Gonzalez-Martinez, R. M. | Search bioRxiv

bioRxiv2026

Synergism of Cry1Aa protein against Grapholita molesta (Busck) by a cadherin fragment from Spodoptera exigua (Hübner)

Bacillus thuringiensis (Bt) is currently the most commercialized biopesticide worldwide. Despite the success of Bt application in biological control programs, diverse strategies have been developed to enhance the toxicity of Bt toxins and delay the emergence of insect resistance, including the addition of cadherin fragments as a synergistic agent. In this study, the synergistic effect of two different cadherin fragments, one from a lepidopteran species, Spodoptera exigua (rSeCad1bp), and the other from a coleopteran species, Tenebrio molitor (rTmCad1p), was evaluated on the toxicity of Cry1Aa, Cry1Ab, and Cry1Ia against S. exigua and Grapholita molesta. Our results show that while the toxicity of Cry1 proteins to S. exigua was not affected by rSeCad1bp, the toxicity of Cry1Aa against G. molesta increased about 2.6-fold. No other synergistic or antagonist effects were observed. The potential mechanisms for the detected toxicity enhancement in G. molesta were studied, including protection against proteolysis, promotion of oligomerization, and increased binding to receptors on midgut brush border membrane vesicles (BBMV). Results revealed a slight increase in Cry1Aa binding to BBMV. These data highlight the great potential of using rSeCad1bp in combination with Cry1Aa for control of G. molesta. Key ContributionOur results show that the cadherin fragment from Spodoptera exigua synergized Cry1Aa toxicity against Grapholita molesta, but not to S. exigua. The synergistic effect observed might be partly associated with an increase in Cry1Aa binding to the target midgut membrane.

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↗