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

Simple Summary The development of effective pest management tools for the radish fly, Delia planipalpis, requires an understanding of the basic biology and reproductive behavior of this pest. In the present study, we investigated the pest's biology on radish and confirmed the identity of the pest by sequencing the COI gene. The development of immature stages lasted 32-33 days. Female flies began mating 1-4 days after emergence, whereas males attempted to mate immediately after emergence. Most females only mated once during the 4-day observation period. Females preferred to lay eggs on radish plants rather than broccoli, although this result may have been influenced by the plant used to rear the insect colony. Male and female flies lived longer when individualized (14.5-22.5 days) compared to insects that were confined in groups (10-11 days). This is the first detailed and statistically rigorous study on the basic biology of this important pest of broccoli and other cruciferous crops. 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 & DEG;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.