Delia planipalpis

Lasa, Rodrigo, Córdova-García, Guadalupe & Williams, Trevor, 2025, Laboratory evaluation of insecticides for the control of Delia planipalpis (Diptera: Anthomyiidae), a nascent pest of broccoli (Brassicaceae) in Mexico, The Canadian Entomologist (e 2) 157, pp. 1-14 : 5-9

Contact toxicity in adults

The two pyrethroid insecticides were the only products that caused knockdown of adult flies 1 hour after treatment. The median (interquartile range; IQR) percentage of knocked-down flies was similar for bifenthrin 100% (100–100%) and lambda-cyhalothrin 80% (73–88%). However, a large fraction of these flies subsequently recovered and were counted as alive in the 23-hour evaluation. The percentage of mortality of flies at 23 hours post-treatment differed markedly among the different products (Kruskal– Wallis: H = 46.2, df = 11, P <0.001). Flies exposed to bifenthrin residues had the highest mortality, whereas all the other products resulted in mortalities of less than approximately 15%, similar to that of the control ( Fig. 1 ).

Ovicidal effects and neonate mortality

The percentage of egg hatch differed significantly among insecticides (Kruskal– Wallis: H = 46.0, df = 13, P <0.001). The only insecticide with significant ovicidal activity was the clothianidin-based product ( Fig. 2 ), whereas egg hatch in all the other treatments was similar to that of the control.

The percentage of mortality observed in neonate larvae also differed significantly among the insecticides (Kruskal– Wallis: H = 117.0, df = 13, P <0.001). Products based on bifenthrin, lambda-cyhalothrin, clothianidin, imidacloprid, thiamethoxam, spinetoram, and spinosad all resulted in neonate mortalities of 80–100%, which were significantly higher than that observed in the control (∼ 15%; Fig. 3 ). Neonate mortalities in the organic-approved insecticides ( Tagetes ( Asteraceae ) extract, S. feltiae , and B. thuringiensis ) and the systemic spirotetramat-based product were similar to that of the control, whereas the neem ( Meliaceae ) oil- and pyriproxyfen-based products resulted in intermediate percentages of neonates mortality.

Mortality in larvae of the second- and third-instar stages

The percentage of larval mortality at the second- and third-instar stages varied significantly following spray application of products (Kruskal– Wallis: H = 65.0, df = 8, P <0.001; Fig. 4A ). The thiamethoxam- and spinetoram-based products resulted in the highest levels of larval mortality, followed by the clothianidin- and spinosad-based products ( Fig. 4A ). The imidacloprid-based product and the nematode S. feltiae generated intermediate levels of mortality that were similar to those observed in insects treated with the spirotetramat- and B. thuringiensis –based products and the control ( Fig. 4A ).

When insecticides were applied through root irrigation, the percentage of larval mortality also differed significantly among products (Kruskal– Wallis: H = 65.0, df = 8, P <0.001), and only the systemic neonicotinoid-based products (thiamethoxam, clothianidin, and imidacloprid) resulted in high levels of mortality (75–100%) of second- and third-instar larvae ( Fig. 4B ).

Radishes were infested with a mean (± standard error) number of larvae that varied between 1.9 ± 0.3 and 3.9 ± 0.5 larvae per radish in the spray application experiment and between 1.3 ± 0.4 and 4.3 ± 1.0 larvae per radish in the root irrigation experiment. Upon inspection at the end of the experiments, 100% of the control radishes contained at least one living larva of D. planipalpis . However, the percentage of radishes that contained at least one living larva differed significantly among insecticides following a spray application (Χ 2 = 55.8, df = 8, P <0.001; percentage values in the box at the top of Fig. 4A ) or root irrigation (Χ 2 = 47.8, df = 6, P <0.001; percentage values in the box at the top of Fig. 4B ). The thiamethoxam-based product was the most effective in controlling larvae, with less than 10% of radishes containing a living larva irrespective of the application method.

Adult emergence of treated pupae and subsequent adult mortality

No adults emerged from pupae treated with 0.5 mL/L of the pyriproxyfen-based product, whereas all the other products resulted in adult emergence of 50–70%, similar to that of the control (Kruskal– Wallis: H = 41.1, df = 11, P <0.001; Fig. 5 ).

In treatments in which adult flies emerged, a similar but low fly mortality (5–14%) was observed among products during the 12-day period after emergence, compared to 10% (10–10%; median, IQR) in the control (Kruskal– Wallis: H = 15.5, df = 11, P = 0.161; data not shown).

The percentage of adults that emerged from pupae treated with the pyriproxyfen-based product at different concentrations (0.1, 0.05, and 0.005 mL/L) was significantly lower than that observed for the control pupae (Kruskal– Wallis: H = 35.3, df = 3, P <0.01; Fig. 6 ). Even at the lowest product concentration (0.005 mL/L), adult emergence was half that observed for the control.

The median (IQR) mortality of flies at 12 days after emergence also differed markedly between the control 10% (10–10%) and pyriproxyfen-treated insects, which varied from 100% (100–100%) mortality for 0.1 mL/L (n = 3) and 100% (88–100%) for 0.05 mL/L (n = 14), compared to 50% (46–100%) mortality for 0.005 mL/L (n = 22) treated insects (Kruskal– Wallis: H = 21.3, df = 3, P <0.01).

Figures

Figure 1. Box plot of the percentage mortality of Delia planipalpis flies after contact with the dry residues of different insecticides. The median (horizontal bar), interquartile range (box), range (vertical whisker), and outliers (dots) are shown. Treatments labelled with different letters differ significantly (DSCF, P <0.05).

Figure 2. Box plot of the percentage of egg hatch in Delia planipalpis after contact with the residues of different insecticides. The median (horizontal bar), interquartile range (box), range (vertical whisker), and outliers (dots) are shown. Treatments labelled with different letters differ significantly (DSCF, P <0.05).

Figure 3. Box plot of the percentage mortality of neonate larvae of Delia planipalpis after contact with the residues of different insecticides. The median (horizontal bar), interquartile range (box), range (vertical whisker), and outliers (dots) are shown. Bars labelled with different letters differ significantly (DSCF, P <0.05).

Figure 4. Box plot of the percentage of larval mortality in Delia planipalpis after the treatment of radish plants with different insecticides by A, spray application, and B, root irrigation. The median (horizontal bar), interquartile range (box), range (vertical whisker), and outliers (dots) are shown. Values in the box above each figure indicate the percentage of radishes that contained at least one living larva. Treatments or percentage values labelled with different letters differ significantly (DSCF, P <0.05).

Figure 5. Box plot of the percentage of adult emergence in Delia planipalpis after the treatment of pupae with different insecticides. The median (horizontal bar), interquartile range (box), range (vertical whisker), and outliers (dots) are shown. Treatments labelled with different letters differ significantly (DSCF, P <0.05).

Figure 6. Box plot of the percentage of adult emergence in Delia planipalpis after the treatment of pupae with different concentrations of a pyriproxyfen-based product. The median (horizontal bar), interquartile range (box), range (vertical whisker), and outliers (dots) are shown. Treatments labelled with different letters differ significantly (DSCF, P <0.05).