Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum du Val (Coleoptera: Tenebrionidae) on stored wheat: influence of dose rate, temperature and exposure interval

Laboratory experiments were conducted in order to assess the insecticidal effect of a diatomaceous earth formulation (Silicosec^®, Biofa GmbH, Germany) against Sitophilus oryzae and Tribolium confusum on stored wheat. Adults of the two species were exposed on wheat treated with diatomaceous earth at four dose rates: 0.25, 0.5, 1 and 1.5 g/kg of wheat, respectively. For each dose rate, the treated wheat was placed at 22°C, 25°C, 27°C, 30°C and 32°C. Dead adults were counted after 24 and 48 h, 7 and 14 d of exposure. After the 14-d interval, the live adults were removed and placed for 7 d in untreated wheat (in the case of S. oryzae) or untreated flour (in the case of T. confusum), and the production of F₁ was recorded. For both species, dose rate, temperature and exposure interval significantly affected mortality (P<0.001). Mortality was higher at longer exposure intervals. The efficacy of SilicoSec against S. oryzae increased with temperature, but for T. confusum mortality was lower at 32°C, compared to 30°C, for 24 and 48 h exposure intervals. Tribolium confusum proved less susceptible to SilicoSec than S. oryzae. In general, the rates of 1 and 1.5 g/kg of wheat provided a satisfactory level of protection against the two species examined. For S. oryzae, F₁ emerged only at 22°C, in wheat treated with 0.25 or 0.5 g/kg. However, for T. confusum, F₁ were recorded at 22°C for 0.5 g/kg and at 22°C, 25°C, 27°C and 30°C for 0.25 g/kg.     

Mortality of Tribolium confusum J. du Val (Coleoptera: Tenebrionidae) in controlled atmospheres at different oxygen percentages

Since the 1990s an ecologically friendly alternative to insecticide treatments for controlling stored-product insect pests has been available: the methods of modified and controlled atmospheres, which involve reducing the quantity of oxygen (O₂) in the air in order to kill insects by anoxia. This study examines the effect of treatments with controlled atmospheres, considering the time necessary to obtain total mortality of insects at percentages of O₂ higher than those normally used in controlled atmospheres and estimating the possible positive influence of a temperature increase in order to compensate for the effects of the reduced anoxia.Adult populations of Tribolium confusum J. du Val were treated at various O₂ percentages (1, 3, 5, 6, 7, 8 and 10%) and temperatures (23, 26, 29, 32, 35, 37 and 40 °C). The relative humidity was very low (<18%) in all the treatments considered.Lethal exposure times varied from less than one day to a week (longer times were not considered).A multiple regression procedure was applied to the experimental data, considering the time necessary to obtain total mortality as the dependent variable. The analysis provided a good fit to the experimental data and indicated a positive correlation with the percentage of O₂ and an inverse one with temperature.     

Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals

Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle, or Tribolium confusum (DuVal), the confused flour beetle, were exposed for variable durations at 36-54 °C. Beetles were placed in laboratory ovens set at a baseline of 27 °C, the temperature was increased by 0.1 °C per minute until the target temperature was achieved, and beetles were then held for specified exposure durations. There was no mortality after initial exposure or after a 1-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 h to 36, 39, or 42 °C. At 45 °C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 h. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 h to 45 °C. There was a sharp increase in mortality after the initial exposures of 4 h at 48 °C; mortality of T. confusum larvae was 90.0±5.7% but was only 10.0±10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 h, and 1-week mortality of beetles exposed for 4 and 8 h was generally greater than initial mortality. At 51 and 54 °C, 2- and 1-h exposures, respectively, killed all life stages of each species. Mortality in conditions of gradual temperature increase was less than previous studies with sudden temperature increases.     

Survival and reproduction of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) following periods of starvation

This study determined the starvation tolerance of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) in terms of both adult survival and reproduction, the impact of starvation on reproduction not having been studied before. Experiments were conducted at 30 °C and 55% or 70% r.h. using a laboratory strain and a field strain of each species. The number of progeny was a better indicator of the impact of starvation on a species than adult survival. Tribolium castaneum was the most tolerant species, requiring up to 35 d starvation before no progeny were produced. Rhyzopertha dominica and S. oryzae required up to 8 d starvation before no progeny were produced. The results suggest that hygiene will have a greater impact on populations of S. oryzae and R. dominica than T. castaneum.     

Efficacy of a volatile formulation of hydroprene (Pointsource™) to control Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae)

Three- and 4-week-old Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed at five different temperature-relative humidity (r.h.) combinations to a volatile formulation of the insect growth regulator (IGR) hydroprene (called Pointsource™). Typical effects associated with IGR exposure, such as arrested larval growth, morphological deformities in adults, twisted and deformed wings, and incomplete adult emergence were produced in both species. Tribolium castaneum and T. confusum were susceptible to Pointsource™, but T. castaneum appeared to be the more susceptible species. More 3-week-old larvae of both species were arrested in that stage compared to the 4-week-old larvae. Nearly all of the 3- and 4-week-old T. castaneum larvae that were able to complete development to the adult stage quickly died after they emerged and were grossly morphologically deformed. In contrast, some emerged adult T. confusum remained alive after they emerged and were not deformed in any manner or had only twisted and incomplete wings. A greater percentage of larvae of both species were arrested in the larval stage and more adults died after they emerged in exposure studies conducted at 32°C, 75% r.h. as compared with 32°C, 30% r.h., but the reverse was true for exposures conducted at 27°C. Pointsource™ appears to have excellent potential for use in controlling Tribolium species within indoor facilities.     

Toxicity of ethyl formate to adult Sitophilus oryzae (L.), Tribolium castaneum (herbst) and Rhyzopertha dominica (F.)

Fumigations were conducted using a continuous flow-through laboratory process to maintain constant concentrations of ethyl formate and low levels (<0.8%) of respiratory carbon dioxide. The procedure minimised the effects of sorption by exposing test insects without media and minimised the effect of carbon dioxide by use of continuous flow. The concentration×time (Ct) products of ethyl formate for adult Sitophilus oryzae, Tribolium castaneum and Rhyzopertha dominica at 25 °C and 70% relative humidity for the 6 h exposure were, respectively: (1) LD₅₀ 107.8, 108.8 and 72.8 mg h L⁻¹ and (2) LD_99.5 207.4, 167.1 and 122.2 mg h L⁻¹. Endpoint mortality was reached within 24 h of initial exposure.     

Impact of physical and biological factors on susceptibility of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) to new formulations of hydroprene

Three separate experiments were conducted to: (1) evaluate two new commercial formulations (202-080 and 202-084) of the insect growth regulator hydroprene, (2) determine residual efficacy of hydroprene-treated concrete stored at different environmental conditions, and (3) assess the impact of accumulated flour on residual efficacy. In the first test, late instars of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed on concrete treated with hydroprene. At 40% relative humidity (r.h.), there was no difference between species regarding the percentage of individuals that stopped development in the larval stage (arrested larvae), but at 75% r.h. there were more arrested T. castaneum than T. confusum in all treatments except the low rate of formulation 202-084. No adult T. castaneum lived after emergence (live adults) at either relative humidity, but the percentage of live adult T. confusum ranged from 1.0% to 41.0%, depending on treatment. In the second test, late instars of T. confusum were exposed at 6 and 12 weeks post-treatment on concrete treated with the two experimental formulations and stored under different environmental conditions. At 6 weeks there was no difference between formulations. At 12 weeks, fewer live adults and more dead emerged adults with gross morphological deformities were found on concrete treated with formulation 202-084 and stored at 32°C, 75% r.h. compared to other treatment combinations. In the final experiment, wheat flour was added to treated concrete for 5 weeks before the bioassays were conducted with late-instar T. confusum. There were few live adults produced in the initial bioassays, and dead adults with gross morphological deformities ranged from 83.1% to 97.6%. However, in bioassays conducted with late-instar larvae at 6 weeks, most adults eventually emerged with few deformities. The presence of the flour apparently compromised residual control and the hydroprene was no longer effective. In summary, the new hydroprene formulations were equivalent to the registered product Gentrol^®. Tribolium confusum was less susceptible than T. castaneum, and residual control of T. confusum on a clean surface without flour lasted about 6-12 weeks.     

Spatial distribution of some beetles infesting a feed mill with spatio-temporal dynamics of Oryzaephilus surinamensis, Tribolium castaneum and Tribolium confusum

Food-bait traps were used to study spatial and temporal distribution of the coleopteran fauna of the first floor of a feed mill in Central Italy. A total of 3396 beetles were captured during the 1-year survey. Beetles were most abundant during July and August and least abundant during February and March. Tribolium confusum du Val was the most abundant and widespread, followed by Oryzaephilus surinamensis (L.), Tribolium castaneum (Herbst), Attagenus brunneus Faldermann, Sitophilus oryzae (L.), and Stegobium paniceum (L.). The spatial patterns of annual catches of these six species were depicted by contour maps. In addition, high catches of O. surinamensis, T. castaneum and T. confusum, allowed construction of contour maps for monthly trap catches. The populations of A. brunneus were located in the bagging, milling, formulation and pelleting sites, and in the area around the conveyer belt. The highest populations of O. surinamensis were in the entry zone of the unloading pit and in the area around the conveyer belt with finished products. Sitophilus oryzae were present near the entry door of the unloading pit room, around the storage bins and in the storeroom. Populations of S. paniceum were found in the unloading pit as far as the conveyer belt and in a corner of storeroom. Tribolium castaneum was limited to a localized area in the room where raw material was processed and in the entry to the unloading pit room. The highest T. confusum populations were located in the milling, formulation and pelleting sites, and near balance and storage bins. Comparison of the spatio-temporal dynamics of these pests showed a segregation of populations, in both time and space, and a strong interaction among species is suggested. On the basis of our results, the spatial and temporal distributions are significantly affected by various factors, such as food availability, processing practices and temperature conditions in different areas.     

Efficacy of diflubenzuron plus methoprene against Sitophilus oryzae and Rhyzopertha dominica in stored sorghum

The efficacy of diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) in sorghum was evaluated in a silo-scale trial in southeast Queensland, Australia. Sorghum is normally protected from a wide range of insects by mixtures of grain protectants. The chitin synthesis inhibitor diflubenzuron was evaluated as a potential new protectant for S. oryzae in combination with the juvenile hormone analogue methoprene, which is already registered for control of R. dominica. Sorghum (ca 200 t) was treated after harvest in 2000 and assessed for treatment efficacy and residue decline during 6.5 months storage. The reproductive capacity of S. oryzae and R. dominica was greatly reduced in bioassays of treated sorghum throughout the trial, and efficacy remained relatively stable during the trial. An initial exposure of S. oryzae adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 80.8-98.8%, but a second exposure of 4 weeks reduced F₁ progeny production by 98.5-100%. In addition, the reproductive capacity of any S. oryzae progeny produced was greatly reduced. Exposure of R. dominica adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 99.6-100%, including a methoprene-resistant strain. The results indicate that S. oryzae or R. dominica adults invading sorghum treated with diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) would be incapable of producing sustainable populations.     

Grain loss caused by Tribolium castaneum, Sitophilus oryzae and Acanthoscelides obtectus in stored durum wheat and beans treated with Beauveria bassiana

The effect of the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Hyphomycete) on the losses caused to durum wheat and beans by storage insects was investigated. Grains were infested with Tribolium castaneum (Herbst), Sitophilus oryzae (L.) and Acanthoscelides obtectus (Say). Beauveria bassiana was produced in inoculated autoclaved rice. The spore formulation (ground rice and B. bassiana) was applied to grain (wheat or bean) and shaken to evenly cover the grain. Adults of T. castaneum or S. oryzae were added to wheat and adults of A. obtectus to bean. Five replicates were set up for each treatment and controls (milled rice but no conidia). The insecticidal effect of B. bassiana was tested by measuring the fresh weight and weight loss of grains after four months of storage. Wheat grains infested with S. oryzae without the conidia was significantly more damaged by weevils than grains treated with B. bassiana. The mean fresh weight of grains with the conidia was significantly greater (18.4%) than the corresponding mean without the fungus when S. oryzae were present. Percentage weight loss decreased by 81.5% and was significantly smaller than the loss from the untreated grain. Significant differences were not found in the fresh weight of seed infested with T. castaneum or A. obtectus in treated or untreated grain nor in the percentage weight loss of grains infested with these insects, with and without B. bassiana.     

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.     

Esterase variation in Tribolium confusum (Coleoptera: Tenebrionidae): genetic analysis of interstrain crosses in relation to malathion resistance

General esterase activity variation among individuals and strains of Tribolium confusum (du Val) is mostly due to a single electrophoretic locus. A strain (CFxlH) selected for very strongly staining isozyme (EST2), was reciprocally crossed with the black mutant laboratory strain (CFbb) which has very weak EST2. EST2 is not linked to the black locus and is inherited as a monogenic, autosomal trait. Similar results were obtained when CFxlH was reciprocally crossed with the sister strain (CFxlL) selected for low activity. Slight deviations from Mendelian expectation in the latter crosses suggest that maternally inherited effects modify EST2 activity in these strains.CFbb and CFxlL both have low EST2 activity, and when intercrossed, all offspring had the EST2L pattern, suggesting that the EST2 loci in the two strains are the same or very tightly linked.Malathion resistance in one strain (MN61) seems to be inherited in a monofactorial fashion, with dominance of the resistant allele. MN61 is fixed for the high-activity EST2 phenotype. Addition of triphenyl phosphate (TPP) synergised the effects of the pesticide, indicating that malathion resistance is due to carboxylesterase activity. CFxlH and CFxlL had similar malathion resistance despite the dramatic difference in EST2 activity: resistance is not due to EST2, the major contributor to the hydrolysis of α-naphthyl acetate (and probably other naphthyl esters).     

Effectiveness of spinosad dust against different European populations of the confused flour beetle, Tribolium confusum Jacquelin du Val

Six populations of the confused flour beetle, Tribolium confusum, obtained from Greece, Italy, Portugal, Denmark, Germany and France were tested for their susceptibility to a spinosad dust formulation, containing 0.125% spinosad. For this purpose, adults and larvae of T. confusum were exposed on wheat treated with two dose rates of the dust formulation, 0.06 and 0.19 ppm of a.i. corresponding to 50 and 150 ppm of the formulation, at 25 °C and 65% r.h. Mortality of the exposed individuals was assessed after 7, 14 and 21 days of exposure on the treated substrate. The increase of dose and exposure interval increased mortality, while adults were more tolerant to spinosad than larvae. Significant differences were noted among populations, for both adults and larvae. The most tolerant to spinosad was the strain from Greece, while the least tolerant were the strains from Germany and Denmark. After 7 days of exposure, on wheat treated with 50 ppm, mortalities of adults of the Greek, German and Danish strains were 2%, 25% and 62% respectively, while the respective figures for 150 ppm were 1%, 31% and 81% respectively. In the case of larvae, of the same strains, mortality at 50 ppm was 6%, 27% and 28% and at 150 ppm 11%, 23% and 40%, respectively. The results of the present study suggest that different strains and stages of T. confusum differ widely in their susceptibility to spinosad-treated wheat.     

Screening of Chinese medicinal herbs for bioactivity against Sitophilus zeamais Motschulsky and Tribolium castaneum (Herbst)

Extracts of 40 species of Chinese medicinal herb from 32 different botanical families were screened for contact, fumigant and feeding-deterrent activities against the two stored-grain insects Sitophilus zeamais and Tribolium castaneum. Thirty Chinese medicinal herbs exhibited insecticidal or feeding-deterrent activities against the two species of insects. Extracts of Artemisia argyi, Dictamnus dasycarpus, Evodia rutaecarpa, Litsea cubeba, Narcissus tazetta var. chinensis, Polygonum aviculare, Rhododendron molle, Sophora flavescens, Stemona sessilifolia, Tripterygium wilfordii, and Torreya grandis were most active.     

Ovarian physiology and age-grading in the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae)

Physiological and morphological changes in the ovarian system in rice weevils, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), reared on wheat seeds were studied as a function of adult age, mating status, and nutrient availability. X-ray analysis was used to determine time of adult eclosion and the duration of development of pre-emergent weevils within the seeds, a process that lasted almost 4 days at 25°C and 60% r.h. There was no follicular differentiation in pre-emergent weevils. Oocyte maturation began after adults emerged from the seeds and started to feed. There was a significant increase in mean germarium length and the size of proximal follicles within the first 5 days when newly emerged weevils were mated and fed ad lib. Maximum number of follicles and mature eggs per ovariole in mated females occurred at 5-30 days of age. The number of mature eggs decreased in 60-days-old weevils, at the same time that adult mortality increased. Development of the ovarian system was much slower in unmated females than in mated females. Although there was follicle development in unmated females, ovulation never occurred and no eggs were laid. Starvation of mated females resulted in a rapid reduction in numbers of follicles and mature eggs, probably as a result of oosorption. Females were categorized into two nulliparous and three parous stages according to ovarian development and the degree of accumulation of follicular relics. Parity was directly correlated with both weevil age and the number of progeny produced and was the physiological basis used to construct an age-grading model for this species. The method will be useful for determining the age structure and reproductive potential of rice weevil populations in the field.     

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.     

Insecticidal activities of aromatic plant extracts and essential oils against Sitophilus oryzae and Callosobruchus chinensis

Methanol extracts from 30 aromatic medicinal plant species and five essential oils were tested for their insecticidal activities against adults of Sitophilus oryzae (L.) and Callosobruchus chinensis (L.), using direct contact application and fumigation methods. Responses varied with plant material, insect species, and exposure time. In a test with a filter paper diffusion method at 3.5 mg/cm², potent insecticidal activity against both species was produced by an extract from Cinnamomum cassia bark, cinnamon (C. cassia) oil, horseradish (Cocholeria aroracia) oil, and mustard (Brassica juncea) oil within 1 day after treatment. Over 90% mortality at 3 or 4 days after treatment was achieved using extracts of Acorus calamus var. angustatus rhizome, Acorus gramineus rhizome, Illicium verum fruit, and Foeniculum vulgare fruit. An extract from Cinnamomum sieboldii root bark gave 100% mortality at 2 days after treatment. At 0.7 mg/cm², extracts from C. cassia, C. sieboldii, and F. vulgare as well as cinnamon oil, horseradish oil and mustard oil were highly effective against both species. In a fumigation test with S. oryzae adults, the oils described were much more effective in closed containers than in open ones, indicating that the insecticidal activity of the oils was attributable to fumigant action. The plant extracts and essential oils described could be useful for managing field populations of S. oryzae and C. chinensis.     

Insecticidal and residual effect of three pyrethroids against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored wheat

Laboratory tests were conducted to assess the use of the pyrethroids, deltamethrin, beta-cyfluthrin and alpha-cypermethrin at the rates of 0.125 and 0.25 ppm, as grain protectants in stored wheat against the rice weevil, Sitophilus oryzae (L.). For this purpose, clean untreated wheat was sprayed with these insecticides and stored for 6 months. During this period, four bioassays were carried out, in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, treated wheat was infested with S. oryzae adults, and dead insects were counted after 1, 2 and 7 d of exposure. In addition, S. oryzae progeny production was estimated on each bioassay, until the production of the F₄ generation. The results indicated that deltamethrin and beta-cyfluthrin, both at 0.25 ppm, were significantly more efficient than the other treatments. Efficacy was notably higher after 7 d of exposure, than after 1 and 2 d. At the same exposure level, 1, 2 and 3.5 months after treatment, at 0.25 ppm, mortality for deltamethrin was approximately 89%, 92% and 86%, respectively, while the corresponding percentages for beta-cyfluthrin were 97%, 83% and 62%, and for alpha-cypermethrin 50%, 49% and 33%. However, at the rate of 0.125 ppm, mortality was ?58% in all cases. In all treatments appearance of F₁-F₄ generations was observed, with the exception of both deltamethrin and beta-cyfluthrin at 0.25 ppm, where only a few F₁ adults were noted, without the production of subsequent generations.     

Insecticidal and antifeedant effects of Junellia aspera (Verbenaceae) triterpenes and derivatives on Sitophilus oryzae (Coleoptera: Curculionidae)

Triterpenes from Junellia aspera (Gillies ex Hook) (Verbenaceae) and chemical derivatives were evaluated for their antifeedant and toxic effects against adults of Sitophilus oryzae (L.). Five triterpenoids were acutely toxic by ingestion. The compounds maslinic acid (II), daucosterol (III), and 3β-hydroxy-12α-bromine-(28→13)-oxide-oleanane (IX) showed the highest toxic effects, while oleanolic acid (I) and oleanonic acid (VII) showed less toxicity. Daucosterol also exhibited important feeding deterrence activity. No toxicity was observed when the assayed compounds were topically applied.     

Survival of Sitophilus oryzae (L.) on wheat treated with diatomaceous earth: impact of biological and environmental parameters on product efficacy

A series of experiments was conducted to evaluate the effects of temperature, relative humidity (r.h.), population density, concentration, exposure interval, and residual aging on susceptibility of Sitophilus oryzae (L.), the rice weevil, to diatomaceous earth (DE). In the first experiment, hard red winter wheat was treated with 300 ppm of the Protect-It™ formulation of DE, and 10, 20, or 30 1-2 week-old mixed-sex adult weevils were exposed on 35 g of wheat for 1 week at combinations of 22°C, 27°C, or 32°C; 40%, 57%, or 75% r.h. No weevils survived when exposed at 40% or 57% r.h., but at 75% r.h. survival was related to both population density and temperature. A higher percentage of adults survived when 30 were exposed compared to 10 and 20, and within each density, survival decreased with increasing temperature. No F₁s were produced at any r.h. on wheat held at 22°C. At 27°C and 32°C, the maximum number of F₁s was produced on wheat held at 75% r.h. In the second experiment, wheat was treated with 25%, 50%, 75%, or 100% of the label rate of 300 ppm, and 10 mixed-sex adult S. oryzae were exposed on 35 g of wheat for either 1, 2, or 3 weeks at 27°C, 57% and 75% r.h. Survival decreased with increasing exposure interval and concentration, but within exposure interval and concentration, survival was usually greater at 75% versus 57% r.h. In the final experiment, wheat was treated with 300 ppm, held at 22°C and 27°C, 57% r.h., and bioassayed at monthly intervals for 3 months by exposing 20 adult mixed-sex S. oryzae on 35 g of wheat for 1 or 2 weeks. At each month, survival of S. oryzae was greater when exposed at 22°C compared to 27°C and when exposed for 1 week compared with 2 weeks. Survival gradually increased with each monthly bioassay, except for those conducted at 3 months. Results of these studies show that S. oryzae is susceptible to DE, but survival of exposed insects will depend in part on the temperature and r.h. humidity (or grain moisture content) at which they are exposed. Survival is directly related to temperature, and as r.h. increases either higher concentrations or longer exposure intervals will be necessary to maintain a certain level of mortality. There may also be a loss of efficacy with residual aging.