Using 'parasitization rates' to determine natural enemy impact: what are we measuring?

The term ‘parasitization rate’ has not been clearly defined, despite being commonly used in the literature. In a meta-analysis, we found that some studies measured exclusively attack rates of parasitoids on hosts, while the majority measured exclusively emergence rates. Only occasionally were both of these measured. Although they are related, neither attack nor emergence alone can be used to define the interaction between parasitoid and host. Emergence rate is equal to attack rate minus parasitoid death rate in the host (killing the host as well), minus death rate in the host without host death (usually via encapsulation). From the host's perspective, total mortality is equal to attack rate minus encapsulation rate. Total mortality is also equal to emergence rate plus death rate (killing the host). In the context of testing the slow-growth, high-mortality hypothesis, we use our own rearing and dissection data to show that using emergence as a proxy for ‘parasitization rate’ to estimate the impact of parasitoids on a host, while ignoring parasitoid attack, can be misleading.