Extra baggage: Accidental introductions of cryptogenic pathogens of invasive insects

Pathogens of invasive insects are often assumed to have arrived in or with infected individuals of that invasive host species. This assumption is not always correct, in part due to the lack of knowledge about the hosts of the pathogen in the invaded continent or in the continent of presumed origin. Discoveries of invasive insect pathogens raise questions about their origin and their potential benefit or detriment in the invaded continent. Pathogens can be co-introduced with an invasive insect host (direct transmission), which may or may not be the host species in which it was discovered, or introduced as contaminants with environmental samples (environmental transmission). Invasive pathogens may also become pathogens of native host species. We present three diverse examples of invasive insect host/invasive pathogen systems where sources, means and rates of spread, and impacts on populations of pest insects differ significantly. Increased knowledge about invasive pathogens can result in enhancing biological control and can help optimize biological control strategies.