Community composition and species diversity of fruit-eating- insects of Gymnacranthera paniculata, Macaranga aleuritoides and Mastixiodendron pachyclado in a Papua New Guinea Primary Forest
Abstract
Community composition and species diversity of fruit-eating-insects were studied in a primary forest at Wanang, Madang, Papua New Guinea (PNG) using fruits regularly sampled and insects attacking them reared, preserved and identified. Sampling was done indifferent areas of the forest including low and high abundance of the host trees. Fruits of three predominant host trees, G. paniculata (Myristicaceae), M. aleuritoides (Euphorbiaceae) and M. pachyclados (Rubiaceae) were regularly collected and insects associated with them studied. The emergence from the fruits were 13 insect families and 16 species from G. paniculata, 17 insect families and 21 species from M. aleuritoides and 17 insect families and 25 species from M. pachyclados. Diversity assessment showed M. pachyclados was more diverse (H=2.0258) followed by G. paniculata (H=2.007). M. aleuritoides was the least diverse (H=1.443). A high percentage of scavengers and wood eaters were found in G. paniculata and M. aleuritoides. In M. pachyclados, more seed eaters, chewers and parasitoids were found instead. These results have implications for management of the community composition and diversity of the fruit-eating insects of the three host three species.
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Introduction
Frugivorous insect biodiversity has not been documented in New Guinea Forests in regard to their communities and composition on G. paniculata, M. aleuritoides and M. pachyclados. These trees are predominant in Wanang Conservation Area and throughout the New Guinea forests, and have economic importance to the local people. A tropical tree species supports a number of species of insect herbivores which are often large and unknown [1, 2]. [3] reared Dacine fruit flies (Tephritidae: Dacinae) from a sample size of more than 100 fruits weighing more than 1 kg of fruits from plant species while other insect taxa from this guild and seed predators in species of Lepidoptera, Coleoptera and Diptera were not studied [3]. A diversity of frugivorous insects exist in tropical forests were quantitatively reared. With 57 frugivorous weevil species representing 10,485 individuals from 326 woody plant species in lowland rainforest in PNG [4]. These frugivorous insects can be partitioned into two feeding guilds; mesocarp feeders (flesh feeders) and those feeding on endocarp (seed predators). Plants possess chemical and mechanical defences in seeds versus mesocarp that adheres to these specific feeding guilds [4]. Seeds are often shield by high concentrations of secondary compounds [5, 6, 7, 8], thus contribute to narrow attack by group of specialized predators that possesses detoxifying counteract mechanisms unlike against generalists which lack such protection [9]. Scolytine beetles attack palms [10] while Revena rubiginosa Boheman (curculionidae) predates on seeds of single-stemmed palm Syagrus romanzoffiana Cham (Arecaceae) [11, 12]. [13] recorded about 60% of fruit attack by seed predators in which weevils, katydids, and moth larvae were predominant on understory palm Calyptrogyne ghiesbreghtiana [14]. Most seed-beetles are oval shape [15] and have dietary specialization [16].
Parasitoids also strive with insect since they depend on them as hosts to complete their life cycles. [17] and [18] studied seven species of Braconid parasitoids under sub-family Opiinae: Doryctobracon areolatus Szépligeti, Utetes anastrephae Viereck, and Opius sp. Muesebeck, and Alysiinae: Asobara anastrephae Muesebeck, Phaenocarpa pericarpa Foerster, Idiasta delicata Papp, and Asobara sp. Nees. [19] stated that Braconid wasps were frequently reared from Cydia sp. larvae (Tortricidae: Grapholitini) from understorey palm (Calyptrogyne ghiesbreghtiana Linden) in Costa Rica where fruits containing Cydia have oviposition punctures of parasitoid and explains high parasitism due to few adults reared. Twenty-two Braconid species belonging to Agathidinae, Braconinae, Helconinae, Homolobinae and Rogadinae subfamilies were recorded from Brazil, Chile, Costa Rica, Guatemala, Mexico and Panama [20, 21]. In this study, the community composition and species diversity of host-specific fruit eating insects of G. paniculata, M. aleuritoides and M. pachyclado were studied.
Conclusion
The diversity of fruit-eating insects in PNG forests and their roles in maintaining high plant diversity in the tropical forests are not often documented. The resulted of this study showed that the diversity of frugivorous insects differ between tree species. The highest insect diversity was recorded on M. pachyclados (H=2.0258), followed by G. paniculata (H=2.007) and M. aleuritoides (H=1.443). Feeding guild assessment showed there were more scavengers and wood eaters in G. paniculata and M. aleuritoides than in M. pachyclados. Comparatively, there were more seed eaters, chewers and parasitoids in M. pachyclados. Communities of frugivorous insects feed on fruits of tropical forest trees and their feeding guilds pertain to distribution and thus diversity on plants. Therefore, the results of the feeding communities of fruit-eating insects on the tress thus contribute to better understanding of the ecology of tropical forests, particularly the dynamics of tree species, and the potential role of frugivorous insects. The findings of this study have implication for management of the fruit-eating-insects of primary forests of PNG.
