[4] However current taxonomic keys aim to be more thorough by not only including morphological diagnostics for males, females, and immature specimens of various species, but also their genetic make-up or molecular barcode.

The larvae of these flies, which tunnel into roots and stems of host plants, can cause considerable yield losses.

[5] Specialists typically have the ability to tolerate and/or enzymatically detoxify the harmful allelochemicals produced by the plants they feed on.

Morphologically speaking, adult Delia flies resemble the common housefly and species possess subtle differences in size, colouring, and location and length of bristles throughout the body.

[4] Six species of Delia (D. antiqua, D. floralis, D. florilega, D. planipalpis, D. platura, D. radicum) are common agricultural pests during their larval stage, causing severe economic loss throughout North America and Europe.

For example, D. radicum maggots feeding on the roots of canola crops cause damage to the plants’ phloem, periderm, and xylem parenchyma.

[17] For example, as a specialist of cruciferous crops, D. radicum, is attracted to the organic compound isothiocyanates found in these variety of plants in order to identify it as a suitable host.

[18] In addition to the plant itself, studies with D. radicum and D. floralis have shown that other environmental factors such as soil moisture,[16] average daily air temperature, and total precipitation[19] can all have a positive correlation with the crop’s susceptibility to infestation.

[20] Studies have shown that damaged or crushed onion bulbs left behind after harvest were major sources of D. antiqua food and an overwintering site.

However, recent studies have observed that neither of these sites are important infestation sources as conditions within deep cull piles are unfavourable to larval survival and larvae are unable to establish on undamaged volunteer plants in the spring.

[21] While crop rotation may be effective on certain soil- inhabiting pests that have low mobility and low dispersal capabilities, this practice is not commonly seen as a control for specialist Delia species such as D. radicum and D. antiqua since they can disperse 2000–3000 meters from the site of infestation and can have a wide host range.

Primarily, the goal is to avoid invasion by the pest, reduce crop vulnerability to oviposition, and decrease infection from insect vectors.

[25] Furthermore, in some cases, such as D. antiqua flies in the Netherlands, the pests developed a resistance to the insecticides and crops continued to be destroyed.

[26] Chemosterilants used in some studies include tepa [tris-(l -aziridinyl) phosphine oxide] which is very effective at sterilizing adult flies but less so on eggs.

[28] Contrastingly, other studies in the Netherlands have recorded more success in sterilizing D. antiqua without lowering their competitiveness and thus were able to outcompete the wild population.

[29] However, this method requires that the sterile flies are released for at least five years before they start having a significant effect on population numbers[29].

Additionally, SIT projects on D. antiqua in Quebec have also shown a reduction in fertile adult populations, and the continuation of this technique is expected to result in a decrease in both the release rates of sterile insects and the overall cost of the program.

[32] These volatiles act as chemical cues to attract predators and parasitoids of the herbivore feeding on the plant as a defensive measure.

[32] Once attracted to the infested crops, T. rapae females may use antennal searching, ovipositor probing, or vibrotaxis to locate the Delia larvae buried within the plant and lay their eggs within them.

[3] Second, the glucosinolates produced by brassicaceous plants when they are physically damaged, infected or fed on by pests will be converted into isothiocyanates.

[39] Studies of laboratory experiments have observed that Metarhizium anisopliae, Beauveria bassiana, and Paecilomyces fumosoroseus are all pathogenic to the second and third larval instars of D. radicum and D.

[39] Entomophthora muscae is another entomopathogenic fungi that thrives in warm, moist environments, and can infect and kill adult Delia flies, primarily D.

[41] Strongwell-sea castrans, a fungus commonly found in Europe as opposed to North America, is known to sterilize the adult flies of D.