Quantifying host potentials: indexing postharvest fresh fruits for spotted wing Drosophila, Drosophila suzukii

Abstract

Novel methodology is presented for indexing the relative potential of hosts to function as resources. A Host Potential Index (HPI) was developed as a practical framework to express relative host potential based on combining results from one or more independent studies, such as those examining host selection, utilization, and physiological development of the organism resourcing the host. Several aspects of the HPI are addressed including: 1) model derivation; 2) influence of experimental design on establishing host rankings for a study type (no choice, two-choice, and multiple-choice); and, 3) variable selection and weighting associated with combining multiple studies. To demonstrate application of the HPI, results from the interactions of spotted wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae), with seven "reported" hosts (blackberries, blueberries, sweet cherries, table grapes, peaches, raspberries, and strawberries) in a postharvest scenario were analyzed. Four aspects of SWD-host interaction were examined: attraction to host volatiles; population-level oviposition performance; individual-level oviposition performance; and key developmental factors. Application of HPI methodology indicated that raspberries ( (mean)HPIvaried = 301.9±8.39; rank 1 of 7) have the greatest potential to serve as a postharvest host for SWD relative to the other fruit hosts, with grapes ( (mean)HPIvaried = 232.4±3.21; rank 7 of 7) having the least potential.

Figure 1. Correlation of spotted wing drosophila host volatile response to preference probabilities.

Spotted wing drosophila attraction (i.e., recapture percentage) to host volatiles was evaluated in two-choice horizontal flight chamber bioasssays and correlated to the actual probability of preference, A (Eq. 1)(R ² = 0.93, F_(1,5) = 69.09, P<0.001). Dashed lines indicate 95% confidence interval for the correlation.

Figure 2. Potential HPI values when weighting coefficients are varied across four studies.

The probability distributions of resultant Host Potential Index values derived from varying the weighting coefficieints (β) in the equation for the individual fruits shows the influence of coefficient weight selection. Vertical lines indicate the mean HPI value of each fruit.