Predator Insect Families Associated With Melon Crop in a Semiarid Region in Brazil

Knowledge of diversity of natural enemies in agroecosystems is vital for the integrated pest management. However, surveys of beneficial insects (predators and parasitoids) in the melon crop (Cucumis melo L.) in the semiarid region in Brazil are scarce. Thus, the objective of this study was to know the families of predator insects associated with melon crop in a semiarid region in the state of Rio Grande do Norte (RN), one of the main melon producers in Brazil. The survey study was carried out in a commercial melon area, in the municipality of Baraúna (RN). The samples were collected weekly during the cycle of melon, using passive (Pitfall and Moericke traps) and active (sweep net) collection methods. A total of 13 families of predator insects were collected. The families with the highest relative abundances in the passive collection method were Labiduridae (89.53%) and Formicidae (6.91%), while in the active collection method were Chrysopidae (59.81%) and Staphylinidae (20.56%). These families contain important species of predator which can promote crop pest suppression in melon agricultural systems.


Introduction
Melon crop (Cucumis melo L.) is one of the main segments of agribusiness in the Northeast region of Brazil, where the state of Rio Grande do Norte is the largest melon producer (IBGE, 2016).This region is characterized by semiarid climate (high temperatures and reduced rainfall throughout the year) and vegetation of the Caatinga type (xerophilous and deciduous plants) (Prado, 2003).In the Brazilian semiarid region, the melon crop is usually infested by pests such as whitefly Bemisia tabaci (Hemiptera: Aleyrodidae), leafminer Liriomyza sativae (Diptera: Agromyzidae) and melonworm Diaphania nitidalis (Lepidoptera: Pyralidae) (Araujo et al., 2008).
In order to ensure plant health and productive potential of melon, it is essential to use integrated pest management (IPM).However, many melon farmers widely use chemical control as the primary measure of pest suppression and these products are rarely applied as part of IMP.Successful IPM requires a thorough knowledge of the pest insect's biology, their natural enemies, and the crop to allow rational use of a variety of cultivation and control techniques under differing circumstances (Gullan & Cranston, 2017).In this context is essential to know and conserve the diversity of agents of biological control (predators and parasitoids) present in the agroecosystems (Crowder & Jabbour, 2014).
Studies on natural enemy diversity around the world in melon relates the presence of several predatory from the orders Coleoptera, Mantodea, Hemiptera, and Odonata (Vinutha, Kotikal, Venkateshalu, Manjunath, & Patil, 2017).Although, despite the melon economic importance, little is known about the diversity of predatory insect families that occur in melon production areas in the Brazilian semiarid (Araujo et al., 2008).However, research on the watermelon crop [Citrullus lanatus (Thunb.)], in the semiarid region of Rio Grande do Norte, reports the presence of several families of predators from the orders Coleoptera (Staphylinidae, Carabidae and Coccinellidae) (Costa, Araujo, Silva, Nogueira, & Silva, 2014a) Collected insects were stored in plastic containers with 70% alcohol, labeled (place and collection date), and then transported to the laboratory.In the laboratory, the triage, counting and identification of predator insects at family level were carried out with support of a stereoscopic microscope and the taxonomic key of Triplehorn & Johnson (2011).
For each taxonomic group collected, the relative abundance (RA) was determined by the following formula: AR (%) = n/N × 100, where, AR (%) = relative abundance; n = Total number of individuals in the taxon; N = Total number of individuals captured.The data were also interpreted using descriptive statistics, mainly for the most abundant taxa.

Passive Collection Method
A total of 5,704 insects were collected, distributed in six orders and 13 families (Table 1).Most of these insects (96.6%) were recorded in the Pitfall traps.The order Dermaptera (earwigs), with a single family (Labiduridae), showed the highest relative abundance in the passive collection method, with 89.53% of the total number of insects caught, being most of them collected in Pitfall traps.Hymenoptera was the second group most captured (9.18%), it also had the highest diversity of families, with four taxa: Formicidae, Vespidae, Mutillidae and Sphecidae.Formicidae was the most abundant with 6.91% of the captured specimens.The other orders (Diptera, Hemiptera, Coleoptera and Neuroptera) were less collected, with 1.32% of the insects caught (Table 1).The Pitfall trap is characterized by estimating the species richness and relative abundance of various insect groups that preferentially exploit the soil surface (Gullan & Cranston, 2017).This trap provided an expressive collection of earwigs, which shows a strong association of these insects with melon crop.The more abundance of earwigs could be explained by the habitat conditions.First, the studied area was located near maize crops (Zea mays L.), where these predators are usually found and second melon is grown during dry period of the year (between July and January), when there is less availability of shelter and food resources for natural enemies in the native vegetation of the semiarid region (Caatinga).It is very likely that earwigs search for more suitable environments, such as irrigated areas of melon crops.Studies in the guava crop (Psidium guajava L.) showed that the population peaks of these predators coincide with the harvest season, when there is greater food availability and higher temperatures which may increase the chances of survival in these environments (Galli, Seno, & Cividanes, 2003).Recently, similar results were also recorded in watermelon crops, indicating that this family could be common in areas of cucurbit production in the semiarid region of Rio Grande do Norte (Costa et al., 2014b). jas.ccsenet.
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Table 1 .
Number (Nº) and relative abundance (RA%) of predator insects families caught in passive collection method (Pitfall and Moericke traps) in melon crop in a semiarid region, from August to September 2012, municipality of Baraúna (RN), Brazil