Insects decline with host plants but co-extinctions seem unlikely

It is commonly assumed that the loss of wild plant populations leads to co-extinctions, especially among specialized insects. Despite global declines in both terrestrial insects and plants, the relationship between these trends remains elusive. Here, we address this gap by analyzing the relationship between population trends of insects and their host plants in Germany, encompassing over 150,000 interactions among 3429 plant and 2239 insect species, including both symbiotic pollinators (bees and hoverflies) and parasitic herbivores (butterflies, moths, and sawflies). Our findings reveal generally positive relationships between the short- and long-term population trends of insects and their host plants across taxa, except in the more generalist hoverflies. However, when we simulated extinctions of threatened host plants, we found that 97% of the insect species studied could potentially survive by using alternative, non-threatened host plants. Even the most specialized insects may persist because they tend to specialize in common, non-threatened plant species. Our findings suggest the declining abundance of many plant species can contribute to insect decline yet challenge the frequent assumption that the extinction of threatened plant species will necessarily trigger an extinction wave of associated insects. Interaction networks seem to be more resilient.