Unraveling the role of male reproductive tract and haemolymph in cantharidin-exuding Lydus trimaculatus and Mylabris variabilis (Coleoptera: Meloidae): a comparative transcriptomics approach

Background Meloidae (blister beetles) are known to synthetize cantharidin (CA), a toxic and defensive terpene mainly stored in male accessory glands (MAG) and emitted outward through reflex-bleeding. Recent progresses in understanding CA biosynthesis and production organ(s) in Meloidae have been made, but the way in which self-protection is achieved from the hazardous accumulation and release of CA in blister beetles has been experimentally neglected. To provide hints on this pending question, a comparative de novo assembly transcriptomic approach was performed by targeting two tissues where CA is largely accumulated and regularly circulates in Meloidae: the male reproductive tract (MRT) and the haemolymph. Differential gene expression profiles in these tissues were examined in two blister beetle species, Lydus trimaculatus (Fabricius, 1775) (tribe Lyttini) and Mylabris variabilis (Pallas, 1781) (tribe Mylabrini). Upregulated transcripts were compared between the two species to identify conserved genes possibly involved in CA detoxification and transport. Results Based on our results, we hypothesize that, to avoid auto-intoxication, ABC, MFS or other solute transporters might sequester purported glycosylated CA precursors into MAG, and lipocalins could bind CA and mitigate its reactivity when released into the haemolymph during the autohaemorrhaging response. We also found an over-representation in haemolymph of protein-domains related to coagulation and integument repairing mechanisms that likely reflects the need to limit fluid loss during reflex-bleeding. Conclusions The de novo assembled transcriptomes of L. trimaculatus and M. variabilis here provided represent valuable genetic resources to further explore the mechanisms employed to cope with toxicity of CA in blister beetle tissues. These, if revealed, might help conceiving safe and effective drug-delivery approaches to enhance the use of CA in medicine.

Seasonal abundance of Blister Beetle, Mylabrispustulata Thunberg on Pigeonpea and Mungbean

Seasonal abundance and activity period blister beetle (Mylabrispustulata) on pigeonpea and mungbean were recorded at Research Farms of Pulses Section, Department of Plant Breeding and Genetics, Punjab Agricultural University, Ludhiana. The results showed that the blister beetle started appearing in pigeonpea and mungbean in late August under Punjab conditions. During the crop season, its activity increased and reached at its peak in the end of September (13.90 beetles / 4 meter row length in pigeonpea and 5.48 beetles / 1 sq. meter quadrate in mungbean) coincided with the maximum flowering and afterwards it started declining due to the termination of flowers. The activity of blister beetle was more in the morning (20.23 beetles / 4 meter row length in pigeonpea and 8.04 beetles / 1 sq. meter quadrate in mungbean) and evening hours (21.04 beetles / 4 meter row length in pigeonpea and 8.06 beetles / 1 sq. meter quadrate in mungbean) as compared to the noon hours (0.43 beetles / 4 meter row length in pigeonpea and 0.33 beetles / 1 sq. meter quadrate in mungbean).

Bioefficacy, environmental safety and synergistic impacts of biorational formulations against whitefly, leafhopper and blister beetle in organic okra ecosystem

Whitefly (Bemisia tabaci Gennadius), leafhopper (Amrasca biguttula biguttula Ishida) and large yellow-banded blister beetle (Mylabris phalerata) cause considerable damage to okra, especially under organic farming. Thus, the present study was carried out to test the bioefficacy and environmental safety of six naturally derived components [indigenous water plant extracts, i.e. chilli (Capsicum annum), garlic (Allium sativum L.) and neem (Azadirachta indica A. Juss.) along with cow urine in three different combinations, one commercial botanical (azadirachtin 0.15%), and two formulated entomopathogenic fungi (Verticillium lecanii and Beauveria bassiana)] on aforesaid pests for two consecutive years at field scale. In addition to this, the eco-toxicological effect of naturally derived components was also studied on natural enemies’ populations, viz. spiders and coccinellids. Quaternary mixture application of chilli, garlic, neem leaf and cow urine (CGNC) at 10% w/v was found effective in reducing leafhoppers (94.6%), whiteflies (95.2%) and blister beetle (94.6%) over control. Okra treated with CGNC produced a higher marketable fruit yield (18.44 mg/ha) than those of other treatments. It was also observed that the application of CGNC had no phytotoxic symptoms on okra plants. Application of CGNC was found safer to the natural enemy's population (spiders and coccinellids). Thus, the study suggests that CGNC can be considered as a potential source for managing the population of whitefly, leafhopper and blister beetle without affecting the ecology of natural enemies and it could be a viable eco-friendly option in organic okra production for ensuring food safety and healthy environment.

Sexual behaviour of the blister beetle Epicauta atomaria (Germar), with remarks on the bionomics of Epicauta maculata species group (Meloidae: Meloinae: Epicautini)

The sexual behaviour of the blister beetle Epicauta atomaria (Germar) (Meloidae: Meloinae: Epicautini), a pest that affects diverse crops of economic importance in South America, was evaluated for the first time under laboratory conditions. Twelve pairs of E. atomaria adults were collected from low-lying roadsides adjacent to grazed areas in Diamante, Entre Ríos, Argentina. To describe the sexual behaviour of this species, the number of events and their duration within different courtship phases in E. atomaria males were compared. An ethogram was built, showing that males perform three different behaviours during courtship phases: the quiescent period, antennal rubbing, and mounting. Our results showed that, during courtship, the number of events and the time of the mounting were low and significantly lower compared to behaviours undertaken during the quiescent period and antennal rubbing. In conclusion, the courtship of E. atomaria was clearly dominated by the quiescent period and antennal rubbing. To date, this is the first study to investigate sexual behaviour in E. atomaria, providing a foundation for future phylogenetic studies.

Entomological Surveillance and Cantharidin Concentrations in Mylabris variabilis and Epicauta rufidorsum Blister Beetles in Slovenia

True blister beetles (genus Epicauta, family Meloidae) produce cantharidin, which can cause toxicosis in humans and animals. Some recent reports suggest that poisoning by the blister beetle has occurred in the Mediterranean part of Slovenia, which has never been reported before. Drought and modern harvesting techniques are thought to increase the likelihood of blister beetle forage contamination and cantharidin intoxication in animals. A survey of fields associated with blister beetle contamination was conducted and the Meloid species present were identified. Entomological surveillance was conducted for Mylabris variabilis and Epicauta rufidorsum. Cantharidin concentrations were also measured in both blister beetle species. Cantharidin concentration in Mylabris variabilis (n = 17) ranged from 0.038 to 0.354 µg/mg (mean 0.151 µg/mg). Cantharidin concentration in Epicauta rufidorsum (n = 36) ranged from 0.055 to 0.341 µg/mg (mean 0.142 µg/mg). Both species exhibited variable concentrations of cantharidin that could not be associated with their biology, sex, age, size, and/or reproductive status. Epicauta rufidorsum have never previously been studied as a possible source of forage contamination, nor have cantharidin concentrations been determined in this species. It is the most likely source of forage contamination due to its abundance in the investigated fields, its swarming activity, and its tendency to reside in the green parts of plants immediately after cutting. Delaying the simultaneous processing and storage of forage after cutting would reduce the likelihood of forage contamination by blister beetles, as they can then retreat to the ground or fly away.