Katariya Lakshya, Ramesh Priya B, Gopalappa Thejashwini, Desireddy Sathish, Bessière Jean-Marie, Borges Renee M
Centre for Ecological Sciences, Indian Institute of Science, Bangalore, 560012, India.
Ecole Nationale Supérieure de Chimie de Montpellier, 8 rue de l'Ecole Normale, 34296, Montpellier Cedex 5, France.
J Chem Ecol. 2017 Oct;43(10):986-995. doi: 10.1007/s10886-017-0902-4. Epub 2017 Nov 9.
Mutualistic associations such as the fungal farms of insects are prone to parasitism and are consequently vulnerable to attack by weeds and pests. Therefore, efficient farm management requires quick detection of weeds for their elimination. Furthermore, if the available weedicides are non-specific, then the ability of insects to discriminate between crop and weeds becomes essential for targeted application of such compounds. Here, we demonstrate for the first time in fungus-farming insects, that worker castes of the fungus-growing termite Odontotermes obesus discriminate between their crop (Termitomyces) and the weedy (Pseudoxylaria) fungi, even if exposed to only fungal scents. Termites respond to the presence of fungal mycelium or scent alone, by burying the weed with the offered material such as soil or agar, possibly anointing the weed with chemicals in the process. The scent profiles of crop and weedy fungi are distinct and the differences are likely exploited by termites to selectively mount their defences. Sesquiterpene compounds such as aristolene and viridiflorol, which are absent from crop odours, may constitute the "weedy scent". Our results provide a general mechanism of how other fungus-farming insects could avoid indiscriminate application of non-specific fungicides which could lead to poisoning their crops, and have bearing on the stability of the mutualism between termites and their crop fungus in the face of parasitism by weedy fungi.
诸如昆虫的真菌养殖场这类互利共生关系容易受到寄生作用的影响，因此容易受到杂草和害虫的侵袭。所以，高效的养殖场管理需要快速检测出杂草以便将其清除。此外，如果可用的除草剂没有特异性，那么昆虫区分作物和杂草的能力对于有针对性地施用此类化合物就变得至关重要。在此，我们首次在培育真菌的昆虫中证明，即使仅暴露于真菌气味中，培菌白蚁 Odontotermes obesus 的工蚁等级也能区分它们的作物（鸡枞菌）和杂草类真菌（拟层孔菌）。白蚁仅对真菌菌丝体或气味的存在做出反应，通过用土壤或琼脂等提供的材料掩埋杂草，在此过程中可能会用化学物质涂抹杂草。作物真菌和杂草类真菌的气味特征截然不同，白蚁可能利用这些差异来选择性地进行防御。诸如aristolene和viridiflorol等倍半萜化合物不存在于作物气味中，可能构成“杂草气味”。我们的研究结果提供了一种普遍机制，说明其他培育真菌的昆虫如何能够避免非特异性杀真菌剂的无差别施用，这种施用可能导致毒害它们的作物，并且对于面对杂草类真菌寄生时白蚁与其作物真菌之间互利共生关系的稳定性具有重要意义。
