Bean Weevil Acanthoscelides Obtectus Research Articles

Inheritance of the Resistance to Acanthoscelides obtectus (Say.) in a Heterogeneous Inbred Families Population of Common Bean (Phaseolus vulgaris L.)

The bean weevil Acanthoscelides obtectus is one of the world’s main pests of stored beans. The heterogeneous inbred family (HIF) population of near-isogenic lines (NILs) could be an exceptional strategy to study the inheritance of the resistance against A. obtectus. We developed a HIF population of 148 NILs of R-bufa-80-12. The objectives of this research were as follows: (1) to study and understand the genetics of the attack resistance to A. obtectus in a HIF population and (2) to identify the best lines to provide weevil resistance. The pure lines of the HIF population showed a great variability for all the analyzed traits. The traits studied in this research have a normal distribution showing continuous variation, so they are considered to be quantitatively inherited. The heritabilities for resistance traits were low and very low, ranging from 0.09 to 0.17. The heritability for 100 seed weight was the highest, with a significant value of 0.90. The best lines of the HIF population for resistance to A. obtectus comprised Line-45, Line-129, Line-124, Line-142 and Line-47. In general, these lines presented lower preference of adults, and lower consumption in grams and in percentages. However, lines 45 and 129 are the most interesting from a commercial point of view because they combine resistance and seed weight.

Bean weevil Acanthoscelides obtectus (Say) survival and progeny production affected by residual insecticide deposits, and related damage of two types of bean

The bean weevil, Acanthoscelides obtectus (Say) is a serious pest of stored bean seeds. In an effort to improve current management programs the intention of our study was to assess in the laboratory the impact of insecticide deposits on weevil survival and progeny production after 0, 7, 14, 30, 75, 120 and 165 days of residual activity on beans, and the related bean damage. Two bean types (Gradištanac and Biser) were dusted by malathion (10 mg AI/kg, DP formulation), and treated by water dilutions of spinosad (1 mg AI/kg, SC formulation) and two deltamethrin products, either without the synergist piperonyl butoxide – PBO (0.25 mg AI/kg, SC formulation) or with PBO (0.25 mg AI/kg + 2.25 mg AI/kg, EC formulation). Weevil survival was assessed after 2, 7 and 14 days of exposure and after 0 and 7 days of recovery. Progeny production and damage (kernel damage and weight loss), were assessed after additional 8 weeks. Malathion residual deposits showed the highest effectiveness on survival (no survived weevils), while deltamethrin deposits with PBO were the least effective, i. e at the same level or lower than weevil survival in untreated beans. The highest impact in terms of progeny production and damage were showed by the residual deposits of both deltamethrin formulations (no progeny or damage). In the presence of spinosad and malathion deposits, we recorded low progeny and damage, significantly under the economic threshold. No significant differences between Gradištanac and Biser types were recorded in treatments, while higher progeny and damage we recorded by the control Gradištanac bean than the Biser type, which exceeded economic threshold. Our data show that residual deposits of all tested insecticides on bean kernels demonstrated high control potentials against A. obtectus but deltamethrin deposits, especially with PBO, caused high variation in weevils response.

Insecticidal Effect of Pătârlagele Diatomaceous Earth Against Acanthoscelides Obtectus Adults

In the present study there are presented the results obtained in laboratory tests to evaluate the efficacy of the Romanian diatomaceous earth from Pătârlagele deposit in Buzău County (DE PatRom) against adults of three population of the bean weevil Acanthoscelides obtectus L. (one maintained in laboratory conditions at the Plant Protection Institute Bucharest and the others two came from fields bean from Buzău and Bacău) compared with two commercial formulations (SilicoSec® and PyriSec® ). The DE PatRom was applied at four doses 100, 300, 500 and 900 ppm while SilicoSec® and PyriSec® at the doses registered in common practice. Tests were carried out at 25±2°C and at 70± 5% relative humidity (RH). Adult mortality was assessed 3, 7 and 14 days after treatment. The PyriSec DE was the most effective reaching a total mortality of adults for all three insect populations tested even after 3 days, followed by SilicoSec DE which caused mortality between 74 and 99% after 3 days and 100% after 7 days. The mortality levels of A. obtectus adults reached by Romanian DE PatRom varied depending on dose, period after treatment and insect population. The mortality of bean weevil increased with increasing dose and period after treatment. The highest mortality (of 93, 96 and 98.5% to adults in Buzău, Bucharest and Bacău population, respectively) was recorded in bean treated with 900 ppm after 7 days. The results in experiments showed that the A. obtectus adults of Bacău population were more susceptible and those of Buzău population were more tolerant to all DEs tested.

Insecticidal Effects of Two Plant Extracts of (Bidens pilosa and Rumex dentatus) and Neem Oil Against Certain Stored Grains Insects.

The insecticidal activities of methanolic extracts of two weedy plants leaves Bidens pilosa L. and Rumex dentatus L. at three different concentrations 3, 5 and 7% were tested against three stored grain pests, Rice weevil Sitophilus oryzae L. Saw-toothed grain beetle Oryzaephilus surinamensis L., and Bean weevil Acanthoscelides obtectus Say, compared to Neem oil as a commercial product at the same concentrations for exposure periods 24, 48, 72 and 96 hrs of treatment under laboratory conditions. Results revealed that different concentrations and exposure periods of the two extracts and Neem oil had significant lethal effects against these tested grain pests. In general, R. dentatus extract was found to be the most toxic against the tested grain pests and caused the highest mortality (100.00%) for the three pests S. oryzae, O. surinamensis and A. obtectus when applied at its highest concentration (7%) for an exposure time of 96 hrs (the highest time), followed by Neem oil 90.0±10.0, 70.00±13.3 and 90.00±2.8%, then B. pilosa extract 75.83±5.8, 79.33±5.46 and 87.50±7.2%, respectively at the same concentration and exposure time, indicating that the obtained mortality percentages were concentration and exposure time-dependent. Finally, these results demonstrate that, R. dentatus extract can be used as a promising pesticide against the three stored products insect pests investigated under this study, and strongly recommended to be used as stored grain protectants in the future.

Toxic, Oviposition Deterrent and Oxidative Stress Effects of Thymus vulgaris Essential Oil against Acanthoscelides obtectus.

Simple SummaryCompounds of botanical origin, including essential oils (EOs), which coevolved as plant defense mechanism against herbivores and pathogens have been proposed as a promising strategy for post-harvest control of stored product insects. Despite several drawbacks, such as low stability, phytotoxicity and food odor changes at high concentrations, EOs are believed to be safe for human and environmental health and thus have an advantage comparing to conventional insecticides. The present study was aimed to examine acute toxicity and effects of thyme (Thymus vulgaris) EO on longevity, behavior and physiology of the bean weevil (Acanthoscelides obtectus), a major pest of stored bean seeds. We found that exposure to thyme oil reduced adult survival and longevity and induced damages to lipids and proteins in a concentration-dependent manner. Sublethal EO concentrations also deterred female egg laying and strongly inhibited adult emergence. Efficacy of such low EO concentrations in suppression of adult emergence implies that thyme EO might be cost-effective and environmentally low risk botanical insecticide for bean seed protection against A. obtectus.The bean weevil Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae) can cause significant losses in production of its primary host common bean Phaseolus vulgaris L. To avoid bean protection with environmentally risky chemical insecticides and provide sustainable and safe production of food, new pest management methods based on natural compounds are investigated. In the present study, we evaluated protective potential of the essential oil (EO) from the common thyme Thymus vulgaris L. applied on bean seeds. We assessed residual contact toxicity of thyme EO and its effects on A. obtectus longevity, oviposition and adult emergence. Furthermore, to elucidate the role of oxidative stress in thyme EO toxicity, we estimated the levels of oxidatively damaged proteins and lipids, as well as the level of thiols which have important role for antioxidant capacity. We found that thyme oil significantly reduced adult survival and longevity, induced oxidative damage to lipids and proteins and depleted protein and non-protein thiols in a concentration-dependent manner. Females appeared to be more tolerant to thyme oil treatment than males. Sublethal EO concentrations affected oxidative stress indices, deterred oviposition and strongly inhibited adult emergence. The results suggest that thyme oil has the potential to be used as an ecofriendly insecticide for A. obtectus control.

Inheritance and metabolomics of the resistance of two F2 populations of Phaseolus spp. to Acanthoscelides obtectus

The bean weevil Acanthoscelides obtectus is one of the major storage pests of dry bean. Tepary bean (Phaseolus acutifolius) is a great source of resistance against A. obtectus to improve dry bean production. We developed two F2 populations of Phaseolus spp. by crossing bean genotypes resistant to A. obtectus × susceptible, to (1) search for metabolites related to bean weevil resistance using an untargeted metabolomics approach and (2) understand the genetics of resistance to A. obtectus attack using the number of adults emerged from seeds as resistance criteria. The segregation of the number of adults emerged from seeds showed that the genetics of resistance (0 emerged adults = resistant, 1 or more emerged adults = susceptible) was controlled by a single dominant gene in two (resistant × susceptible) F2 populations. From nine metabolites detected, pipecolic acid concentration was significantly higher in the testa of resistant individuals than in the testa of susceptible individuals. From a breeding point of view, (P. Saltillo × T. amarillo) F2 is of special interest because it is derived from a cultivated tepary × cultivated common bean cross and showed 3:1 resistant vs susceptible segregation. Therefore, this F2 is a suitable base material for breeding programmes to obtain new bean lines with good agronomic performance, seed quality and resistance to insect attack. Pipecolic acid plays a role in resistance against A. obtectus.

The Beetles (Coleoptera) dangerous for Japanese quail Coturnix japonica Temminck et Schlegel, 1849 (Phasanidae) at farms

Reproduction of the Japanese quail, Coturnix japonica Temminck et Schlegel, 1849, at private farms has led to the formation of a complex of insects harming this species of birds. Darkling beetles Alphitobius diaperinus (Panzer, 1796) and A. laevigatus (Fabricius, 1781) (Coleoptera, Tenebrionidae) are the main pests of Japanese quail. Alphitobius diaperinus had already been recorded causing damage to the poultry industry in Crimea. Its larvae and adults attack chicks in the mass. Significant cannibalism is recorded for A. laevigatus in laboratory conditions. We suppose that complex of harmful insects will be added by species of the genus Ulomoides Blackburn, 1888, namely U. dermestoides (Chevrolat, 1878) imported into Ukraine. Properties of the adopted wreckers, providing their invulnerability in poultry houses, are first shown, namely: mass breeding of A. diaperinus due to feeding on other birds, ability of females of U. dermestoides to oviposit eggs during 1,5 month after the singular copulation, duration of the larval stage up to 96–110 days (usually one month long) due to a cannibalism only. The features of development and behavior of U. dermestoides are shown resembling these of A. diaperinus. The results of studies on the lifecycle’ peculiarities carried out at 2012–2019 under the laboratory conditions are given. The practical role of A. diaperinus, A. laevigatus and U. dermestoides is discussed. The forecast regarding the negative impact of U. dermestoides on the aviculture development in the Southern Ukraine is presented. The data on the poisoning of birds (C. japonica) with beetles of bean weevil Acanthoscelides obtectus (Say, 1831) (Chrysomelidae, Bruchinae) are shown. Present contribution is beneficial not only for specialists in fundamental research, but also for practitioners, in particular for personnel of State Veterinary and Plant Health as well as the State Sanitary and Epidemiological Service. First worked out and recommended a production trap for a fishing-out in the poultry houses of harmfuls beetles and their larvae at the presence of birds.

New Data on Vibrational Communication in the Beetle Acanthoscelides obtectus (Coleoptera, Bruchidae)

Many Bruchidae species are quarantine pests and are widely used as model species. However, as far as we know, acoustic communication has never been studied in detail in this group. Below we present the first data on the repertoire and emission mechanisms of acoustic communication in the bean weevil Acanthoscelides obtectus. Three types of signal emission were recorded in A. obtectus: striking the head and abdomen against the substrate, abdominal tremulations, and wing vibrations. Two types of signals were recorded in males, and one type, in females. All the acoustic signals recorded in A. obtectus contained both stable (pulse duration, pulse period: CV = 5–12%) and variable (duration of the pulse series: CV = 50%) signal elements. The frequency parameters showed low variation in all the signals (CV = 5–11%). Moreover, the dominant frequencies were similar in all the signal types (889–1158 Hz).

Contact application of Lamiaceae botanicals reduces bean weevil infestation in stored beans

The bean weevil (Acanthoscelides obtectus, Say) is a serious pest of stored bean seeds. Bean weevil control relies heavily on the use of synthetic insecticides. In the search for a sustainable alternative, the residual contact toxicity and anti-oviposition activity of thyme (Thymus vulgaris L.), rosemary (Rosmarinus officinalis L.) and basil (Ocimum basilicum L.) essential oils as well as their dominant components (thymol, ?-pinene, 1,8-cineole and linalool) were tested against A. obtectus adults. Out of the seven tested botanicals, T. vulgaris oil, thymol and linalool exhibited the highest toxic potential (>90% mortality). Females were less susceptible than males. The insecticidal activity of these botanicals was much greater when they were applied on glass compared to direct application to the bean. All tested botanicals reduced oviposition by bean weevil females. T. vulgaris oil, thymol and ?-pinene also deterred bean weevil oviposition, as revealed by a two-choice test. Our research shows that T. vulgaris oil and thymol are promising and sustainable alternatives to synthetic pesticides for protecting stored beans against the bean weevil.

Biochemical properties of Turkish common beans and their resistance against bean weevil Acanthoscelides obtectus (Coleoptera: Bruchidae)

Beans (Phaseolus vulgaris L.) with highly nutritional values are cultivated worldwide. Bean seeds are commonly exposed to bruchid attacks throughout the storage. Acanthoscelides obtectus (Say), also known as the bean weevil, is one of the most important insect pests and causes significant economic losses each year in warehouses. Chemical and alternative methods are commonly used to control A. obtectus. However, alternative control methods are getting popular because of negative impacts of chemicals on environment and human health. Identification and development of natural resistant bean genotypes may constitute a good alternative in fighting against bruchid pests. In this study, seed testa thickness and biochemical properties of 13 commonly grown Turkish bean genotypes were investigated, their resistance against damage caused by A. obtectus was determined, and finally the correlations among all these parameters were investigated. The highest ash and oil content was observed in Yakutiye-98 genotype while the highest protein and fiber ratio was observed in Noyanbey-98 and Zulbiye genotypes, respectively. The highest moisture ratio was observed in Karacasehir-90 genotype. Akdag, Akman-98, Noyanbey-98 and Kirikkale genotypes were found to be more resistant against A. obtectus than the other genotypes and the lowest infection rates were detected in these genotypes. Consequently, Akdag, Akman-98, Noyanbey-98 and Kirikkale genotypes which were resistant to A. obtectus can be recommended to farmers for cultivation in Turkey.

Characterization of resistance to the bean weevil Acanthoscelides obtectus Say, 1831 (Coleoptera: Bruchidae) in common bean genotypes

The bean weevil Acanthoscelides obtectus (Say, 1831) (Coleoptera: Bruchidae) is one of the most serious pests of stored beans worldwide because of the damage it causes to grains within warehouses. The use of resistant genotypes may offer a control strategy for this pest. In the current study, we screened common bean genotypes of Andean American and Mesoamerican origin in laboratory and greenhouse bioassays to select the most promising beans for resistance to the bean weevil. In the laboratory, we evaluated number of eggs, period of development (egg-adult), number of emerged adults, dry weight of adults, and weight of consumed grains. In the greenhouse, number of pods per plant and number of grains per pod were evaluated. We also assessed the percentages of damaged pods per plant and damaged grains per pod. Combining the results obtained in the laboratory and greenhouse assays, the common bean genotypes Arc.1, Arc.2, Arc.1S, Arc.5S, and Arc.3S were identified as resistance expressing antibiosis against A. obtectus. The lowest percentages of damaged pods were found in the Arc.1 and Arc.1S genotypes, and their resistance to damage was apparently morphological (antixenotic) because they possessed structures that prevented contact between larvae and grains. The use of resistant genotypes in combination with other techniques may improve management of the weevil. Additionally, the resistant genotypes identified here can be used in breeding programs to develop common bean lines with resistance to A. obtectus.

Changes in the insecticide susceptibility and physiological trade-offs associated with a host change in the bean weevil Acanthoscelides obtectus

For most of the seed weevils (Coleoptera: Chrysomelidae: Bruchinae), the ability to survive environmental stresses like insecticide exposure and reproduction is variable and depends on the host. Here, we evaluated the physiological costs and benefits of a host shift from kidney beans of the landrace “Vermelho” to cranberry beans of the landrace “Manteigao” in the bean weevil Acanthoscelides obtectus. We assessed the susceptibility of A. obtectus to the commercial pyrethroid deltamethrin and clove and cinnamon essential oils as potential alternative insecticides and measured its reproductive performance (e.g., oviposition and emergence rates) on both hosts. The females of A. obtectus reared on kidney beans were less susceptible to both deltamethrin and clove essential oil and showed more sources of energy in the trophocytes although the attraction of adult females to both hosts was similar. However, the females reared on cranberry beans had higher reproductive performances and respiration rates, indicating that more energy was expended on reproduction than on the mitigation of the insecticide actions. Thus, with a change in hosts, a trade-off between reproductive fitness and the susceptibility to insecticides was demonstrated for A. obtectus. These results should not only affect the management of A. obtectus in storage units but also the understanding of these insects’ host adaptativeness.

Genetic diversity and differentiation ofAcanthoscelides obtectusSay (Coleoptera: Bruchidae) populations in China

Bean weevil Acanthoscelides obtectus Say is one of the most destructive pests of bean seeds. Using 10 microsatellite loci, we studied the genetic diversity and differentiation of 13 geographical populations. A total of 79 alleles were detected, with an average of 7.900 alleles per locus. The gene flow and genetic differentiation rate values at the 10 loci varied from 0.376 to 1.560 and 13.8–39.9%, with averages of 0.774% and 24.4%, respectively. Among the 13 populations, the effective number of alleles and observed heterozygosity ranged from 1.865 to 2.848 and 0.457 to 0.646, respectively. Shannon's information index ranged from 0.684 to 1.104. In all comparisons, the fixation index (FST) values ranged from 0.021 to 0.463, with a total FST value of 0.228 among the 13 populations, indicating a moderate level of genetic differentiation among these populations. Analysis of molecular variance revealed that the genetic variation within populations accounted for 67.7% of the total genetic variation. Using the unweighted pair group method with arithmetic mean cluster analysis, 13 populations were clustered into three distinct genetic groups. The pattern of the three concentrated groups from principal component analysis showed a similar result to cluster, although some individuals interpenetrated with one another.

Lipid adsorption of diatomaceous earths and increased water permeability in the epicuticle layer of the cowpea weevil Callosobruchus maculatus (F.) and the bean weevil Acanthoscelides obtectus (Say) (Chrysomelidae)

Newly emerged females of the cowpea weevil Callosobruchus maculatus (F.) and bean weevil Acanthoscelides obtectus (Say) were exposed to diatomaceous earth (DE). The cuticular water loss rate (μg cm−2 h−1) of the DE treated and untreated weevils was determined gravimetrically based on the total body mass changed at 25 ± 1 °C and 75 ± 5% r.h. within a 48 h period. Fatty acid profiles comprising acids with a carbon chain length between 9 and 20 carbon atoms (C9–C20) of C. maculatus (F.) and A. obtectus (Say) were studied comparatively by using extracted DE particles from DE treated weevils, pure DE, water extraction and hexane extraction of the weevils. Peak area percentages of the GC chromatograms were used to compare the cuticular lipid compositions. The cuticular water loss rate (CWLR) of DE treated weevils was significantly higher than that untreated weevils. Despite of the DE treated weevils strive to control their CWLR within the first 10–12 h, CWLR drop significantly until their physical death. DE and hexane extracts contained only fatty acid chain lengths between C16 and C18. The major fatty acid identified in the DE extracts was oleic acid in the C18:1cis9 group which averaged to about 55.7 ± 3.04% and 63.8 ± 3.52% in C. maculatus and A. obtectus, respectively. Hexane extracts showed that cuticular hydrocarbons of the C. maculatus were dominated by C18:2cis9,12 and C16:0 equivalents to the fatty acids of linoleic and palmitic acids, respectively. The loss of these fatty acids due to adsorption of DE may result in a greater water permeability of the insect cuticle and thus lead to desiccation and mortality.

Laboratory Assessment of the Levels of Resistance in Some Bean Varieties Infested with Bean Weevils (Acanthoscelides obtectus and Zabrotes subfasciatus)

The main objective of the study was to assess levels of resistance of some selected bean (Phaseolus vulgaris L.) varieties to storage bruchids (Common bean weevil Acanthoscelides obtectus (Say) and Mexican weevil Zabrotes subfasciatus ). Specifically it aimed at determining bruchids emergence and median development period, finding out the extent of damage caused by the bruchids on each variety and determining the weight loss incurred by each variety due to bruchids infestation. The experiment was laid out in a Complete Randomized Design (CRD) with four replicates. The study was conducted at Bunda college of Agriculture-Department of Crop and Soil Sciences-Entomology Laboratory. It was conducted from September 2012 to January 2013. Seven bean varieties, Kalima, Nasaka, BCB3, Sapelekedwa, BCB1, Bwenzilaana, and BCB2 were used as test materials. 100 g of bean seeds sample from each variety were put in kilner jars and were infested with 16 bruchids of common weevil and Mexican weevil, and it was carried in two phase; the first phase was used collect data for emerging insects and median development period;

Assessment of Insecticidal Efficacy of Diatomaceous Earth and Powders of Common Lavender and Field Horsetail against Bean Weevil Adults.

In the search for an effective and sustainable control method against the bean weevil Acanthoscelides obtectus (Say), an important insect pest affecting stored common beans and other legumes, three different powders were tested against adult been weevils under laboratory conditions. The three powders were diatomaceous earth (DE) (commercial product SilicoSec®), common lavender (Lavandula angustifolia) powder and field horsetail (Equisetum arvense) powder. The substances were tested at five temperatures (15, 20, 25, 30, and 35°C), two relative humidity levels (RH) (55 and 75%), and four concentrations (100, 300, 500, and 900ppm). The mortality of adults was measured after the 1st, 2nd, 4th, and 7th days of exposure. The efficacy of the powders increased with the temperature, whereas in general, RH did not have a significant effect on the adults' survival. According to common practice of storing common beans, we recommend the use of DE against the pest in question, as this inert powder showed the highest efficacy at lower temperatures and concentrations. Concerning the wider use of common lavender and field horsetail powders, we suggest studying their combined use with other environmentally friendly methods with the aim of achieving the highest synergistic effect possible.

Competition between the bean weevils Acanthoscelides obtectus and Zabrotes subfasciatus in common beans

Bruchid pest species of common beans (Phaseolus vulgaris (L.)) in the Neotropics, the bean weevil Acanthoscelides obtectus and the Mexican bean weevil Zabrotes subfasciatus, exhibit niche and range overlaps, frequently co-occurring in bean storage facilities of south-central Brazil. Although both species are well-known and important pest species, the impact of their co-occurrence on their fitness has not been an area of interest. Here, we performed direct competition experiments between both of the species following an additive series. The competitive ability of each species in the presence of its heterospecific competitor was assessed using mixed (adult) insect infestations in common beans. The initial number of insects of one species was fixed at 50, whereas the other species had a number of insects ranging from 0 to 50. Therefore, each species with a variable number of insects started the competition at an initial proportion of 0, 0.17, 0.29, 0.38 and 0.50. The number of adults that emerged and the instantaneous rate of increase (ri) for each species were determined after one generation under direct competition. Our results indicate that the competitive ability of Z. subfasciatus was favored by the presence of its heterospecific competitor (A. obtectus), while the opposite pattern did not occur. Thus, colonization by A. obtectus was not significantly compromised by Z. subfasciatus, while Z. subfasciatus seemed to actually benefit from the presence of A. obtectus under the conditions of our study. These results indicate that these co-occurring species do not exhibit negative interactions in storage facilities, and the presence of A. obtectus may even favor Z. subfasciatus.

The Hohenheimer Box – A new way to rear and release Lariophagus distinguendus to control stored product pest insects

To improve the biological control of stored product pests, the present paper reports on the development of a rearing box for parasitoids of pest insects. The box contains breeding substrate and populations of hosts and parasitoids and is placed in storage sites, where parasitoids are released continuously over several months. The box was developed to rear Lariophagus distinguendus (Förster) (Hymenoptera: Pteromalidae) to control the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae). Due to sanitary reasons, the bean weevil Acanthoscelides obtectus Say (Coleoptera: Bruchidae) was chosen as an alternative host. Rearing experiments revealed that the cowpea Vigna unguiculata unguiculata (L.) Walp. is most suitable as host substrate. For the outlet of the rearing device, a wire gauze mesh size of 0.8–1.0mm was found suitable to release wasps while holding back the bean weevils. The size of the starting populations of hosts and parasitoids was determined experimentally in a storage building. An amount of 5ml weevils plus 21–60 adult parasitoids on 2kg of cowpeas produced an average of 56 and 62 wasps per week respectively, from June to September. Wasps reared in the boxes had the same number of offspring on granary weevils as wasps from regular lab-cultures. This study demonstrates the feasibility of a rearing box for parasitoids of stored product pests that releases large numbers of wasps over several months. We consider our study as a guideline for the development of similar rearing boxes also for other parasitoid-pest systems in stored products protection throughout the world.

Insecticidal Activity of the Essential Oils from Different Plants Against Three Stored-Product Insects

This study was conducted to determine the insecticidal activity of essential oils from oregano, Origanum onites L. (Lamiales: Lamiaceae), savory, Satureja thymbra L. (Lamiales: Lamiaceae), and myrtle, Myrtus communis L. (Rosales: Myrtaceae) against three stored-product insects. Essential oils from three species of plants were obtained by Clevenger-type water distillation. The major compounds in these essential oils were identified using gas chromatography-mass spectrometry and their insecticidal activity was tested against adults of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), the Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae) and the bean weevil Acanthoscelides obtectus Say (Coleoptera: Bruchidae). While the major compound found in oregano and savory was carvacrol, the main constituent of the myrtle was linalool. Among the tested insects, A. obtectus was the most tolerant species against the essential oils. However, the insecticidal activity of the myrtle oil was more pronounced than other oils tested against A. obtectus adults. The essential oils of oregano and savory were highly effective against P. interpunctella and E. kuehniella, with 100% mortality obtained after 24 h at 9 and 25 µl/l air for P. interpunctella and E. kuehniella, respectively. LC50 and LC99 values of each essential oil were estimated for each insect species.

Nonrandom association between host choice and fitness in bean weevil (Acanthoscelides obtectus)

The results presented in this study indicate that host choice significantly increases one of the fitness components (preadult developmental time) in females of the bean weevil (Acanthoscelides obtectus). The host choice also affects the net replacement rate (Ro), as well as the intrinsic rate of increase (r). Using the method developed by Lande and Arnold (1983), we also measured the intensity of nonrandom association between host choice phenotypes and preadult developmental time.