The role of biodiversity in the dynamics and management of insect pests of tropical irrigated rice—a review

Abstract

Biodiversity relevant to pest management of tropical irrigated rice pests is discussed in terms of variation within rice plants, rice fields, groups of rice fields and rice associated ecosystems. It is concluded that, in the unique cropping conditions and stable water supply of tropical irrigated rice, the manipulation of a relatively few manageable components of diversity can confer stability such that pests are mostly kept at levels which do not justify the use of insecticides. Durable rice plant resistance, including moderate resistance, together with ability to compensate for damage by certain key pests, are regarded as fundamental to successful biological control by the natural enemy complex. Reliable natural enemy action is also considered to depend on all-year-round continuity of prey or hosts made possible by the relatively short fallow periods between staggered two to three rice crops per year and by proximity of certain non-rice habitats, notably the vegetation-covered bunds (levees) surrounding each field. In contrast, synchronous cropping could upset stability by destroying the continuity needed for natural enemy success. Such conclusions are supported by the experience of farmers who use little or no insecticide. Much evidence on destruction of natural enemies by certain insecticides supports the contention that insecticide use, especially early in the crop season, upsets natural enemy control of insects such as Nilaparvata lugens (Stal) (Hemiptera: Delphacidae) and also creates heavy selection pressure for strains of pests that can overcome previously resistant rice cultivars. Such circumstances create outbreaks of secondary pests and impair biological control of some key primary pests such as stem borers. It is concluded that pest management of much tropical irrigated rice must be based on natural controls rarely supplemented by insecticides. The success of this approach depends in particular on further research on dynamics of natural enemy and pest communities in rice ecosystems, especially where climatic conditions and water supply are marginally stable. Much more needs to be known about the nature and utilization of rice plant compensation for damage, particularly by defoliators and stem borers. The justification for, and supplementary use of, insecticides needs to be radically reassessed. There is no evidence that a natural control-based approach, as recommended in this review, is incompatible with farmer practicability or with future developments in rice production Correspondence: Professor Michael J. Way, technology, except perhaps the possible mechanization-driven increase in field size which would decrease bund area. In contrast, the insecticide-based approach is not only harmful to natural controls but is costly and mostly demands impracticable decision making by farmers on need-based use.

Effects of tillage practices on spider assemblage in rice paddy fields

“…The importance of generalist predators has also been examined in rice paddy cropping systems (Kenmore et al, 1984;Nakasuji and Dyck, 1984;Kuno and Dyck, 1985;Way and Heong, 1994;Settle et al, 1996). In particular, spiders are one of the most important predators in rice paddy fields because of their abundance and predation activity (Itô et al, 1962;Kiritani et al, 1972;Kawahara et al, 1974;Oraze and Grigarick, 1989).…”

The LEGATO cross-disciplinary integrated ecosystem service research framework: an example of integrating research results from the analysis of global change impacts and the social, cultural and economic system dynamics of irrigated rice production

“…Landscape management decisions like the choice of surrounding crops or the floristic composition of set-aside habitat, including the management of plants on rice bunds influence the functionality of the cropping system in general, and the effectiveness of the natural pest control in particular (Dominik et al 2017;Tylianakis et al 2007). As biodiversity is a decisive factor in this respect (Way and Heong 1994), LEGATO has monitored and inventoried the invertebrate fauna of rice fields and the responses of some of these, particularly egg parasitoids, to variations of herbivore populations. Thus, LEGATO has analysed the predator and parasitoid components as the first step, but also compiled the names of rice varieties used in the fields, documented management practices (Sattler et al, this issue) and defined surrounding habitats as factors influencing biocontrol effectiveness (Rusch et al 2013;Tscharntke et al 2007).…”

Influence of humidity, rainfall, and fipronil toxicity on rice leaffolder (Cnaphalocrocis medinalis)

“…Abiotic and biotic factors are believed to be responsible for the population change 14 . Weather components such as temperature, rainfall, and relative humidity have known to greatly influence the insect population directly by limiting or expanding their distribution, growth, reproduction, diapause, dispersal, and indirectly through plant mechanisms and natural enemies that regulate the insect population [15][16][17][18][19] . The seasonal effects of weather and ongoing changes in climatic conditions will directly lead to modifications in dispersal and development of insect species.…”