Economically significant pests of beans in Serbia

Insects represent a limiting factor in the cultivation of beans (Phaseolus vulgaris L.) in most of the production regions, and often are the main cause of low productivity. During the vegetation, beans, as well as other legumes, are susceptible to the attack of numerous pests. The most significant are soil-dwelling, such as wireworms (fam. Elateridae), and storage pests like the bean weevil (Acanthoscelides obtectus Say). In addition to these two groups of insects, during the season, pests of the aboveground part such as aphids, thrips, stink bugs, and in dry years, mites, often occur causing significant losses.

How bean weevil (Acanthoscelides obtectus, Coleoptera, Bruchinae) larvae die on legume seeds

BackgroundThe host specificity and the range of possible wild and cultivated hosts of the dry bean weevil, Acanthoscelides obtectus (Coleoptera, Chrysomelidae, Bruchinae), a seed predator of beans, is poorly known. In addition, female oviposition preference and larval performance relationship is complicated by the respective importance of seed coat and cotyledon, because, on the one hand, paradoxically, females lay eggs on the basis of stimuli of the seed coat alone, without directly being able to assess the quality of cotyledon’s suitability for larval development. On the other, the thickness of seed coat may prevent first instar larvae from entering the seeds, even if cotyledons were suitable for development.ResultsThe seeds of 62 leguminous species and 82 accessions occurring in Hungary were tested in no-choice tests for egg-laying. The ability of first instar larvae to overcome seed coat, as a physical barrier, was measured with intact seed coat, whereas drilled seed coats allowed assessing the suitability of cotyledon for development. Seeds of 18 species (35% of them Lathyrus) supported larval development to adults, if the seed coat was drilled, however, only nine produced adults, if the seed coat was intact. Seed coats thicker than 0.1 mm could be an obstacle for first instar larvae. There was no overall positive correlation between oviposition preference and larval performance, with the exception of 16 so-called acceptable non-hosts (Kendall’s τ = 0.3088). Bean weevil females also demonstrated an ovipositional hierarchy of legume species even in no-choice tests.ConclusionsResults demonstrate that whereas the use of some acceptable non-host species by the bean weevil is possible in seed stores, the same is unlikely under outdoor conditions, because it requires the recognition of basically different oviposition substrates (pods).

Gene Sequences of Potential Targets of Insecticidal PF2 Lectin Identified from the Larval De Novo Transcriptome of the Mexican Bean Weevil (Zabrotes Subfasciatus; Boheman 1833)

The available genomic and proteomic information of non-model organisms is often underrepresented in public databases hindering their study at molecular, cellular, and physiological levels. Information on Zabrotes subfasciatus (Mexican bean weevil) is poorly represented in databases, yet it is a major pest of common beans. We report the transcriptome of Z. subfasciatus larvae; transcripts were sequenced using an Illumina RNA-Seq technology and assembled de novo identifying 29,029 unigenes with an average size of 1168 bp and an N50 value of 2196 bp. About 15,124 unigenes (52%) were functionally annotated and categorized. Further analysis revealed 30 unigene sequences encoding putative targets of the insecticidal PF2 lectin. The complete deduced amino acid sequences of eight selected proteins potentially related to insecticidal mechanism of Palo Fierro 2 (PF2) were used for predicting probable N-glycosylation sites and analyzing phylogenetic relationships with insect sequences. This work provides a dramatic increase in the genetic resources available for Coleopterans and set the basis for developing future studies on biological aspects and potential control strategies for Z. subfasciatus.

BIOACTIVITY OF EXTRACTS FROM SOLANACEAE AGAINST Zabrotes subfasciatus

The botanical family Solanaceae has many species producing compounds with insecticidal properties, e.g. nicotine and capsaicin, which are used for pest management in agriculture. This fact provides perspectives to identify insecticidal compounds in Brazilian native species of Solanaceae. In this study, we performed a screening with 25 ethanolic extracts from 17 Solanaceae species in order to evaluate their bioactivity against the Mexican bean weevil, Zabrotes subfasciatus(Coleoptera: Chrysomelidae: Bruchinae). The bioactivity of Solanaceae ethanolic extracts (2500 mg kg-1) was tested with residual contact bioassays. Adults ofZ. subfasciatus were exposed to treated bean grains, and adult mortality, oviposition, F1progeny and damages on grains were quantified. Most of the ethanolic extracts from Solanaceae reduced the number of eggs per sample, the egg-adult viability, the F1progeny and the damages on bean grains promoted byZ. subfasciatus, but none of them interfered on its sex ratio. Ethanolic extract from leaves of Solanum lycocarpumA. St.-Hil promoted the most promissory effects on Z. subfasciatus. This ethanolic extracts can be a suitable alternative to control Z. subfasciatus in stored beans, mainly for small farmers and organic farmers.

How bean weevil (Acanthoscelides obtectus, Coleoptera, Bruchinae) larvae die on legume seeds

Background The host specificity of the dry bean weevil, Acanthoscelides obtectus Say (Coleoptera: Bruchinae), a seed predator of beans, is not properly known. Occasional use of leguminous seeds other than beans is reported, however the sphere of possible wild and cultivated hosts is uncertain. Female oviposition preference and larval performance relationship is complicated by the respective importance of seed coat and cotyledon, because paradoxically, females must exercise oviposition preference on the basis of stimuli provided by the seed coat alone, without directly being able to assess the quality of cotyledon’s suitability for larval development.Results Host specificity and host range investigations carried out on seeds of 62 grown and naturally occurring legume species and 82 cultivars of Phaseolus, Pisum, Glycine, Lens and others in Hungary, using no-choice tests for egg-laying, and intact or pierced seed coat for larval development in seeds, showed that there were 18 plant species (35% of them Lathyrus) that supported larval development to adults, however, only nine species (4 of 17 Glycine max accessions, Vigna unguiculata, V. angularis, Phaseolus vulgaris, Ph. coccineus, Cicer arietinum, Vicia faba, Lathyrus sativus and 13 of 27 Pisum sativum accessions) allowed it if the seed coat was intact. Furthermore, there was no overall positive correlation between oviposition preference and larval performance, with the exception for the so-called acceptable non-hosts (Kendall’s τ = 0.3088). Bean weevil females also demonstrated an ovipositional hierarchy of legume species even in no-choice tests.Conclusions Host range expansion is not probable with the bean weevil, primarily because it would require the recognition of basically different oviposition substrates (pods) among outdoor conditions.