Data from choice and no-choice tests associated with the paper cited below. Drought leading to water deficit stress is known to reduce performance of galling insects. The shoot tip-galling fly Parafreutreta regalis has been released for biological control of Cape-ivy (Delairea odorata) in California. Lack of moisture during the dry season causes wilting of Cape-ivy shoots, and subsequent reduced host quantity and quality could influence the fly’s ability to multiply and establish. We imposed water deficit stress on potted Cape-ivy plants, then measured the plant’s and insect’s response to water deficit compared to fully-watered plants. Water deficit stress was imposed during female oviposition (short-term), gall development (long-term), or full insect life cycle (long-term). Plants subjected to long-term water deficit showed declines in shoot growth, leaf area, and total biomass. In choice tests, 72% fewer galls were found on water deficit stressed plants, but there was no difference in the numbers of insects per gall. In no-choice tests, long-term water deficit reduced the number and size of galls by up to 51% and 39%, respectively, and puparia inside the galls were up to 35% smaller. Long-term water deficit also increased the time required for the insect to complete its life cycle (egg to adult) by about 10 days, and up to 80% fewer adults emerged, decreasing the fly’s rate of increase by up to five-fold. Our study shows that P. regalis will oviposit and develop successfully on water deficit-stressed plants, but declines in female preference, insect development and abundance could inhibit fly field establishment and/or population growth under climatic drought conditions. Resources in this dataset:Resource Title: Data from: Host plant water deficit stress impairs reproduction and development of the galling fly (Parafreutreta regalis), a biological control agent of Cape-ivy (Delairea odorata). File Name: CI Fly Drought Stress Biological Control Data Archive.csvResource Description: Tabular data for all choice and no-choice experimentsResource Software Recommended: MS Excel,url: https://www.microsoft.com/en-us/microsoft-365?ms.url=office365com&rtc=1 Resource Title: Data dictionary text file describing column headings in the csv data file.. File Name: Data Dictionary for Archiving Feb17-2021.txtResource Description: Data dictionary text file describing column headings in the csv fileResource Software Recommended: MS Word,url: https://www.microsoft.com/en-us/microsoft-365?ms.url=office365com&rtc=1