Long-term monitoring reveals climate-driven seasonal dynamics of Zeugodacus cucurbitae (Coquillett) in Tanzania and prospects for pest control.

Zeugodacus cucurbitae (Coquillett) is a major and economically important pest of cucurbit crops, causing substantial losses to farmers across the tropics and subtropics. We analyzed a long-term trapping dataset (October 2004 - February 2012), collected from various agro-ecological settings in the Morogoro Region of Tanzania. This included a warm lowland orchard at Sokoine University of Agriculture (SUA) (526 m.a.s.l.) and a cooler highland orchard at Nyandira (1580 m.a.s.l.), as well as five additional locations along the same altitudinal gradient. Adult male Z. cucurbitae were monitored using cue-lure-baited modified McPhail traps. The abundance data was standardised as Flies per Trap per Day (FTD). Climatic-driven data were compiled from multiple sources. Results revealed significant spatial variation in Z. cucurbitae abundance along the altitudinal gradient (p < 0.0001), with sustained high densities at SUA, Kibundi and Mlali, intermediate levels at Langali, and chronically low abundance at Nyandira and Visada. Inter-annual variation was significant (p < 0.0001), with marked regional amplification in 2011-2012, whereas month-of-year effects were not significant (p = 0.7925). Directional increases occurred at Kibundi and Langali, while SUA and Mlali showed episodic dynamics and Nyandira remained stable at low levels. Abundance was negatively associated with elevation and positively associated with temperature (both p < 0.0001). Management should therefore continue in low-altitude areas, while regular monitoring, especially in high-altitude areas, is necessary to detect any steady increase in Z. cucurbitae abundance.