Juliano de Bastos Pazini

Side-effects of pesticides used in irrigated rice areas on Telenomus podisi Ashmead (Hymenoptera: Platygastridae)

Telenomus podisi Ashmead (Hymenoptera: Platygastridae) is an important agent for the biological control of stink bug eggs in irrigated rice areas and the best strategy for its preservation is the use of selective pesticides. The aim of this study was to know the side-effects of pesticides used in Brazilian irrigated rice areas on egg parasitoid T. podisi. We evaluated, under laboratory conditions, 13 insecticides, 11 fungicides, 11 herbicides, and a control (distilled water) in choice and no-choice tests. In the no-choice tests, the pesticides were sprayed at pre and post-parasitism stages (egg and larval stages of T. podisi). In the choice tests, sprays were conducted only at pre-parasitism stages. For all tests, we prepared cards with 25 eggs of the alternative host Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) non-parasitized (pre-parasitism) and parasitized (post-parasitism), which were subjected to pesticide sprays. The parasitism and emergence rates of T. podisi were determined classifying the pesticides in terms of the reduction of parasitism or emergence rates compared to the control. The neurotoxic insecticide cypermethrin, lambda-cyhalothrin, zeta-cypermethrin, etofenprox, thiamethoxam, thiamethoxam + lambda-cyhalothrin, acetamiprid + alpha-cypermethrin, and bifenthrin + alpha-cypermethrin + carbosulfan were more harmful to T. podisi and, therefore, are less suitable for the integrated management of insect pests in irrigated rice areas.

Side effects of insecticides used in wheat crop on eggs and pupae of Chrysoperla externa and Eriopis connexa

In Brazil, chemical control is one of the main tools to manage insect pests in wheat. However, this kind of management can impair the biological control provided by the predators Chrysoperla externa and Eriopis connexa. The present study evaluated the side effects on C. externa and E. connexa of 15 insecticides registered for wheat. Insecticides were sprayed on eggs and pupae via Potter tower at the maximum recommended dose. We evaluated the viability of eggs and pupae as well as the sub-lethal effects on fecundity and fertility of the adults emerged from treated pupae. The insecticides were classified according to the scale of toxicity proposed by IOBC. Regarding the eggs, the insecticide etofenprox was classified as slightly harmful (class 2) to C. externa. Imidacloprid + beta-cyfluthrin, diflubenzuron WG, thiamethoxam + lambda-cyhalothrin A and B, gamma-cyhalothrin, and etofenprox were also classified as slightly harmful (class 2) to E. connexa, while methomyl was classified as moderately harmful (class 3) for the eggs of the predator. The insecticide imidacloprid + beta-cyfluthrin was considered slightly harmful (class 2) to pupae of C. externa, while imidacloprid + beta-cyfluthrin, thiamethoxam + lambda-cyhalothrin A and B, and lufenuron were classified as slightly harmful (class 2) to the pupae of E. connexa. The insecticides beta-cyfluthrin, diflubenzuron SC, lambda-cyhalothrin, permethrin, thiamethoxam, triflumuron, and zeta-cypermethrin were harmless to eggs and pupae of both predators and should therefore be prioritized in the control of insect pests in wheat, thus preserving the natural biological control provided by C. externa and E. connexa.

VALIDAÇÃO DO ARRANJO ESPACIAL DO PERCEVEJO-DO-COLMO EM ARROZ IRRIGADO POR INUNDAÇÃO

In order to spatial arrangement validation of Tibraca limbativentris Stal, 1860 (Hemiptera: Pentatomidae) in flooded rice field located at the “Planalto da Campanha” Region, Rio Grande do Sul (RS), Brazil, was carried out a study in flooded rice fields at Itaqui, Rio Grande do Sul State, Brazil, in the 2009/10, 2010/11 and 2011/12 harvests. Were established georeferenced grids for the samplings, totaling 81 points spaced ~50 m in the 2009/10 harvest and, 693 and 352 points in the 2010/11 and 2011/12 harvests, respectively, both with equidistant points ~10 m. Adults and nymphs samplings were performed on each point of the regular grids. We conducted a descriptive statistical analysis for the adults, nymphs and adults + nymphs variables by calculations the mean, standard deviation and minimum and maximum values and dispersion indices: variance/mean, Morisita index, k index, Green coefficient and Taylor potency. The rice stem bug spatial arrangement has been validated when the dispersion indices showed similar results. The rice stem bug T. limbativentris spatial arrangement in flooded rice is the aggregate type, regardless of the infestation level and life stage of the insect.

Abundância sazonal de percevejo-do-colmo do arroz

The rice stem bug ( Tibraca limbativentris ) population has increased over the last years making it one of the main pests in irrigated rice crops in Planalto da Campanha, Rio Grande do Sul State, Brazil. Favorable factors throughout the year provide conditions for its infestation in crops and subsequent hibernation. This study aimed to determine the variation of rice stem bug population in commercial irrigated rice crop and hibernation sites. Therefore, a population survey of nymphs and adults was carried out. It was concluded that the photoperiod and temperature were the factors that most affected the insect population, leading to a hibernation period of 10 months. Management operations also affected the population reduction.