and 37°C, at 70% r.h.; and 20 and 32°C at 90% r.h. The shortest developmental periods were 25.4 ± 0.2 days in ground maize, CV Golden Beauty, at 32°C, 70% r.h., and 24.1 ± 0.2 days in whole kernel maize, CV Pride 1108, at 32°C, 80% r.h. Ground maize at a density of 750 mg/cc promoted rapid development of larvae accompanied by lower mortality and fewer malformed adults than ground maize at a density of 450 mg/cc. P. truncatus laid 430 eggs per female in blocks of maize consisting of 6-cemented kernels during 22 weeks compared with 205 eggs per female in ground maize during 15 weeks, and 36 eggs in loose maize kernels during 4 weeks. Viable eggs were laid at 18°C, 70% r.h., and 32°C, 70–80% r.h. The rate of self-multiplication and the intrinsic rate of increase per week, were: 1.94–2.24 and 0.665–0.806, respectively, at 30–32°C, 70–80% r.h. The highest rate was on field maize, CV Pioneer 3993, at 30°C, 70% r.h. The wide range of temperatures and relative humidities at which P. truncatus can develop in maize favor its establishment in tropical and subtropical regions where maize is grown and stored.     

Pasta preference and ability to penetrate through packaging of Sitophilus zeamais Motschulsky (Coleoptera: Dryophthoridae)

Results of bioassays of the maize weevil, Sitophilus zeamais, on different types of special commercial pasta are reported. The attraction to eight types of pasta was compared: barley and buckwheat, dietetic, egg pasta, gluten-free, spelt and lentils, tricolour pasta (a mixture of semolina, tomato, and spinach), vitamin enriched, and whole wheat semolina. The results obtained demonstrated that adult S. zeamais revealed significant preferences for whole wheat semolina and tricolour pasta, followed by vitamin enriched pasta, egg pasta, spelt and lentils pasta, gluten-free pasta, barley and buckwheat pasta, and dietetic pasta. The ability of S. zeamais to penetrate packages of commercial pasta was also determined using a folded carton box or a plastic pillow pouch with or without gussets. Sixteen types of commercial pasta packages were compared. S. zeamais was found inside packages of barley and buckwheat pasta, durum wheat pasta, egg pasta, five cereals pasta, kamut pasta, rice pasta, spelt pasta, spelt and lentil pasta, tricolour pasta, vitamin enriched pasta, and whole wheat pasta. The adults entered into carton boxes and infested the pasta through openings not well sealed by glue. The large or enlarged air vent micro-holes present on polypropylene pasta packages facilitated the entry of adults.     

Influence of grain type on the susceptibility of different Sitophilus oryzae (L.) populations, obtained from different rearing media, to three diatomaceous earth formulations

Bioassays were carried out to assess whether the commodity, from which adults of the rice weevil Sitophilus oryzae emerged, influences the insecticidal efficacy of three diatomaceous earth (DE) formulations: Protect-It™, PyriSec^® and DEBBM. Protect-It™ is a DE formulation that contains 10% silica gel, while PyriSec^® and DEBBM are enhanced DEs that contain natural pyrethrum and the plant extract bitterbarkomycin, respectively. The S. oryzae populations tested were reared on wheat, barley or maize and the susceptibility of each to the DE formulations was assessed on all three commodities. The DE application doses were: 500 ppm for Protect-It™ and PyriSec^®; 150 and 75 ppm for DEBBM. Mortality of S. oryzae adults was counted 7 and 14 d after their exposure on the treated commodities. Bioassays were carried out at 25 °C and 55% r.h. Barley-reared S. oryzae were the most tolerant of all formulations and treated commodities, whereas maize-reared were the most susceptible ones. DE effectiveness was always lower in maize than in wheat or barley irrespective of the commodity from which the populations were obtained. Furthermore, Protect-It™ and PyriSec^® were more effective than DEBBM in wheat or barley, but not in maize.     

Insecticidal effect of spinetoram against six major stored grain insect species

Spinetoram is a novel insecticide that belongs to the spinosyn class of insecticidal chemicals. The efficacy of spinetoram against numerous insect pest species in a variety of field crops has been well demonstrated. However, there are no data available for the effectiveness of spinetoram against stored grain insects. In the present study, we evaluated spinetoram as a grain protectant, against six stored-product Coleoptera. The species tested were: the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the larger grain borer, Prostephanus truncatus, the confused flour beetle, Tribolium confusum, the granary weevil, Sitophilus granarius and the sawtoothed grain beetle, Oryzaephilus surinamensis. All species were tested at the adult stage, on wheat (or maize in the case of P. truncatus) treated to achieve spinetoram concentrations of 0.01, 0.1, 0.5, 1, 2, 5 and 10 ppm. Mortality was recorded after 1, 2, 7, 14 and 21 d of exposure, and 65 d later the wheat and maize were examined for offspring emergence. Among the species examined, P. truncatus and R. dominica were by far the most susceptible, given that mortality was close to 100% after 7 d on wheat treated or maize with 0.1 ppm of spinetoram. At this concentration, progeny production of P. truncatus and R. dominica was negligible. On the other hand, T. confusum was the least susceptible; mortality reached 95% only at 10 ppm, and only after 14 d of exposure. Similarly, O. surinamensis was of limited susceptibility to spinetoram; mortality reached 95% only after 14 d of exposure on wheat treated with 5 ppm. Nevertheless, offspring emergence of these species was extremely low. For S. granarius and S. oryzae, complete (100%) mortality was recorded after 14 d of exposure, at 0.5 and 1 ppm, respectively. At these concentrations or higher, progeny production was notably reduced. The results of the present study demonstrate that spinetoram is effective as a grain protectant, but its efficacy varies according to the target species, concentration and exposure interval.     

Residual toxicity of a commercial cypermethrin formulation on grains against four major storage beetles

In the present study, we investigated the residual insecticidal efficacy of a commercial cypermethrin formulation applied on grains (wheat, maize) against adults of Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Prostephanus truncatus (Horn) in laboratory bioassays. The insecticide was applied in its label dose on the grains and a bioassay was initiated at the day of application and every month for four consecutive months (5 bioassays in total). In each bioassay, adult mortality levels were determined after exposure for 7, 14 and 21 d. After the final evaluation, all beetles (dead and alive) were removed and the number of offspring was assessed after an additional interval of 65 d. Based on our results, the application of the tested cypermethrin formulation as a grain protectant provided long-term protection against R. dominica and P. truncatus adults, as in most cases complete control was achieved for these two species, even after four months of storage of the treated commodities. In the case of S. oryzae and O. surinamensis, adult mortality did not reach 100% in any of the cases, moreover, a gradual decline of mortality levels was recorded over the 4-month period of storage. Finally, for S. oryzae and P. truncatus progeny production was notably suppressed by cypermethrin. Results show that the cypermethrin formulation tested could be a valuable tool for stored grain protection, however, factors such as the target species and the storage interval should be taken into consideration.     

The biology,ecology and management of the larger grain borer,Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

The invasive larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), originating from Meso-America, is a devastating stored product pest of maize (Zea mays L.) and cassava (Manihot esculenta). This species can destroy up to 40% of stored maize within four months. Despite four decades of research, P. truncatus has spread throughout Africa, while decimating maize and cassava production. Given the continuing problems with P. truncatus, the likelihood for its continued range expansion under climate change, and its status as a species of concern in many countries, the objective of this review was to provide an updated and comprehensive freely accessible record of the distribution and spread, biology, development, and ecology, host preferences, chemical ecology, detection, and monitoring, and management of P. truncatus. We conducted a search of the literature from 1911 to 2021 using Google Scholar and Web of Science to find all papers related to key search terms. We found that P. truncatus has been recorded in 36 countries across the globe, including 21 now in Africa. A recent predictive model found that the insect has been limited to tropical and subtropical regions but could likely spread to temperate regions as temperatures rise with climate change. Conspecifics respond to their two component, male-produced aggregation pheromone early after eclosion, but quickly switch to other cues as older adults. At close-range, P. truncatus may use food cues, but host volatiles are not involved in long-range host finding of commodities. Research on managing P. truncatus has mostly focused on chemical control to the detriment of other tactics, with the most promising tactic likely to be the different hermetic storage technologies. Many outstanding areas of basic behavior and ecology remain to be assessed for P. truncatus. We highlight specific areas that should be prioritized for further work in order to better manage and reduce the impact of this invasive insect pest.     

Evaluation of six insecticides against adults and larvae of Trogoderma granarium Everts (Coleoptera: Dermestidae) on wheat,barley, maize and rough rice

We evaluated the following six insecticides: cypermethrin, deltamethrin, pirimiphos-methyl, silicoSec, s-methoprene and spinosad, that are registered as grain protectants, against adults or larvae of the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) on wheat, barley, maize and rough rice. Three doses were tested: the half of the label dose, the label dose and the double label dose for each insecticide and mortality was assessed after 1, 3, 7 and 14 days (d) post exposure. For parental adults, progeny production was estimated after an additional period of 46 d of exposure. All tested insecticides were able to suppress T. granarium adults, even at the lowest dose. Pirimiphos-methyl and silicoSec were found to be most effective than the other insecticides, as these were the only ones that caused application resulted in 100% mortality at the 7-d exposure interval, at the half label or label dose. Conversely, the majority of the insecticides tested were found to be ineffective against T. granarium larvae. Pirimiphos-methyl was the only insecticide on which larval mortality reached 100% on all commodities tested and by far more effective than the other insecticides. For both adults and larvae, mortalities were generally higher on wheat and barley, than on rough rice and maize, for most of the combinations tested. Our findings indicate that the biological stage (i.e., adults or larvae) and the type of infected commodity should be seriously considered when insecticidal management strategies with cypermethrin, deltamethrin, pirimiphos-methyl, silicoSec, s-methoprene or spinosad are planned against T. granarium.     

PHOSPHORUS AND PHOSPHATE LEVELS IN THE ALEURONE CELLS OF CEREAL GRAINS

The aleurone cells of barley, wheat, rice, rye, oats and triticale contained, comparatively, higher percentages of phosphorus than the aleurone cells of sorghum, maize or millet. The aleurone tissues of barley, wheat and rice had more phosphate than corresponding tissues of sorghum and maize. Phosphate was not detected in the aleurone tissue of maize but was found in trace amounts in the aleurone tissue of sorghum.     

Insecticidal potential of zeolite formulations against three stored-grain insects,particle size effect,adherence to kernels and influence on test weight of grains

Laboratory studies were conducted in order to evaluate the insecticidal potential of three commercially available zeolite formulations against adults of Sitophilus oryzae, Tribolium confusum and Oryzaephilus surinamensis in wheat. For each zeolite formulation, three particle size levels were tested, i.e. 0–50, 0–150 and 0–500 μm. Zeolites were applied at three dose rates, 250, 500 and 1000 ppm, and insect mortality was assessed after 2, 7, 14 and 21 d of exposure. After the final mortality count, dead and alive insects were removed and offspring numbers were determined following an additional period of 65 d. In another series of laboratory bioassays, the effect of zeolite application on the test weight of wheat, maize and barley, as well as the adherence of zeolite particles to wheat, maize, barley and rice kernels was also measured. Oryzaephilus surinamensis was the most susceptible species to zeolite application, regardless of the zeolite formulation, dose and particle size level tested, whereas T. confusum was the most tolerant. No significant differences in efficacy were recorded among the three tested zeolite formulations. At the same time, particle size did not affect zeolite efficacy, at least for the particle size levels tested. All zeolites caused a significant reduction on the test weight of the treated grains. Moreover, zeolite particles showed different adherence among wheat, maize, barley and rice kernels. The results of the present study indicate that zeolites can be used with success as grain protectants, but there is a considerable effect on some physical properties of the grains. This information aims to encourage further evaluation of zeolites as grain protectants.