Effect of inert dust on the mortality of Sitophilus zeamais (Coleoptera: Curculionidae).

The maize weevil, Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), generally reaches pest status in stored grain. Chemical control is the most used method for population suppression, which can cause adverse impacts, thus creating a need for alternatives such as using inert powders. The present work aims to verify the effect of different concentrations of different types of inert powders on the mortality of S. zeamais in the laboratory. To this end, the experiments were carried out in a completely randomized design, with 13 treatments and four replications, ten adults per replication, where the effect of different inert powders (basalt powder, gypsum powder, and diatomaceous earth) was tested at concentrations of 0.025 g, 0.05 g, 0.1 g and 0.2 g/20 g of corn grains. Variance, normality, and homoscedasticity tests were applied in addition to controlling efficiency (CE%), median lethal time (TL50), and survival curves. All treatments caused mortality in S. zeamais, and all concentrations with diatomaceous earth were more efficient, with 100% mortality at 20 days, followed by the treatment of 0.2 g of gypsum powder/20 g of corn grains, with superior efficiency, to 95% in 20 days and 100% in 30 days. The results indicated that treatments with diatomaceous earth had the highest mortality rate and the best average survival time.

Are Pesticides Used to Control Thrips Harmonious with Soil-Dwelling Predatory Mite Cosmolaelaps sabelis (Mesostigmata: Laelapidae)?

Edaphic predatory mites could be introduced in pest management programs of pests that live, or spend part of their life cycle, in the soil. Some mesostigmatic mites have been widely used for the management of different species of thrips (Thysanoptera), especially in protected cultivation. The edaphic predator Cosmolaelaps sabelis (Mesostigmata: Laelapidae) was a model species in this study, being exposed to the most applied insecticides for the control of thrips in Brazil. After lethal, sublethal and transgenerational effects were evaluated. The pesticides acephate, acetamiprid + etofenprox, azadirachtin, spinetoram, formetanate hydrochloride, and imidacloprid were classified according to the IOBC/WPRS (International Organization for Biological Control-West Paleartic Regional Section) recommendation, considering the acute toxicity and the effects on adult females' reproduction, in the maternal and first generation. The pesticides acetamiprid + etofenprox and azadirachtin were classified as slightly harmful (Class 2), while spinetoram was classified as moderately harmful (Class 3). Acephate and formetanate hydrochloride were classified as harmful (Class 4). Only imidacloprid didn't cause negative effects on the females. Regarding effects on the first generation, acetamiprid + etofenprox, azadirachtin, and spinetoram caused reduction in the oviposition rates. Therefore, we suggest that complimentary bioassays should be done under semi-field and field conditions using the pesticides that were considered harmful in this study, to assess their effects on this predator in other environments prior to recommending not to use them in integrated programs to manage soil-based pests using chemical and biological tools.

Predicting Rice Stem Stink Bug Population Dynamics Based on GAMLSS Models.

The rice stem stink bug, Tibraca limbativentris Stål (Hemiptera: Pentatomidae), is one of the most harmful insects for Brazilian rice fields. Aiming to define the most appropriate time and place for pest management measures in commercial paddy fields, we adjusted regression models (Poisson, Zero Inflated Poisson, reparametrized Zero Inflated Poisson, Negative Binomial and Zero Inflated Negative Binomial) for modeling the population variation of T. limbativentris along the phenological cycle of the flooded rice cultivation. We hypothesize that the rice stem stink bug population's size is influenced by the rice cycle (time) and geographical positions within the crop. It was possible to predict the occurrence of the rice stem stink bug in the commercial flooded rice crop. The population of the rice stem stink bug increased significantly with the time or phenological evolution of rice. Our results indicated that the start of T. limbativentris monitoring should occur up to 45 d After Plant Emergence (DAE), from the regions along the edges of the rice paddies, which are the points of entry and higher concentration of the insect. In addition, 45 and 60 DAE were considered the crucial times for T. limbativentris control decision making in flooded rice paddies.