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The frequency and duration of heat waves are expected to increase under global warming, so parasitoids could increasingly encounter heat waves at some stage of their life cycle. However, few studies have focused on how host-feeding parasitoids respond to heat waves. We investigated how the frequency of heat waves during different developmental stages (larva, pupa and adult) of a host-feeding parasitoid, Eretmocerus hayati, affects its life history traits and life table parameters. The results showed that when continuous heat waves were experienced during a single stage, the development time of the stage that encountered the heat waves (either the larval or pupal stage) was significantly prolonged, while one heat wave did not have the same effect. Regardless of which stage (larval or pupal stage) of parasitoids encountered continuous heat waves, life history traits (host feeding, fecundity and longevity) and life table parameters (intrinsic rate of increase, r) were significantly decreased. Moreover, heat waves at the pupal stage had greater detrimental effects on adult performance than heat waves at the larval stage. However, when adult parasitoids experienced continuous heat waves, their lifetime fecundity did not differ significantly from that of parasitoids that experienced heat waves only once during a single stage. When two or three stages faced continuous heat waves, adult performance sharply decreased, especially in terms of r. Hence, these findings suggest that the timing and duration of heat waves should be assessed before releasing a parasitoid as a biological control agent. If such an assessment is not performed, the biological control efficiency could be greatly decreased.

Biocontrol has broad application prospects, and developing new microbial strains as potential biocontrol agents is a major task. Paenibacillus terrae strain NK3-4 has the potential for use as a biocontrol agent. To characterize the potential biocontrol capacity of this strain, we evaluated its antagonism against pathogens of rice blast (Magnaporthe oryzae), corn spot disease (Exserohilum turcicum), soybean bacterial spot disease (Xanthomonas campestris pv. glycines), and rice sheath blight disease (Rhizoctonia solani), we also evaluated its effect on the development of rice blast disease in greenhouse and field trials. Strain NK3-4 exhibited distinct antagonism against M. oryzae and the other tested plant pathogens. An antifungal protein component that was able to trigger plant immune responses was isolated from the culture supernatant of strain NK3-4, and was identified as a β-1,3-glucanase (designated as PteNI). Strain NK3-4 controlled rice blast development in a greenhouse (prevention efficacy: 90.3%) and under field conditions (prevention efficacy: 35.8% and 41.3% after 7 and 14 days of treatment, respectively, in Jiamusi; 23.0% and 31.4% after 7 and 14 days of treatment, respectively, at Qixing Farm). In conclusion, P. terrae NK3-4 is a promising biocontrol agent against rice blast and other plant diseases. The antifungal activities of this strain are likely due, at least partially, to the β-1,3-glucanase PteNI.

When two parasitoids exploit a common host simultaneously, competitive interactions between them usually occur, and are more complex among host-killing species. Diglyphus isaea (Walker) and Neochrysocharis formosa (Westwood) are larval parasitoids of agromyzid leafminers. They have widespread distributions and share the same host resources when sympatric. In this study, interactions between these two parasitoids and different parasitoid release modes were investigated. Parasitoids were exposed to leaves infested with late second to early third instar Liriomyza sativae at two different host densities in Petri dishes. The total death rate of N. formosa released alone was density-dependent. And release modes also impacted the total death rate of parasitoids at a high host density. However, the oviposition number of D. isaea was significantly greater than that of N. formosa when they coexisted. In addition, host-feeding proportions were greatest among three host-killing behaviors: parasitism, host feeding and host stinging. These results contribute to a further understanding of parasitoids’ host-killing strategies.

Neochrysocharis formosa (Westwood), an important biocontrol agent of agromyzid leafminers worldwide, is a host-feeding, idiobiont parasitoid. Female wasps have three types of host-killing behaviors: reproductive (parasitism), non-reproductive host feeding (host feeding), and host stinging without oviposition or feeding (host stinging). In this study, we compared the life history and host-killing behaviors of female parasitoids under four adult diets: starvation, hosts only, hosts plus honey (10% w/v honey solution), and honey only. Furthermore, we analyzed the host-feeding and oviposition preferences of adult females in the hosts-only and hosts-plus-honey treatments. Female parasitoids feeding on hosts had significantly increased longevity, higher fecundity, more host-stinging events, and caused a higher total host mortality than parasitoids in the starvation treatment. The honey supplement significantly increased longevity, fecundity, host-stinging events, and total host mortality, as well as average daily fecundity, but did not alter host-feeding events, host-stinging events, or daily total host mortality. However, the honey supplement did reduce the number of daily host-feeding events and induced a shift toward oviposition. Finally, we found that the non-reproductive host killing caused by host feeding and host stinging enhanced the control potential of N. formosa . These results should contribute to a better understanding of the biocontrol efficiency of destructive host feeders.