Temporal dynamics of host use by Drosophila suzukii in California’s San Joaquin Valley: Implications for area-wide pest management

Authors: Wang, Xingeng; GÜLAY, KAÇAR - University Of California; KENT, DAANE - University Of California

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2019
Publication Date: 7/15/2019
Citation: Wang, X., Gülay, K., Kent, D.M. 2019. Temporal dynamics of host use by Drosophila suzukii in California’s San Joaquin Valley: Implications for area-wide pest management. Insects. 10: 2016. https://doi.org/10.3390/insects10070206.
DOI: https://doi.org/10.3390/insects10070206

Interpretive Summary: The spotted wing drosophila (SWD), originally from Asia, has become a global economic pest of small fruits and cherries. California’s San Joaquin Valley is one of the world’s most important fruit production regions, with a diverse agricultural landscape of cultivated and unmanaged host fruit crops. Such diverse landscapes result in SWD populations that challenge the management of this polyphagous pest. We showed that only the early seasonal fruits such as cherries are at greatest risk to SWD. Many later seasonal fruits are not as vulnerable to this pest because their intact skin reduces oviposition or they ripen during a period of low SWD abundance, or their flesh has chemical attributes that retard survival. Some of these alternative hosts, such as citrus and damaged, unharvested stone fruit, may shelter overwintering populations and provide sources of infestation of the more susceptible crops. Area-wide management strategies should consider (1) fruit sanitation to lessen overwintering populations; (2) suppressing fall and winter populations by releasing natural enemies; and (3) reducing pest pressure in susceptible crops through ‘border-sprays’ and/or ‘mass trapping’ to kill adults before they move into the vulnerable crop.

Technical Abstract: A major challenge to area-wide management for Drosophila suzukii is understanding the fly’s host use and temporal dynamics, which may dictate local movement patterns. We determined D. suzukii’s seasonal host use in California’s San Joaquin Valley by sampling common crop and non-crop fruits in a temporal sequence of fruit ripening. We then evaluated the suitability of selected fruits as hosts. Drosophila suzukii emerged from both intact and damaged cherries during the cooler, early season period. Fly density remained low through the hot spring-summer period, and re-surged as temperatures lowered in fall when the fly did not cause damage to intact peach, nectarine, plum, pear, grape, pomegranate, apple, persimmon and citrus (in order of ripening), but did emerge from damaged fruits of these crops. The fly also utilized two ornamental fruits (loquats and cactus), but was not found on wild plum and two endemic wild fruits (buckthorn and bitter berry). Drosophila suzukii completed development (egg to adult) on cactus, mandarin carpel, pomegranate seed, wild plum and buckthorn at survival rates similar to cherry (51.2 – 68.8%), whereas they had a lower survival rate on bitter cherry (33.2%), table grape (31.5%), raisin grape (26.5%), and wine grape (4.5%). High acidity levels of grapes negatively affected the fly’s fitness. Among 10 cherry cultivars, survival rate was not affected by sugar content, but decreased with increasing egg density per gram of fruit. Results suggest that in California’s San Joaquin Valley, the early season crops are most vulnerable, summer fruits ripen during a period of low pest pressure, and late season fruits, when damaged, serve to sustain D. suzukii’s populations in this region.