The parasitoid, Coccophagus japonicus Compere (Hymenoptera: Aphelinidae) is a dominant natural enemy of Parasaissetia nigra Nietner (Hemiptera: Coccidae), an important pest of rubber trees. Much of Chinese rubber is cultivated in hotter regions such as Yunnan and Hainan, exposing applied parasitoids to non-optimal temperatures. Therefore, C. japonicus must adapt to avoid temperature-related impacts on survival and population expansion. In this study, we monitored the survival rate, developmental duration, parasitism rate, and fecundity of C. japonicus during short-term exposures to 36 °C, 38 °C, and 40 °C for 2, 4, and 6 h, as well as continuous exposures to 32 °C and 34 °C for 3 days. The results show that short-term exposure to high-temperature stress leads to decreased survival rate of C. japonicus larvae and pupae, with survival rates declining as temperature and duration increase. High-temperature stress also delayed insect development, reduced mature egg production, shortened the body length of newly emerged females, and decreased female lifespans. Moreover, continuous high-temperature stress was found to significantly impact the development and reproduction of C. japonicus. Compared with the CK (27 °C), 3 d of continuous exposure to 34 °C prolonged developmental duration, shortened the body length and lifespan of newly emerged females, reduced survival rate and single female fecundity, and significantly decreased offspring numbers and parasitism rates. Temperatures of 36 °C, 38 °C, and 40 °C decreased the mortality time of adult females to 28.78, 16.04, and 7.91 h, respectively. Adverse temperatures also affected the insects’ functional response, with 8 h of stress at 36 °C, 38 °C, and 40 °C causing the control efficiency of C. japonicus on P. nigra. This level of stress in the parasitoids was found to reduce the immediate attack rate and search effect, prolong processing time, and attenuate interference between small prey. Parasitoid efficiency was lowest following exposure to 40 °C. In this study, we determined the range of high temperatures that C. japonicus populations can tolerate under short- or long-term stress, providing guidance for future field applications.

Scutellista ciruela Fonscolombe has a significant controlling effect on the rubber tree pest, Parasaissetia nigra Nietner. To identify the optimal conditions for the population growth of S. caerulea, we assessed how temperature, photoperiod, and supplementary nutrition affected its development and reproduction. The results demonstrated that the number of eggs laid and parasitism rates of S. caerulea were the highest at 33 °C. The developmental rate of S. caerulea was the fastest and the number of emerged adults the highest. The number of eggs laid and the parasitism rates increased when the light duration increased within a day. Females did not lay any eggs when the whole day was dark. At a photoperiod of 14:10 (L:D), the developmental duration was the shortest and the number of emerged adults was the highest. Adult life span was the longest under a 12:12 (L:D) photoperiod. During the adult stage, supplementary nutrition, such as sucrose, fructose, honey, and glucose, increased the life span of S. caerulea. The life span of S. caerulea was longer when provided with a supplementary diet of sucrose or honey, compared to other tested diets. The results suggested that the most suitable conditions for S. caerulea’s population growth were the following: 30 to 33 °C, with 12 to 14 h of daylight, and the provision of sucrose or honey as supplemental diet for the adults.

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.

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.

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.