Conservation biological control of arthropod pests using native plants

Native Japanese Polygonaceae Species as Potential Native Insectary Plants in Conserving Indigenous Natural Enemies

Conservation biological control (CBC) is the application of agricultural practices that utilize insectary plants to conserve and enhance natural enemies, thereby increasing their efficiency to suppress pests. Most of the insectary plants used in CBC are non-native invasive insectary plants, which are costly and pose threats to the local ecosystems and biodiversity. Alternative to non-native insectary plants, the use of native plants is proposed. Hence, the aim of this study is to identify native plant species that can be used as alternatives to non-native insectary plants to conserve and promote indigenous natural enemies (INEs) for sustainable pest management. To achieve this, first, we bio-prospected the surrounding habitats of organic fields in the western region of Japan (i.e., Hiroshima Prefecture) to identify native plant species as prospective native insectary plants. As a result, among various Japanese native plants surveyed, Polygonaceae plant species seem to host a variety of INEs, showing potential as a native insectary plant. We then conducted open field experiments to test the role of Polygonaceae plants in promoting INEs, thereby indirectly suppressing pest densities on vegetable crops such as eggplants. Results show that significantly high densities of INEs (green lacewing, p = 0.024; Orius spp., p = 0.001: GLM) were observed on eggplants with Polygonaceae plants compared to eggplants without Polygonaceae plants, leading to a significant reduction in pest densities (thrips, p = 0.000; whiteflies, p = 0.002: GLM) on the eggplants with Polygonaceae plants. Furthermore, molecular analysis revealed that Orius spp., as a representative INE in this study, migrated from Polygonaceae plants to eggplants, suggesting that Polygonaceae plants may conserve and promote INEs to vegetable crops, resulting in pest suppression. Here, we discuss the roles of Polygonaceae plants (and other native plants) in regulating pest densities on crops.

Monarch Butterflies in Western North America: A Holistic Review of Population Trends, Ecology, Stressors, Resilience and Adaptation

Monarch butterfly populations in western North America suffered a substantial decline, from millions of butterflies overwintering in California in the 1980s to less than 400,000 at the beginning of the 21st century. The introduction of neonicotinoid insecticides in the mid-1990s and their subsequent widespread use appears to be the most likely major factor behind this sudden decline. Habitat loss and unfavorable climates (high temperatures, aridity, and winter storms) have also played important and ongoing roles. These factors kept overwintering populations stable but below 300,000 during 2001-2017. Late winter storm mortality and consequent poor spring reproduction drove winter populations to less than 30,000 butterflies during 2018-2019. Record high temperatures in California during the fall of 2020 appeared to prematurely terminate monarch migration, resulting in the lowest overwintering population (1899) ever recorded. Many migrants formed winter-breeding populations in urban areas. Normal seasonal temperatures in the autumns of 2021 and 2022 enabled overwintering populations to return to around the 300,000 level, characteristic of the previous two decades. Natural enemies (predators, parasitoids, parasites, and pathogens) may be important regional or local drivers at times but they are a consistent and fundamental part of monarch ecology. Human interference (capture, rearing) likely has the least impact on monarch populations. The rearing of monarch caterpillars, particularly by children, is an important human link to nature that has positive ramifications for insect conservation beyond monarch butterflies and should be encouraged.

Effects of Fabaceae and Poaceae Pollen Accessibility and Traits on the Pollinivory of Adult Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae)

Pollen is a food source for adult Chrysoperla externa (Hagen), whose larvae are biocontrol agents against pests. However, adults may face challenges in foraging for pollen due to differences in pollen accessibility and variability in pollen morphology and chemistry. In the laboratory, we investigated the ability of adult C. externa to consume pollen from flowers of Cajanus cajan, Canavalia ensiformis, Crotalaria juncea, Flemingia macrophylla, Avena strigosa, Pennisetum glaucum, Sorghum bicolor, and Zea mays, and we explored whether adults chose any of these pollens based on their quantitative and qualitative features. Cajanus cajan and F. macrophylla pollen were the only ones not consumed by adults when confined to flowers. Pollen removed from the preanthesis buds was offered simultaneously for 24 and 48 h. In both periods, adults consumed more of the medium-sized P. glaucum (with the second largest exine thickness) and large-sized Z. mays (with the thinnest exine) pollen, even though they had significantly less crude protein than Fabaceae pollen, whose sizes varied from medium (C. juncea, with the thickest exine) to large (C. ensiformis, whose exine thickness was equal to that of P. glaucum). Overall, adults consumed more Poaceae pollen than Fabaceae pollen, but the palynological features and the protein contents did not affect this choice. Our results highlighted that C. juncea, P. glaucum, S. bicolor and Z. mays are good pollen sources for adult C. externa and should be considered promising candidates in the selection of insectary plants to deploy in biocontrol programs aimed at the conservation of this lacewing.