Biology subjects

Millan-Leiva, A.

Publications and source records attributed to Millan-Leiva, A..

3 recordsLinked to original sources

bioRxiv2020

Mutations associated with pyrethroid resistance in Varroa mites, a parasite of honey bees, are widespread across the USA

BACKGROUNDManaged honey bees are key pollinators of many crops and play an essential role in the United States food production. For more than 10 years, beekeepers in the US have been reporting high rate of colony losses. One of the drivers of this colony loss is the parasitic mite Varroa destructor. Preserving healthy honey bee colonies in the US is dependent on a successful control of this mite. The pyrethroid tau-fluvalinate (Apistan(R)) was among the first synthetic varroacide registered in the US. With over 20 years of use, population of mites resistant to Apistan(R) have emerged, and so it is unsurprising that treatment failures have been reported. Resistance in US mite populations to tau-fluvalinate is associated with point mutations at position 925 of the voltage-gated sodium channel, L925I and L925M. RESULTSHere, we have generated a distribution map of pyrethroid resistance alleles in Varroa samples collected from US apiaries in 2016 and 2017, using a high throughput allelic discrimination assay based on TaqMan(R). Our results evidence that these kdr-type mutations are widely distributed in Varroa populations across the country showing high variability among apiaries. CONCLUSIONWe highlight the relevance of monitoring the resistance in mite populations to achieve an efficient control of this pest, and the benefit of implementing this methodology in pest management programs for varroosis.

pharmacology and toxicology↗

bioRxiv2020

Reduced levels of membrane-bound alkaline phosphatase in Vip3Aa-resistant Heliothis virescens

The Vip3Aa insecticidal protein from Bacillus thuringiensis (Bt) is produced by specific transgenic corn and cotton varieties for efficient control of target lepidopteran pests. The main threat to this technology is the evolution of resistance in targeted insect pests, thus understanding the mechanistic basis of resistance is crucial to deploy the most appropriate strategies for resistance management. In this work, a laboratory-selected colony of Heliothis virescens (Vip-Sel) highly resistant to the Vip3Aa protein was used to test whether an alteration of membrane receptors in the insect midgut might explain the resistance phenotype. Binding of 125I-labeled Vip3Aa to brush border membrane vesicles (BBMV) from 3rd instar larvae from Vip-Sel was not significantly different from binding in the reference susceptible colony. Interestingly, BBMV from Vip-Sel larvae show dramatically reduced levels of alkaline phosphatase activity, which was further confirmed by a strong down-regulation of the membrane-bound alkaline phosphatase 1 (HvmALP1) gene. However, its involvement as a receptor for the Vip3Aa protein was not supported by ligand blotting and viability assays with insect cells expressing HvmALP1. These data support that reduced alkaline phosphatase, previously observed in insect colonies resistant to Cry proteins from Bt, may also serve as an indirect marker that is not mechanistically involved in resistance to Vip3Aa. IMPORTANCEThe Vip3Aa insecticidal protein remains the only lepidopteran-specific trait in transgenic Bt crops with no cases of field-evolved resistance. While laboratory-selected resistance to Vip3A has been reported elsewhere, the mechanism for resistance is unknown. Results in this work show lack of significant Vip3Aa binding alterations in resistant and reference colonies of H. virescens. These observations are in contrast to most cases of high levels of resistance to insecticidal Bt proteins for which decreased binding is commonly detected. In addition, this study provides the first evidence of down-regulation of membrane bound alkaline phosphatase (mALP) associated with Vip3Aa resistance, a phenomenon commonly associated with resistance to Cry proteins from Bt. Results from this work suggest that mALP down-regulation may be a useful biomarker yet reject its direct participation in resistance to Vip3Aa.

microbiology↗

bioRxiv2019

Identification of new viruses specific to the honey bee mite Varroa destructor

Large-scale colony losses among managed Western honey bees have become a serious threat to the beekeeping industry in the last decade. There are multiple factors contributing to these losses but the impact of Varroa destructor parasitism is by far the most important, along with the contribution of some pathogenic viruses vectored by the mite. So far, more than 20 viruses have been identified infecting the honey bee, most of them RNA viruses. They may be maintained either as covert infections or causing severe symptomatic infections, compromising the viability of the colony. In silico analysis of available transcriptomic data obtained from mites collected in the USA and Europe as well as additional investigation with new samples collected locally allowed the description of three novel RNA viruses. Our results showed that these viruses were widespread among samples and that they were present in the mites and in the bees but with differences in the relative abundance and prevalence. However, we have obtained strong evidence showing that these three viruses were able to replicate in the mite, but not in the bee, suggesting that they are selectively infecting the mite. To our knowledge, this is the first demonstration of Varroa-specific viruses, which open the door to future applications that might help controlling the mite through biological control approaches.

microbiology↗