Efficacy of filter cake and Triplex powders from Ethiopia applied to wheat against Sitophilus zeamais and Sitophilus oryzae

The efficacy of filter cake and Triplex powders applied to wheat was evaluated in the laboratory against the maize weevil, Sitophilus zeamais Motschulsky and rice weevil, Sitophilus oryzae (Linnaeus)—two most common insect pests associated with stored grain in Ethiopia. Efficacy of these powders was determined by exposing 20 adults of each species to 100 g of wheat treated with 0, 100, 500, 700 and 1000 mg/kg of filter cake and Triplex. Adult mortality was determined 7 and 14 d after exposure. In addition, adult progeny production, percentage of insect damaged kernels, and percentage of grain weight loss at each species-powder-concentration-time combinations were determined after 42 d. The 7 and 14 d mortality was 100% for adults of both species exposed to 1000 mg/kg of filter cake; only the 14 d mortality of Sitophilus species was 100% for adults exposed to 700 mg/kg. Mortality of S. oryzae adults was 100% when exposed for 14 d to1000 mg/kg of Triplex. Mortality of S. zeamais never reached 100% in any Triplex treatments. Adult progeny production of S. zeamais was completely suppressed at filter cake concentrations of 700 and 1000 mg/kg, whereas 1000 mg/kg was necessary for complete suppression of S. oryzae adult progeny production. Complete suppression of adult progeny production was not observed in any Triplex treatments. Complete reduction in percentage of insect damaged kernels and percentage of grain weight loss were obtained when S. zeamais and S. oryzae adults were exposed to 1000 mg/kg of filter cake; similar reductions with S. zeamais occurred only at 1000 mg/kg of Triplex. In the case of S. oryzae, complete reduction of insect damaged kernels and grain weight loss were not achieved at any concentration of Triplex. These powders can be used as alternatives to chemical insecticides for management of Sitophilus species.     

Effectiveness of spinosad and spinetoram against three Sitophilus species: Influence of wheat endosperm vitreousness

The influence of wheat endosperm vitreousness on the effectiveness of spinosad and spinetoram against lab populations of Sitophilus granarius, Sitophilus oryzae (from Serbia) and Sitophilus zemais (from Serbia and Slovenia) were evaluated in a laboratory conditions. Characteristics of two test wheat varieties were determined, i.e. a variety with high (HVWG) and another with low (LVWG) endosperm vitreousness. Spinosad and spinetoram were applied at the doses of 0.5, 1 and 2 mg/kg (ppm) to both wheat varieties. Mortality was assessed after 7, 14 and 21 days, while impact on progeny production/reduction PR (%) was assessed after 8 weeks. All doses of spinosad applied to the HVWG variety and 1–2 mg applied to the LVWG variety achieved high mortality (93–100%) of S. granarius after 14 days, while high mortality of the other test species (97–100%) was achieved by 1–2 mg doses on the HVWG and 2 mg on LVWG varieties. After 14 days, all doses of spinetoram achieved high mortality (96–100%) of S. granarius on both wheat varieties, while high mortality of S. oryzae (97–100%) and both populations of S. zeamais (93–100%) was achieved using 1–2 mg doses on the HVWG and 2 mg dose on the LVWG variety. The highest S. granarius PR (>90%) was found in both wheat varieties treated with 2 mg/kg of spinosad or spinetoram, while the highest PR of S. zeamais was observed in HVWG treated with 2 mg/kg of spinosad and 1–2 mg/kg of spinetoram, and in LVWG treated with 2 mg/kg of spinetoram. The greatest PR (91–94%) of S. oryzae in both wheat varieties was observed only in grain treated with 2 mg/kg spinetoram. In general, endosperm vitreousness was found to influence the effectiveness of spinosyns to all Sitophilus species, especially their doses not causing high mortality.     

The use of modified atmospheres to control Sitophilus zeamais and Sitophilus oryzae on stored rice in Portugal

This study reports the efficacy of using CO₂ against Sitophilus zeamais and Sitophilus oryzae as an alternative treatment to fumigation for rice stored in a rice mill in Portugal. The trials were conducted in a silo containing 40 tonnes of polished rice and in four hermetic big bags of 1 tonne capacity; two with paddy and two with polished rice. The composition of the atmosphere ranged from 90 to 95% CO₂ and 0.7–2.1% O₂. Three trials were carried out at different temperatures and treatment times; stored rice in the silo at 29.6 ± 0.1 °C for 26 days (first trial), at 34.1 ± 0.2 °C for 10 days (second trial), and in big bags at 22 °C for 26 days (third trial).To evaluate the efficacy of each treatment, metal cages with 16 g of infested rice where placed at bottom, middle, top and surface of the polished rice in the silo. Four replications of each type of infested rice containing one-week-old S. zeamais adults, or eggs of S. zeamais or S. oryzae, were incubated in the laboratory, at the same temperature as in the silo, to serve as a control.In all modified atmosphere treatments adults of S. zeamais, and eggs of both S. oryzae and S. zeamais, showed mortality close to 100% and no F1 emergence was recorded in any treatment sample. This was the first time that a Portuguese rice mill used modified atmospheres.     

Evaluation of Carifend® for the control of stored-product beetles

In the present study, the effectiveness of Carifend® (BASF AG, Ludwigshafen, Germany), an alpha-cypermethrin-coated net, was evaluated in laboratory tests against major stored-product insects. The insecticide-treated net was adjusted at the bottom of plastic petri dishes, and adult insects were placed in each dish and exposed for different exposure intervals (1, 3, 5, 7 and 14 days), after which mortality and knockdown was measured. The tests were carried out against a wide spectrum of stored-product insects, i.e. Sitophilus oryzae, Sitophilus granarius, Sitophilus zeamais, Oryzaephilus surinamensis, Tribolium castaneum, Tribolium confusum, Prostephanus truncatus, Rhyzopertha dominica and Cryptolestes ferrugineus. The results showed that O. surinamensis, R. dominica and P. truncatus were highly susceptible to Carifend®, as complete control was achieved for all three species, after 5, 14 and 5 days, respectively. Regarding Sitophilus species, S. zeamais was the most tolerant species, as mortality levels did not exceed 46%, even after 14 days of exposure. In contrast, S. oryzae and S. granarius mortality was >98% after 14 days of exposure. So far, Carifend® has been registered in many parts of the world for the protection of stored tobacco against major tobacco pests, i.e. Lasioderma serricorne and Ephestia elutella. However, our results clearly indicate that this net can be used effectively for the control of other stored-product insects that infest durable food, such as grains and related amylaceous commodities.     

Effects of flameless catalytic infrared radiation on Sitophilus oryzae (L.) life stages

A laboratory benchtop flameless catalytic infrared emitter was evaluated against all life stages of the rice weevil, Sitophilus oryzae (L.), an insect species associated with stored wheat. The emitted infrared radiation was in the 3-7 μm range. A non-contact infrared thermometer measured grain temperatures continuously during exposures of infested wheat. Insect mortality was a function of the final grain temperature attained. In general, higher grain temperatures were attained when using 113.5 versus 227.0 g of wheat, and at 8.0 cm from the emitter versus 12.7 cm, and during a 60 s exposure versus a 45 s exposure. Complete mortality of all life stages of S. oryzae was achieved at 8.0 cm from the emitter using 113.5 g of wheat, with a 60 s exposure; the mean grain temperatures attained ranged from 108.4 to 111.8 °C. The log odds ratio tests showed that eggs (0 days old) were the least susceptible stage to infrared radiation, followed by adults within kernels (28 days old), pupae (24 days old), young larvae (7 days old), larvae that were 14-21 days old, and adults (42 days old). These data using small amounts of grain indicate infrared radiation from the flameless catalytic emitter to be a viable option for disinfesting wheat containing various life stages of S. oryzae.     

Responses of phosphine susceptible and resistant strains of five stored-product insect species to chlorine dioxide

Adults of phosphine susceptible laboratory strains and phosphine resistant field strains of five stored-product insect species were exposed in vials with 0 or 10 g of wheat for different time periods to 0.54 g/m³ (200 ppm) of chlorine dioxide gas. After exposure, adult mortality was determined 5 d later at 28 °C and 65% r.h. The 5-d mortality was 100% in laboratory and field strains of the red flour beetle, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); lesser grain borer, Rhyzopertha dominica (F.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.) that were exposed in vials with 10 g of wheat to chlorine dioxide for 26, 16, 24–34, 18–24, and 15–18 h, respectively. Corresponding exposure durations for these species and strains in vials without wheat were 15, 3, 18–20, 7–15, and 5–7 h, respectively. Dosages of chlorine dioxide producing 99% mortality (LD₉₉) of T. castaneum, O. surinamensis, R. dominica, S. zeamais, and S. oryzae strains in vials with wheat ranged from 14.79−22.57, 8.20–8.41, 15.79–21.60, 10.66–14.53, and 7.67–12.20 g-h/m³, respectively. In vials without wheat, corresponding LD₉₉ values for T. castaneum, R. dominica, and S. zeamais strains were 6.51–8.66, 11.46–23.17, and 5.79–10.26 g-h/m³, respectively. LD₉₉ values for O. surinamensis and S. oryzae could not be computed, because of 100% mortality after a 3–5 h exposure to chlorine dioxide. No adult progeny production of T. castaneum and O. surinamensis was observed after 8 weeks in control and chlorine dioxide-exposed samples. Adult progeny production of Sitophilus spp. was found only in the control samples. The dosage for 99% adult progeny reduction relative to control for R. dominica strains ranged from 10.07 to 18.11 g-h/m³. Chlorine dioxide gas is effective in killing phosphine susceptible and resistant strains of five stored-product insect species and suppressing adult progeny production of three out of the five species.     

Progress towards a lure to attract three stored product weevils, Sitophilus zeamais Motschulsky, S. oryzae (L.) and S. granarius (L.) (Coleoptera: Curculionidae)

The behavioural responses of Sitophilus granarius, S. oryzae and S. zeamais to synthetic 4S,5R-sitophinone alone and in combination with volatiles from kibbled carob have been investigated with a view to the development of a single lure to attract all three species. Sitophilus zeamais and S. oryzae were shown to respond to 4S,5R-sitophinone at amounts as low as 0.025 ng. Sitophilus granarius gave a significant response to 50 ng 4S,5R-sitophinone. Volatiles from kibbled carob were also shown to attract all three species. This is the first time that attraction of S. zeamais and S. oryzae to carob volatiles has been demonstrated. Fresh lures containing 4S,5R-sitophinone and carob volatiles attracted significantly more insects in pitfall bioassays for all three species than when either component was used alone. However, after 6 weeks a significant increase in response compared to the control was found only for S. oryzae and S. zeamais. The effect of insect age on response to the pheromone and carob volatiles was also studied for all three species. The response to carob volatiles decreased with increasing insect age for all three species. A significant response to 4S,5R-sitophinone was found only for 1-2-day-old adults of S. oryzae and S. zeamais but for all ages tested of S. granarius. The effect of the combination of pheromone and carob volatiles also decreased with increasing insect age.     

Influence of medium and physical disturbances during rearing on development and numbers of Sitophilus progeny

Four Sitophilus populations (Sitophilus zeamais Motschulsky from Mexico, S. zeamais from Arkansas, U.S.A., Sitophilus oryzae L., and Sitophilus granarius L.) were studied. Hard red winter wheat, sorghum, and maize were used to determine effects of rearing media on progeny production of insects from the four populations.Mechanically disturbing infested samples to remove newly-emerged adult weevils every 48 hr reduced numbers of progeny surviving to the adult stage, especially for Arkansas S. zeamais and S. granarius reared in any of the three grains.With one exception, reproduction for all populations in all three grains was highest when parents were reared in wheat; other differences are discussed. Also, progeny developmental periods for all four populations were shortest when parents were reared in wheat. Progeny of all four populations had the longest developmental periods when reared in maize regardless of the medium in which their parents were reared.In 250 g samples of wheat, and 125 g samples of sorghum, 50 parent S. oryzae produced statistically as many progeny as in 500 g and 625 g samples of wheat and 250, 500, and 625 g samples of sorghum, respectively. In maize, 625 g samples produced significantly more progeny than 500 g samples.Sex ratios of progeny from each grain were 1:1, except that females of S. oryzae reared in maize outnumbered males.     

The effectiveness of low temperature (5 °C) on Sitophilus oryzae (L.), Sitophilus zeamais (Motch.) and Sitophilus granarius (L.) in wheat grain: The impact of pre-acclimation

Laboratory trials were conducted in wheat grain to assess the effectiveness of low temperature (5 °C), applied at intervals of 5, 7, 9, 11, 20, 25, 30 and 35 days (d), as a control measure for stored product insect pests of the genus Sitophilus, and compared the results with the impacts of 7 d pre-acclimation at 15 °C and non-acclimation. Mortality was determined after 1, 2 and 7 d of recovery in the laboratory at 25 ± 1 °C and 60 ± 5% r. h., while progeny were assessed 7 weeks later. Acclimation had the strongest impact on S. oryzae after 5 d exposure to 5 °C and 7 d recovery, while the same effect on S. zeamais was shown after 20 and 25 d of exposure and 1 d recovery, and the same impact on S. granarius occurred after 30 and 20 d of exposure and 1 and 7 d recovery, respectively. Low temperature was found to be the most effective against S. oryzae, and the least effective against S. granarius. Mortality was high (≥96%) in both S. oryzae test groups after 11 d of exposure and 7 d recovery, S. zeamais mortality was high (>97%) after 35 and 30 d of exposure and 2 and 7 d of recovery, respectively, and S. granarius mortality was ≤87% in all test variants. Total reduction (100%) of non-acclimated S. oryzae, S. zeamais and S. granarius progeny required 8, 25 and 30 d of exposure to 5 °C, respectively, while acclimated weevils required 11, 30 and 30 d, respectively.     

Rice cultivars affect fitness-related characteristics and digestive physiology of the rice weevil,Sitophilus oryzae (L.) (coleoptera: Curculionidae)

The rice weevil, Sitophilus oryzae (L.), is one of the main pests of rice and other stored grains. Due to the negative effects of synthetic pesticides on the environment and non-target organisms, more environmentally benign alternative control techniques are needed for controlling pests. In the present study, the development, reproduction, and digestive enzyme activity of Sitophilus oryzae (L.) were evaluated on 12 rice cultivars under laboratory conditions [28 ± 1 °C, 60 ± 5% RH, and a photoperiod of 16:8 (L: D) h]. Among tested rice cultivars, the developmental time of S. oryzae immature stages was the shortest on DomSiah (33.0 days), Hashemi var. Guilan (34.0 days) and Hashemi var. Mazandaran (34.0 days) and the longest on Neda (44.5 days). The highest fecundity was recorded for beetles reared on cultivars DomSiah (316.8 eggs), Hashemi var. Mazandaran (301.1 eggs), and Hashemi var. Guilan (293.3 eggs); and the lowest for beetles reared on cultivar Neda (147.0 eggs). The highest survival of immature stages was recorded on cultivars Hashemi var. Mazandaran (80.0%), AliKazemi (75.2%), DomSiah (73.6%), and Hashemi var. Guilan (71.0%) whereas those on cultivar Neda (25.3%) had the lowest survival. The female adults that developed from larvae reared on cultivars Neda, Govhar, and Fajr had the lowest body mass (67.7, 68.6, and 69.4 mg). Also, the males’ mass was the lowest on cultivars Neda, Fajr, Shiroudi, and Govhar (60.7, 62.2, 62.9 63.3 mg, respectively). The adults developed from larvae reared on cultivars Fajr and Neda had the lowest levels of α-amylase activity (1.77 and 1.64 mU/min/individual, respectively). Also, those reared on cultivar Neda had the lowest levels of protease activity (0.067 OD/min/individual). Results suggest cultivar Neda, as an unsuitable food for S. oryzae development that negatively affects the amylolytic and proteolytic activity of this pest, could be considered in the integrated management programs of this pest.     

Effectiveness of insecticide-incorporated bags to control stored-product beetles

Adults of seven stored-product beetle species were exposed on the inside and outside surfaces of polypropylene polymer bags incorporated with the insecticide deltamethrin (approx. concentration of 3000 ppm; ZeroFly^® Storage Bags (3 g/kg). Beetles were exposed for 60, 120, and 180 min, and 1, 3 and 5 days on the same treatment arenas, and after the 5 d interval the insects were removed and placed in untreated arenas for 5 more days. All Trogoderma variable (Ballion), the warehouse beetle, Prostephanus truncatus (Horn), the larger grain borer, Rhyzopertha dominica (F.), the lesser grain borer, and Tribolium castaneum (Herbst), the red flour beetle, were knocked down on the outside and inside surfaces of the bag after one hour of exposure. Mortality of T. variable, P. truncatus, and R. dominica increased during the exposure period, with generally lower mortality on the inside versus the outside of the bag after either 3 or 5 days of continual exposure. However, maximum mortality of T. castaneum, the red flour beetle, was only 5.6 ± 3.4% after 5 days of exposure. While it took longer for 100% knockdown of Sitophilus oryzae (L.), the rice weevil, compared to the above species, all S. oryzae were dead after 5 d of exposure on both surfaces. In contrast, after 5 days knockdown of Sitophilus zeamais (Motschlulsky), the maize weevil, did not exceed 30% and there was no mortality. After the Sitophilus species were transferred to untreated arenas, knockdown of all species decreased and mortality increased, indicating delayed mortality and no recovery from knockdown. Mortality of Dermestes maculatus (DeGeer), the hide beetle, did not exceed 5.6% at any time and there was no delayed mortality, indicating a potential tolerance of this particular strain of D. maculatus used in the study. Our results show that the ZeroFly^® Storage Bags could effectively limit penetration of stored-product beetles through the bag into stored grains or milled grain products.     

Fumigant toxicity of essential oils from three Thai plants (Zingiberaceae) and their major compounds against Sitophilus zeamais, Tribolium castaneum and two parasitoids

Fumigant toxicity of essential oils from rhizomes of Alpinia conchigera, Zingiber zerumbet, Curcuma zedoaria and their major compounds; camphene, camphor, 1,8-cineole, α-humulene, isoborneol, α-pinene, β-pinene and terpinen-4-ol was investigated with adults of Sitophilus zeamais, Tribolium castaneum, Anisopteromalus calandrae and Trichogramma deion larvae. The last two insects are parasitoids commonly used to control stored-product weevils and moths. The trial was evaluated at 0, 37, 74, 148, 296, 444, 593 μL/L in air after 12, 24 and 48 h for S. zeamais, T. castaneum and A. calandrae, and 24 h for T. deion. Alpinia conchigera oils were toxic to S. zeamais, T. castaneum and T. deion, while the other two plant oils had low toxicity. Adults of S. zeamais and T. castaneum were more susceptible to A. conchigera oils than their eggs, larvae or pupae. Sitophilus zeamais adults (LC₅₀ 85 μL/L in air) were slightly more tolerant of A. conchigera oils than T. castaneum (LC₅₀ 73 μL/L in air) after 48 h exposure. Synthetic essential oils, a mixture of pure compounds in the same ratios of the extracted essential oils, were tested with S. zeamais and T. castaneum adults. Synthetic essential oils were more toxic than the extracted essential oils to both insects. Zingiber zerumbet oils (LC₅₀ 26 μL/L in air) and C. zedoaria oils (LC₅₀ 25 μL/L in air) were significantly more toxic to adults of A. calandrae than A. conchigera oils (LC₅₀ 37 μL/L in air) whereas T. deion larvae were more sensitive to A. conchigera oils (LC₅₀ 62 μL/L in air) than Z. zerumbet and C. zedoaria oils (LC₅₀ > 593 μL/L in air). Tribolium castaneum was more susceptible than S. zeamais to the eight pure compounds. Terpinen-4-ol was highly toxic to both insects.     

DNA identification of two laboratory colonies of the weevils, Sitophilus oryzae (L.) and S. zeamais Motschulsky (Coleoptera: Curculionidae) in Taiwan

DNA amplification fingerprinting (DAF) and nuclear ribosomal DNA (nrDNA) amplification were used to discriminate between two laboratory colonies of two closely related species of weevils: the rice weevil, Sitophilus oryzae (L.), and the maize weevil, S. zeamais Motschulsky. For DAF, three sets of primers (aldolase, prolactin receptor, and interleukin-1β) were used for identification by polymerase chain reaction (PCR) and agarose gel electrophoresis, and the highly similar patterns of the resultant amplicons reconfirmed that the two weevils are closely related. The fragments of nrDNA amplification showed that for S. oryzae and S. zeamais, the homologies of the nucleotide sequences of the internal transcribed spacer regions, ITS-1 and ITS-2, were unusually high, at 96% and 97%, respectively. Based on the ITS-1 and ITS-2 sequences, two species-specific primer sets were designed: with the primer set ITS3/So, the predicted 450 bp DNA fragment was yielded with S. oryzae genomic DNA after PCR amplification (n=10), but no PCR product was obtained with S. zeamais (n=10); with the primer set ITS3/Sz, the same 10 S. zeamais specimens yielded a 550 bp DNA fragment, but S. oryzae yielded no amplicons. In view of the difficulty of distinguishing between these two closely related species, the specificity and availability of these two primer sets might prove to be a useful tool for distinguishing between them. However, the nrDNA sequences of the ITS-1 and ITS-2 regions of geographically isolated populations of both weevils still need to be elucidated, and the applicability of this technique to different geographical populations will need to be confirmed by further study.     

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle (Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth (Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil (Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil (S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.     

Molecular techniques for the detection of granary weevil (Sitophilus granarius L.) in wheat and flour

The granary weevil (Sitophilus granarius L.) is a stored grain pest that causes major economic losses. It reduces the quantity and quality of the grain by its feeding and excretion. Sequences of S. granarius mitochondrial cytochrome oxidase subunits genes mtCOI and mtCOII were analysed and compared with mtCOI/II sequences available in GenBank. The analysed genes displayed a high level of homology between corresponding subunits. Attempts were undertaken to develop detection methods for contamination by S. granarius in wheat and wheat flour based on the molecular biology techniques: standard and real-time polymerase chain reaction (PCR) with a TaqMan® molecular probe. (TaqMan probes are dual-labelled hydrolysis probes) Specific primers designed based on available sequences for mtCOI and mtCOII genes were applied and optimal reaction conditions established. The specificity of both methods was studied by using a species closely related to S. granarius: S. oryzae and S. zeamais. It is shown that the sensitivity threshold was very high?–?we were able to detect the equivalent of one beetle per 100 kg of flour when the real-time PCR with TaqMan probe method was applied to model samples. The primer sets used turned out to be species specific, and the technique was rapid, reliable and very sensitive.     

Influence of rearing medium on size and weight of adults of four Sitophilus populations and on weight loss of host kernels (Coleoptera: Curculionidae)

Four populations of Sitophilus (S. zeamais Motsch. from Mexico, S. zeamais from Arkansas, U.S.A., S. oryzae (L.) and S. granarius (L.) were studied. Hard red winter wheat (“Cloud” variety), brown commercial sorghum, and yellow and white “dent” maize (mixed varieties) were used to determine the effect of parent-and progeny-rearing media on the adult elytron length in each population. Kernel weight loss caused by individuals of each population and weevil weights were determined.Elytron lengths of S. oryzae progeny were significantly (P < 0.05) but only slightly longer, when parents were reared in wheat rather than sorghum or maize; otherwise parent-rearing medium had no effect. Progeny-rearing medium, not parent size, was most responsible for differences in elytron lengths. S. granarius progeny from wheat were significantly larger than those from maize or sorghum; progeny from all other populations were significantly larger from maize than from wheat or sorghum.S. oryzae caused less weight loss in kernels of wheat and sorghum, and were significantly lighter (P < 0.05) than other insects. The Arkansas S. zeamais was significantly heavier than Mexican S. zeamais in wheat, otherwise their weights were similar. Weight losses (actual and percentages) of kernels of all grains were similar for Arkansas S. zeamais and Mexican S. zeamais. S. granarius were heavier and produced greater weight loss in wheat kernels than other populations did.     

Electrophoretic analysis of amylase isozymes in geographical strains of Sitophilus oryzae (L.), S. zeamais Motsch., and S. granarius (L.) (Coleoptera: Curculionidae)

Electrophoretic analysis of adult intestinal tracts indicated that two strains of Sitophilus oryzae (L.) (Japan and Tanzania-90) lacked the major α-amylase isozyme present in 12 other geographical strains. Amylase zymograms of adults of 17 strains of Sitophilus zeamais Motschulsky were not only different from those of S. oryzae but showed significant between-strain variation. Strains of S. zeamais could be arranged into approximately four groups based on isoamylase patterns. There was no apparent correlation between geographical origin or culture diet and isoamylase pattern within these groups. One strain of Sitophilus granarius (L.) (3SG) had an additional minor isozyme not present in five other strains of this species. Although the biological or functional significance of the wide strain to strain variation in isoamylase patterns of S. zeamais has yet to be determined, the qualitative and quantitative differences in amylases between these weevil species indicate these enzymes may be useful chemotaxonomic markers. In addition to differences in amylase composition, there was significant strain variation in weights of wheat-fed weevils from each species.     

Development of resistance in stored grain pest,Trogoderma granarium (Everts) against deltamethrin and its effective control by synergistic toxicity of bifenthrin and chlorpyrifos

The current investigation was conducted to estimate the resistance level against deltamethrin in fourth and sixth instar larvae of Trogoderma granarium collected from wheat storage warehouses of Dera Ghazi Khan (DGK), Okara (OKR) and Gujranwala (GUW). Results showed that the fourth and sixth instar larvae of collected strains warehouses moderately resistant to deltamethrin compared with the same developmental stages of insecticide susceptible laboratory strain (LAB-S). Efficacies of bifenthrin, chlorpyrifos and their various combinations were analyzed against fourth and sixth instar larvae of different strains of pest populations to minimize the development of resistance against deltamethrin. LC_50s of bifenthrin against fourth and sixth instar larvae of all the four populations were recorded at low concentrations compared to deltamethrin. The LC₅₀ values of bifenthrin against fourth instar larvae of LAB-S, DGK, OKR and GUW populations were 359.32, 416.58, 524.01 and 598.91 ppm, respectively, while these values were 204.30, 262.98, 301.89 and 355.22 ppm against sixth instar larvae of those populations, respectively. Chlorpyrifos was found to be the most effective insecticide compared to bifenthrin and deltamethrin. The LC₅₀ values of chlorpyrifos were 189.33, 305.37, 376.30 and 459.15 ppm against fourth instar larvae of LAB-S, DGK, OKR and GUW populations, respectively, whereas for sixth instar larvae those values were 98.24, 129.61, 163.43 and 230.74 ppm, respectively. Various combinations of bifenthrin and chlorpyrifos viz., 1:1, 2:1, 3:1, 1:2 and 1:3 were also tested. Based on the values of LC₅₀ and relative toxic unit, 1:3 combination was observed as the most effective among all combinations. The LC₅₀ values of fourth instar larvae of all the four populations against each insecticide and their combinations were recorded at high concentration compared to that of sixth instar larvae. Results of current investigation need to be considered in present stored grain insect pest control program of warehouses in Punjab¹.     

Assessment of eight rice cultivars flour for feeding resistance to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is an important pest of processed stored grains worldwide. Study of life history, feeding efficiency and digestive function of an insect on different host cultivars can indicate their resistance for the insect's population increase. Due to the economic importance of T. castaneum on stored rice flour, this research was aimed to investigate the life history, feeding indices and digestive enzymatic activity of T. castaneum on flour of eight rice cultivars (Ali-Kazemi, Dom-Siah, Fajr, Gilaneh, Gohar, Hashemi, Khazar, and Neda). A delay in the developmental time of T. castaneum was detected on cultivar Gohar. The lowest fecundity and egg fertility were observed on cultivar Gohar. Feeding indices of fourth instar larvae were the lowest on cultivars Gohar and Neda. The amylolytic activity of fourth instar larvae was the highest on cultivars Hashemi, Dom-Siah, Ali-Kazemi and Gilaneh, and the lowest on cultivar Gohar. Also, the highest and lowest proteolytic activities of fourth instar larvae were on cultivars Khazar and Hashemi, respectively. Significant correlations were detected between tested parameters of T. castaneum with starch and protein value of examined cultivars flour. The results of cluster analysis indicate that Dom-Siah, Hashemi and Ali-Kazemi are relatively susceptible cultivars, and other tested cultivars, especially Gohar, are relatively resistant cultivars for feeding of T. castaneum. The resistant rice cultivars could be further evaluated to identify secondary biochemicals that contribute to T. castaneum resistance.     

Repellency and attractancy of plant extracts against Plodia interpunctella and Sitophilus zeamais

Plodia interpunctella and Sitophilus zeamais are among the most destructive insect pests of stored processed food products. The use of natural materials rather than conventional pesticides to control these pests is a promising alternative to conventional neurotoxic insecticides. In this study, we tested organic extracts from 13 species of plants; most showed different effects on S. zeamais and P. interpunctella. Eleven of the extracts had repellent effects on S. zeamais but either an attractant effect or no effect on P. interpunctella. These results suggested that different species of insects have different reactions to plant extracts, and such extracts may have applications as storage products to prevent infestation by both P. interpunctella and S. zeamais.