Stored-grain Insect Pests Research Articles

Vulnerability of different life stages of Sitophilus oryzae insects in stored rice grain to ozone treatment and its effect on physico‐chemical properties in rice grain

AbstractOzone has emerged as a reactive gas with insecticidal activity with the capability to manage insect pests in stored grains. The study focused on the effect of moisture content with exposure time and ozone concentration in achieving mortality of different life stages of Sitophilus oryzae. The ozonation process was done with a moisture content (MC) of 12%–16%, ozone concentration of 1.0–2.0 g/m3 and exposure time of 2–6 h. The responses studied were percentage mortality of eggs, larvae, pupae, and adults. The ozone effect on rice physico‐chemical, spectral FTNIR (Fourier transform near infrared spectrophotometer), and morphological attributes (X‐ray micro CT) of optimized samples were compared with control sample. The adult stage of S. oryzae was the least vulnerable stage to the ozonation process among eggs, larvae, and pupae, whose mortality ranged from 44.13% to 99.02%. The optimized condition with the desirability of 0.99, MC of 12.31%, ozone of 1.93 g/m3, and time of exposure 5.86 h for mortality of different life stages of S. oryzae was obtained. The standard error mean and SD were in the range of 2.81–1.91 and 3.67–3.21, respectively. Protein, amylose, and MC of ozone‐treated rice had lower values in comparison to fresh rice. Microstructural changes in ozonated samples were distinct with X‐ray micro CT images and FTNIR peaks. The loss in the micro structure was attributed to the insect infestation and degradation of protein molecules due to oxidation of the disulphide bonds during ozone treatment.

Detection of Phosphine Resistance in Field Populations of Four Key Stored-Grain Insect Pests in Pakistan.

Simple SummaryThe resistance of coleopteran stored-product pests to phosphine fumigation is becoming a global phenomenon. However, there is limited literature available and a lack of knowledge on this issue in Pakistan. Thus, in the current study, we estimated the status of phosphine resistance among ten populations of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), Sitophilus granarius (L.) (Coleoptera: Curculionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Trogoderma granarium Everts (Coleoptera: Dermestidae), originated from different regions of Pakistan. Laboratory-susceptible populations of all insect species were also considered in the tests. Concentration–response bioassays were conducted for each insect species. All of the tested populations of each species were found to be resistant to phosphine. However, they varied with regard to their levels of resistance. Overall, R. dominica exhibited the highest resistance level, followed by T. castaneum, T. granarium and S. granarius. Although phosphine is effective against several stored-product pests, the development of resistance may lead to failures in its application in Pakistan.In Pakistan, the control of stored-product insect pests mainly relies on the use of phosphine gas along with other control tactics. The aim of this study was to determine the level of phosphine resistance among ten differently located populations of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae). Laboratory-susceptible populations of all insect species were also considered in the experiments. Concentration–response bioassays were conducted for each species. All of the tested populations (10 out of 10) of each species were found to be resistant to phosphine, but varied in their level of resistance. Probit analysis estimated LC50 at 2.85, 1.90, 2.54 and 2.01 ppm for laboratory-susceptible populations of R. dominica, S. granarius, T. castaneum and T. granarium, respectively. Against R. dominica, the highest and lowest resistance levels were observed in the Rahim Yar Khan (LC50 at 360.90 ppm) and Rawalpindi (LC50 at 210.98 ppm) populations, respectively. These resistant populations were 126.67- and 74.02-fold more resistant than the laboratory population. The Multan and Lahore populations of S. granarius exhibited the maximum (LC50 at 122.81 ppm) and minimum (LC50 at 45.96 ppm) resistance levels, respectively, i.e., they were 64.63- and 24.18-fold more resistant than the laboratory population. The Layyah population of T. castaneum showed the maximum resistance level (LC50 at 305.89 ppm) while the lowest was observed in the Lahore population (LC50 at 186.52 ppm), corresponding to 120.42- and 73.43-fold more resistant than the laboratory population, respectively. Regarding T. granarium, the Layyah population showed the maximum resistance level (LC50 at 169.99 ppm) while the Lahore population showed the minimum resistance (LC50 at 74.50 ppm), i.e., they were 84.57- and 37.06-fold more resistant than the laboratory population, respectively. Overall, R. dominica presented the highest resistance level, followed by T. castaneum, T. granarium and S. granarius. The current study suggests that the application of phosphine may not be an adequate control strategy for the management of the above tested insect pests in Pakistan.

Performance of diatomaceous earth and imidacloprid as wheat, rice and maize protectants against four stored-grain insect pests

Laboratory experiments were conducted in Pakistan to investigate the effectiveness of the diatomaceous earth (DE) formulation, Protect-It, at 150 ppm and imidacloprid, at 1.25, 2.5 and 5.0 ppm, alone or in combination, against the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The bioassays were conducted at 25 °C, 65% relative humidity (r.h.) and continuous darkness by using adults of each insect pest that were exposed on treated or untreated wheat, rice and maize. Adult mortality counts were performed 1, 2, 4 and 7 days post-exposure. Progeny production was also evaluated 62 and 30 days after the last mortality count for beetles and psocid respectively. Results showed that mortality was increased with the increase of dose and exposure interval. Imidacloprid was more effective at the highest dose than the DE alone. The combination of DE plus imidacloprid resulted to higher mortalities than DE or imidacloprid alone at almost all exposure intervals. There was higher mortality on wheat than on rice or maize. In general, T. castaneum was the most tolerant insect species to any treatment while L. paeta was the least tolerant. The highest progeny production was observed for T. castaneum (i.e., 33.1 individuals per vial) while the lowest for L. paeta (i.e., 11.1 individuals per vial) on maize treated with Protect-It alone. The findings of the current study indicate that the combined use of DE and imidacloprid, as wheat, rice and maize protectants, may provide adequate level of management to several important stored-product insects.

Sunflower seed hulls waste as a novel source of insecticidal product: Pyrolysis bio-oil bioactivity on insect pests of stored grains and products

The edible oil industry produces abundant sunflower seed hulls (SSH) as waste. Pyrolysis offers a sustainable method for producing high-value bioproducts from this lignocellulosic residue. This paper reports on the bioefficacy of SHH pyrolysis bio-oils from raw SSH (named SSH bio-oil) and acid pretreated hulls (named PTH bio-oil) as bioinsecticides against Sitophilus oryzae, Lasioderma serricorne and Tribolium castaneum. Raw SSH and pretreated hulls with 10% H3PO4 were subjected to fast pyrolysis in a vertical reactor at 450 °C. Results show that PTH bio-oil is a furfural enriched bio-liquid with storage stability and a yield of 33%. SSH bio-oil was unsuitable for evaluating biological activity since it produce high variability in mortality data. In contrast, PTH bio-oil produces high insecticidal activity in S. oryzae (LC50 = 0.51 mg cm−2) by contact toxicity bioassay, followed by L. serricorne and T. castaneum. In behavioral assays, PTH bio-oil shows a slight repellent effect and mobility reduction. Moreover, PTH bio-oil affects the nutritional physiology of S. oryzae and T. castaneum producing a modification of nutritional indices and antifeedant effects. Our study provides information on the potential of fast pyrolysis bio-oils from SSH waste to develop novel bioinsecticides as an alternative to the use of conventional synthetic pesticides.

Plants in the Genus Tephrosia: Valuable Resources for Botanical Insecticides.

Simple SummaryThere is an increasing interest in botanical insecticides worldwide. Plants from the genus Tephrosia are rich in bioactive phytochemicals, particularly rotenoids which include rotenone, deguelin, rotenolone, and tephrosin. Rotenoids have strong insecticidal activities against a wider range of pests. However, there has been no treatise thus far focusing on Tephrosia as insecticidal plants. This article is intended to review phytochemicals produced by selected species, their insecticidal activities, and the current status on the use of Tephrosia as botanical insecticidal plants for insect pest control.Synthetic insecticides are effective in controlling insect pests but can also harm nontarget organisms and the environment. During the last 40 years, there has been an increasing interest in alternative insecticides, particularly those derived from plants, commonly known as botanical insecticides. However, commercially available botanical insecticides remain limited. Rotenone is one of the earliest identified compounds and was used as fish poison and pest management. Due to its link with Parkinson disease, the use of rotenone was banned in many developed countries. Rotenone used to be isolated from Derris spp. and Lonchocarpus spp., and it can also be isolated from Tephrosia species. In this article, we present basic botanical information on selected Tephrosia species and their major compounds related to insecticidal activities and highlight the current use of extracts derived from some species, Tephrosia vogelii in particular, for control of insect pests in stored grains and crop production. The crude extracts contain multiple bioactive compounds, mainly rotenone, deguelin, rotenolone, and tephrosin, which act in either additive or synergistic fashion, resulting in effective control of insect pests. There are about 400 species in the genus Tephrosia, and species and even strains or variants vary greatly in these active compounds. We argue that a systematic evaluation of bioactive compounds in different species are needed, and species or strains with high insecticidal activities should be selected for use in the sustainable control of insect pests.

Efficacy of ethylenesulphonyl fluoride against stored grain psocids, Liposcelis bostrychophila Badonnel and Liposcelis entomophila (Enderlein)

Phase-out, impending ban, and developing insect resistance to the commonly used insecticides for stored grains pose serious challenges to the scientific community and it is imperative to develop effective pest management strategies. Identification and testing of new compounds are potential options to deal with the growing threat. Ethylenesulphonyl fluoride (ESF), a new synthetic compound, is one of the most promising alternative fumigant insecticides that can be used to control the insect pests in stored-grains. However, limited evidence is available to support its efficacy to control the stored-product psocids. This study evaluates the ESF as a prospective control reagent to exterminate different life stages of the psocids Liposcelis bostrychophila Badonnel and L. entomophila (Enderlein). We conducted a 4 h toxicity trials and 12 h simulated efficacy trials with adults of the two species in wheat. Adults and nymphs were highly susceptible to ESF. Complete adult and nymph mortality (LD99) was also recorded at dosages ranged from 1.97 μL/L to 3.80 μL/L. Moreover, complete (LD99) egg mortality was recorded at dosages between 3.59 μL/L and 7.60 μL/L. Remarkably, the mortality of adults decreased with increasing depth of the grain bulk. Our study establishes ESF as a potential reagent that can be used effectively to control a variety of commonly known stored grain psocids.

Characterization of chitinase from Shewanella inventionis HE3 with bio-insecticidal effect against granary weevil, Sitophilus granarius Linnaeus (Coleoptera: Curculionidae)

A 40 kDa chitinase from Shewanella inventionis HE3 was purified (ChiA-Si40) and characterized. Using fermentor with an optimized medium for 48 h at 37 °C, enzyme activity was enhanced by 10-times compared to those using shaking-flask-culture. Purified chitinase is a homogenous monomer with molecular mass of 40 kDa. Its N-terminal residues revealed significant identity with glycoside hydrolase family 18 (GH18) chitinases from Gammaproteobacteria. Using colloidal chitin as a substrate, its finest activity was accomplished at pH 4 and a temperature of 70 °C. Its catalytic efficiency (kcat/Km) was superior to that of some bacterial GH18 chitinases and commercial enzyme, Chitodextrinase®. For scale-up and with regards to the improvement of ChiA-Si40 with PEG 6000 storage stability (6 months), the atomizing process was more pronounced than that of lyophilizing. Bio-assay of ChiA-Si40 against grain weevil Sitophilus granarius, indicates that it had an efficient insecticidal effect. About 10–100 % mortality rates were obtained 1-h after insect came in contact with ChiA-Si40. Histological study clearly demonstrated that luxury larval mid-gut, peritrophic-membrane, and epithelial-cells have been affected considerably after ChiA-Si40 treatment. These properties make ChiA-Si40 a potential bio-insecticidal agent for the biological control of S. granarius that is popular among insect pests of stored grains in Algeria.

Stored grain pest prevalence and insecticide resistance in Egyptian populations of the red flour beetle Tribolium castaneum (Herbst) and the rice weevil Sitophilus oryzae (L.)

As a consequence of the widespread use of insecticides against insect pests in grain warehouses and in the food industry, insecticide resistance has greatly increased among these species all over the world. Nonetheless, insecticide resistance in stored grain insects in Egypt was little studied. Therefore, our study aimed to forecast infestation risks and determine the insecticide resistance level in Egyptian populations of the main insect pests of stored grains. To achieve this goal, we surveyed the populations of stored-product insects in wheat in two different sites in the Alexandria governorate (Egypt) between June and August 2017. Moreover, insecticide resistance levels in Egyptian populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.) collected from wheat storage facilities (granaries and flour mills) in Alexandria governorate were also determined. Three contact insecticides, namely malathion, pirimiphos-methyl and cypermethrin, were tested. Tarsal contact bioassays on filter paper were carried out on adults following FAO methods and concentration-mortality lines were estimated to determine the resistance ratios for each insecticide and population. The data from the monitoring of insects revealed that T. castaneum and S. oryzae were the most common species infesting wheat in both Alexandria granaries and mills. Populations of S. oryzae were generally more resistant to malathion than the populations of T. castaneum. However, T. castaneum populations were more resistant to pirimiphos-methyl than the S. oryzae populations. Both populations of T. castaneum and S. oryzae were susceptible to cypermethrin. The detected levels of insecticide resistance indicate that this phenomenon takes place and should be a concern in Egyptian populations of T. castaneum and S. oryzae requiring monitoring and design of resistance management practices.

Morphological characteristics of local entomopathogenic protozoan strains isolated from insect cadavers of certain stored-grain pests in Egypt

The present study has documented, for the first time in Egypt, the natural occurrence of four entomopathogenic protozoans (EPP) among five of the most abundant and damaging insect pests of stored grains or their products. These insect pests (Laemophloeus (Cryptolestes) turcicus (Grouvelle), Rhyzopertha dominica (Fabricius), Sitophilus zeamais (Motschulsky), Tribolium castaneum (Herbst), and Plodia interpunctella (Hobner) were infesting lots of crushed-maize grains, wheat grains, and wheat flour, brought, in 2015, from El-Behera Governorate, Egypt. The morphological characteristics, including spore size, of the entomopathogen infective units, spores, of the isolated entomopathogenic protozoans, were closely fit with the description to the following genera: Mattesia, Farinocystis, Adelina, and Nosema. The prevalence of these entomopathogens ranged between 9 and 89%. This study seems to be the first report of Mattesia sp. on S. zeamais; Adelina sp. on L. turcicus or R. dominica, and the second report of Nosema sp. on R. dominica. The rate of natural infection by the neogregarine, Mattesia sp. (tentatively, M. dispora), was the highest in L. turcicus beetles (89%) followed by that in P. interpunctella moths (48%), larvae (40%), and pupae (32%) and then in S. zeamais weevils (42%) and R. dominica beetles with a low rate of infection (9%). The microsporidian entomopathogen, Nosema sp., (tentatively, N. whitei) was naturally occurred in 11% of the examined adult cadavers of R. dominica. The coccidian entomopathogen, Adelina sp., was found, respectively, in 60% and 27% of larval and adult cadavers of T.castaneum, while the Adelina-natural infection rates in R. dominica and L. turcicus adult cadavers were 34% and 14%, respectively. A high rate of natural infection with another neogregarine, Farinocystis sp. (tentatively, F. tribolii), has also been recorded in T. castaneum adult (50%) or larval cadavers (36%).

Insecticidal and repellent efficacy of the essential oil from Lobularia maritima and trans-3-pentenenitrile against insect pests of stored grains

ABSTRACT The essential oil from the aerial parts of Lobularia maritima was investigated for its chemical composition, and its repellent and insecticidal efficacy against the grain pests Callosobruchus maculatus, Tribolium castaneum and Sitophilus oryzae. A number of 41 compounds were identified by GC-MS from which azeleonitrile (39.7%), trans-3-pentenenitrile (36.3%) and 4-isothiocyanato-1-butene (10.9%) were the most abundant. A fumigant bioassay-guided fractionation of the essential oil constituents led to the isolation of trans-3-pentenenitrile. Its structure was confirmed by EI-MS and NMR techniques. Fumigant effect of the essential oil was strong (LC50 = 7.48 μL/L) on C. maculatum and moderate on S. oryzae and T. castaneum (LC50 = 35.37 and 59.94 μL/L, respectively). trans-3-pentenenitrile showed strong fumigant effect on the three pest species (LC50 = 6.62–8.36 μL/L). Both the oil and trans-3-pentenenitrile showed strong contact effect with LD50 values in the range 4.84–7.81 µg/adult. The oil showed a repellency of 100% on C. maculatus and S. oryzae at concentrations higher than 0.05 and 0.1 nL/cm2, respectively, and 93% against T. castaneum yet at 0.2 nL/cm2. trans-3-pentenenitrile also showed 100% repellency against C. maculatus (≥ 0.05 nL/cm2), S. oryzae (≥ 0.15 nL/cm2) and T. castaneum (0.2 nL/cm2). The results in this study indicated that the essential oil of L. maritima is an important source of trans-3-pentenenitrile which can be used in the development of insecticidal agents against the three grain pests.

Comparative toxic potential of some plant extracts and spinetoram against Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae)

The comparative toxicity of lemon grass, Cymbopogon citratus (Stapf) (Poales: Poaceae); neem, Azadirachta indica (A. Juss.) (Sapindales: Meliaceae); castor oil plant, Ricinus communis (L.) (Malpighiales: Euphorbiaceae); and yellow oleander, Thevetia peruviana (L.) Lippold (Gentianales: Apocynaceae) and spinetoram alone and in combinations were evaluated against Tribolium castaneum (Herbst, 1797) in the Entomology Laboratory of Punjab Bioenergy Institute, University of Agriculture, Faisalabad, Punjab, Pakistan from May to October, 2018. Different concentrations of plant extracts (5, 10 and 15%) and spinetoram (0.01, 0.02 and 0.03%) were applied in filter paper toxicity bioassay. The results of single applications of all treatments showed that spinetoram was more effective with the highest mortality of 79.8% by followed by 57.9% for A. indica , 49.5% for C . citratus , 40.1% for T . peruviana and 28.9% for R . communis extracts. In combinations, A. indica + spinetoram gave the highest mortality of 84.9% with a lower mortality of 25.2% observed for R. communis + spinetoram. LC 50 values of spinetoram were comparatively low indicating that it is the more toxic than the plant extracts. Overall the results indicated that these plant extracts and spinetoram can be used as combined form in IPM for the efficient management of insect pests of stored grains.

Efficacy of entomopathogenic fungi against the stored-grain pests, Sitophilus granarius L. and S. oryzae L. (Coleoptera: Curculionidae)

Efficacy of the five native entomopathogenic fungi (EPFs), Beauveria bassiana, Isaria fumosorosea, Lecanicillium muscarium, Metarhizium anisopliae, and Simplicillium lamellicola, against adults of the stored-grain insect pests, Sitophilus granarius and Sitophilus oryzae (Coleoptera: Curculionidae), was evaluated under laboratory conditions at two different temperatures. Conidial suspensions (1 × 108 conidia ml−1) of the fungi were directly applied to both the pests in Petri dishes (2 ml per dish), using a Potter spray tower. All the dishes were incubated both at 20 and 25 °C in 16 h light/8 h dark and in 75 ± 5% relative humidity (RH). Dead individuals were counted daily, following treatments, for 7 days. Lethal time values (LT50 and LT90) for EPFs were calculated. The results demonstrated that the mortality rates varied according to both the temperature and the tested EPFs. The highest effect among EPFs at (1 × 108 conidia ml−1) concentration on S. granarius at 20 °C at the end of day 7 was showed by I. fumosorosea (92.69%) and M. anisopliae (90.35%), followed by the other EPFs. Similarly, M. anisopliae and I. fumosorosea were the most effective ones with 90.48 and 84.21% mortality rates, respectively, at 25 °C. However, while M. anisopliae (85.68%) showed the highest effect among all the EPFs applied on S. oryzae at 20 °C, B. bassiana with a mortality rate of 93.66% was the most effective one at 25 °C. LT50 values for I. fumosorosea and M. anisopliae were 2.75 and 2.88/days, respectively, and LT90 values were 4.17 and 4.47/days, respectively, at 20 °C for S. oryzae. However, LT50 values for M. anisopliae on S. granarius in both temperatures were the lowest. This study indicated that M. anisopliae and I. fumosorosea had a significant potential as a biological control agent against S. granarius and S. oryzae. Further studies are necessary to evaluate the efficacy of the isolate on the pests under storage conditions.

Repellent and fumigant toxic potential of three essential oils against Ephestia kuehniella

Essential oils, when used as bio-insecticides in the control of insect pests of stored grains have shown specificity and variation in the potentiality of their mode of action. In the present study, three essential oils extracted from three aromatic plants of different families, white wormwood (Artemisia herba alba, Asteraceae), oregano (Origanum vulgare, Lamiaceae) and rue (Ruta montana, Rutaceae), were evaluated for their repellent and fumigant toxic potential against the flour moth larvae, Ephestia kuehniella (Lepidoptera, Pyralidae), under laboratory conditions. The essential oils extraction was done by the hydrodistillation method. The repellent activity was carried out in Petri dishes using a filter paper treated with different oil dilutions (25, 75, 100, 120, 130, 150 µL/mL). The fumigant toxicity was determined on three concentrations (50, 130, 150 µL/L air). Two plants were shown to be repellent against the E. kuehniella larvae. Origanum oil was the most repellent with 67% of repellency rate followed by Artemisia oil (46%) at 120µL/mL after 2 hours of exposure. The oil of R. montana had an attractant activity against the larvae and was the most toxic with 56.7% of larval mortality in the first 24 hours. The median lethal concentrations (LC50) recorded were 11.6, 175.4 and 1100.0 µL/L air for the plant oils R. montana, O. vulgare and A. herba alba, respectively. R. montana and O. vulgare essential oil are shown to be efficient with high toxic and repellent properties against E. kuehniella larvae. Their specific potential could be integrated in the selection of the best bioinsecticides for the optimum protection of stored grain.

CFD modelling of diffusive-reactive transport of ozone gas in rice grains

The search for alternatives to the use of chemical products to control insect pests in stored grains has stimulated the development of new techniques that allow the maintenance and preservation of grain quality without posing risks to people and the environment. One of these alternatives is the use of ozone gas (O3) as a fumigant, mainly due to its oxidising and biocidal characteristics. To investigate the transport mechanisms involved in the flow of the O3 gas through rice grains, the CFD (Computational Fluid Dynamics) analysis was used, and from this evaluation, it was possible to predict the decomposition reaction constant and the O3 effective diffusion coefficient. In the experiment, grains were submitted to fumigation process in a prototype adapted from a diaphragm cell. Data on the ozone gas concentration were collected from a monitoring point immediately above the grain layer every 10 min. Parallel to the experimental procedure, the modelling of the O3 gas flow using the CFD technique was performed. The adjustment parameters input to the CFD model were the effective diffusion and the decomposition reaction constant of the O3 gas in the rice grains. The estimated diffusivity value (1.0 × 10−6 m2 s−1), and decomposition reaction constant (0.00167 s−1) are of the same order of magnitude of several other gases for agricultural grains.

Oxygen and Arsenite Synergize Phosphine Toxicity by Distinct Mechanisms.

Phosphine is the only fumigant approved globally for general use to control insect pests in stored grain. Due to the emergence of resistance among insect pests and the lack of suitable alternative fumigants, we are investigating ways to synergistically enhance phosphine toxicity, by studying the mechanism of action of known synergists, such as oxygen, temperature, and arsenite. Under normoxia, exposure of the model organism Caenorhabditis elegans for 24 h at 20°C to 70 ppm phosphine resulted in 10% mortality, but nearly 100% mortality if the oxygen concentration was increased to 80%. In wild-type C. elegans, toxicity of phosphine was negatively affected by a decrease in temperature to 15°C and positively affected by an increase in temperature to 25°C. The dld-1(wr4) strain of C. elegans is resistant to phosphine due to a mutation in the dihydrolipoamide dehydrogenase gene. It also exhibits increased mortality that is dependent on hyperoxia, when exposed to 70 ppm phosphine at 20°C. As with the wild-type strain, mortality decreased when exposure was carried out at 15°C. At 25°C, however, the strain was completely resistant to the phosphine exposure at all oxygen concentrations. Arsenite is also a synergist of phosphine toxicity, but only in the dld-1(wr4)-mutant strain. Thus, exposure to 4 mM arsenite resulted in 50% mortality, which increased to 89% mortality when 70 ppm phosphine and 4 mM arsenite were combined. In stark contrast, 70 ppm phosphine rendered 4 mM arsenite nontoxic to wild-type C. elegans. These results reveal two synergists with distinct modes of action, one of which targets individuals that carry a phosphine resistance allele in the dihydrolipoamide dehydrogenase gene.

Male multiple matings and reproductive success in commodity-adapted strains of Sitophilus oryzae

Multiple matings occur in many species of stored-grain insect pests, such as the rice weevil Sitophilus oryzae (L.), with both female and male mating more than once and with more than one partner. Multiple female mating in S. oryzae increased lifetime fecundity by extending the period of time progeny were produced, but consequences of multiple male mating in S. oryzae were not yet studied although it is likely to increase male fitness by increasing offspring production. Here, the effects of polygynous mating on male mating behavior, success, and fitness were assessed in two strains of S. oryzae, one adapted to barley and another to wheat. Two insect strains were considered because they may differ in response depending on the host grain, which present distinct nutritional value to the insects. Mating by pairs formed between the two strains did not impact mating success, but wheat-adapted females exhibited longer mating duration, which was positively correlated with progeny production. Wheat-adapted males exhibited higher fertility than barley-adapted males. When male multiple matings were considered in successive polygynous matings, late matings led to lower non-cumulative values of progeny production, but higher cumulative performance, and wheat-adapted S. oryzae always performed better. Thus, male fitness and grain losses in wheat are higher than in barley, even when S. oryzae was adapted to the latter.

Resistance of Selected Sorghum Genotypes to Maize Weevil (Coleoptera: Curculionidae).

The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is a major insect pest of stored grain. This study evaluated resistance of grain of 26 sorghum genotypes, Sorghum bicolor (L.) Moench, to maize weevil under laboratory conditions. Three female and two male newly emerged maize weevils were reared with 5 g of grain in each of 10 vials for each of the 26 sorghum genotypes in a laboratory experiment. The weevils and grain of each genotype were scored once every 3 wk for a total of five times during 105 d. The numbers of live and newly emerged maize weevils, dead weevils from the initial population, damage score (scale of 1-5), and grain weight loss were used to indicate resistance. The least percentage weight loss of 23.9 and 24.1% was recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had the most weight loss, 70.6 and 67.7%, at 105 d after infestation. Genotypes B.HF8 and (A964*P850029)-HW6 consistently exhibited the highest numbers of maize weevil, 63 and 84, per vial at 105 d after infestation. Sorghum genotypes Sureño, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotype across the five sampling dates. On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with the highest damage rating. Our results indicate that grain of genotype Sureno is most resistant to the maize weevil among screened genotypes.

Diversity and distribution of stored grain insect pests of pulses and their natural enemies

Biodiversity of stored grain insects is often neglected as many of the workers think that it has limited or no diversity as consumer tolerance towards insect pests in stored grains is zero. Survey was conducted in six districts of Hyderabad-Karnataka region to find out the diversity and insects infesting major stored pulses during 2014-15. Callasobruchus analis L., C. maculates F., C. chinensis L. and T. castaneum H. were insect pests observed in collected pulse samples. Dinarmus basalis R., D. vagabundus T.,Dinarmus sp. and Uscana sp. were the hymenopteran parasitoids on pulse beetle collected from the samples. Rank abundance showed that C. analis was dominant species found on stored pulses.

Effects of Dietary Intake of Volcanic ash from Puyehue Cordon Caulle onTenebrio molitor(Coleoptera: Tenebrionidae) Larvae Under Laboratory Conditions

The Puyehue Cordon Caulle volcanic outbreak from 2011 affected the Patagonian Region of Argentina. The insecticidal effect of volcanic ash, as well as other inert dusts, has been proven to occur by contact exposure, disturbing the water balance in insects. However, little has been studied on sublethal effects of volcanic ash or inert dusts on coleopterans through chronic dietary intake. The aim of this study was to gain further understanding on the impact of volcanism on tenebrionid larvae by studying the chronic dietary exposure of volcanic ash in laboratory bioassays. For this purpose, Tenebrio molitor L. (Coleoptera: Tenebrionidae), an insect pest of stored grain, was used as an experimental model organism. Larvae were fed with flour discs prepared with volcanic ash at 500, 1,000, 5,000, 30,000, and 50,000 ppm. Chronic dietary intake of volcanic ash was dose-dependent, with effects visible after long-term exposure (15 and 27 d). Mortality was observed at the two highest concentrations tested (30,000 and 50,000 ppm). At the lower concentrations (500, 1,000, and 5,000 ppm), sub-lethal effects were observed, including larval size decrease, weight loss, and reduction in the number of molts. Thus, chronic dietary intake of volcanic ash causes adverse effects on T. molitor larvae that leads to mortality at high concentrations and decrease of larval size at sub-lethal concentrations.

Variant Linkage Analysis Using de Novo Transcriptome Sequencing Identifies a Conserved Phosphine Resistance Gene in Insects.

Next-generation sequencing methods enable identification of the genetic basis of traits in species that have no prior genomic information available. The combination of next-generation sequencing, variant analysis, and linkage is a powerful way of identifying candidate genes for a trait of interest. Here, we used a comparative transcriptomics [RNA sequencing (RNAseq)] and genetic linkage analysis approach to identify the rph1 gene. rph1 variants are responsible for resistance to the fumigant phosphine (PH3) that is used to control insect pests of stored grain. In each of the four major species of pest insect of grain we have investigated, there are two major resistance genes, rph1 and rph2, which interact synergistically to produce strongly phosphine-resistant insects. Using RNAseq and genetic linkage analyses, we identified candidate resistance (rph1) genes in phosphine-resistant strains of three species: Rhyzopertha dominica (129 candidates), Sitophilus oryzae (206 candidates), and Cryptolestes ferrugineus (645 candidates). We then compared these candidate genes to 17 candidate resistance genes previously mapped in Tribolium castaneum and found only one orthologous gene, a cytochrome b5 fatty acid desaturase (Cyt-b5-r), to be associated with the rph1 locus in all four species. This gene had either missense amino acid substitutions and/or insertion/deletions/frameshift variants in each of 18 phosphine-resistant strains that were not observed in the susceptible strains of the four species. We propose a model of phosphine action and resistance in which phosphine induces lipid peroxidation through reactive oxygen species generated by dihydrolipoamide dehydrogenase, whereas disruption of Cyt-b5-r in resistant insects decreases the polyunsaturated fatty acid content of membranes, thereby limiting the potential for lipid peroxidation.