Granary Weevil Sitophilus Granarius Research Articles

Acceptance and utilization efficiency of a purple durum wheat genotype by Sitophilus granarius (L.)

The granary weevil (Sitophilus granarius L.) is a major primary pest of stored cereals throughout the world. Among the major classes of plant secondary metabolites, flavonoids can affect insect feeding behaviour and their growth rate. In this study, the susceptibility of an anthocyanin-rich purple durum wheat genotype (T1303) to the granary weevil was evaluated in comparison with two yellow durum (Ofanto) and bread (Mec) wheat varieties. The feeding response and food utilisation efficiency by adult insects was also investigated by calculating nutritional indices in whole flour disk bioassays. Different levels of susceptibility to granary weevil emerged among genotypes tested. The mean food consumption by an insect, F1 progeny, and female parental offspring calculated for the T1303 genotype were significantly lower than those of yellow kernel wheat varieties. Moreover, T1303 genotype induced deterrence in the adult insects as demonstrated by the positive values of the food deterrence index. Besides, relative grow rate and efficiency conversion of ingested food indices were negative for T1303 and positive for both yellow wheat varieties indicating respectively a decrease and an increase of insect body weight during the bioassays. Finally, a higher mortality rate was recorded for insects fed on T1303 flour disks compared to disks obtained from yellow wheat varieties. These results provide evidence for the antifeedant and toxic effects of anthocyanins present in the T1303 pericarp against the granary weevil. Overall, this study contributes new insights into the mechanisms of host acceptance and food utilization by S. granarius and would be useful to identify antifeedant flavonoids as well as to develop varietal resistance-based strategies against this pest.

Effectiveness of some plant oils and Malathon 1% dust against the coleopteran beetles the rice weevil Sitophilus oryzae(L). and the granary weevil Sitophilus granarius.

Effectiveness of some plant oils and Malathon 1% dust against the coleopteran beetles the rice weevil Sitophilus oryzae(L). and the granary weevil Sitophilus granarius.

Impact of Short-Term Atmospheric Heat Transfer on the Survival of Granary Weevil in Stored Winter Wheat

The granary weevil Sitophilus granarius L. is a pest causing substantial damage to stored wheat worldwide, against which the elaboration of sustainable control methods has recently been gaining importance. Our objective was to assess the efficacy of a rapid atmospheric convection heat transfer method against S. granarius under laboratory conditions. We examined the changes in adult mortality and progeny survival triggered by heat and the effect of this on the quality parameters of treated wheat items. The insecticidal efficacy, achieved by the treatment of infested grains, was also analyzed at 37, 47, 67, 87, and 107 °C for 5, 6, and 7 min under 40% and 60% rh exposure to atmospheric heating with the progeny production assessed 45 days after the treatment. The quality parameters of the treated wheat were analyzed by a germination test and NIR grain analysis. Our findings showed that adequate eradication of S. granarius was obtained at 107 °C for 5 min of exposure under suboptimal (40% rh) relative humidity values. At 60% relative humidity, mortality averages were more dispersed, and efficacies above the expected 95% occurred over longer exposures. The progeny-suppression effect from short-term heating was affirmed. The atmospheric convection heat transfer method, under the applied temperature and exposure time combinations, did not induce detectable changes in the quality parameters or the germination ability of the treated wheat. Overall, our findings indicated that the use of short-term heating for the post-harvest protection of cereals is feasible, which may contribute to the realization of residuum-free pest management and provide an effective and sustainable technique in integrated pest management.

The Correlation between Volatile Compounds Emitted from Sitophilus granarius (L.) and Its Electrophysiological and Behavioral Responses.

The granary weevil Sitophilus granarius (L.) is one of the most serious primary insect pests of stored products. When S. granarius present in grains, various volatile organic compounds are released as chemical signals which can be used to detect the insects. In this study, volatile chemical compounds released from S. granarius were analyzed using the headspace solid phase micro-extraction (HS-SPME) coupled with gas chromatography (GC)-mass spectrometry (MS) techniques. Two key compounds, 3-hydroxy-2-butanone and 1-pentadecene, were identified from mixed gender of S. granarius adults at high density. Moreover, both male and female adults showed dose-dependent electroantennography (EAG) responses to 3-hydroxy-2-butanone. In behavioral assays, S. granarius was attracted to 3-hydroxy-2-butanone at 0.001 µg/10 µL but repelled at 10 µg/10 µL or higher. S. granarius was consistently repelled by 1-pentadecene at concentrations at 0.001 and 1000 µg/10 µL. 3-hydroxy-2-butanone and 1-pentadecene have considerable potential to offer in the development of new approaches for the monitoring and management of this destructive stored grain insect pest.

The modes of action of Mentha arvensis essential oil on the granary weevil Sitophilus granarius revealed by a label-free quantitative proteomic analysis

Although synthetic pesticides are still used to control insect pests, greater efforts have been made to develop healthier and more environmentally friendly pesticides. Because of their insecticidal properties, botanical essential oils (EOs) are considered as promising alternatives to the use of synthetic insecticides. However, little is known about mechanisms underlying the insecticidal activity of most these natural compounds. In the present study, we evaluated the contact toxicity and the modes of action of the EO from Mentha arvensis against the granary weevil, Sitophilus granarius L. (Coleoptera: Curculionidae), a cosmopolitan insect pest that causes extensive damage to stored cereals. M. arvensis EO caused high contact toxicity in S. granarius adults, resulting in a rapid paralysis and rapid alteration of walking behavior. Our label-free quantitative proteomics approach revealed that M. arvensis EO induced dramatic physiological changes in exposed insects. The majority of the differentially expressed proteins (DEPs) were upregulated and are related to the development and functioning of the muscular and nervous systems, cellular respiration, protein synthesis, and detoxification. These results suggest that M. arvensis essential oil is capable of affecting a variety of biological processes, and shed light on the repair mechanisms put in place in surviving insects to counter the damage inflicted. This work opens new perspectives on the proposed mechanisms of insecticidal activity of a promising EO for controlling pests of stored cereals and may represent a first step in the development of novel bio-rational insecticides.

Effects of Different Infra-Red Irradiations on the Survival of Granary Weevil Sitophilus granarius: Bioefficacy and Sustainability.

Simple SummaryThe granary weevil Sitophilus granarius is a cosmopolitan insect that causes substantial damage to many stored products. Control methods based on the use of sustainable, residual insecticide-free methods are gaining importance due to their features such as bioactivity, biodegradability, and ecological safety. However, despite the finding that different irradiation methods have proven efficacious, infrared treatment has not gained widespread application, as different aspects of its application have not yet been explored. In this study, we evaluated the activity-inducing and mortality effect profile of infrared irradiation on S. granarius. The impact of the distance between the radiation emitter and the treated material on the mortality rate was tested in search of optimal results. Adult-perishing and progeny-suppressive effects caused by infrared irradiation in S. granarius were confirmed. Our results point out that the efficacy of treatment depends on the optimal distance between the treated specimen and the emitter. Information on adult-activity triggered by radiation facilitates the application of other control methods and the optimization of their timing. In summary, our findings indicate that the use of infrared irradiation for the post-harvest protection of cereals is feasible, which can contribute to the realization of endeavors aimed at environmentally friendly and residuum-free pest management.Sitophilus granarius (L.) is an important pest of stored grain worldwide. In recent years, sustainable methods against it have received attention as grain stock protective means. Our aim was to obtain information about the efficacy of infrared irradiation (IR) against S. granarius in laboratory conditions. The change in adult-activity and median lethal dose (LD50) triggered by IR in S. granarius was examined. The insecticidal efficacy in the infested grains was also analyzed at 12, 24, 48, and 72h following exposure to IR (250W), and the progeny-production was assessed 45 days upon the treatment. Based on our findings, total mortality ensued in a grain stock of 50 g at 412 s and a for 100 g grain at 256 s. A significant increase in S. granarius mortality could be observed in the higher grain weight regime, which can be accounted for by the higher heat-absorbance of objects with higher weight. The activity of pests immediately after the beginning of IR increased and subsequently became moderated. The observation of activity-peak brought about by irradiation contribute to the optimization of chemical intervention. This treatment could provide an effective and sustainable technique in integrated pest management.

Insecticidal Activity of 25 Essential Oils on the Stored Product Pest, Sitophilus granarius.

The granary weevil Sitophilus granarius is a stored product pest found worldwide. Environmental damages, human health issues and the emergence of resistance are driving scientists to seeks alternatives to synthetic insecticides for its control. With low mammal toxicity and low persistence, essential oils are more and more being considered a potential alternative. In this study, we compare the toxicity of 25 essential oils, representing a large array of chemical compositions, on adult granary weevils. Bioassays indicated that Allium sativum was the most toxic essential oil, with the lowest calculated lethal concentration 90 (LC90) both after 24 h and 7 days. Gaultheria procumbens, Mentha arvensis and Eucalyptus dives oils appeared to have a good potential in terms of toxicity/cost ratio for further development of a plant-derived biocide. Low influence of exposure time was observed for most of essential oils. The methodology developed here offers the possibility to test a large array of essential oils in the same experimental bioassay and in a standardized way. It is a first step to the development of new biocide for alternative management strategies of stored product pests.

Insecticidal Action of Several Isolates of Entomopathogenic Fungi against The Granary Weevil Sitophilus granarius

The insecticidal virulence of various entomopathogenic fungal isolates retrieved from soil samples was tested on adults of the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae). Bioassays were carried out in the laboratory where experimental adults were sprayed with 1 mL of conidial suspension (108 conidia/mL) from each isolate. Mortality was recorded at 7, 14, and 21 days after exposure. Mean mortality, mean lethal time, survival, and hazard effect were estimated for each isolate. Two isolates of Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae), one isolate of Aspergillus insuetus (Bainier) Thom & Church (Eurotiales: Trichocomaceae) and Metarhizium anisopliae (Metschinkoff) Sorokin (Hypocreales: Clavicipitaceae) resulted in the highest mortality (97–100%). The isolates with both the highest hazard effect and the lowest survival rate were Aspergillus sp. and M. anisopliae. Our results indicate that entomopathogenic fungi have the potential to become a very useful tool in reducing chemical applications in storage facilities.

Reproductive isolation due to prezygotic isolation and postzygotic cytoplasmic incompatibility in parasitoid wasps.

The reproductive barriers that prevent gene flow between closely related species are a major topic in evolutionary research. Insect clades with parasitoid lifestyle are among the most species‐rich insects and new species are constantly described, indicating that speciation occurs frequently in this group. However, there are only very few studies on speciation in parasitoids. We studied reproductive barriers in two lineages of Lariophagus distinguendus (Chalcidoidea: Hymenoptera), a parasitoid wasp of pest beetle larvae that occur in human environments. One of the two lineages occurs in households preferably attacking larvae of the drugstore beetle Stegobium paniceum (“DB‐lineage”), the other in grain stores with larvae of the granary weevil Sitophilus granarius as main host (“GW‐lineage”). Between two populations of the DB‐lineage, we identified slight sexual isolation as intraspecific barrier. Between populations from both lineages, we found almost complete sexual isolation caused by female mate choice, and postzygotic isolation, which is partially caused by cytoplasmic incompatibility induced by so far undescribed endosymbionts which are not Wolbachia or Cardinium. Because separation between the two lineages is almost complete, they should be considered as separate species according to the biological species concept. This demonstrates that cryptic species within parasitoid Hymenoptera also occur in Central Europe in close contact to humans.

Molecular and cytogenetic differentiation within the Lariophagusdistinguendus (Förster, 1841) species complex (Hymenoptera, Pteromalidae).

Several strains of the apparently well-known cosmopolitan synanthropic parasitoid of coleopteran stored-product pests, Lariophagusdistinguendus (Förster, 1841) from Western Europe, were studied using DNA sequencing and chromosomal analysis. The presence of at least two cryptic species with different COI sequences and chromosome numbers (n = 5 and 6) was supported. The species with n = 6 is associated with the drugstore beetle Stegobiumpaniceum (Linnaeus, 1758), whereas the other one with n = 5 mostly develops on the granary weevil Sitophilusgranarius (Linnaeus, 1758). A phylogenetic study revealed that the karyotype with n = 6 represents an ancestral character state in this complex. Consequently, the chromosome set with n = 5 which is characteristic of a particular internal clade, apparently originated via chromosomal fusion which was probably preceded by a pericentric inversion. If this is true, inverted chromosome segments could accumulate a number of genetic loci responsible for certain interspecific differences.

Bluefume (HCN) and EDN ® as fumigation alternatives to methy bromide for control of primary stored product pests: Presentation

The presented paper provides preliminary results on the fumigation potential of two preparations: Bluefume (HCN - hydrogen cyanide) and EDN®. (Ethane-dinitrile). Their biological efficacy was tested on Granary weevil (Sitophilus granarius; Curculionidae; Coleoptera) as a primary stored product pest in the Czech Republic. In fumigation chamber, we tested temporal survival of various S. granarius strains following exposure of a dose of 9 g.m-3 HCN (Bluefume). We compared differential sensitivity of one laboratory (i.e. sensitive) CRI-strain and 9 field strains collected from the Czech stores and mills. The HCN Ct products required to kill the tested S. granarius strains ranged from CTp= 30.5 g.m-3.h-1 to CTp= 51.7 g.m3.h-1. The efficacy of EDN (30 g.m-3) on various developmental stages S. granarius was tested in a fumigation chamber. No live individual of S. granarius belonging to any life stage was recorded following 18 hours of EDN exposure.

Twelve years (2005-2017) of scientific and professional work in the field of stored products pests protection in Slovenia:

Scientific and professional work in the field of stored products pests protection in Slovenia began in 2005, when we tested the efficacy of entomopathogenic nematodes against the granary weevil (Sitophilus granarius) and the sawtoothed grain beetle (Oryzaephilus surinamensis) adults under laboratory conditions. In 2007, we participated as partners in the project SEE-ERA.NET “Development of a non-toxic, ecologically compatible, natural-resource based insecticide from diatomaceous earth deposits of South Eastern Europe to control storedgrain insects pests” (coordinated by C. Athanassiou), and we thus became acquainted with the research work in the field of investigation the efficacy of diatomaceous earth in controlling beetles from the Sitophilus genus. We have continued the research of different aspects of diatomaceous earth (the influence of geochemical composition and abiotic factors on its efficiency, the effects of individual and combined application, the effects on various harmful insect pests, etc.). In search for comparable substances to diatomaceous earth (regarding the efficacy), we have studied insecticidal effects of quartz sand and entomopathogenic nematodes from Slovenia, plant powders and essential oils on various harmful beetles. In the recent years, our research work has been mainly dedicated to studying the efficacy of wood ash and zeolites as natural insecticides, which have demonstrated sufficient efficiency in suppressing Sitophilus beetles. In the same period, we studied the seasonal dynamics of the Indian mealmoth (Plodia interpunctella), the Mediterranean flour moth (Ephestia kuehniella) and the Angoumois grain moth (Sitotroga cerealella) in cereal stores, where we were also searching for possible indigenious natural enemies of stored product insects pests. We have confirmed the occurrence of two parasitoids, Anisopteromalus calandrae and Dibrachys microgastri. In 2017, we have organized the 11th Conference of the IOBC/wprs Working Group on Integrated Protection of Stored Products (Ljubljana, 3-5 July), which was attended by 136 participants from 25 countries. We also transfer knowledge to Slovenian agricultural specialists about the harmfulness and possible ways of controlling stored products insects pests. In 2014, we have organized a workshop on this topic (“From Technological Maturity to Storing of Cereals and Legumes“). In 2015, we have hosted C. Athanassiou as an invited lecturer at the 12th Slovenian Conference on Plant Protection with international participation in Ptuj. In recent years, we have been working with experts from other countries with the aim of studying the efficacy of environmentally acceptable insecticides (spinosad, spinetoram) and the influence of cereal production technologies on grains’ susceptibility to attack by Sitophilus beetles. Furthermore, we participate in the research regarding the efficiency of new formulations of insecticidal preparations. The paper presents the chronology of activities in this area of our work.

Comparative cytogenetics and derived phylogenic relationship among Sitophilus grain weevils (Coleoptera, Curculionidae, Dryophthorinae).

Cytogenetic characteristics and genome size are powerful tools for species characterization and identification of cryptic species, providing critical insights into phylogenetic and evolutionary relationships. Sitophilus Linnaeus, 1758 grain weevils can benefit from such tools as key pest species of stored products and also as sources of archeological information on human history and past urban environments. Moreover, the phylogenetic relationship among these weevil species remains controversial and is largely based on single DNA fragment analyses. Therefore, cytogenetic analyses and genome size determinations were performed for four Sitophilus grain weevil species, namely the granary weevil Sitophilus granarius (Linnaeus, 1758), the tamarind weevil S. linearis (Herbst, 1797), the rice weevil S. oryzae (Linnaeus, 1763), and the maize weevil S. zeamais Motschulsky, 1855. Both maize and rice weevils exhibited the same chromosome number (2n=22; 10 A + Xyp). In contrast, the granary and tamarind weevils exhibited higher chromosome number (2n=24; 11 A + Xyp and 11 A + neo-XY, respectively). The nuclear DNA content of these species was not proportionally related to either chromosome number or heterochromatin amount. Maize and rice weevils exhibited similar and larger genome sizes (0.730±0.003 pg and 0.786±0.003 pg, respectively), followed by the granary weevil (0.553±0.003 pg), and the tamarind weevil (0.440±0.001 pg). Parsimony phylogenetic analysis of the insect karyotypes indicate that S. zeamais and S. oryzae were phylogenetically closer than S. granarius and S. linearis, which were more closely related and share a more recent ancestral relationship.

Assessment of insecticidal responses of extracts and compounds of Drimys winteri, Lobelia tupa, Viola portalesia and Vestia foetida against the granary weevil Sitophilus granarius

Extracts and compounds from the Chilean plants canelo, Drimys winteri J.R. Forst. & G. Forst. (Winteraceae), tabaco del diablo, Lobelia tupa L. (Campanulaceae), huevil, Vestia foetida Hoffmans. (Solanaceae) and violeta, Viola portalesia Gay (Violaceae) were evaluated against Sitophilus granarius L. (Coleoptera: Curculionidae), one of the most widespread and destructive primary pests of stored cereals. Total extracts at concentrations of 2.5%w/w in diets, over 6-days, display insecticidal effects against S. granarius. D. winteri caused the mortality of 87.5% of insects; L. tupa 80%, V. foetida 56% whereas V. portalesia killed 45% of insects under the same conditions. In an effort to determine the active compounds, the extracts of Lobelia tupa and Drimys winteri were purified by preparative chromatography. The piperidine alkaloid lobelanidine was isolated from L. tupa and the drimane sesquiterpenes drimenin, drimenol and polygodial were isolated as the major components in the extract from D. winteri. The purified compounds compounds displayed insecticidal activity against S. granarius in a concentration/dependent-time manner (% mortality at 0.5%w/w over 6-days): polygodial 80%, drimenol 60%, lobelanidine 47%, and drimenin 20%. In agreement with these results, grains treated with polygodial showed greater protection against the feeding attack by the granary weevil. These results provide evidence of the importance of elements of the native Chilean flora as new potential sources of botanical pesticides for the insect pest control.

Comparison of insecticidal efficacy of four natural substances against granary weevil (Sitophilus granarius [L.]) adults: does the combined use of the substances improve their efficacy?

Laboratory tests were carried out to evaluate the insecticidal efficacy of different natural inert dusts (diatomaceous earth, wood ash, quartz sand) and the leaf powder of Azadirachta indica A. Juss. against granary weevil (Sitophilus granarius [L.]) adults. The efficacy of the substances was tested individually and in combination with each other. The substances were applied at different concentrations, and bioassays were carried out at four different temperatures (20, 25, 30 and 35°C) and two different relative humidity (RH) levels (55% and 75%). The adult mortality was recorded after the 7th, 14th and 21st days of exposure. The progeny production of individuals exposed to different combinations was also assessed. Wood ash proved to be the most efficient inert dust in our research. We detected 100% mortality in the treatment exposed to a higher concentration (5 w%) of wood ash at 35°C and 55% RH after 7 days of exposure. A lower RH level had also a negative impact on the progeny production. We can conclude that wood ash can be efficient in controlling granary weevil adults as a single substance or in combination with other substances. Further surveys should focus on the impact of the wood ash dose rates. Due to the high percentage of area covered with forest in some European countries, the main ingredient is present locally, but additional surveys are needed to help improve the practical use of wood ash.

Larval cannibalism and fitness in the stored grain weevils Sitophilus granarius and Sitophilus zeamais

Resource limitation is an important determinant of life history and behavior while mediating competition and reproduction among organisms. Discreet and closed systems such as grain kernels and seeds impose drastic restrictions to grain beetles that spend their immature stages within a single kernel selected by their mother. This is the case of internally feeding stored grain beetles, such as the grain weevils. Female egg-laying decisions and larval competition largely determine resource limitation for such insects where clustered egg distribution and contest competition with larval interference and cannibalism take place. As the clustered eggs within a grain lead to larval competition and conspecific weevil larvae face each other off during development allowing the emergence of one or two larvae per kernel, we hypothesized that such competition and consequent cannibalism will have fitness consequences for the competing individuals and their offspring. Thus, larvae of the granary weevil (Sitophilus granarius L.) and the maize weevil (Sitophilus zeamais Motsch.) were subjected to larval competition with cannibalism, and lack of it, to assess the potential fitness consequence of cannibalism on these non-carnivorous pest species of stored grains. Larval cannibalism reduced developmental time of maize weevil, but not of granary weevil. However, such condition led to heavier adult weevils of both species exhibiting higher reproductive output generating more and better quality progeny than non-cannibal weevils. These findings indicate direct nutritional benefits of cannibalism to grain weevils favoring their status of key pest species of stored cereal grains.

Walking Responses of Tribolium castaneum (Coleoptera: Tenebrionidae) to Its Aggregation Pheromone and Odors of Wheat Infestations.

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is a worldwide pest of stored grains. Using "Y"-tube olfactometry we studied the response of T. castaneum to odors from simulated wheat infestations containing conspecifics, and infestations containing the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae). Tribolium castaneum larvae were significantly attracted to odors from all three test species. Tribolium castaneum adults were attracted to grains infested by R. dominica and flour infested by T. castaneum but repelled from grains infested by S. granarius. Further behavioral analysis with pheromones showed that T. castaneum were significantly attracted to their aggregation pheromone, dimethyldecanal (DMD), but not to the R. dominica aggregation pheromone, a mixture of dominicalure 1 and 2. Female T. castaneum adults were attracted to ∼50-fold less DMD than larvae and 100-fold less than male adults, suggesting they are more sensitive to DMD. This study improves our understanding of T. castaneum behaviors to infested grain volatile compounds and pheromones, and may help develop new control methods for grain pest species.

Sensitization to Sitophilus granarius in selected suburban population of South Poland

Storage insects may cause occupational allergies in humans. The identification of the prevalence of IgE reactions were measured from protein fractions prepared from multiple life stage of granary weevil Sitophilus granarius [SG] is reported. Sera of 30 patients from a suburban population of Upper Silesia (South Poland) were tested for the presence of IgE antibodies to antigens from larvae, pupae and adults of both sexes of the beetle. To identify protein fractions containing potential allergens, proteins collected from four life stages of granary weevil were fractionated by SDS-PAGE and probed with anti-human, anti-IgE monoclonal antibodies. The proteins were fractionated by SDS PAGE and identified by Western blot. The patients’ antibodies against particular antigens were identified using anti-human anti-IgE monoclonal antibody. The conducted immunological analysis showed the existence of many protein fractions for each life stage of SG which give positive reactions with IgE antibodies. The largest number of allergenic potential fractions was shown in pupae (60 protein fractions) while the smallest amount was shown in larvae (44 protein fractions). Summarizing, the obtained results suggest the existence of many protein fractions with an allergenic potential multiple life stages of SG. This indicates that all developmental stages of SG may be a serious source of antigens and potential risk factors for the exposed persons.

Lost in space? Host-finding ability of the parasitoids Lariophagus distinguendus and Anisopteromalus calandrae in empty grain storage facilities to control residual pest populations

We studied the ability of the parasitoid species Lariophagus distinguendus (Forster) and Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) to locate populations of the granary weevil Sitophilus granarius (L.) (Coleoptera: Dryophtoridae) in grain residues. Experiments were conducted under laboratory and storage-like conditions. Generally both parasitoid species were able to find hosts up to 10 m from the release spot. Under laboratory conditions with excluded air movement and a centered light source, host finding was largely random, declining with increasing distance of baits from the release spot. Under storage-like conditions, host finding was strongly reduced and was not influenced by distance. A. calandrae seems to have been influenced by positive phototaxis. L. distinguendus showed a weaker host-finding success than A. calandrae, which was increased by a higher number of wasps from 10–50 per release. This resulted in a 5-fold higher number of parasitizations. It is discussed that host finding of residual pest populations by L. distinguendus and A. calandrae in empty storages is difficult to predict and influenced by light and air conditions. Based on our results, we provide recommendations for the release of parasitoids against residual pest populations.

Efficacy of three essential oils and their nano-particles againstSitophilus granariusunder laboratory and store conditions

The effect of three essential oils and their nano-preparations (castor, mustard and purslane) were tested against the granary weevil Sitophilus granarius under laboratory and stored conditions. Purslane oil (bulk and nano) had strong insecticidal efficacy and was significantly highly effective tested oil against granary weevil with 86.64, 75.21, 55.32, and 18.61% mortality obtained at 5, 2.5, 1.25 and 0.63% concentrations, respectively. While, the mortality values reached 95.61, 73.51, 58.39 and 20.61% when the adults were exposed to 0.5, 0.25, 0.13, 0.06 concentrations of nano-purslane, respectively. Castor oil had moderate effect and mustard was the least one. Nano-purslane was highly significantly more effective as sterilizer against adult weevils in comparison with other tested nano-oils. The mean number of eggs/female recorded 3.0 ± 3.8, 22.0 ± 7.8 and 28.8 ± 7.9 eggs/female in case of purslane, castor and mustard, respectively in comparison to control (198 ± 4.9 eggs/female). After 125 days of storage, the percentage of emerged weevils were 21 and 7% in case of purslane oil (bulk and nano), respectively comparing with untreated control (98%).