Larvae of Scarabeoidea (known as "white grubs") can be beneficial to rice growth: Case study on Hexodon unicolor unicolor (Dynastidae) in the Highlands of Madagascar

In the highlands of Madagascar, beetles (Scarabeoidea) are a major threat to the sustainability of rice and maize crops. These edaphic insects include a diverse range of species, but despite having varying habitats some species can coexist. The Dynastidae and Melolonthidae families are the most important groups. Most of them, both adults and larvae (known as `white grubs'), are often considered to be crop pests. However, not all white grubs are harmful. The larvae of some species of Scarabeoidea play an important role in soil structure. Among them, Hexodon unicolor unicolor (Dynastidae) is a very abundant species on the highlands of Madagascar, varying in population density according to land use and cover plant species. Laboratory-based experiments provided improved understanding of the behavior and functional roles of the larvae of this species. Mesocosm experiments were conducted, with the aim of (i) improving the feeding behavior of larvae in the presence of cow dung, and (ii) studying the effects of the H. unicolor unicolor larvae on the growth ofrainfed rice (cv. FOFIFA 161) in the presence or absence of exogenous organic matter (i.e. residues of Stylosanthes guianensis, residues of Glycine max, residues of Zea mays and cow dung). The results of the first experiment showed that the larvae of H. unicolor unicolor were attracted by cow dung. A second experiment demonstrated that the larvae neither attacked rice roots nor affected rice germination when in the presence of exogenous organic matter (residues or cow dung); the strongest effect was observed for cow dung. The processes by which larvae positively affect rice growth do not seem to be direct: burrowing and residue decomposition by larvae contribute to soil aeration and soil quality, thus favoring root and aerial biomass up to the tillering stage. Further experiments will be conducted in the field to investigate the behavior and functional roles of the larvae of other species, in order to propose effective pest control strategies.

Bibliographic Details

Main Authors:	Randriamanantsoa, R., Raharinindrina, S., Blanchart, Eric, Quaranta, Baptiste, Krishna, N., Ratnadass, Alain, Rafamatanantsoa, Emile, Rakotosolofo, H.
Format:	conference_item biblioteca
Language:	eng
Published:	ADRAO [Centre du Riz pour l'Afrique]
Subjects:	H10 - Ravageurs des plantes,
Online Access:	http://agritrop.cirad.fr/572302/
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