Abstract
ABSTRACT Insect-resistant cultivars are essential for improving the management of pests such as Oryzophagus oryzae (Coleoptera: Curculionidae), which significantly decreases flooded rice yields. However, the degree of benefit brought to the crop varies with the type of resistance. This study aimed to evaluate the resistance of rice cultivars to O. oryzae, inferring about antixenosis and antibiosis effects on the development of larvae and adults. Under natural infestation conditions, a biennial experiment was carried out using a latin square design, with six treatments (cultivars) and plots with 30 plants (five rows of six plants equidistant 20 cm) irrigated with water depth of 15 cm. The number and weight of larvae by size, as well as the number, weight, emergence rate, and sex ratio of adults, were evaluated using standard soil, plant and root samples. Except for adult sexual ratio, the cultivars differed (p ≤ 0.05) for the other variables, whose relationship evidenced antibiosis effects at the larval stage, making possible to conclude that: the BRS Firmeza cultivar has resistance to O. oryzae due to antixenosis and/or antibiosis effects; BRS Ligeirinho is susceptible to this insect species, resulting in a relatively higher number of well-developed larvae and adults; and IRGA 417 shows an antibiosis action, restricting the adult emergence rates. The weight of adults gives a greater accuracy to the evaluation of the harmful effects of rice cultivars on the O. oryzae development.
Highlights
Rice (Oryza sativa L.) has social and economic importance as a staple cereal, in Brazil
The cultivars with significant differences in the number of larvae of intermediate size formed three groups: BRS Atalanta and BRS Firmeza; BRS Pelota and BRS Querência; and BRS Ligeirinho and IRGA 417 (Table 1)
The difference in larval populations among the rice cultivars may be due to antixenosis and antibiosis effects, revealing a possible preference for oviposition or inhibition of larval development (Table 1)
Summary
Rice (Oryza sativa L.) has social and economic importance as a staple cereal, in Brazil. Around 80 % of the national rice production comes from irrigated crops grown in 1.2 million hectares in the southern part of the country (Conab 2017). In this region, the insect species Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae) is harmful to the crop plants and produces at least two generations per year (Martins & Cunha 2015). O. oryzae is known as rice water weevil and has autochthonous populations. At the beginning of flooding, new rice fields are infested.
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