No abstract

Aim To identify geographical drivers determining the relative partitioning of species replacement and richness difference or nestedness‐resultant components of beta diversity in spider groups with differing dispersal modalities. Location Thousand Island Lake, China. Methods We sampled spider assemblages on 31 land‐bridge islands for two years. Each species was classified into a dispersal group based on ballooning propensity (frequent, occasional or non‐ballooners). Two frameworks were used to separate beta diversity (βcc or βjac) of each group into either species replacement (β‐3) and richness difference (βrich) components, or turnover (βjtu) and nestedness‐resultant (βjne) components. Mantel and partial Mantel tests were performed to determine correlations between pairwise dissimilarities and difference in island area, difference in distance to mainland and inter‐island distance for each group. Results The multiple‐island dissimilarity of spiders was primarily driven by turnover. Beta diversity (βcc or βjac) was positively associated with difference in island area in frequent ballooners, and negatively associated with difference in island area in occasional ballooners. Difference in island area had positive effects on βjne for all groups, but negative effects on β‐3 and βjtu for occasional or non‐ballooners. βrich was positively associated with difference in island area in frequent and non‐ballooners. We did not find any significant isolation effects for these three measures of dissimilarity. Main conclusions The dominant process of extinction resulted in a high contribution of turnover to the multiple‐island dissimilarity of spiders. Specifically, frequent ballooners contributed less turnover to multiple‐island dissimilarity than occasional and non‐ballooners. The most likely explanation for this is that frequent ballooners were potentially able to colonize all islands, whereas occasional and non‐ballooners were constrained by water barriers and were unable to occupy most islands. Contrasting dissimilarities among dispersal groups of spiders demonstrates the importance of beta diversity partitioning, and the mechanistic insight gained on trait‐dependence in community assembly.

BackgroundTea is one of the most economically important crops in China. However, the tea geometrid (Ectropis obliqua), a serious leaf-feeding pest, causes significant damage to tea crops and reduces tea yield and quality. Spiders are the most dominant predatory enemies in the tea plantation ecosystem, which makes them potentially useful biological control agents of E. obliqua. These highlight the need for alternative pest control measures. Our previous studies have shown that tea saponin (TS) exerts insecticidal activity against lepidopteran pests. Here, we investigate whether TS represents a potentially new alternative insecticide with no harm to spiders.MethodsWe investigated laboratory bioactivities and the field control properties of TS solution against E. obliqua. (i) A leaf-dip bioassay was used to evaluate the toxicity of TS to 3rd-instar E. obliqua larvae and effects of TS on the activities of enzymes glutathione-S-transferase (GST), acetylcholinesterase (AChE), carboxylesterase (CES) and peroxidase (POD) of 3rd-instar E. obliqua larvae in the laboratory. (ii) Topical application was used to measure the toxicity of 30% TS (w/v) and two chemical insecticides (10% bifenthrin EC and 50% diafenthiuron SC) to two species of spider, Ebrechtella tricuspidata and Evarcha albaria. (iii) Field trials were used to investigate the controlling efficacy of 30% TS against E. obliqua larvae and to classify the effect of TS to spiders in the tea plantation.ResultsThe toxicity of TS to 3rd-instar E. obliqua larvae occurred in a dose-dependent manner and the LC50 was 164.32 mg/mL. Activities of the detoxifying-related enzymes, GST and POD, increased in 3rd-instar E. obliqua larvae, whereas AChE and CES were inhibited with time by treatment with TS. Mortalities of E. tricuspidata and E. albaria after 48 h with 30% TS treatment (16.67% and 20%, respectively) were significantly lower than those with 10% bifenthrin EC (80% and 73.33%, respectively) and 50% diafenthiuron EC (43.33% and 36.67%, respectively). The highest controlling efficacy of 30% TS was 77.02% at 5 d after treatment, which showed no difference to 10% bifenthrin EC or 50% diafenthiuron SC. 30% TS was placed in the class N (harmless or slightly harmful) of IOBC (International Organization of Biological Control) categories for natural enemies, namely spiders.ConclusionsOur results indicate that TS is a botanical insecticide that has a good controlling efficacy in E. obliqua larvae, which suggests it has promise as application in the integrated pest management (IPM) envisaged for tea crops.

No abstract