Immature development of parasitoid wasps is restricted to resources found in a single host that is often similar in size to the adult parasitoid. When two or more parasitoids of the same or different species attack the same host, there is competition for monopolization of host resources. The success of intrinsic competition differs between parasitoids attacking growing hosts and parasitoids attacking paralyzed hosts. Furthermore, the evolution of gregarious development in parasitoids reflects differences in various developmental and behavioral traits, as these influence antagonistic encounters among immature parasitoids. Fitness-related costs (or benefits) of competition for the winning parasitoid reveal that time lags between successive attacks influence the outcome of competition. Physiological mechanisms used to exclude competitors include physical and biochemical factors that originate with the ovipositing female wasp or her progeny. In a broader multitrophic framework, indirect factors, such as plant quality, may affect parasitoids through effects on immunity and nutrition.

Rice orange leaf phytoplasma (ROLP) causes clear orange to yellowish leaf discoloration and severe stunting in rice seedlings. The ecological and biological characteristics of ROLP are largely unknown because the disease has not widely caused serious problems in rice cultivated areas, thereby leading to the low accumulation of research data. However, in the past decade, the disease became a threat to rice production, particularly in South China and India; it has also been recognised in other Asian countries, such as Vietnam, Thailand and the Philippines. Here, we observed the occurrence of ROLP in paddies of the Southeast Asian counties (Cambodia, Vietnam and the Philippines) and found that the isolates in the Philippines and Vietnam were monophyletic, while those in India, Thailand and Cambodia were more diverse, suggesting their potential origins. In Cambodia, it was revealed that following polymerase chain reaction (PCR) detection, the known ROLP-insect vectors, N. virescens Distant and Recilia dorsalis Motchulsky, were ROLP-positive, indicating their roles in pathogen dispersal. Moreover, fluorescent and scanning electron microscopy revealed the intensive accumulation of the phytoplasma in phloem tissues and massive accumulation of storage starch in vascular bundle sheath and parenchyma. Altogether, this study illustrated the genetic variability of global ROLP isolates and the pathogen’s biological impact on rice tissue.

Many parasitoid wasps are highly specialized in nature, attacking only one or a few species of hosts. Host range is often determined by a range of biological and ecological characteristics of the host including diet, growth potential, immunity, and phylogeny. The solitary koinobiont endoparasitoid wasp, Cotesia vestalis, mainly parasitizes diamondback moth (DBM) larvae in the field, although it has been reported that to possess a relatively wide lepidopteran host range. To better understand the biology of C vestalis as a potential biological control of hosts other than the DBM, it is necessary to determine suitability for potential hosts. In this study, the potential host range of the wasp and its developmental capacity in each host larva were examined under laboratory conditions using 27 lepidopteran species from 10 families. The wasp was able to parasitize 15 of the 27 species successfully. Some host species were not able to exclude C vestalis via their internal physiological defenses. When parasitization was unsuccessful, most hosts killed the parasitoid at the egg stage or early first-instar stage using encapsulation, but some host species disturbed the development of the parasitoid at various stages. No phylogenetic relationships were found among suitable and unsuitable hosts, revealing that host range in some endoparasitoids is not constrained by relatedness among hosts based on immunity.

Rice (Oryza sativa) is the staple crop of Cambodia. The heavy use of pesticides has caused significant financial losses to local farmers. This study examined the necessity and economic viability of insecticide use for rice cultivation, and the multiple interactions between the populations of both insect pests and natural enemies in dry-season rice fields. The outcomes of calendar-based insecticide-sprayed and non-sprayed rice fields were compared at three provincial research stations in Cambodia in terms of rice growth, economic returns, damage caused by insect pests, and population dynamics of insect pests and arthropod natural enemies. The results showed that rice fields without insecticide application did not suffer significant damage by insect pests or by diseases and had similar yields to those treated with insecticide application in two provinces. Although the occurrence of caseworm was observed in the third province, this was successfully controlled by an integrated pest management (IPM) treatment without using insecticides. Insufficient densities of natural enemies appeared to correlate with the caseworm outbreak in this location, whereas high densities of natural enemies relative to those of insect pests contributed to control potential pest expansion in the other two provinces. Natural enemy populations were significantly decreased by insecticide applications. Reduced insecticide input in the insecticide-free control and IPM plots resulted in higher net profits than those in insecticide-applied plots, except for plots in the region with a caseworm outbreak (insecticide-free). Overall, this study provides encouraging insight into cost effective and environmentally friendly pest management in Cambodian rice fields.