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INTRODUCTION

The production of citrus fruits in Ecuador is especially important in the Pacific coastal region. Among the various citrus species and varieties, orange, Citrus x sinensis (L.) Osbeck (Rutaceae), represents the most widespread citrus crop with some 22,282 hectares planted in 2015, but with a low yield of 4.25 tons/ha (Sinagap, 2015). As with other agroecosystems, citrus fruits are affected by both native and exotic phytosanitary problems (Cornejo and Chica, 2014) that limit their yield. One of the potential problems for the citrus industry in Ecuador is the bacterial disease Huanglongbing (HLB); although currently it has not been detected yet, its main insect vector, the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) (Parra et al., 2016), has been recorded in the country since 2013 (Cornejo and Chica, 2014). Diaphorina citri has a wide distribution and an extensive list of host plants in about 25 genera of the Rutaceae family (Halbert and Manjunath, 2004). HLB is probably the most devastating citrus disease in the world, surpassing even the Citrus tristeza virus. In the Americas, it is caused by the phloem-limited bacteria Candidatus Liberibacter asiaticus and Candidatus Liberibacter americanus that lodge in the phloem and obstruct the functioning of these conductive vessels causing the eventual death of the plant (Bové, 2006). The disease leads to the regressive dieback of the leaves, non-uniform maturation and fruit fall, which consequently reduces the total yield. Given the recent introduction of the insect vector, its direct damage on young shoots, as well as the potential problem of transmission of the bacteria that cause HLB, it is necessary to find control alternatives for this insect pest in Ecuador. In order to find control strategies, inventories of natural enemies are required and the importance of these biological control agents in the regulation of D. citri populations needs to be estimated.

The most common insect natural enemies of D. citri include syrphids, lacewings, coccinellids and parasitic wasps (Kondo et al., 2015). Little is known about the natural enemies of D. citri in Ecuador. Recently, two parasitoids of D. citri, Tamarixia radiata Waterston (Chavez et al., 2017; Portalanza et al., 2017) and Diaphorencyrtus aligarhensis (Shaffee, Alam and Agarwal) (Portalanza et al., 2017), were reported in Ecuador. Also, two predators of the psyllid, namely, Zelus sp. (Hemiptera: Reduviidae) and an adult of an unidentified species of coccinellid (Coleoptera: Coccinellidae) have been reported in Ecuador (Navarrete et al., 2016). Additionally, Chavez et al. (2017) reported two phenotypic morphs of the coccinellid Cheilomenes sexmaculata (Fabricius) preying on D. citri. However, these studies did not provide information on levels of parasitism and knowledge of existing predators is even more scarce. In this context, this study had two objectives: (1) to estimate the population fluctuations of D. citri and (2) to record the diversity and abundance of some natural enemies on orange jessamine, Murraya paniculata L., and citrus trees, Citrus spp. in the provinces of Guayas and Santa Elena, in the Pacific coast of Ecuador.

MATERIALS AND METHODS

During the period April 2016-July 2017, field and laboratory studies were conducted to observe population fluctuations and to record some natural enemies (predators and parasitoids) associated with D. citri.

Population fluctuation studies of D. citri were conducted on M. paniculata at Parque Los Samanes, Guayaquil (02°06′13″N, 79°54′12″E). Diaphorina citri infested twigs and shoots (4 shoots or twigs/plant) of M. paniculata were collected from 10 plants and taken to the entomology laboratory of the Agricultural University of Ecuador for observation under a stereoscopic microscope (Motic SMZ 140 series, Hong Kong, China) with a magnification of 10 to 40X. Nymphs of D. citri were separated into three categories: (A) non-parasitized nymphs (yellow coloration), (B) parasitized nymphs (with brown coloration showing the typical symptoms of a mummified nymph without exit holes), and (C) mummified nymphs with exit holes. With this information, the percentage of parasitization was calculated [% Parasitization = (B+C)/(A+B+C) x 100). The first three population fluctuation studies were conducted in the months of April, June and October 2016; due to the recent dispersion of the parasitoids associated with D. citri in Ecuador (Chávez et al., 2017; Portalanza et al., 2017). Samples were afterwards taken biweekly from November 2016 until July 2017 for a total of 24 samples.

The survey of natural enemies was carried out in four areas of Guayaquil Canton, Guayas: two areas in the north, i.e., La Alborada (02°00′00″N, 79°54′36″E), Parque Los Samanes (02°06′13″N, 79°54′12″E) and in the southern region, Parque Forestal (02°12′41″N, 79°53′39″E) and Avenue Los Esteros (02°14′38″N, 79°53′47″E). In Santa Elena, observations were made in Chanduy Canton (01°54′20″N, 80°38′44″E). Insect samples were taken from M. paniculata or Citrus spp. The parasitized nymphs (B) were removed from the branches and placed individually in transparent gelatin capsules to observe the eventual emergence of the adult for identification. After separating the nymphs with symptoms of parasitization, the branches were placed in entomological cages to obtain adult parasitoids from parasitized psyllid nymphs that were overlooked. Emerged adult parasitoids of T. radiata (males and females) were identified using the characteristics given by Graham (1987) and Kondo et al. (2012).

Immature and adult predators that were found preying on D. citri on the host plants were collected and taken to the laboratory. For identification purposes, the larvae of the collected predators were reared in the laboratory until adult, providing nymphs of D. citri. Pupae of predators found on the branches also were collected. The lady beetles (Coleoptera: Coccinellidae) were identified by comparing their morphology and color patterns with specimens deposited in the private collection of G. González (Santiago, Chile). Lacewings (Neuroptera: Chrysopidae) and assassin bugs (Hemiptera: Reduviidae) were identified by comparing their morphology with specimens deposited in Museum of Arthopods of University of Zulia, Maracaibo, Venezuela. After identification, the number of individuals per species or genus were counted in order to calculate the percentage abundance [(% abundance of the species or genus = number of individuals of the species or genus/total of individual predators) x 100].

Percentage of parasitized D. citri nymphs was plotted monthly. Because of the high rainfall during January-May 2017, which was higher than the previous years, the precipitation data from the sampling period based on data from the Ecuadorian Navy Oceanographic Institute (INOCAR) were included.

The averages of the biweekly values of population fluctuation were plotted monthly. A correlation analysis was performed between the percentage of parasitized and non-parasitized nymphs of D. citri, as well as the total number of nymphs (A+B+C) and rainfall (P <0.05). Specimen samples of the parasitoid and predators are deposited in the entomological collection of the Agricultural University of Ecuador, Guayaquil, Ecuador.

RESULTS

All collected parasitoids were identified as T. radiata (figu­re 1 A–C), however, a few D. citri nymphs (n=20) had parasitoid exit holes in the posterior part of the body, characteristic of the endoparasitoid Diaphorencyrtus aligarhensis (figure 1D) suggesting the presence of this species in the sampling areas. However, their low number could indicate small population sizes of D. aligarhensis.

Figure 2 shows that during the first two months, the numbers of non-parasitized nymphs of D. citri were high (34 and 92 nymphs, respectively), whereas the percentages of parasitism were low (8.8% and 32.6%, respectively), when compared to the following months. Subsequently, the situation changed, with an increase in the percentage of parasitism and a decrease in the number of non-parasitized nymphs, which would indicate the beginning of the time of establishment of the parasitoid in the area.

From January to March 2017 there was a rainy season with higher precipitation compared to other recent years according INOCAR. The heavy rains affected D. citri populations that decreased drastically on the plants. In fact, rainfall was inversely associated with D. citri populations; an estimated correlation was highly significant (r: -0.611, P <0.05). Thus, the rainfall probably had a suppressive effect on the population density of the psyllid. The torrential and atypical rains during January-May 2017 reached up to 490 mm in the month of March (range: 172-490 mm) with an average of 319.3 mm. During that period no infestations of D. citri were observed (figure 2).

After rainfall, the percentage of non-parasitized nymphs remained low during the months of June and July 2017. Thus, when the parasitism due to the natural dispersion of T. radiata began, the population densities of non-parasitized nymphs were high but once established, parasitism reached levels of up to 90% (December 2016, figure 2) with an average parasitism of 67.2%. The high inverse correlation between non-parasitized nymphs and the percentage of parasitism (r: -0.819; P<0.05) suggests that over time the population density decreased when the percentage of parasitism increased

A total of 1660 specimens of predators in three insect orders: Coleoptera, Hemiptera and Neuroptera (figures 1E-K) were collected in association with D. citri during the present study with differences in species abundance. Of these, the coccinellids (Coleoptera: Coccinellidae) accounted for 59.8% of the collected predators, with Cheilomenes sexmaculata being the most abundant species (39.9%) and showed three phenotypic morphs that differ in shape and coloration of elytra (figure 1E-G). Ceraeochrysa sp. (Neuroptera: Chrysopidae) (figure 1J) was the second most abundant predator (22.4%), followed by Zelus sp. (Hemiptera: Reduviidae) (figure 1K) and Cycloneda sanguinea L. (Coleoptera: Coccinellidae) (figure 1I) with an abundance of 17.8% and 15.8%, respectively. Paraneda pallidula guticollis (Mulsant) (figure 1H) was the least abundant species (4.1%).

DISCUSSION AND CONCLUSIONS

Tamarixia radiata and D. aligarhensis have been reported in Ecuador in field collecting studies carried out in the period November 2015-March 2016 in the Province of Guayas (Portalanza et al., 2017). Hoddle et al. (2014) also detected a higher percentage of incidence of T. radiata (58%) with respect to D. aligarhensis (28%) in Pakistan. The low populations in early period coincides with the first detection of T. radiata in Ecuador (Chavez et al., 2017; Portalanza et al., 2017) suggesting the parasitoid’s recent colonization and dispersal.

The suppressive effect of rainfall is similar to those obtained by Chávez-Medina et al. (2016) who observed that precipitation was the most important limiting factor for the development of D. citri populations in a study carried out on Persian lime, Citrus × latifolia Tanaka ex Q. Jiménez in Sinaloa during 2015. Likewise, Aubert (1987) reported that monthly rainfall exceeding 150 mm is generally associated with low populations of D. citri due to the washing of eggs and nymphs from the plant surface.

The high levels of parasitism detected coincided with those reported in some studies on the population fluctuation of D. citri. Pluke et al. (2008) observed levels of parasitism that ranged between 70-100% and 48-70% for Citrus spp. and M. paniculata, respectively. Qureshi et al. (2009) noted that the percentage of parasitism in commercial citrus in Florida reached an average of 20% in spring and summer, but in November it increased to 56%. Kistner et al. (2016) obtained levels of parasitism that varied between 0% to 83% in an experimental citrus plot in California, USA.

Regarding predators, except for P. pallidula guticollis, the rest of the predators found in the present study have been reported as natural enemies of D. citri in other countries (Kondo et al., 2015; Kistner et al., 2016). Additionally, eggs of possible predator of D. citri, an assassin bug identified as Zelus sp. have been recorded in Ecuador in the Province of Manabí (Navarrete et al., 2016). The variation in the coloration of the elytra in Ch. sexmaculata has been associated to its genetic constitution, environmental conditions and the geographic region in which it occurs (Singh et al., 2016). Two of the morphs found in this study were previously reported preying on D. citri in Ecuador (Chavez et al., 2017). Paraneda palidulla guticollis is a neotropical species described by Mulsant in 1850, is distributed in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Peru, Venezuela, Guatemala and Mexico (González, 2018). Until now, only in Mexico, it was found feeding on other psyllids (Hemiptera: Psyllidae) on trees of Pithecellobium dulce (Roxb.) Benth. (Fabaceae) (Trejo-Loyo and Arriola, 2012). However, it has not been associated with D. citri and therefore this study constitutes, to our knowledge, the first record of P. pallidula guticollis feeding upon D. citri.

In conclusion, the only adult parasitoid detected in the present study was T. radiata. Furthermore, the presence of exit holes in parasitized D. citri nymphs on the posterior part of the dorsum, suggests the presence of a second parasitoid D. aligarhensis. Five species of predators of D. citri are reported. These results suggest the importance of T. radiata as a natural mortality factor of D. citri, whose action together with that of other natural enemies would make the current applications of chemical insecticides unnecessary for the control of D. citri, especially because in Ecuador, trees with symptoms of HLB have not yet been found. To our knowledge, this work constitutes the first report of P. palidulla guticollis feeding upon D. citri.

Acknowledgments

Many thanks to Dr. Penny Gullan (The Australian National University, Canberra, Australia) for kindly reviewing an early version of the manuscript and to the Collaborative Research entitled “Evaluation of wild and hybrid lines of Tamarixia radiata to optimatize its mass production in China to control Diaphorina citri, a vector of citrus HLB disease” for co-financing to the present investigation.

REFERENCES

AUBERT, B. 1987. Triozaerytreae Del Guercio and Diaphorina citri Kuwayama (Homoptera: Psyllidae), the two vectors of citrus greening disease: biological aspects and possible control strategies. Fruits 42: 149-162.

BOVÉ, J.M. 2006. Huanglongbing: A destructive, newly-emerging, century-old disease of citrus. J. Plant Pathol. 88 (1): 7-37.

CHAVEZ, Y.; CHIRINOS, D.T.; GONZÁLEZ, G.; LEMOS, N.; FUENTES, A.; CASTRO, R.; KONDO, T. 2017. Tamarixiaradiata (Waterston) and Cheilomenessexmaculata F. as biological control agents of Diaphorinacitri Kuwayama in Ecuador. Chilean J. Agricultural Res. 7 (2): 180-184.

CHÁVEZ-MEDINA, J.A.; FLORES-ZAMORA, G.L.; GÓNGORA-GÓMEZ, A.M.; GÓMEZ PERAZA, R.L.; GARCÍA-NEGROE, C.B. 2016. Distribución temporal de Diaphorinacitri Kuwayama (Hemiptera: Psyllidae) en limón persa (Citrus latifolia Tanaka) en el municipio de Sinaloa, Sinaloa. Entomol. Mex. 3: 324-329.

CORNEJO, J.F.; CHICA, E.J. 2014. First Record of Diaphorina citri (Hemiptera: Psyllidae) in Ecuador Infesting Urban Citrus and Orange Jasmine Trees. J. Ins. Sci. 14 (1): 1-3.

GONZÁLEZ, G. 2018. Los Coccinellidae de Chile. (Available at: https://www.coccinellidae.cl/paginasWebChile/PaginasOriginal/autor.php verified: May 8th, 2018).

GRAHAM, M.W.R.V.A. 1987. Reclassification of the European Tetrastichinae (Hymenoptera: Eulophidae), with a revision of certain genera. Bull British Mus (Natural History). Entomology. 55: 1-392.

HALBERT, S.E.; MANJUNATH, K.L. 2004. Asian citrus psyllids (Sternorrhyncha: Psyllidae) and greening disease of citrus: A literature review and assessment of risk in Florida. Fl. Entomologist. 87 (3): 330-353.

HODDLE, M.S.; HODDLE, C.; TRIAPITSYN, S.V.; KHAN, S.Z.; ARIF, Z.M. 2014. How Many Primary Parasitoid Species Attack Nymphs of Diaphorina citri (Hemiptera: Liviidae) in Punjab, Pakistan. Fl. Entomol. 97 (4): 1825-1828.

KISTNER, E.J.; MELHEM, N.; CARPENTER, E.; CASTILLO, M.; HODDLE, M.S. 2016. Abiotic and Biotic Mortality Factors Affecting Asian Citrus Psyllid (Hemiptera: Liviidae) Demographics in Southern California. Ann. Entomological Soc. Am., 109 (16): 860-871.

KONDO, T.; GONZÁLEZ, G.; TAUBER, C.; GUZMÁN-SARMIENTO, Y.C.; VINASCO MONDRAGON, A.F.; FORERO, D. 2015. A checklist of natural enemies of Diaphorina citri Kuwayama (Hemiptera: Liviidae) in the department of Valle del Cauca, Colombia and the World. Insecta Mundi. 457: 1-14.

KONDO, T.; QUINTERO, E. M.; CAMPUZANO, M.; WYCKHUYS, K.A.G.; HERATY, J. 2012. First report of Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae), a parasitoid of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) in the department of Valle del Cauca, Colombia. Bol. Mus. Entomol. Universidad del Valle 13 (1): 48-51.

NAVARRETE, J.B.; CAÑARTE, E.G.; VALAREZO, G.O. 2016. Primer reporte de la presencia de Diaphorina citri (Hemiptera: Liviidae) en Manabí. Espamciencia, 7(2): 141-145.

PARRA, J.R.; ALVES, G.; DINIZ, A.J.; VIEIRA, J. 2016. Tamarixiaradiata (Hymenoptera: Eulophidae) x Diaphorina citri (Hemiptera: Liviidae): mass rearing and potential use of the parasitoid in Brazil. J. Integrated Pest Manag., 7 (1): 1-11.

PLUKE, R.W.; QURESHI, J.A.; STANSLY, P.A. 2008. Citrus flushing patterns, Diaphorinacitri (Hemiptera: Psyllidae) populations and parasitism by Tamarixiaradiata (Hymenoptera: Eulophidae) in Puerto Rico. Fl Entomologist, 91 (1): 36-42.

PORTALANZA, D.E.; SANCHEZ, L.; PLÚAS, M.; FELIX, I.; COSTA, V.A.; DIAS-PINI, N.; SHERYL FERREIRA-STAFANOUS, N.; GÓMEZ-TORRES, M.L. 2017. First records of parasitoids attacking the Asian citrus psyllid in Ecuador. Rev. Bras. Entomol., 61 (2): 107-110.

QURESHI, J.A.; ROGERS, M.E.; HALL, G.D.; STANSLY, A.P. 2009. Incidence of invasive Diaphorinacitri (Hemiptera: Psyllidae) and its introduced parasitoid Tamarixia radiata (Hymenoptera: Eulophidae) in Florida citrus. J Econ Entomol. 102 (1): 247-256.

SINAGAP, 2015. Boletín situacional 2015. Naranja. (Available at: http://sinagap.agricultura.gob.ec verified: May 8th, 2018).

SINGH, V.; GOYAL, V.; DEVI, S. HOODA, S.; MALIK, V. 2016. Polymorphism of Cheilomenessexmaculata (Fabricius) (Coleoptera: Coccinellidae) in Haryana, India. J. Entomol. Zool. Studies. 4 (5): 548-551.

TREJO-LOYO, A.G.; ARRIOLA, N. 2012. Nuevos registros de Coccinellidae para el estado de Morelos, México. Acta Zool. Mex. 28 (3): 640-664.

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