Li Li

Pine wilt disease, caused by Bursaphelenchus xylophilus and vectored by Monochamus alternatus, is a devastating forest disease. The parasitoid Sclerodermus guani and entomopathogenic fungus Beauveria bassiana are effective biocontrol agents against wood-boring pests, but their compatibility remains poorly understood. We exposed adult female S. guani to three concentrations of B. bassiana conidia (1 × 10⁵, 1 × 10⁶, and 1 × 10⁷ conidia mL⁻¹) and assessed parasitoid mortality, infection, reproduction, and parasitism capacity against M. alternatus larvae. Mortality and infection rates increased significantly with concentration and exposure time. At 30 days post-exposure, corrected mortalities were 72.47%, 91.30%, and 100% for the three concentrations, respectively. Time–dose–mortality analysis yielded LT₅₀ values of 27.69, 20.00, and 5.92 days, confirming faster kill at higher doses. Fungal exposure reduced offspring production and development at high concentrations, yet fungus-carrying females still successfully parasitized M. alternatus. Importantly, low fungal concentrations caused only minor reductions in parasitism success and offspring survival. These findings demonstrate that the compatibility between B. bassiana and S. guani is strongly concentration-dependent. Therefore, optimizing fungal dosage is essential to balance fungal dispersal and parasitoid fitness in fungus-carrying biocontrol systems. Our study provides valuable insights into ecological interactions between entomopathogenic fungi and parasitoids, facilitating integrated pest management strategies for wood-boring pests.

In the complex interplay among parasitic wasps, their insect hosts, and pathogenic microbes, the system involving Sclerodermus guani (Hymenoptera: Bethylidae) (a parasitoid wasp), Monochamus alternatus (Coleoptera: Cerambycidae) (the pine sawyer beetle, its host), and Beauveria bassiana (Hypocreales: Cordycipitaceae) (a fungus) presents a unique scenario where wasp offspring develop within a nearly sealed host gallery. This nursery is vulnerable to fungal invasion, often introduced by the foraging female wasps or M. alternatus itself, creating a three-way interaction where the fungus can infect both M. alternatus and S. guani. To assess how the route and timing of fungal exposure impact the S. guani population, we simulated this system by introducing different concentrations of B. bassiana either directly to the female wasps or to M. alternatus prior to parasitism. We further examined the effect of exposure timing by applying the fungus at different developmental stages of the S. guani offspring. Key population parameters, including the reproductive capacity of female wasps, the survival and developmental fitness of S. guani offspring and the germination period of hyphae, were measured. The results indicated that the most severe damage to populations of S. guani occurs when its host, M. alternatus, is infected by B. bassiana. Among the various developmental stages, S. guani offspring exhibited the greatest vulnerability during mid-to-late larval stages, whereas the egg and pupa within cocoon stages demonstrated a higher tolerance. We conclude that both the pathway and the timing of fungal exposure are critical factors influencing its impact. These findings provide valuable insights for optimizing the integrated use of biological agents in pest management, informing strategies that mitigate adverse effects on beneficial parasitoid wasps.

Gastrolina depressa (Coleoptera: Chrysomelidae) has been found to damage many walnut plants in China. It prefers to feed on the annual leaves of an important economic plant, Pterocarya stenoptera (Fagales: Juglandaceae), and causes extensive cosmetic destruction, even plant death. Nevertheless, its biological characteristics are mostly unknown. In this study, we investigate the harmful and biological characteristics of G. depressa with different developmental stages. The results showed that G. depressa had four developmental stages: egg, larva (1^st -3^rd instar), pupa, and adult, the life history lasted nine days, with obvious overlapping generations. The food intake of the larvae increased with the increase of the instar, and the maximum food intake of the 3^rd instar larvae was 448.19 mm². The abdomen of the females was enlarged before oviposition, and the average number of eggs laid was 47.63 ± 13.53. Bioassay showed that there was no difference in the search time for the young (2.03, 1.25, 1.15, and 0.91 min) and old leaves (1.68, 1.15, 0.90, and 1.93 min) of P. stenoptera between 1^st -3^rd instar larvae and adults; the feeding preference of 1^st -3^rd instar larvae and adults for young leaves was higher than that to old leaves (23.33%, 26.67%, 33.33%, and 21.67%, respectively). The successful selection rates of 1^st -3^rd instar larvae and adults to young leaves (81.67%, 80%, 85.00%, and 70.00%, respectively) was higher than to old leaves (8.35%, 11.67%, 3.34%, and 11.67%, respectively).

Dendrobium plays a key role in the orchid industry, with ornamental, medicinal, and economic value. Recently, we found a newly recorded boring pest damaging Dendrobium in Guizhou Province, China. The species is identified as Nassophasis sp. (Coleoptera: Curculionidae: Rhynchophorinae) by morphological and anatomical features. The occurrence and biological characteristics of this species were verified through field investigation and indoor experiments. The results showed that detailed external morphological and genitalia characters and male-female differences are described to identify Nassophasis sp. The pest produces three generations per year, with overlapping generations. The adults overwinter in the root stains of Dendrobium and emerge in mid-March of the following year. Adults feed on stems, leaves, and flowers, often laying their eggs inside the stems; larvae then bore into the stems causing decaying and hollowing until complete immature development. There are three larval instars, grouped according to their head capsule width and body length, which were measured following Dyar’s law and Crosby’s law of growth and showed a significant linear regression (p < 0.0001). The results of this study provide a theoretical basis for the prediction and comprehensive control of the insect.

Complex interspecific relationships between parasites and their insect hosts involve multiple factors and are affected by their ecological and evolutionary context. A parasitoid Sclerodermus guani (Hymenoptera: Bethylidae) and an entomopathogenic fungus Beauveria bassiana (Hypocreales: Cordycipitaceae) shared the same host in nature, Monochamus alternatus (Coleoptera: Cerambycidae). They often encountered the semi-enclosed microhabitat of the host larvae or pupae. We tested the survival and reproduction of the parasitoid’s parent and its offspring fitness under different concentrations of B. bassiana suspension. The results show that S. guani parent females carrying higher concentrations of the pathogen shorten the pre-reproductive time and regulate their own fertility and their offspring’s survival and development. This minimal model of the interspecific interactions contains three dimensionless parameters, vulnerability (θ), dilution ratio (δ), and P_R, which were used to evaluate the mortality effect of the parasitoid S. guani on its host M. alternatus under the stress of the entomopathogenic fungus B. bassiana. We compared the infection and lethal effect of the fungus B. bassiana with different concentrations to the parasitoid S. guani and the host larvae M. alternatus. At higher concentrations of the pathogen, the parasitoid parent females shorten the pre-reproductive time and regulate their own fertility and their offspring’s survival and development. At moderate concentrations of the pathogen, however, the ability of the parasitoid to exploit the host is more flexible and efficient, possibly reflecting the potential interspecific interactions between the two parasites which were able to coexist and communicate with their hosts in ecological contexts (with a high overlap in time and space) and cause interspecific competition and intraguild predation.