Assessment of Sitotroga cerealella losses in different sorghum varieties under controlled conditions

Crop seeds are generally stored for next crop season and bear losses from vertebrate and invertebrate pests. In invertebrates, stored grain insect pests are mainly responsible for loss in weight and viability issues. Five sorghum varieties, viz. RS-29, Rari-S-4, Rari-SV-10, SPV-462 and Johar-1 were compared for infestation of Sitotroga cerealella under laboratory and semi-field conditions. RS-29 was found to be the most resistant variety and Johar-1 to be the most susceptible when losses were observed after 30, 60 and 90?days of infestation. Maximum infestation and weight loss was observed in Johar-1 (28%). Germination percentage was found to be decreased to 65% in RS-29 and 47% in Johar-1 in laboratory, and 60% in RS-1 and 43% in Johar-1 under semi-field conditions. Possibilities to decrease these losses have been discussed for effective management of stored grain pest losses.     

Assessment of maize and beans storage insect pest in major grain markets,Morogoro-Tanzania

Post-harvest losses for maize and beans are common storage challenges affecting Tanzania's smallholder and large-scale farmers' storage facilities. Consequently, this leads to a reduction of over 50% of harvested grain qualitatively and quantitively per year. Therefore, this experimental study was conducted at the entomological laboratory of the Sokoine University of Agriculture Tanzania, where the research was aimed to assess different common storage insect pests of beans and maize at Morogoro major markets (i.e., Kihonda, Mazimbu and Morogoro Central Market) with similar storage conditions in Morogoro municipality. The complete block design (CBD) with three experimental replications was used. Where locations (Kihonda, Mazimbu and Central market) markets were considered as experimental treatments. The results obtained show that there were no significant differences in number of insect pests (such as maize weevils and bean bruchids) identified between the Kihonda and Central markets (P > 0.05). However, there is a significant difference (P< 0.05) between Mazimbu and other markets regarding the number of insect pest multiplication resulting from the storage condition of those grains in a particular market. Nevertheless, continuous winnowing of stored grains was observed to significantly intensify the infestation of the storage pest in maize and common beans. Therefore, alternatively, to reduce insect pest infestation to maize and common beans in storage facilities, it is important to avoid constant winnowing of stored grains.     

RNAi in the cereal weevil Sitophilus spp: Systemic gene knockdown in the bacteriome tissue

Background  

The weevils Sitophilus spp. are among the most important cosmopolitan pests of stored cereal grains. However, their biology and physiology are poorly understood, mainly because the insect developmental stages take place within cereal grains and because of the lack of gene specific molecular manipulation.     

Comparative insecticidal activity of different plant materials from six common plant species against Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is one of the major insect pests of stored grains. Due to export legislation and zero-tolerance for live insect in trade commodities, extensive use of synthetic insecticides is in practice in order to eliminate pest infestations from the lots. Currently, the one and only acceptable chemical to be used in stored grain is phosphine but due to its excessive usage the stored grain pests are becoming resistant against it. Hence discovery of alternative compounds is much needed. In this study we have compared insecticidal efficacy of different plant materials from six commonly grown plants of Pakistan, viz. Allium sativum (Alliaceae), Zingiber officinale (Zingiberaceae), Cymbopogon citratus (Poaceae), Eucalyptus globulus (Myrtaceae), Nicotiana tabacum (Solanaceae), and Azadirachta indica (Meliaceae) against T. castaneum infesting stored wheat, rice, corn and gram pulse. Various plant parts were dried, powdered, and used as admixtures to the stored commodities in the experiments. The results have suggested that A. sativum (garlic) and Z. officinale (ginger) were more effective resulting into 15 times higher adult mortality and 4 to 5 times reduction in grain weight losses when mixed with rice grains. Similarly, A. indica when admixture with wheat checked the population growth in the resources resulting into 3.5 times less adult production compared to controls. A subsequent experiment was conducted to study the dose response of neem seed powder against the beetle pest infesting milled products. Surprisingly, better control was observed either at lowest (1% w/w) or the highest doses (5% w/w). This finding is of great interest to understand the underlying phenomenon which we assume is the ability of T. castaneum to feed selectively in flour mediums, however, further research on this aspect is required to be investigated. The results of this study support the use of botanicals for stored product pest management.     

Imaging techniques for the detection of stored product pests

Stored grains are subject to deterioration and losses through various factors, but mainly insects and fungi. Various techniques are employed to detect stored product pests; however, there is an urgent need for an industrial-scale on-line detection technique. Near-infrared hyperspectroscopic imaging and soft X-rays have shown the potential for real-time application. These techniques are particularly effective for detecting internal infestations of stored grains. The digital images of the scanned objects are analyzed for various spectral and image features using statistical techniques such as complex multivariate tools. Classification accuracies as high as 80–100 % have been achieved for various pest and grain combinations. Dual-energy X-rays have been shown to detect the concealed eggs of stored product insect pests. The main threats to stored cereals come from Aspergillus spp., Penicillium spp., and Fusarium spp., which may produce mycotoxins. These imaging techniques have shown good results in the detection of fungal infections of stored grain.     

Relative resistance of paddy varieties to Sitotroga cerealella (Lepidoptera: Gelechiidae)

Relative resistance of paddy varieties to the Angoumois grain moth, Sitotroga cerealella was investigated in the laboratory at a temperature of 28 ± 1.0°C and relative humidity of 65 ± 1.5%. The study was carried out on Indian Agricultural Research Institute (IARI), New Delhi, India varieties and a Taiwan variety. The larvae of S. cerealella were allowed to feed and developed inside the grain while adults did not feed. Results showed that the performance of S. cerealella was least in T (N)-1 (Taichung Native-1), with the longest developmental time (26.3 days) and egg to adult survival of 38% making the variety the most resistant. The performance was best in Pusa 44 with the shortest developmental time (23.0 days) and egg to adult survival of 68.7% making the variety the least resistant. The heaviest females and males with 4.04 g and 2.38 g, respectively, were reared on Pusa sugandh 3, which are large seeds. Moths reared on T (N)-1 had the lowest weights for males and females. Unmated females lived longer than their mated counterparts while females generally lived longer than males. Fecundity was highest (164.2 eggs/female) in Pusa 44 and lowest (108.1 eggs/female) in T (N)-1. Hatchability ranged from 81.2% in T (N)-1 to 96.2% in Pusa 834. Generally, grain characters tested in this study influenced moth herbivore performance but the influence was not significant except for grain width which appeared to be the most important trait. With advances in biotechnology, it is possible to transfer desirable characters to other varieties to improve their resistance to S. cerealella and other stored products insects. However, care must be taken since this could change the grains susceptibility to some pests affecting pest-host relationships.     

Elimination ofSitotroga cerealella (Olivier) bySitophilus zeamais Motschulsky from mixed laboratory cultures on maize

This paper describes a series of experiments conducted to determine why Sitophilus zeamaisMots . and Sitotroga cerealella (Oliv. ) could not survive together in maize cultures in the laboratory. The effect of S. zeamais on different developmental stages of S. cerealella was investigated. The presence of adult S. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination of S. cerealella by S. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.     

Behavioural responses of Oryzaephilus surinamensis, Tribolium castaneum and Tribolium confusum to naturally and artificially damaged durum wheat kernels

Observations on behavioural activity involved in the host selection by secondary pests of stored grains, Oryzaephilus surinamensis (Linnaeus), Tribolium castaneum (Herbst) and Tribolium confusum J. du Val, with respect to intact and mechanically or naturally damaged kernels are reported. Our results indicate that the attraction of secondary pests is facilitated by broken grain kernels, which resulted from either mechanical damage during harvesting and/or binning procedures, or the feeding activity of primary insect pests. Insect damaged kernels were more attractive to O. surinamensis, T. castaneum and T. confusum than whole kernels; in addition insect damaged kernels elicit more attractiveness than mechanically split kernels. The damage caused by primary pests, such as Rhyzopertha dominica (Fabricius) and Sitophilus oryzae (Linnaeus), on whole kernels may facilitate colonization by secondary pests, which continue damaging the cereals. O. surinamensis, T. castaneum and T. confusum utilize the grain volatile odours to distinguish whether the grain kernels of the stored cereals are damaged mechanically or by insects.     

Combining intercropping with semiochemical releases: optimization of alternative control of Sitobion avenae in wheat crops in China

Overreliance on pesticides has large environmental and human health costs that compel researchers and farmers to seek alternative management tactics for crop pests. For insect pests, increasing crop species diversity via intercropping and using semiochemicals to alter local arthropod populations have separately proven effective at reducing pest densities. Here, we combine these two tactics in an effort to gain better control of Sitobion avenae (Fabricius) (Hemiptera: Aphididae), the English grain aphid, a major pest of cereal production worldwide. We conducted field experiments over 2 years testing the effectiveness of combining intercropping of wheat and oilseed rape with release of methyl salicylate (MeSA). We found that maximum and mean aphid densities were highest in wheat monocultures, significantly lower in intercropped plots and MeSA plots, and lowest when intercropping and MeSA release were combined by obtaining highest densities of predatory lady beetles and parasitoids rates. Importantly, grain yield and quality showed a similar pattern: they were highest for combined intercropped/MeSA plots, intermediate in plots with intercropping or MeSA alone, and lowest in control monoculture plots. Our results suggest that combining these two tactics holds significant promise for improved management of aphid populations and emphasize the need to integrate alternative pest control approaches to optimize sustainable insect pest management.     

Insecticidal efficacy of three vegetable oils as post-harvest grain protectants of stored wheat against Rhyzopertha dominica （F.） （Coleoptera： Bostrychidae）

The lesser grain borer, Rhyzopertha dominica is a major insect pests of stored grain in the tropics. Vegetable oils （chamomile, sweet almond and coconut） at 2.5, 3.5, 5.0, 7.0 and 10.0 mL/kg were tested against Rhyzopertha dominica （F.） in wheat grain. All bioassays were conductr, d at 30℃ and 65% ＋ 2% RH. Treatments with vegetable oils at high dose （10.0 mL/kg） achieved over 95% control within 24 h of exposure to freshly treated grain, There was little difference between the three oils in their effect. Persistence of oils in grains was tested at short-term storage intervals （48, 72 and 96 h） and intermediate-term intervals （10, 20 and 30 days） after treatments. The activity of all products decreased with storage period. Seed viability was reduced by the high dose rate （10.0 mL/kg） of oil treatments. The potential use of vegetable oils as supplementary or alternative grain protectants against insect damage in traditional grain storage in developing countries is discussed.     

Interspecific competition between Sitophilus zeamais and Sitotroga cerealella in a patchy environment

The maize weevil, Sitophilus zeamais (Motchulsky) (Coleoptera: Curculionidae), and the Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), are important insect pests of stored products. The coexistence in nature of the two species on maize has been difficult to explain from laboratory set‐ups, as the moth is inevitably eliminated by S. zeamais. However, early laboratory experiments ignored the spatial dimension, while several studies have lately revealed that two competing species may coexist in a spatially divided environment even though one of the species is competitively superior in a simpler universe. Two hypotheses for coexistence were examined by studying the interactions in a system where the resources were spatially divided. It was found that spatial subdivision in the current experiment was insufficient to ensure coexistence between the two species, so neither of the hypotheses could be confirmed. A simple model describing the population dynamics of S. zeamais was fitted to the data. Its parameters provide important information about how resource depletion influences the per capita growth rate. Finally, the study indicates that the mechanism responsible for S. zeamais's rapid elimination of S. cerealella is the superiority of the former species to colonize and monopolize new patches. The design of this study may serve as a template for further laboratory experiments revealing the effect of a spatially divided environment on competitive interactions. However, the present study also indicates that choosing the appropriate spatial scale may be critical for relating the results to natural environments.     

Predator‐parasitoid‐host interaction: biological control of Rhyzopertha dominica and Sitophilus oryzae by a combination of Xylocoris flavipes and Theocolax elegans in stored cereals

Post‐harvest management constraints are economically significant in Africa for a broad range of commodities, resulting in a substantial negative impact on food security and livelihoods. Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) coexists with Sitophilus oryzae (L.) (Coleoptera: Dryophthoridae) – they infest stored cereal grains, especially in sub‐Saharan Africa, and cause significant losses in storage. Laboratory studies were carried out to determine the efficacy of Xylocoris flavipes (Reuter) (Hemiptera: Anthocoridae) and Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae), alone or in combination, in suppressing populations of R. dominica and S. oryzae in stored rice and wheat grains. The weight loss and moisture of the infested grains were assessed, for the various combinations of the two pest insects and the two natural enemies. In rice there was a synergistic effect of the combined release of T. elegans and X. flavipes against both R. dominica and S. oryzae compared to the effect of one natural enemy alone. With the combined release, only 2% F₁ progeny of the pest beetles emerged compared to the untreated control (100%), whereas 3.5 and 6% emerged when X. flavipes and T. elegans, respectively, were released alone. When the two natural enemies were released in combination, 0.4% R. dominica F₁ progeny emerged, compared to 1.6% with X. flavipes or T. elegans alone. In the combined release only 0.3% S. oryzae F₁ progeny emerged, whereas 65% emerged with X. flavipes alone and 41% with T. elegans alone. No synergistic effect of the combined release of the two natural enemies was detected in wheat. In stored rice, the lowest percentage of weight loss (44%) was found when both natural enemies and both beetle species were present. We conclude that the combination of the predator and the parasitoid should be recommended when R. domininca and S. oryzae coexist and feed on stored cereals, especially rice.     

Rapid method for the detection of storage mites in cereals: feasibility of an ELISA based approach

This paper describes the development of rapid immunodiagnostic tests for the detection of storage mite infestations in cereals and cereal products. The study's first phase (proof of concept) involved the production of a species-specific enzyme-linked immunoassay (ELISA) for the flour mite, Acarus siro (L.), a major pest of stored commodities. The specificity of this new assay was assessed against key stored product contaminants (13 species of mites of which three were predatory, five species of insects and five species of fungi) in the presence and absence of grain. The assay was species-specific (no cross-reactivity to other storage contaminants) and was unaffected by the presence of cereal antigens in the extract. In the study's second phase, species- and genera-specific ELISAs were developed for a range of key storage mite pests: the cosmopolitan food mite (Lepidoglyphus destructor), the grocers' itch mite (Glycyphagus domesticus), the grainstack mite (Tyrophagus longior), mites of the Tyrophagus and Glycyphagus generas, and all storage mites. All tests were demonstrably specific to target species or genera, with no cross-reactions observed to other storage pest contaminants or cereals. The final, validation phase, involved a comparative assessment of the species-specific A. siro and the genus-specific Tyrophagus ELISAs with the flotation technique using laboratory and field samples. Both ELISAs were quantitative (0-30 mites per 10 g wheat) and produced good comparative data with the flotation technique (A. siro r(2)=0.91, Tyrophagus spp. r(2)=0.99).     

Predicting insect pest status under climate change scenarios: combining experimental data and population dynamics modelling

Climate change could profoundly affect the status of agricultural insect pests. Several approaches have been used to predict how the temperature and precipitation changes could modify the abundances, distributions or status of insect pests. In this article it is demonstrated how the use of simple models, such as Ricker’s classic equation, including a mechanistic representation of the influence of exogenous forces may improve our predictive capacity of the dynamic behaviour of insect populations. Using data from classical experiments in population ecology, we evaluate how temperature and humidity influence the density of two stored grain insect pest, Tribolium confusum and Callosobruchus chinensis, and then, using the A2 and B2 scenarios proposed by the Intergovernmental Panel on Climate Change and the previous modelling, we develop predictions over the future pest status of T. confusum along South America austral region, and specifically for eight cities in the continental Chilean territory. Tribolium confusum and C. chinensis show qualitatively different responses to the exogenous forcing of temperature and humidity, respectively. Our simulations predict a change in the equilibrium density of T. confusum from 10 to 14% under the moderate B2 scenario and 12 to 22% under the extreme A2 scenario to the period, 2071–2100. Both results imply a severe change in the pest status of this species in the southern region. This study illustrates how the use of theoretically based models may improve our predictive capacity. This approach provides an opportunity to examine the link between invasive species and climate change and how new suitable habitat may become available for species whose niche space is limited in some degree by climatic conditions. The use of different scenarios allows us to examine the sensitivity of the predictions, and to improve the communication with the general public and decision‐makers; a key aspect in integrated pest management.     

两种书虱微卫星富集文库的构建及比较

利用链霉亲和素与生物素之间的强亲和性原理,将链霉亲和素偶联的磁珠与微卫星探针(AC)12、(TC)12、(ATC)8、(ATG)8、(AAC)8、(ATAC)6及(GATA)6退火结合后,再亲和捕捉含接头和微卫星序列的单链书虱基因组DNA限制性酶切目的片段,经PCR扩增形成双链后进行克隆、建库。结果表明本研究成功构建了嗜卷书虱和嗜虫书虱共13个微卫星富集文库,包括6个嗜卷书虱文库,7个嗜虫书虱文库,其平均阳性克隆率为71.17%。经检测发现共得到两种书虱260个微卫星位点。这两种书虱微卫星富集文库的建立和高多态性微卫星位点的筛选将为嗜卷书虱和嗜虫书虱的种群遗传与进化、基因连锁图谱构建、分子系统发育研究等提供大量分子遗传标记,对其在实仓中的持续控制提供遗传学信息。     

Postgenomics of Tribolium: Targeting the endocrine regulation of diuresis

Coleopteran insects comprise a highly successful taxon, representing more than 25% of eukaryotic species, many of which are economically important. One of these, the red flour beetle (Tribolium castaneum H.), is a major pest of stored grain and cereal products and is also an excellent genetic model for the Coleoptera. The Tribolium genome sequencing project was recently completed, the first for an agricultural insect pest species. This genome sequence and annotation, in combination with the tractability of Tribolium for genetic dissection and functional genomic analysis, makes it one of the most useful subjects for studies of insect development, genetics and physiology. Tribolium has a number of interesting physiological adaptations, including desiccation tolerance associated with specialized cryptonephridial organs for active rectal absorption of atmospheric water. The study of endocrine regulation of diuresis in this species has led to the identification of a number of osmoregulatory peptides, including the novel arginine‐vasopressin‐like peptide.     

Euserica modesta Fairmaire (Coleoptera: Scarabaeidae): a new record for a chafer insect pest attacking citrus orchards in Egypt

Many pests and diseases are widely spread and attack several plants and agricultural products. During September 2008, a new chafer insect pest, Euserica modesta Fairmaire (Coleoptera: Scarabaeidae) was recorded for the first time in the south Sinai region, north of Egypt. This insect was shown to attack and destroy flowers and leaves of citrus orchards. It was identified by the Department of Classification, Plant Protection Research Institute, Agriculture Research Center, Giza, Egypt. In the present study, preliminary investigations offered some information about infestation symptoms. Sites of damage in the host plant and suggested control of the pest E. modesta were described.     

Response of Tribolium castaneum and Rhyzopertha dominica to various resources,near and far from grain storage

Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) are common cosmopolitan pests of stored grain and grain products. We evaluated the relative attraction of T. castaneum and R. dominica to wheat, sorghum and cotton seeds in the field, near grain storage facilities and well away from storages in southern and central Queensland using multiple trapping techniques. The results show that T. castaneum is more strongly attracted to linted cotton seed relative to wheat, whereas R. dominica did not respond to cotton seed at all and was attracted only to wheat. Significantly more adults of T. castaneum (10–15 times) were attracted to traps placed on the ground, near grain storage, than to equivalent traps that were suspended (1.5 m above the ground) nearby. These results suggest that Tribolium beetles detect and respond to resources towards the end of their dispersal flight, after which they localize resources while walking. By contrast R. dominica was captured only in suspended traps, which suggests they fly directly onto resources as they localize them. The ability of both species to colonize and reproduce in isolated resource patches within the relatively short time of 1 month is illustrated by the returns from the traps deployed in the field (at least 1 km from the nearest stored grain) even though they caught only a few beetles. The results presented here provide novel insights about the resource location behaviours of both T. castaneum and R. dominica. In particular, the relationship of T. castaneum with non‐cereal resources that are not conventionally associated with this species suggests an emphasis on these other resources in investigating the resource location behaviour of these beetles. This new perspective on the ecology of T. castaneum highlights the potential role of non‐cereal resources (such as the lint on cotton seed) in the spread of grain pest infestations.     

Pleiotropic Impact of Endosymbiont Load and Co-Occurrence in the Maize Weevil Sitophilus zeamais

Individual traits vary among and within populations, and the co-occurrence of different endosymbiont species within a host may take place under varying endosymbiont loads in each individual host. This makes the recognition of the potential impact of such endosymbiont associations in insect species difficult, particularly in insect pest species. The maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), a key pest species of stored cereal grains, exhibits associations with two endosymbiotic bacteria: the obligatory endosymbiont SZPE (“Sitophilus zeamais Primary Endosymbiont”) and the facultative endosymbiont Wolbachia. The impact of the lack of SZPE in maize weevil physiology is the impairment of nutrient acquisition and energy metabolism, while Wolbachia is an important factor in reproductive incompatibility. However, the role of endosymbiont load and co-occurrence in insect behavior, grain consumption, body mass and subsequent reproductive factors has not yet been explored. Here we report on the impacts of co-occurrence and varying endosymbiont loads achieved via thermal treatment and antibiotic provision via ingested water in the maize weevil. SZPE exhibited strong effects on respiration rate, grain consumption and weevil body mass, with observed effects on weevil behavior, particularly flight activity, and potential consequences for the management of this pest species. Wolbachia directly favored weevil fertility and exhibited only mild indirect effects, usually enhancing the SZPE effect. SZPE suppression delayed weevil emergence, which reduced the insect population growth rate, and the thermal inactivation of both symbionts prevented insect reproduction. Such findings are likely important for strain divergences reported in the maize weevil and their control, aspects still deserving future attention.     

Electroantennographic responses of red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) to volatile organic compounds

The red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is the most encountered and destructive stored product insect pest of cereal grains and seeds. Although this beetle has been used as a model organism for many decades, there is no systematic knowledge about antennal detection of host and non‐host volatiles. Electroantennogram responses to 94 selected volatile organic compounds including alkanes, alkenes, alcohols, aldehydes, ketones, carboxylic acids, esters, terpenoids and aromatic compounds were recorded from both sexes of T. castaneum. Overall, female and male T. castaneum exhibited similar electroantennography (EAG) responses. Compounds eliciting the strongest EAG responses within compound groups of chemical similarity were undecane, 1‐hexen‐3‐ol, octanal, 2‐heptanone, hexanoic acid and ethyl hexanoate. Comparison of vapour pressure and EAG amplitudes within homologous series of compounds revealed responses to undecane, octadecane, octanal, nonanal, 2‐heptanone, hexanoic acid and octanoic acid as outstanding. Given that systematic EAG screenings have not been conducted before, these are the best candidates for evaluation in future behavioural studies to unravel their potential for application in integrated pest management strategies of T. castaneum.