doi: 10.12741/ebrasilis.v14.e919 e-ISSN 1983-0572 Creative Commons License v4.0 (CC-BY) Copyright © Author(s) Article Full Open Access General Entomology Spatial and temporal distribution of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) and Euxesta spp. (Diptera: Otitidae) in the corn crop Jessica Vasconcelos Ferreira1 , Ivan Carlos Fernandes Martins1 , Raiana Rocha Pereira2 , Rayane Rocha Pereira1 , Mateus Higo Daves Alves1 , Lourival Dias Campos1 , Marcello Neiva de Mello1 & Francisco José Sosa Duque3 1. Universidade Federal Rural da Amazônia, Campus Capanema - PA, Brazil. 2. Universidade Federal Rural da Amazônia, Campus Belém - PA., Brazil. 3. Universidade Federal Rural da Amazônia, Campus Capitão Poço - PA, Brazil. EntomoBrasilis 14: e919 (2021) Edited by: Abstract: The aim of this study was to verify the pattern and the spatial and temporal behavior of William Costa Rodrigues the corn earworm and corn-silk fly in the corn crop. Hybrid corn was planted without chemical insect control in one hectare, this area was divided into 100 plots of 100 m2. For the occurrence of Euxesta Article History: spp. all parts of the plants were visually analyzed, whereas for Helicoverpa zea (Boddie) 10 ears were Received: 10.vii.2020 removed at random from each plot, totaling 1,000 ears per sample. Population fluctuation was related Accepted: 25.xi.2020 to the phenological stages of corn. For spatial behavior, the dispersion indices, frequency distribution Published: 13.i.2021 models and geostatistics (Krigagem) were analyzed. The corn earworm (small and large) and corn-silk fly showed aggregate pattern and spatial behavior. The reach of caterpillars < 1 cm had an area of Corresponding author: influence greater than caterpillars > 1 cm, with spatial dependence being considered moderate. The Ivan Carlos Fernandes Martins corn-silk fly had a maximum area of influence of 1.33 ha with moderate and weak spatial dependence. [email protected] The maps demonstrated that these insects occur dispersed throughout the corn area, but with Funding agencies: aggregations influenced by the adjacent areas and edges of the crop. The largest occurrence of corn earworms was at the R3 stage. It was also found that the corn-silk fly followed the occurrence of the Conselho Nacional de corn earworm. It is concluded that the studied pests have an aggregate spatial tendency in the corn Desenvolvimento Científico e crop and with the influence of adjacent areas, in addition to presenting related population peaks in Tecnológico (CNPq) the reproductive period of the corn crop. Keywords: Aggregate; Corn-silk fly; Corn earworm; Geostatistics, Population fluctuation. he corn (Zea mays L.) is important in world agricultural walking. In the larval phase, it can cause injuries and damage production, due to its widespread use, such as for to the ears, causing losses in productivity. At this stage, the human and animal food, even the production of larvae feed on the grains during their development, which biofuels. Brazil has an area of approximately 17 million can cause direct and indirect damage by facilitating the entry hectares with production of more than 92 million tons and and colonization of microorganisms (LIMA et al. 2016). occupies the third place in world production (CONAB 2019). Therefore, the use of extensive areas allows pests to appear It is necessary to know what factors can influence the on crops, which causes losses to the producer (VENÂNCIO & management of insect pests, so it is important to know COSTA 2012). the spatial and temporal behavior and carry out sampling correctly. Geostatistical analyzes have shown adequate There are several insects that affect the corn crop, the corn responses to the spatial behavior of insect pests, in addition earworm [Helicoverpa zea (Boddie)] and the corn-silk fly of the to providing an understanding of insect interpolation and genus Euxesta (Diptera: Otitidae) can cause injuries to the ear dispersion, facilitating the application of management and become potential pests. Both pests oviposit in stigma- practices (DAL PRÁ et al. 2011; DIONISIO et al. 2016). styles, interfering with pollination and grain formation, due to their mode of feeding (CRUZ et al. 2011a). Insects have variations in space and time, and analyzing this population dynamics, together with the influence of biotic The attack of H. zea starts in the stigmas, which compromises and abiotic factors in agricultural ecosystems, makes it fertilization, the caterpillar penetrates the ear epically to possible to infer the greatest occurrence preference, as well consume the milky grains, leaving holes that facilitate the as to determine the main factors involved in this occurrence entry of microorganisms that cause diseases to the plant (ENNIS & PHILPOTT 2019). (GOYAL et al. 2012; VALICENTE 2015). Therefore, this study aimed to verify the pattern and the The appearance of stigmas-style and the filling of grains spatial and temporal behavior of the corn earworm (H. zea) leads to an increase in the population of Euxesta, indicating and corn-silk flies (Euxesta spp.) in the corn crop in Igarapé- that the insect has the potential for a key pest in areas of Açu, Northeast Pará, Eastern Amazon. commercial corn production (CRUZ et al. 2011a). This fly has an intense movement of opening and closing its wings when © The Author(s) 2021. Published by Entomologistas do Brasil This article is published by Entomologistas do Brasil and licensed under Creative Commons Licence 4.0 (CC-BY) Spatial and temporal distribution of Helicoverpa zea (Boddie)… Ferreira et al. (2021) MATERIAL AND METHODS The tested models were: spherical model, exponential model, Gaussian model and random model (nugget effect). The study was conducted at the Experimental Farm of Igarapé-Açu - FEIGA (01º07’33” South and 47º37’27” West, Subsequently, Kriging interpolation maps were constructed, 39 m), municipality of Igarapé-Açu - PA, belonging to the showing the observed frequency values and the interpolation Universidade Federal Rural da Amazônia - UFRA. The region between the values. The R software for Windows was used to has soil with a predominance of dystrophic Yellow Argisol obtain semivariograms and kriging maps. The semivariogram with sandy texture (GUERINO et al. 2017). The climate is function is used in geostatistics to express spatial variability defined as Ami, with an average annual rainfall of 2,500 mm in a predefined direction (STURARO 2015). To adjust the and an average annual temperature of 25 °C, according to semivariogram models, the maximum likelihood method the Köppen classification. was used. The Akaike criterion (AIC) was used to select the most appropriate model, that is, the model with the lowest The area used for the implantation of the study was of AIC was selected. 10,000 m² (1.0 ha) divided into 100 plots of 100 m2 (10 m x 10 m), with adjacent areas composed by an experimental In this study, the Spatial Dependency Index (SDI) was also area of grassland, Megathyrsus maximus (Jacq.) BK Simon evaluated through the result calculated by the k index & SWL Jacobs (0.6 ha); mango agroecosystem, Mangifera (k=C /C +C ) in which k values < 0.25 are considered strong indica L. (1.7 ha); and fragments of secondary forest. The dependencies, 0.25 ≤ k ≥ 0.75 is considered moderate hybrid corn Priorizi M274 Morumbi was used, with an early dependence₀ ₀ ₁ and, of k > 0.75, there is weak spatial dependence cycle that presents rusticity and tolerance to the main corn (BASTOS et al. 2019). diseases; with the aid of a seeder-fertilizer, it was sown without chemical control for insects, with a spacing of 0.90 RESULTS AND DISCUSSION m between rows and 0.15 m between plants. Sampling was carried out weekly, randomly selecting 10 plants per plot, for For Euxesta spp. a total of 165 individuals were observed a total of 1,000 plants/sampling. throughout the sampling period. There was a low occurrence of adults of corn-silk flies until the beginning of the tassel To evaluate Euxesta spp. the presence of adults in all parts stage (VT 49 DAE), from the reproductive period (R2) with of the plants was visualized, the number of individuals per 56 DAE, an increase in those of adults of corn-silk fly was plot was noted, from April 16 to June 25, 2016, starting the observed. The highest occurrence was verified on the last visualization seven days after the emergency (DAE). day of sampling with 48 dipterans already in the R5 stage (Table 1). CRUZ et al. (2011b) reported that adults from Euxesta To check for the presence of the H. zea caterpillar, sampling have been found in the corn crop since the early stages, with started at the reproductive stage of corn R2 (56 DAE), 10 a significant increase during the reproductive stages R1 and ears of corn were randomly removed per plot with a total of R2. The attraction of adults from Euxesta to ears attacked by 1,000 ears/samples, afterwards the material was sent to the other pests can be related to the attractiveness of this fly by Biodiversity Laboratory the UFRA Capanema campus. volatile semiochemicals (Owens et al. 2017). In the laboratory, the husks of the ears were removed, the For this study, 4,000 ears of corn were analyzed, a total of occurrence was visually analyzed in all parts of the ear, 2,755 individuals of H. zea was observed, corresponding to mainly in the ear tip and in the corn silks, and the number of 68.88% of the ears sampled with infestation (Table 1). In the caterpillars per plot was noted. To verify the spatial behavior reproductive period (R2) there was a predominance of small of the different stages of development of the caterpillars, caterpillars < 1 cm (672 caterpillars), but in this period also these were separated into small (< 1 cm) and large (> 1 caterpillars > 1 cm were observed, demonstrating that since cm) caterpillars, there were four evaluations during the the appearance of the style-stigmas oviposition should occur.