Cockroach cold preference: A behavioral strategy to defend fungal infection

Entomopathogenic fungi have emerged as promising alternatives to insecticides for overcoming insecticide resistance, particularly in controlling prevalent public indoor pests. However, insects have developed powerful defense strategies against infection, including host behavior preferences. In this study, using the German cockroach-Metarhizium anisopliae model, we found that infected cockroaches prefer colder living environments (20 °C versus 28 °C). Toxicity and conidial adhesion experiments showed that colder environments could significantly prolong the LT₅₀ of infected cockroaches and reduce conidial adhesion to the host cuticle. Histopathology and fungal conidia culture revealed that the active cold-seeking behavior of cockroaches significantly reduced the infection efficiency of fungi in the host. Further studies showed that cold preference could promote the enhancement of phenol oxidase-induced cell nodulation and high expression of immune effector defensin invertebrate_1 (DEFI_1), (NT_vs_LT = 10.210 versus 669.705, P = 0.000), in cockroaches. RNAi confirmed that DEFI_1 may be one of the important factors in reducing mortality rates in low-temperature environments. In summary, this study contributes to the understanding of the behavioral value of insect pests infected with pathogens and is beneficial for the development of biological control strategies using insect pathogens as active ingredients.