Pests don’t touch my papa negra: Native potatoes and biological control of invasive tuber pests in the Venezuelan Andes

Background/Question/Methods

In partial response to a growing epidemic of seed-potato shortages and exotic tuber pest outbreaks, some farmers in the Venezuelan Andes complement their cultivation of imported Solanum tuberosum ssp. tuberosum seed-potato varieties with native  Solanum tuberosum ssp. andigenum varieties, locally known as papa negra. While papa negra varieties are widely perceived by Andean potato farmers to be “more resistant” to tuber pest damage, the role of native potato varieties in managing exotic tuber pests remains unclear. In this study I assessed the suceptibility of a native variety, Imilla Negra cv., to damage from a key exotic pest, Tecia solanivora Povolny (Lepidoptera: Gelechiidae) relative to two imported varieties, Andinita and Unica cv. I also examined the influence of native/imported potato polycultures on natural enemy impacts and marketable tuber yield. On a 8 ha farm in an Andean potato producing community of Merida State, Venezuela, I conducted exclusion experiments with sentinel Tecia solanivora larvae to determine the impacts of natural enemies on potato tuber infestation.  Tuber assesments in monoculture and polyculture plots of native Imilla Negra, Andinita, and Unica were also conducted to determine the effects of varietal diversification on T. solanivora damage, natural enemy impacts, overall disease incidence, and yield.

Results/Conclusions

The native variety, Imilla Negra, was less suceptible to T. solanivora damage both per plant (% damaged tubers) and per tuber (no. of perforations per tuber) than the imported varieties. While natural enemies did significantly reduce overall T. solanivora damage per plant, varietal diversification did not significantly increase natural enemy impacts, reduce tuber pest damage, or improve overall tuber yield. These findings support local farmer knowledge regarding the heightened “resistance” of native varieties to exotic pests, and suggest that low intensity management practices associated with native varieties may be key in promoting conservation biological control.