Biology and Ecology of Delia planipalpis (Stein) (Diptera: Anthomyiidae), an Emerging Pest of Broccoli in Mexico

Abstract

Delia planipalpis (Stein) (Diptera: Anthomyiidae) is a pest of crucifers, such as broccoli, radish, cauliflower, turnip and cabbage. It has been recently described in Mexico as a significant emerging pest of broccoli. Due the lack of knowledge of this pest, the present study aimed to determine its life cycle, female sexual maturation, copulation, oviposition behavior and adult longevity. The identity of the fly in Mexico was confirmed genetically by sequencing the cytochrome oxidase subunit 1 gene (COI). The mean development time of D. planipalpis was 32-33 days on radish at 24 °C under laboratory conditions. Females became sexually mature 1-2 days after emergence, and the highest incidence of matings was recorded on the second day (60%). Under choice conditions, D. planipalpis females preferred to oviposit on radish plants, rather than broccoli plants, possibly due to the use of radish for rearing the laboratory colony. Oviposition and the mean number of eggs laid varied among the broccoli varieties, with the highest oviposition observed on the Tlaloc variety. Repeated attempts to rear the laboratory colony on broccoli plants failed. Radish-reared insects of both sexes lived longer when individualized in the adult stage (14.5-22.5 days) than when adult flies were maintained in groups (10-11 days). This study contributes to the understanding of D. planipalpis biology and provides information that can be used to establish future control strategies against this pest.

Keywords: genetic identity; lifecycle; longevity; oviposition behavior; sexual behavior; sexual receptivity.

Figure 1

Characteristic damage of Delia planipalpis larvae in (A) a broccoli plant stem, (B) inflorescence and (C) leaf axil. Arrows indicate position of larvae.

Figure 2

Survival of adult females and males of Delia planipalpis when individualized or maintained in groups at 24 ± 1 °C. Both sexes were reared on radish.

Figure 3

Mean (± SE) cross-sectional area of ovaries of Delia planipalpis females 1, 2, 3 and 4 days post-emergence. Different lowercase letters indicate significant differences (ANOVA, Tukey’s test, p < 0.05).

Figure 4

Mating percentage of 1-, 2-, 3- and 4-day-old Delia planipalpis after emergence. Numbers within parentheses represent sample size (total n = 51).

Figure 5

Mean number of eggs oviposited (± SE) per female in choice experiments with radish (gray columns) and three varieties of broccoli (yellow columns) in three separate experiments. Numbers above bars indicate mean values. Numbers followed by different letters differ significantly (paired t-test, p < 0.05). The results of experiments involving Emerald and Gypsy broccoli varieties were not analyzed statistically due to an absence of oviposition on broccoli.

Figure 6

Mean number of eggs (±SE) per female on three varieties of broccoli under choice conditions (A) or no-choice conditions (B). Columns headed by different letters differ significantly (GLM and ANOVA for A and B, respectively, p < 0.05).