on Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae)

A study was undertaken on the ovicidal and larval repellent activity of Tagetes erecta leaf and flower extracts on Rhipicephalus sanguineus (Latreille, 1806), an important tick species in the world from an economic and medical point of view. Ethanol and methanol extracted plant products tested against the eggs and larvae of R. sanguineus indicated that the ethanol extract of flower had maximum ovicidal activity (86.1%), followed by the ethanol extract of leaf (75%) at 25 mg ml-1 concentration. In all analyses, the homogeneity of variance was significant. The probit analysis clearly indicated that the ethanol extract of the flower has a higher ability to kill the eggs. In the case of larval repellency tested, both extracts of leaf showed the highest repellency (83%) at 2.5 mg ml-1. Significant tick repellency (> 90%) was found in both methanol and ethanol extracts of flower at 2.5 mg ml-1. GC-MS analysis of extracts revealed the presence of bioactive insecticidal compounds such as yangambin, cyclohexane and neophytadine.

Discovery of mosquitocides from fungal extracts through a high-throughput cytotoxicity-screening approach

Background Mosquitoes transmit a variety of diseases. Due to widespread insecticide resistance, new effective pesticides are urgently needed. Entomopathogenic fungi are widely utilized to control pest insects in agriculture. We hypothesized that certain fungal metabolites may be effective insecticides against mosquitoes. Methods A high-throughput cytotoxicity-based screening approach was developed to search for insecticidal compounds in our newly established global fungal extract library. We first determined cell survival rates after adding various fungal extracts. Candidate insecticides were further analyzed using traditional larval and adult survival bioassays. Results Twelve ethyl acetate extracts from a total of 192 fungal extracts displayed > 85% inhibition of cabbage looper ovary cell proliferation. Ten of these 12 candidates were confirmed to be toxic to Anopheles gambiae Sua5B cell line, and six showed > 85% inhibition of Anopheles mosquito cell growth. Further bioassays determined a LC50, the lethal concentration that kills 50% of larval or adult mosquitoes, of 122 µg/mL and 1.7 µg/mosquito, respectively, after 24 h for extract 76F6 from Penicillium toxicarium. Conclusions We established a high-throughput MTT-based cytotoxicity screening approach for the discovery of new mosquitocides from fungal extracts. We discovered a candidate extract from P. toxicarium that exhibited high toxicity to mosquito larvae and adults, and thus were able to demonstrate the value of our recently developed approach. The active fungal extracts discovered here are ideal candidates for further development as mosquitocides. Graphical abstract

Taxonomic Insights and Its Type Cyclization Correlation of VolaTile Sesquiterpenes in Vitex Species and Potential Source Insecticidal Compounds: A Review

Sesquiterpenes (SS) are secondary metabolites formed by the bonding of 3 isoprene (C5) units. They play an important role in the defense and signaling of plants to adapt to the environment, face stress, and communicate with the outside world, and their evolutionary history is closely related to their physiological functions. This review considers their presence and extensively summarizes the 156 sesquiterpenes identified in Vitex taxa, emphasizing those with higher concentrations and frequency among species and correlating with the insecticidal activities and defensive responses reported in the literature. In addition, we classify the SS based on their chemical structures and addresses cyclization in biosynthetic origin. Most relevant sesquiterpenes of the Vitex genus are derived from the germacredienyl cation mainly via bicyclogermacrene and germacrene C, giving rise to aromadrendanes, a skeleton with the highest number of representative compounds in this genus, and 6,9-guaiadiene, respectively, indicating the production of 1.10-cyclizing sesquiterpene synthases. These enzymes can play an important role in the chemosystematics of the genus from their corresponding routes and cyclizations, constituting a new approach to chemotaxonomy. In conclusion, this review is a compilation of detailed information on the profile of sesquiterpene in the Vitex genus and, thus, points to new unexplored horizons for future research.

The use of Annona squamosa seed, leaf and bark as an alternative in the control of Cryptotermes brevis

The changes in human behavior towards the environment, the disorderly urban development, globalization and climate change are some of the factors that promote the occurrence and spread of pests that somehow bring damage. This occurrence is aimed at termites, which are insects known for their habit of feeding on cellulose, that is, papers, books, and wooden structures, causing accidents. Cryptotermes brevis are a major cause of damage to various wood species commonly used throughout the country, which cause major public health problems. Annonaceae have been extensively investigated because they present many species as a source of insecticidal compounds with different modes of action on insects. Therefore, this work aims to develop a natural, economical and sustainable product by using the extracts of the seeds of the fruit of the earl (Annona squamosa) as a resource to combat dry wood termites. From the results, it was possible to prove the veracity of the hypothesis that the natural insecticides developed from the extract of the seeds of the fruit of the earl (Annona squamosa) are very efficient, and are effective in the issue of mortality rates of Cryptotermes brevis.

Photorhabdus spp.: An Overview of the Beneficial Aspects of Mutualistic Bacteria of Insecticidal Nematodes

The current approaches to sustainable agricultural development aspire to use safer means to control pests and pathogens. Photorhabdus bacteria that are insecticidal symbionts of entomopathogenic nematodes in the genus Heterorhabditis can provide such a service with a treasure trove of insecticidal compounds and an ability to cope with the insect immune system. This review highlights the need of Photorhabdus-derived insecticidal, fungicidal, pharmaceutical, parasiticidal, antimicrobial, and toxic materials to fit into current, or emerging, holistic strategies, mainly for managing plant pests and pathogens. The widespread use of these bacteria, however, has been slow, due to cost, natural presence within the uneven distribution of their nematode partners, and problems with trait stability during in vitro culture. Yet, progress has been made, showing an ability to overcome these obstacles via offering affordable mass production and mastered genome sequencing, while detecting more of their beneficial bacterial species/strains. Their high pathogenicity to a wide range of arthropods, efficiency against diseases, and versatility, suggest future promising industrial products. The many useful properties of these bacteria can facilitate their integration with other pest/disease management tactics for crop protection.

New Insights into the Degradation Path of Deltamethrin

Pyrethroids are among the insecticidal compounds indicated by the World Health Organization for mitigation of vector-borne diseases. Active deltamethrin (with chiral configuration α-S,1-R-cis) is one of the most effective pyrethroids characterized by low toxicity to humans, and it is currently tested as active ingredient for insecticidal paints. Nevertheless, several degradation processes can occur and affect the insecticidal efficacy in the complex paint matrix. In the present study, a detailed NMR analysis of deltamethrin stability has been carried out under stress conditions, mimicking a water-based insecticidal paint environment. Two novel by-products, having a diastereomeric relationship, were identified and their structure was elucidated by combining NMR, HPLC, GC-MS, and ESI-MS analyses. These compounds are the result from a nucleophilic addition involving deltamethrin and one of its major degradation products, 3-phenoxybenzaldehyde. Given the known toxicity of the aldehyde, this reaction could represent a way to reduce its concentration into the matrix. On the other hand, the toxicology of these compounds towards humans should be addressed, as their presence may adversely affect the performance of deltamethrin-containing products.

RNAi efficacy is enhanced by chronic dsRNA feeding in pollen beetle

Double-stranded RNAs (dsRNAs) represent a promising class of biosafe insecticidal compounds. We examined the ability to induce RNA interference (RNAi) in the pollen beetle Brassicogethes aeneus via anther feeding, and compared short-term (3 d) to chronic (17 d) feeding of various concentrations of dsRNA targeting αCOP (dsαCOP). In short-term dsαCOP feeding, only the highest concentration resulted in significant reductions in B. aeneus survival; whereas in chronic dsαCOP feeding, all three concentrations resulted in significant mortality. Chronic dsαCOP feeding also resulted in significantly greater mortality compared to short-term feeding of equivalent dsαCOP concentrations. Our results have implications for the economics and development of dsRNA spray approaches for managing crop pests, in that multiple lower-concentration dsRNA spray treatments across crop growth stages may result in greater pest management efficacy, compared to single treatments using higher dsRNA concentrations. Furthermore, our results highlight the need for research into the development of RNAi cultivars for oilseed rape protection, given the enhanced RNAi efficacy resulting from chronic, compared to short-term, dsRNA feeding in B. aeneus.

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.