Evaluating toxicity of Varroa mite (Varroa destructor)-active dsRNA to monarch butterfly (Danaus plexippus) larvae

Abstract

Varroa mites (Varroa destructor) are parasitic mites that, combined with other factors, are contributing to high levels of honey bee (Apis mellifera) colony losses. A Varroa-active dsRNA was recently developed to control Varroa mites within honey bee brood cells. This dsRNA has 372 base pairs that are homologous to a sequence region within the Varroa mite calmodulin gene (cam). The Varroa-active dsRNA also shares a 21-base pair match with monarch butterfly (Danaus plexippus) calmodulin mRNA, raising the possibility of non-target effects if there is environmental exposure. We chronically exposed the entire monarch larval stage to common (Asclepias syriaca) and tropical (Asclepias curassavica) milkweed leaves treated with concentrations of Varroa-active dsRNA that are one- and ten-fold higher than those used to treat honey bee hives. This corresponded to concentrations of 0.025–0.041 and 0.211–0.282 mg/g leaf, respectively. Potassium arsenate and a previously designed monarch-active dsRNA with a 100% base pair match to the monarch v-ATPase A mRNA (leaf concentration was 0.020–0.034 mg/g) were used as positive controls. The Varroa mite and monarch-active dsRNA’s did not cause significant differences in larval mortality, larval or pupal development, pupal weights, or adult eclosion rates when compared to negative controls. Irrespective of control or dsRNA treatment, larvae that consumed approximately 7500 to 10,500-mg milkweed leaf within 10 to 12 days had the highest pupal weights. The lack of mortality and sublethal effects following dietary exposure to dsRNA with 21-base pair and 100% base pair match to mRNAs that correspond to regulatory genes suggest monarch mRNA may be refractory to silencing by dsRNA or monarch dsRNase may degrade dsRNA to a concentration that is insufficient to silence mRNA signaling.

dsRNAs Targeted to the Brown Planthopper Nilaparvata lugens: Assessing Risk to a Non-Target, Beneficial Predator, Cyrtorhinus lividipennis

“…curviseta . Also, Varroa destructor -active dsRNA had no significant adverse effects on Danaus plexippus, although there were some 21 base pair matches between them . As we stated before, the analysis of 21 contiguous nt matches could predict some non-target effects, while other factors including the gene family of the target dsRNA, the RNAi sensitivity of different NTOs, and the dsRNA exposure concentrations could also affect the result of the risk assessments of dsRNAs. , Thus, the principle of case-by-case safety assessments was suggested to be followed in the risk assessment of RNAi-based products on NTOs.…”

RNAi-Based Biopesticides Against 28-Spotted Ladybeetle Henosepilachna vigintioctopunctata Does Not Harm the Insect Predator Propylea japonica

“…Similarly, feeding on a high concentration of Euschistus heros -active dsRNA did not lead to adverse effects on the survival or parasitism capacity of the parasitoid wasp Telenomus podisi , even though there were 17–21 nt matches between them . Although the predictions based on gene sequence information can be used to avoid some potential risks to NTOs, other factors, including the degree of RNAi sensitivity among NTOs, concentration of the exposed dsRNA, dsRNA degradation conditions, the position of mismatches within the siRNA sequence, and the position of the dsRNA within the off-target could affect the result of the risk assessments of dsRNAs. ,− Therefore, the association between the number of 21 nt matches and dsRNA activity in the specific organism should be characterized.…”

Are increasing honey bee colony losses attributed toVarroa destructorin New Zealand driven by miticide resistance?

“…Another strategy currently under development which shows more promise is the utilisation of RNA interference technology (RNAi) against Varroa mites (Garbian et al 2012). This method has been observed to reduce mite populations (Garbian et al 2012, Huang et al 2019 and is thought to be species-specific to Varroa, likely making it harmless to honey bees and other non-target species (Tan et al 2016, Krishnan et al 2021.…”