Stored-grain Pests Research Articles

Using elemental profiling to determine intrinsic markers to track the dispersal of Prostephanus truncatus, a pest of stored grain with alternative natural hosts

AbstractDetecting sources of insects attacking grain stores can help to develop more effective pest management tools. This study considers combinations of chemical elements as intrinsic markers for tracing resource use by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), a pest of stored maize (Zea mays L., Poaceae) which occurs in natural environments where alternative hosts may support reservoirs of infestation. Prostephanus truncatus were laboratory‐reared on maize or field‐caught in pheromone‐baited flight‐traps. Beetles and hosts were screened for multiple elements using inductively coupled plasma atomic emission spectrometry (ICP‐AES). For elements above detection limits, we tested relationships between determinations for various host plants, and for beetles according to environment where captured. An alternative host, Spondias purpurea L. (Anacardiaceae), contained more Al, B, Ca, Cu, Fe, Mg, Si, and Sr than maize, and less P and Zn. Elemental profiles of beetles were associated with environment, with significantly lower Al, Ca, Cu, Cr, Fe, P, S, Si, Sr, Ti, and Zn determinations in maize‐reared beetles than in beetles captured in agricultural or natural environments. Additionally, Al, Ba, K, P, Sr, and Ti determinations of field beetles captured in agricultural vs. natural environments were significantly different. This suggests Al, Sr, and Ti as candidate markers for environment, and possibly others as elemental concentrations (except B, Ba, Ni, and P) were significantly different in comparisons of all field‐collected vs. maize‐reared beetles. We present a robust practical solution which successfully identified combinations of elemental markers for remotely tracing resource use and dispersal by P. truncatus. We discuss the application of chemical characterisation for identifying intrinsic markers of pests, particularly species with alternative hosts. We discuss how to manage the low replication and unbalanced sample sizes inherent in insect elemental screening, particularly when rarer elements are potential markers.

FUMIGATION TOXICITY OF ESSENTIAL OILS AGAINST Rhyzopertha dominica (F.) IN STORED MAIZE GRAIN

ABSTRACT: The Rhyzopertha dominica F. (Coleoptera: Bostrichidae) is a primary pest of stored grains in many regions of the world. In this work we evaluated the fumigant activity of essential oils of Ocimum basilicum L., Citrus aurantium L., Mentha spicata L. and Croton pulegiodorus Baill on adult R. dominica in stored maize. Tests were conducted to determine lethals concentrations (CL50 and CL100) and mortality (fumigation).The fumigation test was done in containers made of glass containing 10 individuals of R. dominica, where essential oils were applied at different concentrations: O. basilicum and M. spicata (5, 10, 15, 20, 30 and 40µL/L of air), C. aurantium (10, 20, 30, 40, 50 and 60µL/L of air) and C. pulegiodorus (0, 20, 30, 50, 70 and 90µL/L of air). After 48 hours of exposure to the oils the percentage of insect mortality was evaluated. According to LC50 and LC100 the toxicity of essential oils decreased in the following order: O. basilicum> M. spicata> C. pulegiodorus> C. aurantium. The essential oil of O. basilicum exhibited strong fumigant toxicity against R. dominica adults, with a LC50 value of 17.67 µL/L air and LC100 value of 27.15 µL/L air. The C. aurantium essential oil required higher concentrations than O. basilicum, M. spicata and C. pulegiodorus to kill insects. However, all oils evaluated presented fumigating property to promote the control of R. dominica and demonstrated potential use in the management of this coleoptera.

Evaluation of different plant powders as seed protectants against rice moth, Corcyra cephalonica Stainton

The present study was aimed to develop the eco-friendly and economic approaches to keep the stored food grains free from insect attack would be using the plant products as grain protectants. In the context of biological control as an alternative to chemical control, under laboratory conditions, different plant powders viz., dharakkernel and leaf (Melia azadirach L.), neem kernel and leaf (Azadirachta indica Adr. Juss), karanj kernel (Pongamia glabra), aak leaf (Calotropis procera Br.), datura leaf (Datura alba Nees.), citrus leaf (Citrus lemon L.), podina leaf (Mentha arvensis) and tulsi leaf (Ocimum sanctum L.) were compared, at three rate of application (1.0, 2.5 and 5.0 g per 100 g seeds), as protectants against infestation of sorghum (Sorghum bicolor (L.) Moench) seeds by the storage pest Corcyra cephalonica Stainton. The larval period of test insect got progressively increased with the increase in dose level of different plant powders. The maximum (77.83%) and minimum (37.83%) reduction in adult emergence was observed in dharak kernel powder and tulsi leaf powder, respectively. The test insect developed on seeds treated with dharak kernel powder laid significantly (P? 0.5) minimum number of eggs (80.33 eggs/ female) followed by neem kernel powder (85.66 eggs/female). The dharak and neem kernel powders were found most effective in reducing the longevity of male (3.96 and 5.13 days) and female adults (4.63 and 4.97 days), respectively. The results suggest that these materials tested have the potential in the development of post-harvest protection technology against, C. cephalonica, the major pest of stored grains.

Real-time cell analysis and heat shock protein gene expression in the TcA Tribolium castaneum cell line in response to environmental stress conditions.

The rust red flour beetle, Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae), is a pest of stored grain and one of the most studied insect model species. Some of the previous studies involved heat response studies in terms of survival and heat shock protein expression, which are regulated to protect other proteins against environmental stress conditions. In the present study, we characterize the impedance profile with the xCELLigence Real-Time Cell Analyzer and study the effect of increased temperature in cell growth and viability in the cell line BCIRL-TcA-CLG1 (TcA) of T. castaneum. This novel system measures cells behavior in real time and is applied for the first time to insect cells. Additionally, cells are exposed to heat shock, increased salinity, acidic pH and UV-A light with the aim of measuring the expression levels of Hsp27, Hsp68a, and Hsp83 genes. Results show a high thermotolerance of TcA in terms of cell growth and viability. This result is likely related to gene expression results in which a significant up-regulation of all studied Hsp genes is observed after 1 h of exposure to 40 °C and UV light. All 3 genes show similar expression patterns, but Hsp27 seems to be the most affected. The results of this study validate the RTCA method and reveal the utility of insect cell lines, real-time analysis and gene expression studies to better understand the physiological response of insect cells, with potential applications in different fields of biology such as conservation biology and pest management.

A garlic substance disrupts odorant-binding protein recognition of insect pheromones released from adults of the angoumois grain moth, Sitotroga cerealella (Lepidoptera: Gelechiidae).

The angoumois grain moth, Sitotroga cerealella, is one of the most serious stored-grain pests worldwide. Control of this moth may be achieved by interfering with olfactory pathways to disrupt male-female communication with sex pheromones, using plant volatiles like garlic or its active substances. Here, three odorant-binding protein (OBP) genes [namely Si. cerealella general OBP 1 (ScerGOBP1), ScerGOBP2 and Si. cerealella pheromone-binding protein (ScerPBP)] were cloned from Si. cerealella antennae, and quantitative real-time PCR showed that these genes were predominantly expressed in adult antennae. ScerPBP expression was male-biased, but ScerGOBP1 and ScerGOBP2 were similar between sexes. The results of competitive binding assays indicated that a garlic substance, diallyl trisulphide (DATS), had similar or even higher binding affinity to ScerPBP than Si. cerealella sex pheromone, 7Z, 11E-hexadecadien-1-ol acetate (HDA). In olfactometer bioassays, DATS significantly reduced the response of adults to HDA when they were exposed to air filled with HDA and DATS. Surprisingly, ScerGOBP2, which is postulated to be involved in the detection of general odours, displayed higher affinity with HDA than did ScerPBP, indicating that ScerGOBP2 may also have a role in pheromone perception. These data suggest that DATS may interfere with recognition of female-produced sex pheromone, disrupting female and male mating behaviour and resulting in a new idea for controlling stored grain pests.

The life cycle of Gregarina cuneata in the midgut of Tribolium castaneum and the effects of parasitism on the development of insects

Tribolium castaneum Herbst 1797 (Coleoptera: Tenebrionidae), an important pest of stored grains and byproducts, is naturally infected by Gregarina cuneata Stein 1848 (Apicomplexa: Gregarinidae). Changes in the life cycle of insects caused by the parasite development in the midgut were studied. Trophozoites, gamonts (solitary and associated), and gametocysts were present in the midgut of the insects. In young trophozoites, the apical region differentiated into an epimerite that firmly attached the parasite to the host epithelial cells. With maturation, trophozoites developed in gamonts that were associated with the initiation of sexual reproduction in the cell cycle, culminating in the formation of the spherical gametocyst. Morpho-functional analyses indicated that gregarines absorb nutrients from infected cells and can occlude the midgut as they develop. Consequently, nutritional depletion may interfere with the host's physiology, causing decreased growth, delayed development, and high mortality rates of the parasitized insects. These results suggest G. cuneata could be an important biological agent for controlling T. castaneum in integrated pest management programs.

Survey of insect pests of stored grain in New Zealand

Producers and processors of cereal grains in New Zealand were invited in August 2015 to submit grain samples to allow extraction and identification of any insect pest species present Sixty grain samples were received of which 73 were infested with one or more insect species These were predominantly Coleoptera and Psocoptera The most frequently encountered beetle species were Oryzaephilus surinamensis Cryptolestes ferrugineus and Cortinicara hirtalis The Psocoptera were predominantly unidentified species of Liposcelis Sitophilus species and lepidopteran pests were notable by their absence The proportion of storage facilities infested by insects in this survey (73) was higher than two previous surveys (38 5063) and the proportion of storage facilities treated with insecticides (62) was lower than a previous survey (83)

Chemical pesticides and vegetal extracts on Sitophilus zeamais control in stored corn grains

Sitophilus species are major pests of stored grain and their control is achieved mainly with the use of chemical insecticides, but the indiscriminate use of these products is resulting in several undesirable factors to man and to the environment. Thus, the use of natural insecticides comes as an option to control the insects, while lessening risks to the environment. The study was conducted at the Institute of Agricultural Sciences and Technologies, Rondonopolis campus of the Federal University of Mato Grosso, in the period from March to September 2012. The experiment was conducted under three different storing conditions. Aqueous extracts were obtained by the addition of Allium sativum L , Azadirachta indica A. Juss . and Cymbopogon winterianum Jowitt vegetable powders in distilled water, at a ratio of 5 g per 100 ml, and the levels of chemical insecticides were of 0.04 and 0.15 ml/100 ml of water for deltamethrin and chlorpyrifos, respectively. Treatments were added to the corn grains, which were placed in a 2.5 L glass container, mixed by manual shaking and infested with 20 adults of unsexed Sitophilus zeamais . Grains were stored for 60 days. At 30 and 60 days, the following items were analyzed: bugs count, water content in grains and electrical conductivity. The data were submitted to analysis of variance, and means were compared by Tukey test at 5% probability. At 30 days, the efficiency of chemical insecticides in the control of Sitophilus zeamais was observed in the three storage environments. Vegetal extracts were not effective in controlling insects. The larger number of insects increased the electrical conductivity and humidity values in the grains. n.

Insecticidal properties of some plant products againstSitophilus oryzaefrom hill and tarai region of Uttrakhand

Experiments were conducted to test the effectiveness of 12 botanical powders against Sitophilus oryzae, a pest of stored grain attacking PBW 343 variety of wheat. Percent grain weight loss and percent reduction in adult emergence of the pest was recorded to evaluate the extent of damage caused by insects. Overall finding indicate that out of 12 plant products tested Acorus calamus @ 1.5 and 0.75 % w/w was most effective in controlling the population of the pests.

Use of sulfuryl fluoride in the management of strongly phosphine-resistant insect pest populations in bulk grain storages in Australia

Sulfuryl fluoride (SF), an effective structural fumigant, is registered recently as Profume™ for controlling insect pests of stored grains and processed commodities. Information on its effectiveness in disinfestation of bulk grain, however, is limited. The ongoing problem with the strong level of resistance to phosphine has been addressed recently through deployment of SF as a ‘resistance breaker’ in bulk storages in Australia. This paper discusses important results on the efficacy of SF against key phosphine- resistant insect pests, lesser grain borer, Rhyzopertha dominca, red flour beetle, Tribolium castaneum, rice weevil, Sitophilus oryzae and the rusty grain beetle, Cryptolestes ferrugineus. We have established CT (g-hm3) profiles for SF against these insect pests at two temperature regimes 25 and 30°C, that showed that both temperature and exposure period (t) has significant influence on the effectiveness of SF than the concentration. Over a seven days fumigation period, CTs of 800 and 400 g-hm3 achieved complete control of all the target pests, including the most strongly phosphine - resistant species, C. ferrugineus at 25 and 30°C, respectively. Results from four industry scale field trials involving currently registered rate of SF (1500 g-hm3) over 2–14 d exposure period, confirmed its effectiveness in achieving complete control of the target pest species. The assessment of postfumigation grain samples across all the test storages indicated that the reinfestation occurs after three months. Monitoring resistance to phosphine in C. ferrugineus over a six year period (2009–2015), showed a significant reduction in resistant populations after the introduction of SF into the fumigation strategy at problematic storage sites. Overall our research concludes that SF is a good candidate to be used as a ‘resistance breaker’ where phosphine resistance is prevalent.

Storage insect pests and their damage symptoms: an overview

Stored product pests gain access to the grain storage from the standing crop in the field to various stages of grain processing and storage. Although, about one thousand species of insects have been associated with stored products in different parts of the world, a few pests are considered as pests causing severe damage to the stored grains. The stored grain insect pests can be categorized on the basis of their feeding behaviour as internal and external feeder or as major and minor pests based on the severity of damage, they cause. This paper gives an overview of damage symptoms and biology of some of the major pests of stored grains viz., rice weevil, Sitophilus oryzae, lesser grain borer, Rhyzopertha dominaca, khapra beetle, Trogoderma granarium, red flour beetle, Tribolium castaneum, cigarette beetle, Lasioderma serricorne, drug store beetle, Stegobium paniceum, pulse beetles Callosobruchus spp., Angoumois grain moth, Sitotroga cereallela, rice moth Corcyra cephalonica, saw toothed grain beetle Oryzaephilus surinamensis, long headed flour beetle, Latheticus oryzae, and almond moth Cadra cautella.

Evaluación de extractos totales como repelente para el control de Tribolium castaneum Herbst, 1979 (Coleoptera: Tenebrionidae)

Objective: To evaluate the repellent activity of six total extracts derived from plants of the departmento de Choco. The repellent activity of the total extracts was tested against adult insects of Tribolium castaneum Herbst, 1979, pests of stored grains. Methodology: During in vivo tests, the repellent activity was measured using the area preference technique by quantifying the obtained percentage of repellency at different exposure concentrations. The results were analyzed by paired t-test to determine signi cant differences (p<0.05). Moreover, the comparison between the repellency percentages (RP) the different extracts was performed using analysis of variance (ANOVA) by means of Dunn’s post test to assess comparisons with the positive control. Results: The evaluated extracts showed a proportional increase of its repellent activity to the concentration increase showing an independent effect. As a result, the more effective extracts were the derived from Ocimum campechianum variedad blanca, Piper divaricatum and Palicuria guianensis with repellency percentages of 92%, 75% and 74% respectively. Conclusions: These results presents suggest a potential use of the six plants extract tested to control T. castaneum from which, O. campechianum var white extract is the most recommended as it showed high repellent activity. Additionally, this study constitu- tes a big contribution to bio-prospecting of Choco Flora and to the sustainable development of the region.

English

The maize weevil Sitophilus zeamais is a primary pest of stored grains, and it is primarily controlled through the use of synthetic insecticides, which are directly connected to increases in the resistance of these insects. In this study, populations of S. zeamais acquired from small farmers in southern Piaui were obtained, and an experiment was performed with the insecticide K-Obiol EC25, with dose-response concentrations ranging from 3.5 ´ 10-4 to 0.05 g i.a/cm2. Five replicates containing 20 insects were used. For the amylase, lipase and total protease assays, 20 adult insects from each population were used separately for each treatment. The experiments performed with K-Obiol for the insect populations from different locations showed different LC50 values. The highest LC50 value was from Currais at 94.0 µg i.a/cm2, and the lowest value was from Bom Jesus at 14.0 µg i.a/cm2. The specific activities of the energy metabolism enzymes (lipase and amylase) responsible for sugar hydrolysis in four populations of S. zeamais exposed to the insecticide K-Obiol at different times (1, 6, 12 and 24 h) were determined. In all of the populations, the greatest amylase activity was observed in the group of insects exposed to the insecticides for 12 h. The population from Currais showed greater lipase activity in the treatment with 1 h of exposure to deltamethrin, whereas the population from Colonia showed the lowest lipase activity in the treatment with 24 h of exposure. Key words: Deltamethrin, enzyme activities, amylase, lipase, protease.

Phytochemical Analysis of Methanolic Extracts of Artemisia absinthium L. 1753 (Asteraceae), Juniperus phoenicea L., and Tetraclinis articulata (Vahl) Mast, 1892 (Cupressaceae) and evaluation of their biological activity for stored grain protection

Research is increasingly focused on identifying alternatives to the use of chemicals for the management of pests in stored grains. In this context, we tested the insecticidal and antifungal activities of methanolic extracts of Artemisia absinthium L. (Asteraceae), and two Cupressaceae species, namely Juniperus phoenicea L. and Tetraclinis articulata (Vahl) Mast., collected in the north of Algeria, against Sitophilus oryzae L. (Coleoptera, Curculionidea)—a pest of primary infestation of stored grains—and Fusarium sp., mycotoxigenic fungi. The extracts were analyzed by UPLC-PDA-MS. The extraction yield was in the range of 11–21 %. UPLC chromatographic data showed the presence of several phenolic acids, flavonoid glycosides, and flavonoid aglycones. Insecticidal activity was evaluated by means of contact toxicity test, which showed that all three extracts were highly effective. Pest mortality was recorded after 24 h for A. absinthium. The LC50 results revealed that the most toxic extract was that of A. absinthium (15.53 mg/cm2), followed by that of J. phoenicea (22.14 mg/cm2), and T. articulata (24.05 mg/cm2). The antifungal activities of these extracts were evaluated using the poisonous medium technique on potato dextrose agar medium. All three extracts reduced the growth of Fusarium culmorum and F. graminearum under in vitro conditions. T. articulata had the greatest inhibitory effect (55.8 %) on mycelial growth of the former. Our results reveal the potential of plant methanolic extracts to control pests common to stored grains.

English

Essential oil fractions from dried seed powder of Piper guineense were analyzed by gas chromatography-mass spectrometry (GC-MS) and evaluated for their insecticidal effects on Sitophilus oryzae L. The GC-MS analysis showed quantitative and qualitative differences between the oil fractions. Chromatographic results revealed chemical constituents like eugenol, piperanol, pinene, carene, copaene with insecticidal properties. New chemotypes were seen in the different fractions. Instead of &beta;-caryophyllene reported in literature, &alpha;-caryophyllene was found in all the different fractions. Caryophyllene oxide, an oxygen-containing sesquiterpene was present in all fractions except n-hexane. In addition to &alpha;-phellandrene present in all, &beta;-phellandrene, a monoterpene hydrocarbon was found in the n-Hexane fraction. Contact toxicity on wheat grains showed that all fractions caused significant (P &lt; 0.001) mortality of the weevils. The oil fractions also showed variable contact toxicity on impregnated filter paper. All doses of the n-hexane fraction were very toxic to the test insect than the control, causing 100% mortality after five days of exposure. All the fractions produced a strong repellent activity against the test insect. These results suggest that P. guineense has potentials for development as an organic insecticide against S. oryzae and other pests of stored grains. Key words: Piper guineense Schum. et Thonn., essential oil fractions, chemotypes, toxicity, repellency, Sitophilus oryzae (L.).&nbsp

New ‘stimuli-enriched’ laboratory bioassay used to identify improved botanical repellent treatment, Lem-ocimum, to control the stored-grain pest Tribolium castaneum

A laboratory study of Tribolium castaneum, a major pest of stored grain, was conducted to develop a more efficient and effective ‘choice’ bioassay for identification of new repellent botanical treatments. Standard bioassays to test the repellency of candidate plants include pit-fall traps and open arena choice tests, environments lacking in some of the most important natural stimuli that guide the movement of food-searching beetles, e.g., 1) materials they can burrow through, which stimulate ‘positive thigmotaxis’, 2) a range of light and dark areas, which stimulate ‘negative phototaxis’ and 3) three-dimensional habitats, which stimulate ‘positive geotaxis.’ The lack of these stimuli can lead to two common problems; ‘low efficiency’ (high proportion of beetles remain in the area that surrounds treatments without making a ‘choice’), and ‘low efficacy’ (high variability in proportions found in control and treated samples). The new ‘stimuli-enriched’ bioassay, which included all three of the above stimuli, was significantly more efficient (P < 0.0001) and effective than three standard bioassays. The stimuli-enriched bioassay was used to compare the repellency of four candidate plants; Ocimum basilicum (Sweet Basil) and Cymbopogon nardus (Lemongrass) were significantly more repellent than Vernonia amygdalina or Nauclea diderrichii (Tukey Contrasts; P < 0.01). A novel method of applying repellent material (a paste of repellent plant is applied between the layers of double bagged grain) was tested on the most promising repellent plants materials; a combination of C. nardus and O. basilicum (‘Lem-ocimum’) at 0.5% w/w of each was significantly more effective than O. basilicum on its own (Tukey Contrasts; P < 0.05). These results show that the stimuli-enriched bioassay provides more consistent and accurate assessments than the standard bioassays of the repellency of candidate botanicals, and that Lem-ocimum treated double-bags are a promising new method of protecting sorghum from T. castaneum.

Grain storage and insect pests of stored grain in rural Niger

We surveyed 1293 farmers and traders in southern Niger to learn about their grain storage practices and their views on the storage pest problem. We identified the insect species found in samples obtained from 40 localities in three regions of the country. We stored 371 grain samples collected from respondents in the laboratory for seven months to allow populations of the insects present to develop and emerge and the resultant grain weight loss to be determined. The commodities most commonly stored in Niger were millet and sorghum, kept in storage on average for about 6 months by 53% and 80% of respondents respectively. When millet samples from respondents were kept in the laboratory for seven months, two pests were found, the rice moth Corcyra cephalonica Stainton, and Tribolium spp. This millet experienced a weight loss of 17.1% during seven months storage. Tribolium castaneum Herbst, Sitophilus granarius L., Cryptolestes spp, Sitotroga cerealella Oliver, Trogoderma granarium Everts, Rhyzopertha dominica F. and C. cephalonica were found in stored sorghum, which lost 10.1% weight after seven months. Eleven other grains or foods were stored by 2.9–24.4% of respondents. Recorded weight losses were 15.9% for groundnuts, 12.6% for paddy rice, 7.6% for sesame and 7.4% for maize. Seeds of Hibiscus sabdariffa L. and Bambara groundnut were essentially destroyed by bruchids during storage, mean weight losses being 83.9% and of 61.8% respectively. Most respondents took no measures to control insect pests in their stored grains. Food security and quality in Niger would be greatly improved if Africa-manufactured technology that is safe, low-cost, insecticide free, and widely available could be implemented for postharvest storage of food grains.

Detrimental effects of electron beam irradiation on the cowpea bruchid Callosobruchus maculatus.

Electron beam (eBeam) irradiation technology is an environmentally friendly, chemical-free alternative for disinfesting insect pests of stored grains. The underlying hypothesis is that specific doses of eBeam will have defined detrimental effects on the different life stages. We evaluated the effects of eBeam exposure in a range of doses (0.03-0.12 kGy) on the development of the cowpea bruchid (Callosobruchus maculatus) at various stages of its life cycle. Differential radiosensitivity was detected during egg development. Early and intermediate stages of eggs never hatched after exposure to a dose of 0.03 kGy, whereas a substantial portion of black-headed (i.e. late) eggs survived irradiation even at 0.12 kGy. However, further development of the hatched larvae was inhibited. Although midgut protein digestion remained intact, irradiated larvae (0.06 kGy or higher) failed to develop into normal living adults; rather, they died as pupae or abnormally eclosed adults, suggesting a detrimental effect of eBeam on metamorphosis. Emerged irradiated pupae had shorter longevity and were unable to produce any eggs at 0.06 kGy or higher. At this dose range, eggs laid by irradiated adults were not viable. eBeam treatment shortened adult longevity in a dose-dependent manner. Reciprocal crosses indicated that females were more sensitive to eBeam exposure than their male counterparts. Dissection of the female reproductive system revealed that eBeam treatment prevented formation of oocytes. eBeam irradiation has very defined effects on cowpea bruchid development and reproduction. A dose of 0.06 kGy could successfully impede cowpea burchid population expansion. This information can be exploited for post-harvest insect control of stored grains.

Morpho-functional characterization and esterase patterns of the midgut of Tribolium castaneum Herbst, 1797 (Coleoptera: Tenebrionidae) parasitized by Gregarina cuneata (Apicomplexa: Eugregarinidae)

Tribolium castaneum (Coleoptera: Tenebrionidae) is a common pest of stored grains and byproducts and is normally infected by Gregarina cuneata (Apicomplexa: Eugregarinidae). The life cycle of this parasite includes the sporozoite, trophozoite, gamont, gametocyte, and oocyst stages, which occur between the epithelium and lumen of the host's midgut. This study aims to describe the morphofunctional alterations in the midgut and determine the esterase patterns in T. castaneum when parasitized by gregarines. To achieve this purpose, midguts of adult insects were isolated, processed, and analysed using light and electron microscopy. We determined total protein content, amylase activity, and the expression and related activities of the esterases by using polyacrylamide gel electrophoresis (PAGE). The midgut of T. castaneum is formed by digestive, regenerative, and endocrine cells. The effects of parasitism on the digestive cells are severe, because the gregarines remain attached to these cells to absorb all the nutrients they need throughout their development. In these cells, the most common alterations observed include expansion and fragmentation of the rough endoplasmic reticulum, development of the smooth endoplasmic reticulum, changes in mitochondrial cristae, cytoplasmic vacuolization, formation of myelin structures, spherites, large intercellular spaces, autophagic vesicles, expansion of the basal labyrinth, and cytoplasmic protrusions. Deposits of glycogen granules were also observed. Amylase activity was reduced in parasitized insects. Regenerative cells were found in disorganized crypts and did not differentiate into new cells, thus, compromising the restoration of the damaged epithelium. Though few morphological alterations were observed in the endocrine cells, results suggest that the synthesis and/or release of hormones might be impaired. Nine esterases (EST-1 to 9) were identified in the midgut of T. castaneum and were expressed in varying levels in response to parasitism. Two additional isoforms of esterases were exclusively identified in the parasitized insects. The results of this study suggest that gregarines alter the morphology and physiology of the midgut. The changes may result in nutritional depletion and the impairment of other physiological processes, such as reproduction and development of the host. Thus, further studies are needed to uncover the possibility of utilizing gregarines as biological controllers of the insect pest population.

Identification of chemosensory gene families inRhyzopertha dominica(Coleoptera: Bostrichidae)

AbstractChemoreception is a key process for insects. Odorant messages diffuse through the air and are translated into physiological signals by chemosensory receptor neurons in sensilla that are mainly located on insect antennae. We sequenced the antenna transcriptome ofRhyzopertha dominica(Fabricius) (Coleoptera: Bostrichidae), which is a serious pest of stored grains throughout regions with warm climates, and performed transcriptome analysis onR. dominicaantennae. We obtained 57 million 90-base pair-long reads that we assembled into 37 877 unigenes with a mean size of 1007 base pairs. Predicted protein sequences were matched withTribolium castaneum(Herbst) (Coleoptera: Tenebrionidae) (79.1%),Dendroctonus ponderosaeHopkins (Coleoptera: Curculionidae) (1.7%),Megachile rotundata(Fabricius) (Hymenoptera: Megachilidae) (1.3%),Acyrthosiphon pisumHarris (Hemiptera: Aphididae) (1.2%), and other (16.7%) homologues. In chemosensory gene families, we identified transcripts that encoded the following putative genes: 12 odorant-binding proteins (OBPs), four pheromone-binding proteins (PBPs), eight chemosensory proteins (CSPs), five sensory neuron membrane proteins (SNMPs), six odorant receptors, and eight ionotropic receptors. The diversity of the predicted OBPs, PBPs, and CSPs are also discussed. These findings will advance our understanding of olfaction process by this pest.