Influence of the Site of Oviposition on the Level of Egg Parasitism
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An Acad Bras Cienc (2021) 93(1): e20190686 DOI 10.1590/0001-3765202120190686 Anais da Academia Brasileira de Ciências | Annals of the Brazilian Academy of Sciences Printed ISSN 0001-3765 I Online ISSN 1678-2690 www.scielo.br/aabc | www.fb.com/aabcjournal ECOSYSTEMS Influence of the site of oviposition on the Running title: The oviposition sites level of egg parasitism in the corn leafhopper, of Dalbulus maidis Dalbulus maidis (Hemiptera: Cicadellidae) Academy Section: Ecosystems ERICA LUFT ALBARRACIN, EDUARDO G. VIRLA & MARIANO ORDANO Abstract: The corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), e20190686 transmits three important plant pathogens that adversely affect corn crop and ranges from the USA to Argentina. The vector has a rich natural enemy complex that generates high levels of parasitism, but its populations are persistent and prevalent. We 93 characterized the oviposition sites of D. maidis on young corn plants in order to verify (1) 93(1) the hypothesis that the vector has an oviposition strategy for mitigating parasitism. Oviposition locations on plants were assessed in the laboratory and eggs within corn DOI plants were exposed to natural parasitism in a cornfield. Eggs were located mostly laid 10.1590/0001-3765202120190686 in the unfolded leaves and were attacked by five parasitoid species. Parasitism was significantly affected by the class of leaf and the position of the egg in the leaf.Anagrus virlai Triapitsyn was the most abundant parasitoid species, which emerged significantly higher in the basal blade than other species. Our results suggest that leafhoppers minimize egg parasitism by laying their eggs within concealed locations on the plant. Key words: Anagrus virlai, Cicadellidae, corn leafhopper, egg parasitoids, enemy-free space, oviposition. INTRODUCTION Dalbulus maidis presents a broad distribution throughout the USA and Argentina In tropical and subtropical America, the (Triplehorn & Nault 1985). It is a specific herbivore, corn leafhopper Dalbulus maidis (DeLong) feeding and reproducing only on plants of the (Hemiptera: Cicadellidae) is the cause of genus Zea (maize and teosintes) (Bellota et al. enormous damage to maize (Zea mays L.) 2013) and, while it prefers lower elevations, it since it efficiently transmits three important can be found in a wide range from sea level to plant pathogens that adversely affect this crop: 3200 m in the Peruvian Andes (Nault 1990). Pitre Corn stunt spiroplasma (Spiroplasma kunkelii (1967) indicated that the eggs are laid embedded Whitcomb), Maize bushy stunt phytoplasma into the plant tissues mostly along the midrib on (Candidatus Phytoplasma asteris) and Maize the upper side of more fully developed leaves; rayado fino virus (Marafivirus) (Laguna & Heady et al. (1985) stated that most eggs are laid Gimenez Pecci 2012). In these regions, S. kunkelii in the midrib of the basal half of maize leaves; is the most dominant pathogen affecting maize. and recently Bellota et al. (2013) established The highest infection rates have been found in that at least 99% of eggs were inserted into Central America, Peru, Brazil and Argentina, with the midrib. These data suggest that the corn 100% of the crop plants affected in many maize leafhopper displays an egg-laying behavior that fields (Oliveira et al. 1998). is practically invariable. However, it is unknown An Acad Bras Cienc (2021) 93(1) ERICA LUFT ALBARRACIN, EDUARDO G. VIRLA & MARIANO ORDANO THE OVIPOSITION SITES OF Dalbulus maidis if this pattern is extended throughout the entire The different sectors of the leaves on geographical distribution area. the plant could be considered a “patch” The corn leafhopper has a rich parasitoid and invertebrate herbivores therefore make complex, and they can be divided into two decisions regarding which resource patch to guilds: those that attack eggs and those that visit and how long to stay there for oviposition. affect the nymphs and adults. Dalbulus maidis These are central issues for foraging animals has 18 known egg parasitoid species (16 of since they affect the rate at which they encounter which occur in Argentina); these are members resources and thus their reproductive success. of the Chalcidoidea (Hymenoptera), belonging In this way, for parasitoids, encountering a to Mymaridae, Trichogrammatidae, Aphelinidae, host is directly related to the fitness of an and Eulophidae (Luft Albarracin et al. 2017). individual, and decisions leading to patch and Mortality caused by egg parasitoids is a key host selection are made under strong selective factor in several Auchenorrhyncha populations pressure (Castelo et al. 2003, Williams et al. (Denno & Roderick 1990, Böll & Herrmann 2012). 2004). Previous studies of the impact of egg Dalbulus maidis may present a strategy that parasitoids on D. maidis demonstrated high allows it to escape from the selective pressure levels of parasitism, with mean values exceeding of egg parasitoids by placing a proportion 50% (Luft Albarracin et al. 2017). However, vector of its eggs in concealed sites. In this case, populations in maize fields present an elevated the vector oviposits in different parts of the density (Bushing & Burton 1974, Luft Albarracin plant, but parasitoids are less likely to locate et al. 2008, Meneses et al. 2016). eggs deposited in certain sites and therefore The importance of an enemy free-space the proportion of eggs affected by parasitoids to insect herbivores is widely recognized should differ in different sectors of the plant. (Atsatt 1981, Jeffries & Lawton 1984, Raymond From a biological control perspective, different et al. 2016). Likewise, there is a correlation host location strategies may have strong effects between oviposition preference and offspring in shaping levels of parasitism (Peri et al. 2011). performance, with other phytophagous insects Knowledge of the interactions between an and Auchenorrhyncha in general (Cook & Denno insect pest and its host-plant and parasitoids 1994). Specifically for invertebrate herbivores, is essential for the development of effective the habitat patch is represented by the management strategies. The aims of this study host plant (Vanbergen et al. 2007), which can are therefore to characterize the oviposition sites therefore avoid parasitism through a preference of D. maidis in young maize plants and to verify for oviposition sites in which parasitoids are the hypothesis that this leafhopper presents an rare or absent (Quicke 1997, Williams et al. 2012). escape strategy for mitigating parasitoid attacks. Host use varies during the life of conspecific herbivorous insects (Jaenike 1990). Moreover, preferences for oviposition within a host plant MATERIALS AND METHODS could differ according to age and plant size, Origin of the Dalbulus maidis specimens and given variation in the chemical and physical laboratory rearing properties of the plant tissues (Thompson 1988, A D. maidis colony was established using Williams et al. 2001). individuals collected during the summer in Los Nogales, Tucumán, Argentina (S 26° 42’, W 65° An Acad Bras Cienc (2021) 93(1) e20190686 2 | 13 ERICA LUFT ALBARRACIN, EDUARDO G. VIRLA & MARIANO ORDANO THE OVIPOSITION SITES OF Dalbulus maidis 13’, elevation 588 m). The vector was placed in 3) within the leaf blade: basal and apical region, aluminum breeding cages (50 x 50 x 50 cm) with including eggs laid in the midrib or those in the the lateral and upper sides covered with nylon blade (Fig. 1). mesh (organdy type) for ventilation. Potted maize plants (each pot of 6.3 dm3) were placed Natural egg parasitism inside as a food source and for oviposition. The potted plants containing eggs of D. maidis The maize variety “Leales 25 plus” (INTA 2016) were exposed to parasitization in a maize field was used both for maintenance of the corn at the site “El Manantial” (Tucumán Province, leafhopper colony and for all of the assays. The Argentina: S 26° 49’ 50.2’’, W 65° 16’ 59.4’’, colony was reared in a greenhouse in San Miguel elevation 495 m). These sentinel eggs were de Tucumán (S 26° 48’, W 65° 14’, elevation 500 m) placed inside the maize field at no more than under the following conditions that reflect the 3 m from the edge of the field. After eight days natural field conditions for the leafhopper (23 of field exposure, plants were transferred to the to 30 °C, natural photoperiod and no humidity laboratory. The different parts were cut from control). each plant, labeled and placed in Petri dishes with wet tissue paper on the bottom and covered Location of eggs and its relationship with the with a polyethylene film to avoid desiccation plant architecture of eggs and plant tissues and to contain any In order to avoid corn leafhopper eggs emerging nymphs and/or wasps. The eggs were misidentification, because there are other checked daily to ensure host plant quality until leafhoppers species using corn as host plant the emergence of all nymphs and/or adult (Luft Albarracin et al. 2008), we infested plants wasps, in cases where the eggs were parasitized. into the laboratory and after that exposed The parasitoid specimens were preserved in them as sentinel eggs following the method 70% ethanol and later slide-mounted in Canada described by Luft Albarracin et al. (2017). So, balsam following established standard practices to obtain eggs and characterize the location of (Noyes 1982). The parasitoids were identified the eggs within the plant architecture, potted using available specific keys (Triapitsyn 2015, maize plants in vegetative stage were used (V3 Viggiani 1981). Voucher specimens were and V4 phenological stages with three and four deposited in the entomological collection of the unfolded leaves, respectively). In the laboratory, Instituto Fundación “Miguel Lillo”, San Miguel de each plant was individually exposed for 24 h Tucumán, Argentina (IMLA). to 4-6 females of D. maidis in cages (30 x 30 x 50 cm) covered with nylon mesh. The plants Statistical analysis were then checked for eggs and the location Firstly, we show a general description of the of oviposition recorded.