Using adult emergence to diagnose immature life stage distributions of internally feeding pests developing on fresh fruit and its application in postharvest treatment scenarios

Abstract:  The chronological development of internally feeding insects on fresh fruit is rarely homogenous and depends, to a large extent, on the quality of the host fruit.  Poorer quality fruit hosts tend to exaggerate developmental differences within a cohort with the effect being a dispersion of the developmental stage(s) vs. chronological age(s).  Developing postharvest control treatments against insect pests typically requires the most treatment-tolerant life stage to be identified and used as the target to establish protocols. Treating a specific life stage is not a problem with externally feeding pests which can be readily identified and isolated.  For internally developing pests, however, diagnosing the life stage present during treatment has been difficult and often assumed.  Here, a method to calculate the probability distribution of life stages present at any given point in time from adult emergence is presented and applied to spotted wing drosophila (SWD), Drosophila suzukii (Dipter: Drosophiladae), developing on several types of fresh fruit.  Our results clearly indicate differences in SWD development between fruits.  At a chronological age of 72-96 h, 91.1% of SWD present in blackberries are in the 3rd instar, compared to only 17.9% of SWD in blueberries.  Knowledge of the probability distribution at the time of treatment will likely lead to changes in experimentation and procedures required to develop treatments, whereby identifying the most tolerant “life stage” is modified to the most tolerant “time span,” followed by the probability of each life stage occurring within that time span being respectively listed.  In addition, data indicate that the duration of the 2nd instar can be used as a diagnostic tool to proxy host suitability.