Curculionidae Research Articles

Investigation of 9 True Weevil (Curculionidae Latreille, 1802) Species for Chitin Extraction.

Chitin, the second most abundant biopolymer after cellulose, is an important resource for biosourced materials. The global demand for chitin is rapidly increasing, however, the majority of industrial chitin is sourced from crustacean shells, which may be less accessible in regions without seafood waste. Therefore, it is crucial to explore alternative chitin sources, such as those derived from beetles and other arthropods. This study investigated chitin extraction from nine species of Curculionidae (true weevils), which are recognized as crop pests. The extraction process and yields were described, and the isolated chitin was characterized by SEM, IR spectroscopy, elemental analysis, XRD, and ash and water content measurements. This work highlights the potential of Curculionidae as an alternative chitin source.

Curculionoidea (Coleoptera) Species on Weeds in Kahramanmaras Province Part II

This study was conducted to determine the Curculionoidea species on weeds found in non-agricultural areas in Kahramanmaras province between 2021 and 2022, weekly from late March-early April until the end of September after the weeds begin to germinate, and at fifteen-day intervals when the weeds start to dry towards the end of September. As a result of this study, one genus belonging to the subfamily Apioninae of the family Apionidae of the superfamily Curculionoidea, eleven genera belonging to the family Curculionidae, Lixinae Schoenherr, 1823, Hyperinae Marseul, 1863, Curculioninae Latreille, 1802, Baridinae Schoenher, 1836, Ceutorhynchinae Bedel, 1881, Entiminae Schoenherr, 1823 subfamilies and fifteen species belonging to these genera were identified. A total of eight species, including Hypera striata (Boheman, 1834), Rhinusa (Gymnaetron) bipustulata (Rossi, 1792), Smicronyx jungermanniae (G. C. Reich, 1797), Aulacobaris picicornis (Marsham, 1802), Baris analis (Olvier, 1790) Gyllenhal, 1837, Glocianus distinctus (C. Brisout, 1870) and Rhopalapion longirostre (Olivier, 1807), are new records for Kahramanmaras province. In addition, fifteen weed species were identified as new host plants for the identified Curculionoidea species.

Species composition of phytophages on ornamental plants

Goal. Monitoring the phytosanitary status and determining the species composition of phytophages on decorative coniferous and deciduous plants. Methods. Field — determination of the species composition of pests and the dynamics of the number of main species; laboratory — determination of pests selected on experimental plots. Research was conducted in accordance with generally accepted methods in entomology and plant protection. Results. In the industrial plant nursery of open soil «Megaplant» located in the Kyiv region, Fastiv district, village The monitoring of the phytosanitary state of ornamental plant plantations was carried out in Trilys. The natural saturation of harmful organisms and the level of their harmfulness were studied. Conclusions. It has been established that plants in industrial nurseries in open ground are damaged by a large number of insects and mites. The most dangerous and widespread on conifer ornamental plants were 8 pests from the following families coccids (Coccidae), bark beetles (Scolytidae), adelgids (Adelgidae), snout beetles (Curculionidae) and spider mites (Tetranychidae); 9 most harmful species from the following families were noted on decorative leafy plants: crambid Snout Moths (Crambidae), mealybugs (Pseudococcidae) and аrmored scales or diaspidids (Diaspididae), eriophyidae mites (Eriophyidae), aphids (Aphididae), snout beetles (Curculionidae), scarab beetles (Scarabaeidae).

Preferencia alimenticia y de oviposición de Gonipterus platensis(Coleoptera: Curculionidae) en tres especies comerciales de Eucalyptus en Colombia

Gonipterus platensis (Marelli, 1926), is a beetle that belongs to the family Curculionidae, a phytophagous species within the genus Eucalyptus. It is native to Australia, where it is not considered a pest due to the presence of biological controllers. In Colombia, eucalyptus trees are the second exotic species with the largest planted area, and because in 2016 was recorded the presence of G. platensis in the country, efforts have been made to study and determine the potential damage that this species can cause in plantations through studies of its feeding preferences and oviposition, among others. The present study aims to determine the preference of G. platensis for the three most planted commercial eucalyptus species in the country: Eucalyptus grandis W.Hill ex Maiden, E. urophylla S.T. Blake, and the hybrid E. grandis W.Hill ex Maiden × E. urophylla S.T. Blake (E. urograndis). An experiment was conducted using a multiple-choice design to assess feeding and oviposition preference. Two assays were carried out: one with seedlings and the other with an olfactometer. The present study reveals that G. platensis has a feeding preference for E. grandis, followed by E. urophylla, and to a lesser extent, the hybrid species E. urograndis. Furthermore, G. platensis is capable of ovipositing in all three eucalyptus species studied without making any differentiation.

Curculionoidea (Insecta: Coleoptera) Species Detected on Some Weeds in Kahramanmaraş Province, Türkiye Part I

This study was conducted to determine the Curculionoidea species on weeds found in non-agricultural areas in Kahramanmaraş Province between 2021 and 2022, weekly from late March early April until the end of September after the weeds begin to germinate, and at fifteen-day intervals when the weeds start to dry towards the end of September. Studies were carried out. As a result of this study two genera belonging to the family Curculionidae, Lixinae Schoenherr, 1823 subfamily of the superfamily Curculionoidea, and fourteen species belonging to these genera. Larinus cinerascens Capiomont, 1874, one of the identified species, is a new record for the Curculionoidea fauna of Türkiye. A total of five species, including Lixus algirus L., Lixus vilis (Rossi, 1790), Larinus cinerascens Capiomont, 1874, Larinus hedenborgi Boheman, 1845, Larinus turbinatus Gyllenhal, 1835, are new records for Kahramanmaraş Province. In addition, twelve weed species were identified as new host plants for the identified Curculionoidea species.

Development of parasite complexes in the ecosystem of the rose garden of the main Botanical Garden of the Russian Academy of Sciences

The article reports on studies (2011-2022) monitoring harmful organisms in the ecosystem of the rose garden of the Main Botanical Garden of the Russian Academy of Sciences. The studies yielded data on the detection of pathogens and pests, as well as the phenotypic manifestation of pathologies and lesions. A total of 21 species of pathogens and 16 species of phytophages were identified. The species composition of harmful organisms in the ecosystem of the rose garden was defined. It is shown that at the initial stage (2011- 2013) of ecosystem establishment, no external signs of viral diseases were observed, and a low level of fungal infections was noted. The development of such harmful pathogens as Peronospora sparsa Jacz., Sphaerotheca pannosa Lev., Phragmidium disciflorum James, and Ph. tuberculatum Mull. was controlled by culling plants of susceptible varieties. The predominant pathogens included Marssonina rosae (Lib.) Died., Phyllosticta rosae Desm., and Septoria rosae Desm., and the susceptibility of specific varieties to these pathogens was established. The populations of pathogens causing spot anthracnose (Sphaceloma rosarum Pass.), ascochyta leaf spot (Ascochyta rosicola Sacc.), and cercospora leaf spot (Cercospora rosicola Pass.) were slightly less common. A wide range of signs of viral infections was identified. Nine viruses belonging to five genera were detected. The frequency of their occurrence was analyzed, and the most common viruses were identified: Prunus necrotic ring spot ilarvirus, Apple mosaic ilarvirus, Tobacco ring spot nepovirus, and Arabis mosaic nepovirus. The species diversity of phytophages was noted: leaf beetles, snout beetles, leafroller moths, sawflies, blossom weevils, earwigs, moths, leafhoppers, aphids, and true bugs. It was found that damage to plants by a range of pests reached only an average level, except for individual varieties (Red Blanket and Prosperity). In general, the phytosanitary assessment of the rose gene pool of the garden according to the phytosanitary monitoring and integrated detection revealed a wide range of parasite complexes: fourteen types of pathogenic complexes, four types of entomological complexes, and five types of entomopathogenic complexes. The tactical and basic directions for control of harmful organisms in the ecosystem of the rose garden are discussed.

Delimiting species, revealing cryptic diversity in Molytinae (Coleoptera: Curculionidae) weevil through DNA barcoding.

The subfamily Molytinae (Coleoptera: Curculionidae), being the second largest group within the family Curculionidae, exhibits a diverse range of hosts and poses a serious threat to agricultural and forestry industries. We used 1,290 cytochrome c oxidase subunit I (COI) barcodes to assess the efficiency of COI barcodes in species differentiation and uncover cryptic species diversity within weevils of Molytinae. The average Kimura 2-parameter distances within species, genus, and subfamily were 2.90%, 11.0%, and 22.26%, respectively, indicating significant genetic differentiation at both levels. Moreover, there exists a considerable degree of overlap between intraspecific (0%-27.50%) and interspecific genetic distances (GDs; 0%-39.30%). The application of Automatic barcode gap discovery, Assemble Species by Automatic Partitioning, Barcode Index Number, Poisson Tree Processes (PTP), Bayesian Poisson Tree Processes (bPTP), and jMOTU resulted in the identification of 279, 275, 494, 322, 320, and 279 molecular operational taxonomic units, respectively. The integration of 6 methods successfully delimited species of Molytinae in 86.6% of all examined morphospecies, surpassing a threshold value of 3% GD (73.0%). A total of 28 morphospecies exhibiting significant intraspecific divergences were assigned to multiple MOTUs, respectively, suggesting the presence of cryptic diversity or population divergence. The identification of cryptic species within certain morphological species in this study necessitates further investigation through comprehensive taxonomic practices in the future.

First Record of Phoretic Mite from Red Palm Weevil Rhynchophorus ferrugiuneus (Olivier,1790) from Basrah, Southern Iraq

The red palm weevil Rhynchophorus ferrugineus (Olivier, 1790), which belongs to the family Curculionidae, order Coleoptera, is one of the most important palm pests, which leads to heavy losses in date palms. In the last few years, it has been recorded in Iraq, from Safwan city south of Iraq, where it was detected on date palm trees (Phoenix dactylifera L, Arecales: Arecaceae). In the current study, specimens of adult weevils were collected from infested date palms (Phoenix dactylifera), that showed signs of infection in Safwan district, south of Basra province. The results of the investigation showed the presence of phoretic mites associated with the red palm weevil Rhynchophorus ferrugineus (Olivier, 1790). Two genera of Uropodid mites, deutonymph, were attached by anal pedicel to body parts of adult red palm weevils. They were collected and identified as Centrouropoda (Uropodidae), and Uroovbovella (Urodinychidae), according to accurate taxonomic keys. The differentiation between two genera of mites was studied. The deutonymphs were examined and photographed by an AM Scop camera installed on a light microscope, and the insects were photographed by a LEICA microscope. The infestation symptoms were illustrated with pictures.

The Eucalyptus snout beetle in Colombia: Selection and evaluation of entomopathogenic fungi as bioinsecticides against Gonipterus platensis

The Eucalyptus snout beetles, which belong to the Gonipterus scutellatus species complex, cause heavy damage to Eucalyptus spp. worldwide. The species was reported in Antioquia, Colombia for the first time in 2016, threatening more than 115,000 ha of planted Eucalyptus spp. Elsewhere, its damage has been controlled using Anaphes spp. as classical biological control, but Anaphes spp. are not available in Colombia, where there are no documented control methods for this species to date. We identified the Gonipterus species using molecular methods and isolated entomopathogenic fungi from naturally infected beetles collected from the current distribution area in Colombia. We characterised the fungal isolates, selecting the best to develop a biological control agent. We considered insecticidal activity, UV-B radiation tolerance, yield, germination, and enzyme activity of conidia in making our selection. We confirmed the presence of G. platensis in Colombia, with adults naturally infected by Beauveria spp. and Metarhizium spp. From the isolated native fungi, M. brunneum (CA-3), M. robertsii (RI-1), B. bassiana (CA-1) and (CA-2), B. pseudobassiana (SP-1) were identified. We found remarkable differences in response to different variables between the selected isolates and SP-1 and CA-3 were the most virulent. The SP-1 isolate stood out from the rest for being the most tolerant to UV-B radiation, alkaline media, and low temperatures, germinating faster and producing elevated levels of lipases, chitinases, and proteases. The identified promising native fungus isolate, naturally occurring on field individuals, could be used to develop a biopesticide for controlling G. platensis in Eucalyptus spp. plantations in Colombia.

Insect pests affecting Eucalypts in Portugal: Current situation and future prospects

Eucalypts (Eucalyptus spp.) early established outside their native range have typically benefited from a pest-free environment. However, over time, due to the circulation of people and goods, several Australian insects that attack eucalypts reached the regions where these trees are commercially planted. In Europe, Portugal is the country with the largest area planted with eucalypts (mostly Eucalyptus globulus), covering almost 850,000 hectares. Thirteen insect species native from Australia have already been found in Portugal affecting eucalypts. From these, the snout beetle (Gonipterus platensis), the bronze bug (Thaumastocoris peregrinus), the longhorned borers (Phoracantha semipunctata and P. recurva), and the tortoise beetle (Trachymela sloanei) are the most important pests. This work aims to review the status of these pests, their impacts, and the success of the management strategies that have been employed. Future challenges are also discussed.

Anagonia lasiophthalma (Diptera: Tachinidae): Survey, identification, and biological traits of a new biological control agent of the Eucalyptus snout beetle, Gonipterus platensis (Coleoptera: Curculionidae)

The Eucalyptus snout beetle, Gonipterus platensis, is one of the main pests of eucalypts outside its native range. Among the available control methods for this pest, classical biological control with Anaphes nitens (Hymenoptera: Mymaridae) has been the most widely used, but it is not always effective. To identify other natural enemies that might provide further pest control, a field survey was conducted in Tasmania, Australia, in which Anagonia spp. were found to parasitize 7 % of Gonipterus spp. larvae. One species was subsequently identified as the solitary parasitoid Anagonia lasiophthalma, based on direct comparisons with research collection material in Australia. To assess the potential of this species as a biological control agent, A. lasiophthalma was reared on G. platensis larvae under quarantine conditions, and its biology and reproductive strategy were studied in the laboratory. Global mating success was 58 %, with 66 of the 114 A. lasiophthalma females analyzed mating within an established 10-day period. Most females mated within 48 h after emergence and started to parasitize about a week later. Dissections of mated females showed that this species is ovolarviparous, incubating its eggs in an ovisac, before inserting them “ready-to-hatch” directly into the host using a piercing structure derived from the modification of a sternite in the female terminalia. Over the course of their lifetime, females on average produced 35 offspring and post-mortem dissections revealed an additional 32 eggs in the ovisac. Longevity of females and males was similar, ranging between 55 and 84 days, but females maintained without host larvae lived longer than females exposed to host larvae. These results provide relevant information to improve laboratory rearing protocols and suggest that A. lasiophthalma may be effective against the snout beetle in its invaded range.

Screening five local entomopathogenic nematode species for their virulence against pupae of the Eucalyptus snout beetle, Gonipterus sp. n. 2, under laboratory conditions

The Eucalyptus snout beetle, Gonipterus sp. n. 2, is an important pest of eucalypt trees in South Africa and other countries. The pest is partially controlled with a mymarid egg parasitoid, Anaphes nitens. Identifying additional biological control agents that target other developmental stages of Gonipterus sp. n. 2 is necessary to improve control. Entomopathogenic nematodes (EPNs) are used as biological control agents for numerous soil pests and thus have the potential to be used against the pupal stage of Gonipterus sp. n. 2, which occurs in the soil. In this study, five South African EPN species were screened for their virulence on uncased pupae of Gonipterus sp. n. 2. At a concentration of 200 IJs/pupa in 50 μl of sterile water, Steinernema jeffreyense, S. fabii, Heterorhabditis noenieputensis and H. safricana caused pupal mortality of less than 40 %, while S. yirgalemense caused the highest pupal mortality of 100 % two days post-inoculation. Steinernema yirgalemense was selected and applied at different concentrations, namely 0, 12, 25, 50, 100, 200, and 400 IJs/pupa to determine its lethal concentration. Probit analysis indicated that the LC50 and LC90 of S. yirgalemense were 48.29 and 260.63 IJs/pupa, respectively. The study also showed that the pupal cases do not affect the efficacy of S. yirgalemense as it caused more than 90 % mortality of cased pupae of Gonipterus sp. n. 2 in soil bioassays. In addition, pupal age did not affect the efficacy of S. yirgalemense. Based on our findings, S. yirgalemense is a potential candidate for the biological control of pupae of Gonipterus sp. n. 2.

Phylogenomics illuminates the phylogeny of flower weevils (Curculioninae) and reveals ten independent origins of brood-site pollination mutualism in true weevils.

Weevils are an unusually species-rich group of phytophagous insects for which there is increasing evidence of frequent involvement in brood-site pollination. This study examines phylogenetic patterns in the emergence of brood-site pollination mutualism among one of the most speciose beetle groups, the flower weevils (subfamily Curculioninae). We analysed a novel phylogenomic dataset consisting of 214 nuclear loci for 202 weevil species, with a sampling that mainly includes flower weevils as well as representatives of all major lineages of true weevils (Curculionidae). Our phylogenomic analyses establish a uniquely comprehensive phylogenetic framework for Curculioninae and provide new insights into the relationships among lineages of true weevils. Based on this phylogeny, statistical reconstruction of ancestral character states revealed at least 10 independent origins of brood-site pollination in higher weevils through transitions from ancestral associations with reproductive structures in the larval stage. Broadly, our results illuminate the unexpected frequency with which true weevils-typically specialized phytophages and hence antagonists of plants-have evolved mutualistic interactions of ecological significance that are key to both weevil and plant evolutionary fitness and thus a component of their deeply intertwined macroevolutionary success.

UJI EFEKTIVITAS BEBERAPA TANAMAN OBAT TERHADAP REPELENSI SERANGGA HAMA PERUSAK BERAS PADI VARIETAS CILIWUNG DI GUDANG BERAS


 The purpose of this study was to determine the effectiveness of some plant material as insect repellence agents for rice pests Ciliwung variety. The methods used are field experiments and specimen collection. The research was carried out in one of the rice warehouses in Kuripan District and the Plant Protection Laboratory, Faculty of Agriculture, University of Mataram. The experiment was designed with a Group Randomized Design (GRD) consisting of six treatments. These treatments are; P0 (control), P1 (betel leaf; Piper crocatum), P2 (fragrant pandan leaves; Pandanus amarylifolius), P3 (bay leaf; Syzigium polyanthum), P4 (kaffir lime leaves; Citrus hystrix), and P5 (garlic bulbs; Alium Sativum). The results showed that betel leaf, fragrant pandan leaf, bay leaf, and kaffir lime leaf were effective against the rejection of three insect pests found. Three families of rice-destroying pests were found in Ciliwung varieties, namely; Family Tenebrionidae, Family Curculionidae, and Family Pyralidae. The plant materials used (betel leaf, fragrant pandan leaf, bay leaf, kaffir lime leaf, and garlic bulb) have no real effect on the diversity, dominance, and richness of Ciliwung variety rice pest species

Presence of the Eucalyptus snout beetle in Ecuador and potential invasion risk in South America.

Eucalyptus snout beetles are a complex of at least eight cryptic species (Curculionidae: Gonipterus scutellatus complex), native to mainland Australia and Tasmania, that defoliate Eucalyptus trees and are considered important pests. Since the 19th century, three species of the complex have been introduced to other continents. Here, we document the presence of Eucalyptus snout beetles in Ecuador. We used DNA data for species identification and unambiguously demonstrated that the Ecuadorian specimens belong to the species Gonipterus platensis, which has low genetic diversity compared with other species in the complex. We analyzed G. platensis' potential distribution in South America with ecological niche models and found several areas of high to intermediate climatic suitability, even in countries where the pest has not been registered, like Peru and Bolivia. Accurate identification of species in the G. scutellatus complex and understanding of their potential distribution are essential tools for improved management and prevention tactics.

Susceptibility of Eucalyptus trees to defoliation by the Eucalyptus snout beetle, Gonipterus sp. n. 2, is enhanced by high foliar contents of 1,8-cineole, oxalic acidand sucrose and low contents of palmitic and shikimic acid.

Gonipterus sp. n. 2 (Coleoptera, Curculionidae) is an invasive, commercially important weevil that causes large-scale defoliation of Eucalyptus trees. The weevil specifically feeds on young leaves and new shoots, thus reducing tree growth. The weevil displays a very strong preference for certain Eucalyptus genotypes, however, this behaviour and the chemistry underlying it is poorly understood, thereby complicating the selection of resistant trees. To elucidate the feeding preference of Gonipterus sp. n. 2, we assessed the relative levels of susceptibility of 62 Eucalyptus genotypes from 23 species using a laboratory choice assay. This revealed large intraspecific variation in susceptibility to weevil feeding, which for certain species, exceeded the interspecific variation. A semiquantitative metabolite profile analysis on 13 genotypes revealed strong correlations of 10 metabolites to feeding damage. The behavioural effects of the identified compounds were assessed through an in vitro feeding preference assay using artificial diets as well as under field conditions. This revealed three phagostimulants (1,8-cineole, oxalic acidand sucrose) and two feeding deterrent compounds (shikimic acid and palmitic acid) for Gonipterus sp. n. 2. These chemical markers can be applied to tree breeding programmes for the selection of resistant genotypes to reduce damage caused by Gonipterus weevils.

First record of Sitophilus linearis (Herbst, 1795) (Coleoptera: Curculionidae) from East African copal

Sitophilus linearis (Herbst, 1795) from the subtribe Sitophilina (Curculionidae, Dryophthorinae, Litosomini) firstly recorded from East African copal. It is the fourth representative of the family Curculionidae in this copal. This record of S. linearis confirms the origin of Tamarindus indica L. in East Africa.

Integrative microbial and transcriptomic analysis reveals the lignocellulosic biomass degrading mechanism by bamboo snout beetle

Insects and gut symbiotic bacteria have shown promise in the degradation of lignocellulosic biomass (LCB). Cyrtotrachelus buqueti is being studied as a resource for LCB degradation, but its mechanisms are not fully understood. This study investigates the host transcriptome and gut microbiome to identify the inherent mechanisms behind efficient LCB degradation. The gut secretory protein showed degradation rates of 30.23%− 38.24% for cellulose, 58.56%− 70.96% for hemicellulose, and 28.71%− 43.43% for lignin, while microbiota had degradation rates of 28.41%− 38.31% for cellulose, 53.45%− 66.15% for hemicellulose, and 25.65%− 38.37% for lignin. Core genera (>80%) of bacteria are identified in the foregut, midgut, and hindgut, with the hindgut containing the most abundant lignin degradation potential genera Serratia and Dysgonomonas, and the midgut has the highest abundance of cellulose and hemicellulose degradation likely genera Lactococcus and Enterococcus. The transcriptome reveals highly abundant and diversified lignocellulolytic genes encoding carbohydrate-active enzymes (CAZymes), with lignin-modifying enzyme genes highly expressed in the hindgut and cellulase and hemicellulase genes highly expressed in the foregut and midgut. Integrative analysis reveals a significant correlation between the gut microbiome and transcriptome, contributing to efficient LCB degradation. This study first provides a deeply comprehensive insight into the unique mechanisms of LCB degradation by C. buqueti.

Diversity of Beetle Family Curculionidae and Bostrichidae (Coleoptera) in Two National Protected Areas in Lao PDR

Diversity of Beetle Family Curculionidae and Bostrichidae (Coleoptera) in Two National Protected Areas in Lao PDR

Xylophagous insects associated with the mangrove forest of the Ramsar wildlife refuge protected area, Bahía de Panamá wetland

In Panama, terrestrial forests and mangrove ecosystems are very susceptible to insect damage, due to the increase in exotic species. The objective of this study was to determine the relative abundance of xylophagous beetles in mangrove forest of the Wildlife Refuge RAMSAR protected area, Bay de Panamá wetland. The research was carried out in the mangrove forests located in the areas of El Embarcadero, Costa Sur and Don Bosco, where 5033 individuals, corresponding to 6 families (Kalotermitidae, Termitidae, Cerambycidae, Curculionidae, Elateridae and Scarabaeidae), associated with the mangrove forest were captured. The El Embarcadero was the site with the highest number of xylophagous insects with 3,803 individuals. Of the three areas sampled, the areas closest to the coast (Zone 1) El Embarcadero and Costa Sur showed the greatest number of xylophagous insects, while Don Bosco showed the least number. The beetle family Curculionidae was the most commonly observed family, with the subfamilies Scolitinae and Platypodinae being the most important. 91% of all captured xylophagous insects belonged to the Scolytinae subfamily, while 6% belonged to the Platypodinae subfamily; one particular species, Euplatypus parallelus, was observed to affect many Avicennia germinans. Xylophagous beetle families that presented lower abundances were: Elateridae with 45 individuals, Scarabaeidae with 5 individuals, and Cerambycidae with 2 individuals. Two termite families were observed, Kalotermitidae with 50 nests, and Termitidae with 5 nests. Termites in mangrove ecosystems are important due to their ability to modify soil properties by decomposing organic matter, mainly the wood of mangrove trees that are already very old or dead. They also contribute to protecting nutrients, factors key to maintaining tropical ecosystem stability.