Abstract
ABSTRACT Oebalus poecilus is one of the most important pests of irrigated rice in Brazil. However, the impact of this species on the cultivar IRGA 424 RI, which is the most used, is unknown. Hence, the objective of this work is to evaluate the damage caused by O. poecilus on cv IRGA 424 RI. Panicles of this cultivar were infested for seven days at the R5 stage, using a randomized block design, considering the following factors sex, insect reproductive stage and insect density (number/panicle). In order to analyze the effect of these factors, the qualitative and quantitative damage caused by stink bugs to panicles were evaluated. An interaction was found between the sex and developmental stage for quantitative variables, in which reproductive females were responsible for increasing the damage in comparison to pre-reproductive females and the males, while the greatest qualitative damage was caused by reproductive insects regardless of sex and by females, despite the reproductive stage. Density of only one infesting insect has already increased the qualitative damage, while significant losses on the weight of the grain were verified with the infestation of two insects, demonstrating that IRGA 424 RI is susceptible to the attack of these stink bugs.
Highlights
Rice stink bug, Oebalus poecilus (Dallas) (Hemiptera, Pentatomidae), is one of the main pests of rice crop in Brazil, occurring both in upland and flood irrigated crops (Barrigossi, 2008; SOSBAI, 2016)
An interaction was found between the stage of reproductive development of the insects and sex on the variables panicle weight (PW) (F = 12.0201; gl = 1; p = 0.0019), weight of full spikelets (WFS ) (F = 4.3919; gl = 1; p = 0.0468), reduction in the spikelet weight (RSW) (F = 5.9324; gl = 1; p = 0.0226) and empty spikelets (ES) (F = 5.313, gl = 1, p = 0.0301) (Table 1)
In panicles infested with insects in the prereproductive stage, males and females caused similar damages to PW, WFS, RSW and percentage of ES, such damages were different when the bugs were in the reproductive phase, when the females were responsible for the significantly reduction in PW and the average weight of full spikelets (AWFS), reaching over the 42% reduction on the weight of spikelets, as well as, to increase by over 20% the percentage of empty spikelets in the panicles when compared to the males
Summary
Oebalus poecilus (Dallas) (Hemiptera, Pentatomidae), is one of the main pests of rice crop in Brazil, occurring both in upland and flood irrigated crops (Barrigossi, 2008; SOSBAI, 2016) The importance of this bug relies on the fact that nymphs and adults feed by sucking the endosperm contents of the spikelets, causing direct and indirect damages to the grains (Blackman & Stout, 2017). In the soft dough phase (R6), in addition to favoring fungal contamination and causing stains on the grains, they can weaken them structurally, which facilitates the breakage during the grain processing, reducing the percentage of whole grains (Barrigossi, 2008) Abiotic factors such as temperature and relative humidity of the air and biotic factors, such as the presence of natural enemies and the susceptibility of cultivars may affect the damage intensity (Barrigossi, 2008; SOSBAI, 2016). Several studies have demonstrated differences among genotypes of rice in relation to total spikelet loss (qualitative and quantitative) due to attack of bugs, they were carried out using cultivars adapted to the Central-West region or even to an upland rice system (Silva et al, 2018; Ferreira & Barrigossi, 2006; Krinski & Foerster, 2017)
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