Whitefly population development in the second glasshouse trial with marigolds and limonene “emergency” intercropping treatments to control an established whitefly population (n = 8).

Treatments comprised intercropping eight heavily whitefly-infested tomato plants with eight further tomato plants (control), eight French marigold plants (marigold treatment), or eight limonene dispensers (limonene treatment). The first data point in Fig 3A, 3B and 3C represents whitefly abundance (adults/eggs/nymphs) on the focal tomato plants immediately before treatment plants were introduced. ‘*’ indicates a p value of p value of n = 8). No significant effect on settling adult whiteflies was observed between treatment (rm ANOVA F (2,105) = 1.71, p = 0.185) and treatment x time (rm ANOVA F (8.105) = 0.896, p = 0.522) across the sampling period. Fig 3B displays the average number of eggs laid on each focal tomato plant over the course of the experiment (n = 8). No significant effect on whitefly egg abundance was observed between treatment (rm ANOVA F (2,105) = 0.477, p = 0.625) and treatment x time (rm ANOVA F (8,105) = 0.351, p = 0.943) across the sampling period. Fig 3C displays the average number of whitefly nymphs of all stages counted on each focal tomato plant over the experiment (n = 8). There was no significant effect on treatment (rm ANOVA F (2,105) = 2.72, p = 0.070) but there was a significant effect on treatment x time (rm ANOVA F (8,105) = 2.62, p = 0.011). The limonene treatment had significantly less nymphs than the control on day 29 (t = 4.18, df = 105, p 0.001) and neared significance at day 22 (t = 2.17, df = 105, p = 0.095). The limonene treatment also had significantly less whiteflies than the marigold treatment at day 29 (t = -2.61, df = 105, p = 0.030). Ninety five percent confidence intervals have been calculated and are available in the supporting information (S2 Dataset), but to aid visualisation they have been removed from the figure.