The spider mites Eotetranychus sexmaculatus, Eutetranychus orientalis and Oligonychus biharensisin are severe pests of rubber trees in China. The predatory mite Neoseiulus barkeri has been found to be a natural enemy of these three pests, while nothing is known about the biological performance of this phytoseiid predator against these phytophagous mites. In this study, the development, survivorship, reproduction, adult longevity, fecundity, sex ratio and population growth parameters of N. barkeri fed on these pests were evaluated in comparison to the factitious prey Tyrophagus putrescentiae in the laboratory at 25 ± 1 °C, 75 ± 5% relative humidity and a 12:12 (L:D) h photoperiod. The results showed that N. barkeri could develop from egg to adult and reproduced successfully on the three preys. The survival rate of N. barkeri from egg to adult was higher when fed on E. orientalis (100%) and T. putrescentiae (100%) than when fed on O. biharensisin (93.60%) and E. sexmaculatus (71.42%). The shortest and longest generation time for N. barkeri were observed on E. orientalis with 6.67 d and E. sexmaculatus with 12.50 d, respectively. The maximum fecundity (29.35 eggs per female) and highest intrinsic rate of increase (r_m = 0.226) were recorded when N. barkeri fed on E. orientalis, while feeding on E. sexmaculatus gave the minimum fecundity (1.87 eggs per female) and lowest reproduction rate (r_m = 0.041). The values of these parameters for N. barkeri evaluated on O. biharensisin were found to be comparable to those obtained on T. putrescentiae. The sex ratio of N. barkeri progeny on the preys mentioned above, apart from O. biharensisin, was female biased. According to the findings, N. barkeri could serve as a promising biocontrol agent against E. orientalis and O. biharensisin, and possibly E. sexmaculatus on rubber trees.

The spider mites, Oligonychus biharensis and Eotetranychus sexmaculatus, are two major pests of rubber trees which are very important tropical crop in China (Liu et al. 2022). They normally caused more serious damages in drought seasons and various species showed differences in infestation severity (Wang et al. 2019; Liu et al. 2022). This study aims to understand the effects of drought stress on the occurrence of the spider mites by measuring the development and reproductive characteristics of O. biharensis and E. sexmaculatus on high (30%≤W<40%), moderate (40%≤W<50%), mild (50%≤W<60%) drought-stressed and control plants (60%≤W<80%) under the conditions of 30±1℃, 75±5%RH and 14L:10D photoperiod in artificial climate chambers.

Eotetranychus sexmaculatus has long been recognized as an important spider mite pest of rubber trees. Recently, increasing damage from Oligonychus biharensis has elevated its importance as a key spider mite pest. These two species share highly overlapping ecological niches, with outbreaks strongly associated with high temperatures and drought stresses. However, little is known regarding the potential competition between these spider mite species and the role of temperature in shaping these interactions. This study investigates the development and reproduction of E. sexmaculatus and O. biharensis at varying population densities, and evaluates their dynamics at 27 °C, 30 °C, and 33 °C. Five initial population densities of E. sexmaculatus and O. biharensis were evaluated in mixed populations: 0:30, 10:20, 15:15, 20:10, and 30:0. The results demonstrate both intra- and interspecific competition between E. sexmaculatus and O. biharensis. At all three intraspecific densities, the survival rate and lifespan of both species declined as density increased, with fecundity also decreasing at higher densities. Single-species populations of each mite were larger in number when compared with mixed populations. Across all treatments, the mean and peak values of the intrinsic rate of increase (r_m) were greater in O. biharensis than in E. sexmaculatus. Additionally, increasing temperatures accelerated the displacement of E. sexmaculatus by O. biharensis, regardless of the initial population density. When the mixed populations of E. sexmaculatus and O. biharensis were at densities of 10:20, the highest interspecific competition coefficients were obtained at 33 °C, with values of 0.6591. In conclusion, O. biharensis consistently outcompeted E. sexmaculatus at all tested temperatures, irrespective of initial densities, providing valuable insights into the competitive dynamics of dominant rubber tree pests.

Natural rubber is an important tropical crop. Eotetranychus sexmaculatus Riley has been an important phytophagous mite on rubber trees since the 1980s (Liu et al. 2022). In recent years, Oligonychus biharensis Hirst as presented an increasing trend of damage to rubber trees and has become another crucial phytophagous mite. These two spider mite species both inhabit and damage the leaves. They occur separately or together in the field and have high-overlapped ecological niches. Therefore, we hypothesized that interspecific competition existed between them, and their coexistence might inhibit the population growth of one or both species to obtain food and spatial resources (Li et al. 2018). Additionally, the outbreaks of these two spider mite species have often been found with high temperature and drought stresses. Therefore, focusing on whether there is competition between the two species of spider mites and how temperature affects them, the population dynamics of E. sexmaculatus and O. biharensis (female: male=1:1), and their mixed populations were assessed at 27, 30, and 33°C. For each treatment, 30 pairs of spider mites were used. There are five starting densities of E. sexmaculatus and O. biharensis individuals: 30 vs. 0, 0 vs. 30, 10 vs. 20, 15 vs. 15, and 20 vs. 10, respectively. The virgin male and female adult mites were picked and transferred onto the rubber leaves (96 cm2). These mites were reared in climate chambers with different temperatures and the leaves were replaced regularly. The numbers of each mite stage were recorded every 5 days. The experiments ended when one of the spider mite species was extinct in the mixed populations. The results showed interspecific competition existed between E. sexmaculatus and O. biharensis. Either pure population of two spider mites was greater in numbers than the mixed populations. The populations of E. sexmaculatus were significantly suppressed by O. biharensis. The mean and peak values of the innate capacity of increase (rm) were greater in O. biharensis than E. sexmaculatus in all treatments, indicating that O. biharensis was more competitive than E. sexmaculatus. Additionally, E. sexmaculatus was rapidly replaced by O. biharensis with the increased temperature, regardless of their starting densities. At 33°C, the highest interspecific competition coefficients were obtained (0.5695 and 0.6188, respectively) when the mixed populations of E. sexmaculatus and O. biharensis were 10 vs. 20 and 20 vs. 10. In conclusion, O. biharensis was more competitive than E. sexmaculatus at all tested temperatures, regardless of their starting densities.