The Diversity and the Abundance ofCorn Planthopper(Hemiptera: Delphacidae)inLampung Province

The outbreak of delphacid planthoppers has been detected across corn-growing regions in South Lampung. Survey study was conducted in three corn fields in Natar District, South Lampung Regency. In each study site, five corn plants were randomly sampled. In each sampled plant, one leaf with maximum number of planthoppers was selected for population recording. Based on the morphological identification results, there were two types of corn planthoppers attacking corn fields during sampling periods: the white bellied-planthopper, Stenocranus pacivicus Kirkaldy and Peregrinus maidis Ashmead. During sampling periods, S. pacivicus was most abundant species, while, the Peregrinus planthopper was almost undetectable. There was similar trend peak of density S. pacificus brachypters & nymph and macropters among the three corn fields. The maximum number of S. pacificus brachypters & nymph 412.38 ±23.12 individuals’ leaf−1 was recorded at 70 days after planting (DAP). While the S. pacificus macropters reached the highest population number 43.81 ± 5,76 individuals leaf−1. Extended feeding activity by planthoppers caused the chlorosis and necrosis of the leaf, reduced plant vigor, and stunting, resulting hopperburn symptoms. The results of this study confirm that the explosion of delphacid planthopper sand corn hopperburn are real and become a threat for corn production in Lampung Province.

Extended feeding activity by planthoppers on corn plants can cause "hopperburn" [9], [10]. Symptoms of hopperburn are characterized byleaf chlorosis, followed by necrosis, reduced plantvigor, and stunting [11]. In addition to direct-feeding damage, this planthoppers pest also can act as a vector of plant viruses. In other words, the delphacid-planthoppers have the ability to transmit wide variety of plant viruses [1] [2][3] [12][13]. According to Ammar et al. [14], planthopperP.maidis transmits two corn Leafhopper Sampling. Sampling activity was starting from on 25 th March 2017 and continued at two weeks intervals for5 periods of sampling dates. The sampling activity was completed on 21 th May 2017. The selection of sampling sites was done purposively among the farmers whose land was given voluntarily to be observed and, on Agricultural College Experimental Station of Lampung University. From each selected corn field, five of rows (beds) of corn plants were selected randomly. As a sampled plant, five plants were systematically chosen from each selected corn bed and were tagged at their base by using labeled plastics on which a distinct identification number was marked. In each sampled plant, one leaf with maximum number of planthoppers was selected for the counting. The number of all planthopper stages: adults (macropters and brachypters) and nymphs, number of leaves, number of eggdeposited leaves, and the percentage of egg-deposited leaf area were counted, the plant symptom of infected planthoppers. For the leafhopper-abundance recording, one leaf with maximum number of planthoppers of each sampled plant was selected for leafhopper-counting. The planthopper population abundance was recorded by direct counting using a hand-tally counter.
Insect Collection. Species composition of planthoppers infesting corn plant was determined during this study. For further identification, planthoppers were field collected using an aspirator. All collectedplanthoppers in the aspirator were transferred into a glass vial containing 70% ethanol using a small brush. The vials were then transported to the Laboratory of Arthropod Pests Agricultural College, The University of Lampung for later handling, general morphology observation, and specimen identification. In the laboratory, the adults primarily macropters were mounted on microscopy slides for identification. The specimen of each individual was cleared in 10% KOH to observe certain obscure features. Specimen identification and morphological examination were performed under a dissecting stereo-microscope. Specimens were identified using taxonomic key, provided by Wilson [6], Asche & Wilson [16], and Dupo & Barion [17].

Results and Discussions The corn planthopper composition
Based on the morphological identification results, there were two types of corn planthoppers attacking corn fields during sampling periods. The first species was the white bellied-planthopper (Stenocranus pacivicus Kirkaldy) (Hemiptera: Delphacidae). The name of the white belly is derived from the characteristics of this insect which has a white coating on the abdomen particularly the female (Figure 1). During sampling periods, this species was more abundant compare to other planthoppers. According to Susilo et al. [8], the white coloration of female abdomen was closely related with the secretion and deposition of this white mass while they are laying their legs. The white-cottony wax trench on the corn leaves is one signs of the presence of the species on the corn plants. Based on white-  [8]propose a common name for this planthopper as the corn white-bellied planthopper (CWBP). Nelly et al. [18] also reported the existence of S. pacificus pest in West Sumatra Province. They further reported that these planthopper pests were found to attack vegetative and generative corn plants in three districts, namely Pasaman Barat, Lima puluh Kota and Tanah Datar. The scientific name Stenocranus pacivicus Kirkaldy was first designated in 1907 by Muir in 1916 [19]. Scientific name and author year was reinforced by Fiji PHP: Taxon Details [20] as a Stenocranus pacificus Kirkaldy, 1907. Furthermore, this delphacid planthoppers were first reported to invade corn crops in the Philippines in 2009 and was considered to as invasive pests [21]. According to Cayabyab et al., [21], the corn planthopper was initially placed under the Sogatella genus based on genitalia features, but this insect eventually was confirmed as S. pacificus. [21]. Similarly, Dumayo et al. (2007) reported that Stenocranus pacificus, Kirkaldy (Hemiptera: Fulgoroidea: Delphacidae) was a new pest attacking many corn growing areas in the Philippines.Moreover, Dupo & Barrion [17] reported the threat of S. pacificus as a pest in rice plants throughout the Asia. Beside rice plants, they alsoreported that S. pacificus also attacked sugar cane and other grasses.
The second type of planthopper found during sampling periods was Peregrinus maidis Ashmead (Hemiptera: Delphacidae). In contrast to the white belly planthopper, Peregrinus planthopper was almost undetectable during early May to July. Only in early August, these pests were found in several corn planting locations. The Peregrinus leafhoppers adults are marked by dark brown body color with black spot marks on the front wingtips ( Figure 2). Another characteristic of this species is the presence of a black line mark on the thorax and abdomen (Figure 2). The morphological characteristics of Peregrinus adult is fit with that described by Tsai and Wilson [22]. The main morphological features of these two species are characterized by an enlarged tibial spur (calcar) on the hind legs ( Figure 3). These characteristics are generally the main features of the genus that belong to the Delphacidae family. According to Backuset al. [11] stated that planthoppers constitute a large group of phytophagous insects in the Delphacid family and Hemiptera ordo. Moreover they found that the delphacid planthopper were distributed worldwide and all members of this group are plant-feeders and some species are considered as important pests. All planthoppers members of the Delphacidae family are mainly a group of herbivorous insects that have a mouthpart in the form of a needle-like stylet that are used for piercing and sucking plant sap. Delphacidae is one of the families commonly referred to as "delphacid stem hoppers" to distinguish it from other planthopper. According to Dupo and Barrion [17], there were 9 species of Delphacidae stem-plant hopper reported in association with corn plants in Brasilia. The nine species are Caenodelphax taepae, Delphacidae sp-1, Delphacidae sp-2, Delphacodes saxicola, Peregrinus maidis, Pyrophagus tigrinus, Sogatella kolophon, Tagosodes cubanus, and Toya propinqua. All these corn planthoppers were able to transmit pathogenic virus in corn plants [23], [24].Besides attacking corn plants, the delphacid planthopper of P. maidis, S. kolophon. and T. propinqua were also found to be associated with sugarcane and rice crops in India [18].

Stenocranus pacificus Abundance
Based on the survey study, the most abundant species of the delphacid planthoppers attacking corn plant during sampling periods (starting from 21 th March 2017 and completing 21 th May 2017), was Stenocranus pacificus Kirkaldy (Hemiptera: Delphacidae). In general, this population study indicated that the S. pacificus macropters and brachypters plus nymphs combined density increased as the corn plant grow (Figure 4 and 5).
At first sampling date (plant age ± at 30 DAP), only a few of this planthopper brachypters & nymphs were attacking corn plants in all study sites (Figure 4). On the site-1 (FP Unila's field) and site-2 (Yono's field) there were 1.20 +0,25 and 28.00 +3.37 S. pacificus brachypters & nymph individuals leaf -1 ,respectively. While on the site-3 (Jalal's field), there was no S. pacificus brachypters &nymphs found. However, as the plant age increased, the number of S. pacificus brachypters & nymphs were increased sharply in all corn-field surveyed. On the site-1 (FP Unila's field), the maximum number of412.38 ±23.12 planthopper individuals' leaf -1 was recorded on 6 th May 2017 (plant age ± at 70 DAP). While, the number of S. pacificus brachypters & nymphs at site-2 and site-3 were peaked at 22 th April 2017 (plant age ± at 60 DAP). Similar with the population S. pacificus brachypters & nymph, the trend of population dynamics of S. pacificus macropters were resemble as that of S. pacificus brachypters & nymphs pattern ( Figure  5). On the other hand, the population numbers of planthopper macropters in all sites were lower than that of planthopper brachypters &nymphs during sampling periods. In site-1, the highest population density of S. pacificus macropters, 13.81 ± 2,45individuals leaf -1 was achieved at 6 th May 2017. While, the maximum number of S. pacificus macropters in in site-2 and site-3 were 43.81 ± 5,76 and 38,20 ± 8,3individuals leaf -1 , respectively 22 th April 2017 (plant age ± at 60 DAP. It is likely that the host plant phenology may play an important role in regulating population density of S. pacificus in Lampung Province. The outbreak of Stenocranus pacificus in corn growing area in Lampung is a new case in which threaten the national-corn production. In general, the occurrence of insect outbreak is related to an explosive increase in abundance that occurs over a short period. Such outbreaks of corn planthoppers often have devastating economic impacts when crops are completed destroyed. According to Cheng and Zhu[26], the outbreaks of planthoppers have been triggered by misuse of insecticides, varieties with high nutrition, and other environmental factors related to cultural and climatic factors [27], [28], Cheng 1995). Furthermore, Cheng and Zhu [26]stated that the environmental factors, including cropping systems, variety, usage of chemical fertilizer and pesticide, and temperatures were found to be have impact on planthopper outbreak. On the other hand, our study indicated that one of possible explanation for outbreak of Stenocranus pacificus was related with continuous corn plantings. In 2017, Lampung Province has been assigned one as primary national corn production.

Stenocranus pacificus Damage
The field study results indicated that the S. pacificus macropters are responsible for colonizing and laying eggs on corn plants (Figure 6.a). The S. pacific sfemale inserted its egg into the plant tissue of the mid rib leaf using its saw-like ovipositor. According to Heady and Wilson[29], the external female genitalia, in the "orthopteroid ovipositor" the fused median gonopophyses (valvula) of the 9 th abdominal segment often have a serrated dorsal aspect and serve as a saw-like structure for depositing eggs, usually into plant tissues. The eggs were inserted singly its posterior and positioned near the entrance holes which was also its exit hole. The appearance of S. pacificus eggcan be detected after removal of the white-cottony wax cover (Figure 6.c). Under stereo-microscope, it is clear that the shape of the S. pacificus egg is elongated (Figure 6.c). After oviposition, the female sealed its eggs using the white waxy substance in the abdomen for protection (Figure 6.b). Therefore, the early presence of corn planthopper attack can be detected by the appearance of white-cottony wax trenches or mass on the abaxial sides of the corn leaves ( Figure  6.b). As a result of this oviposition behavior, someone will be difficult to locate the egg in the field. Similar ovipositional behavior also found on Dalbulus corn leafhoppers. Dalbulus females insert their eggs singly into corn plant tissue. The egg is positioned under the plant epidermal layer in the leaf blade or deep in the leaf midrib [30].
The field observation results indicated that the corn plants in in South Lampung, were generally heavily attacked by the S. pacificus of planthoppers (Figure 7a-c). After eggs hatching, planthopper nymphs' colonies emerged on the leaves. The picture of Figure7.a and 7.b that shows abundant nymphs, exuviae, and adult macropters &brachypters. The planthopper colonies stay on the lower parts of corn plants. The presence of dimorphic adults with two wing forms: macropters & brachypters were detected during sampling periods.
Early symptomatic plants harbored significantly more planthoppers at early stages of corn growth the planthopper massive attacks resulted in the loss of plant vigor and appearance of hopperburn damage (Figure 7.c). Symptoms of hopperburn are characterized by leaf chlorosis, followed by necrosis, reduced plant vigor, and stunting. According to Cheng[31],the planthopper damage on corn plants by sucking plant sap from young leaves and leaf sheaths which could lead to stunted plant growth. Moreover, Backus et al. [11]reported that feeding planthoppers move their stylets continuously or intermittently, secreting watery saliva, rupturing plant cells and then ingesting the resulting slurry yield loss.

Conclusions
The corn plant in South Lampung was heavily attacked by the delphacid planthoppers. there were two types of corn planthoppers attacking corn fields during sampling periods: the white belliedplanthopper, Stenocranus pacivicus Kirkaldy) and Peregrinus maidis Ashmead. During sampling periods, S. pacivicus was most abundant species, while, the Peregrinusplanthopper was almost undetectable. The maximum number of S. pacificus macropters in site-1, site-2, and site-3 were 13.81 ± 2,45, 43.81 ± 5,76 and 38,20 ± 8,3individuals' leaf -1 , respectively. The extended feeding activity by planthoppers on corn plants cause the chlorosis and necrosis of the leaf, reduced plant vigor, and stunting, resulting hopperburn symptoms. The results of this study confirm that the explosion of delphacid planthoppers and corn hopperburn are real and become a threat for corn production in Lampung Province.