Ávila-Hernández Eduardo, Molina-Ruiz Cindy S, Gómez-Díaz Juan S, Williams Trevor
Instituto de Ecología AC (INECOL), Xalapa 91073, Veracruz, Mexico.
Instituto Tecnológico Superior de Libres, Libres 73780, Puebla, Mexico.
Viruses. 2025 Feb 21;17(3):298. doi: 10.3390/v17030298.
The production of viable nucleopolyhedrovirus in the feces of infected lepidopteran larvae represents a poorly understood route for virus transmission prior to host death. In the present study, we examined the presence of viable virus in the feces of fourth-instar larvae infected with the Nicaraguan isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV-NIC). Feces production increased in samples taken at 2 to 6 days post-inoculation but was significantly lower in infected insects compared to controls. Second instars experienced 3.9 to 68.3% of polyhedrosis disease following consumption of feces collected at 2-5 days post-inoculation, which subsequently fell to 29.1% in the 6-day sample. Calibration of the insect bioassay using OB-spiked samples of feces indicated that the concentration of OBs varied between 5.4 × 10 and 4.4 × 10 OBs/100 mg of feces in infected fourth instars. Quantitative PCR analysis of fecal samples indicated the presence of 0 to 7629 copies/mg feces following amplification targeted at the polyhedrin gene. However, no correlation was detected between qPCR estimates of virus concentration and time of sample collection or the quantity of feces collected. The qPCR estimates were positively correlated with the prevalence of lethal infection observed in the insect bioassay, but the correlation was weak and several samples did not amplify. Calibration of the qPCR assay using OB-spiked samples of feces provided estimates that were 5- to 10-fold lower than the insect bioassay, indicating inhibition of the amplification reaction or loss of material during processing. In a greenhouse experiment, 2.5-48.3% of second-instar larvae acquired lethal infection following a 24 h period of feeding on maize plants on which fourth instar larvae had deposited their feces at 3 days and 4 days post-infection, respectively. These findings highlight the potential of OB-contaminated feces as a source of biologically significant quantities of inoculum for virus transmission prior to the death of infected insects and represent an additional contribution to the biological control of lepidopteran pests by these pathogens.
在受感染鳞翅目幼虫的粪便中产生有活力的核多角体病毒是宿主死亡前一种了解较少的病毒传播途径。在本研究中，我们检测了感染尼加拉瓜分离株草地贪夜蛾多核多角体病毒（SfMNPV-NIC）的四龄幼虫粪便中是否存在有活力的病毒。接种后2至6天采集的样本中粪便产量增加，但与对照相比，受感染昆虫的粪便产量显著较低。取接种后2至5天收集的粪便喂食二龄幼虫，3.9%至68.3%的幼虫出现多角体病，而接种后6天收集的粪便喂食的幼虫中，这一比例降至29.1%。使用添加了多角体的粪便样本进行昆虫生物测定校准表明，受感染四龄幼虫粪便中多角体的浓度在每100毫克粪便含5.4×10至4.4×10个多角体之间变化。对粪便样本进行的定量PCR分析表明，以多角体蛋白基因为靶点进行扩增后，每毫克粪便中存在0至7629个拷贝。然而，未检测到病毒浓度的qPCR估计值与样本采集时间或采集的粪便量之间存在相关性。qPCR估计值与昆虫生物测定中观察到的致死感染发生率呈正相关，但相关性较弱，且有几个样本未扩增。使用添加了多角体的粪便样本对qPCR测定进行校准后得到的估计值比昆虫生物测定低5至10倍，表明扩增反应受到抑制或处理过程中物质损失。在温室实验中，分别以感染后3天和4天四龄幼虫排出粪便的玉米植株喂食二龄幼虫24小时后，2.5%至48.3%的二龄幼虫受到致死感染。这些发现突出了受多角体污染的粪便作为感染昆虫死亡前具有生物学意义的大量接种源的潜力，并且代表了这些病原体对鳞翅目害虫生物防治的又一贡献。
