Research Article |
Corresponding author: Néstor Bautista-Martínez ( nestor@colpos.mx ) Academic editor: Andreas Köhler
© 2021 Paulina Nava-Ruiz, Ricardo Meraz-Álvarez, Jorge Valdez-Carrasco, Onésimo Chávez-López, Néstor Bautista-Martínez.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Nava-Ruiz P, Meraz-Álvarez R, Valdez-Carrasco J, Chávez-López O, Bautista-Martínez N (2021) Parasitoids of Delia planipalpis (Meigen) and Delia platura (Stein) (Diptera, Anthomyiidae) in Mexico. ZooKeys 1046: 177-187. https://doi.org/10.3897/zookeys.1046.64405
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Among the insect pests that affect crucifer crops in Mexico are Delia planipalpis (Meigen) and D. platura (Stein). They are a threat to the production of these vegetables since the damage they cause directly and indirectly affects yield, quality, and commercialization of these crops. Nevertheless, the existence of natural enemies of these dipterans is still unknown. It is fundamental to determine which parasitoids or predators can be considered possible biological control agents in an integrated pest management program.
The sampling sites were located in Guanajuato, Puebla, and the State of Mexico, where plants of Brassica oleracea var. italica Plenk and capitata L., B. napus L., and Raphanus sativus L. infested with Delia spp. were selected. The symptoms observed were wilting, yellowish, flaccid leaves and individuals less developed than the rest of the crop. These plants were extracted with their root and the surrounding soil. Also, wild crucifers were collected, such as Raphanus raphanistrum L., Brassica campestris L., and Sisymbrium irio L. The first records of Aphaereta pallipes Say (Hymenoptera, Braconidae), Trybliographa rapae (Westwood) (Hymenoptera, Figitidae), and Aleochara bimaculata Gravenhorst (Coleoptera, Staphylinidae) are reported parasitizing the puparia of these anthomyiid flies on cultivated and wild crucifers. This represents only a starting point for the continuous study of these parasitoids, which is needed to consider them useful for the biological control of D. planipalpis and D. platura.
Biological control, crucifers, Hymenoptera, root maggots, soil pests, Staphylinidae
Some species of the genus Delia (Robineau-Desvoidy) (Diptera, Anthomyiidae), commonly called root maggots, attack economically important crops of the family Brassicaceae (
Currently, there are few precedents of D. planipalpis and D. platura associated with crucifers in Mexico. Larvae of these dipterans cause damage mainly to the root crown of some cultivars of B. oleracea, and consequently, they affect the root system. Occasionally, the larvae develop near the broccoli head causing rot and malformation, or no formation of the inflorescence. In addition, in crops such as radish and turnip, direct damage caused by larvae to their edible part makes their commercialization difficult (
Because more than 60% of these crucifers are exported to international markets, compliance with strict sanitation, quality, and food safety regulation is required. These restrictions make it obligatory to use chemical control as one of the most common tactics for pest control (
In addition, larvae of Delia are difficult to control because they are found in the soil or inside plant tissues, where it is difficult for sprayed insecticides to reach. For this reason, it is essential to identify natural enemies of these dipterans in crucifer-producing regions and contribute management options that use them as potential biological control agents. In this sense, the objective of this study was to search for and identify parasitoid insects and/or predators of D. planipalpis and D. platura in cultivated and wild crucifers.
The study was conducted between February 2018 and February 2019 in Guanajuato, Puebla, and the State of Mexico, where some sites infested by Delia spp. were located (Table
Collection sites of samples infested by Delia planipalpis and D. platura.
Host | Site | |
---|---|---|
Location | Date | |
R. raphanistrum | Colegio de Postgraduados Campus Montecillo, Texcoco, State of México 19°28'08.2"N, 98°54'04.7"W | 19-II-2018 |
S. irio | 29-III-2018 | |
R. sativus | 19-V-2018 | |
R. raphanistrum | 20-X-2018 | |
B. campestris | 19-XI-2018 | |
B. oleracea var italica | San Diego de La Unión, Guanajuato 21°24'30.4"N, 100°45'19.3"W | 25-X-2018 |
04-XII-2018 | ||
B. napus | San Felipe Tenextepec, Tepeaca, Puebla 18°57'27.18"N, 97°50'50.24"W | 04-IV-2018 |
B. oleracea var capitata | 21-IX-2018 | |
R. raphanistrum | 08-XI-2018 | |
B. oleracea var italica | 08-XI-2018 | |
R. raphanistrum | Los Reyes, Tepeaca, Puebla 19°00'01.1"N, 97°53'14.4"W | 22-XI-2018 |
R. sativus | 22-XI-2018 | |
B. oleracea var capitata | 22-XI-2018 | |
R. sativus | Guadalupe Calderón, Tepeaca, Puebla 18°57'41.86"N, 97°50'32.44"W | 06-XII-2018 |
R. raphanistrum | 06-XII-2018 | |
B. oleracea var italica | San Diego, Texcoco, State of México 19°30'09.8"N, 98°51'33.1"W | 22-II-2019 |
B. oleracea var capitata | 22-II-2019 | |
22-II-2019 |
Sampling was directed; 10 plants per site were selected, considering those that were observed to be stressed by water deficit and having wilting, yellowish, flaccid leaves and/or less vegetative development than the rest of the crop; these are characteristic symptoms of infestation by Delia spp. Wild crucifer plants were selected at random within and on the outer edges of commercial crops and the sample size varied from 5 to 10 plants depending on their abundance. Each plant was extracted with its root and adhered soil and placed in a polyethylene bag; additionally, with a post hole digger of 15.0 cm in diameter by 20.0 cm long, the soil of the first 10.0 cm of depth was collected taking as a reference point the exact site where the plant was extracted and because in this place the puparia are distributed due to the limited movement of third instar larvae around the plant and from the soil surface (
The collected material was taken to the Entomology Laboratory at the Colegio de Postgraduados Campus Montecillo, Texcoco, Mexico, where the puparia and larvae were separated from the soil. A sieve with 2.0–2.8 mm openings was used to sift the soil and remove the Delia spp. larvae and puparia. To separate the larvae from damaged tissues, small cuts were made on the root and stem of the plants to search for galleries resulting from their feeding. These tissues were observed with an American Optical Model 570 stereoscopic microscope. The larvae obtained were placed in plastic 12.0 cm Petri dishes conditioned with moistened paper at the bottom on which two to three slices of radish were placed to provide them with food. In this way, they continued their development until reaching the pupal stage. The puparia obtained from sifting soil and those that resulted from collected larvae were observed under a microscope to separate D. planipalpis from D. platura using illustrations of
The keys of
A total of 321 Delia planipalpis and 49 D. platura puparia were collected in cultivated and wild crucifers in the states of Guanajuato, Puebla, and the State of Mexico (Table
Parasitoids emerged from Delia planipalpis and D. platura puparia collected in commercial crops and weeds.
Number of puparia collected | Emerged parasitoids | Host | ||||||
D. planipalpis | D. platura | Aphaereta pallipes | Trybliographa rapae | Aleochara bimaculata | ||||
♀♀ | ♂♂ | ♀♀ | ♂♂ | ♀♀ | ♂♂ | |||
0 | 20 | 0 | 0 | 2 | 1 | 0 | 0 | R. raphanistrum |
0 | 14 | 0 | 0 | 2 | 11 | 0 | 0 | R. sativus |
11 | 2 | 0 | 0 | 0 | 0 | 1 | 0 | B. oleracea var italica |
18 | 0 | 7 | 4 | 0 | 0 | 0 | 0 | |
13 | 0 | 6 | 3 | 0 | 0 | 2 | 2 | B. oleracea var capitata |
57 | 8 | 56 | 15 | 0 | 0 | 0 | 0 | R. raphanistrum |
13 | 0 | 29 | 10 | 0 | 0 | 0 | 0 | B. oleracea var italica |
44 | 1 | 13 | 1 | 0 | 0 | 0 | 0 | R. raphanistrum |
34 | 2 | 22 | 7 | 0 | 0 | 0 | 0 | R. sativus |
53 | 2 | 29 | 19 | 0 | 0 | 0 | 0 | R. sativus |
44 | 0 | 93 | 39 | 0 | 0 | 0 | 0 | R. raphanistrum |
Aphaeretha pallipes emerged from puparia of D. planipalpis reared on B. oleracea var. italica, B. oleracea var. capitata, R. sativus, and R. raphanistrum from samples collected in Guanajuato and Puebla, A. bimaculata emerged from puparia of D. planipalpis and D. platura reared on B. oleracea var. italica and capitata from these places, and T. rapae emerged from puparia of D. platura reared on samples of R. sativus and R. raphanistrum from the State of Mexico.
The frequency of Aphaereta pallipes observed in the collected samples was 90%. In contrast, Aleochara bimaculata was present in 20% of the samples; likewise, the appearance of Trybliographa rapae was also minimal. Thus, A. pallipes is the most common parasitoid of Delia planipalpis in Guanajuato and Puebla.
Our findings contrast with what has been reported by other authors, who stated that Aleochara bilineata and T. rapae are the most common parasitoids of several root maggot species, including D. planipalpis and D. platura in Europe and Canada (
Although A. pallipes has not been mentioned as an important parasitoid of Delia spp. in Europe and Canada,
In the case of A. bimaculata, our results are apparently different from those reported by other researchers in that most studies mention that A. bimaculata has been found parasitizing dipterans that develop in manure.
Finally, although in this work no parasitoids were found in the wild crucifers B. campestris and S. irio, alternate hosts are important reservoirs of considerable populations of Delia spp. and consequently of their natural enemies, especially because they provide habitat during the season when there are no crops. In this way, wild crucifers assure that there is no scarcity of hosts for either the insect pest or their parasitoids and predators (
Three species that emerged from puparia of D. planipalpis and D. platura collected in cultivated and wild crucifers were identified: one gregarious parasitoid, Aphaereta pallipes and two solitary parasitoids, Trybliographa rapae and Aleochara bimaculata. Only Aphaereta pallipes and T. rapae were specific to D. planipalpis and D. platura, respectively. Finally, A. bimaculata was associated with both pest species.
This is the first record of parasitoids of D. planipalpis and D. platura that occur naturally in Mexico. Aphaereta pallipes was the most abundant species, found in Guanajuato and Puebla, followed by Aleochara bimaculata, and finally T. rapae, which was found only in the State of Mexico. Knowledge of natural enemies of Delia spp. in crucifer-producing regions is only the starting point from which to broaden the search and begin to study their biological attributes with the aim of incorporating them into a biological control program against D. planipalpis and D. platura.