Populations Of Sitophilus Zeamais Research Articles

Toxicity and sublethal effects of allyl isothiocyanate to Sitophilus zeamais on population development and walking behavior

Essential oils and their derivatives have been suggested as promising alternatives for the control of insect pests. However, the potential sublethal effects of these substances on insects can contribute to the development of resistance strategies that could compromise its control. This study aimed to evaluate the toxicity of allyl isothiocyanate (AITC) on adults of five populations of Sitophilus zeamais (Coleoptera: Curculionidae). The effects of sublethal doses of AITC on the locomotor behavior and development of the insect population were also evaluated. The AITC toxicity was determined by a bioassay for lethal concentrations, wherein the mortality curves were established using increasing concentrations of AITC ranging from 0.5 to 10.0 μL L−1. The locomotor behavior was evaluated by distance walked, walking velocity and resting time. In addition, the daily and cumulative emergencies for all populations were evaluated. The LC50 found indicated a uniform susceptibility among the populations studied, without any indication of resistance to the AITC. All populations of S. zeamais had their population growth rates affected by sublethal exposure to AITC, presenting delayed accumulated emergence and a reduction up to 80.9% in the daily emergence. Although differences have been observed in the pattern of walking of the populations, treatment with AITC did not influence their locomotor behavior. The results indicate a lower risk of resistance development in the short term, suggesting that AITC can be a potential alternative for the control of S. zeamais on stored products.

Ozone toxicity to Sitophilus zeamais (Coleoptera: Curculionidae) populations under selection pressure from ozone

Two populations of Sitophilus zeamais (Coleoptera: Curculionidae) were subjected to selection pressure with ozone (O3), and the possibility of acquiring resistance to O3 was investigated. The pattern of locomotion and the rate of respiration were evaluated following each selection cycle. Two source populations were used in the study: one was a mixture composed of 30 populations (MP), and the other was composed of the population that was the least susceptible to O3 among these 30 populations (LSP). The beetles from each source population experienced selection cycles with O3 using the lethal time for 80% (LT80) of the insect population from each generation. The O3 toxicity (50 ppm at a continuous flow rate of 2 L min−1) to each generation was calculated using time-response bioassays. The locomotor pattern (distance traveled, resting period, and walking speed) and the respiratory rate (CO2 production) were also evaluated. The S. zeamais populations that were subjected to successive cycles of selection with O3 did not acquire resistance to O3, and the pattern of locomotion and the rate of respiration did not change following the selection cycles with O3.

Evidências do efeito Moran na sincronia populacional: uma demonstração em microcosmo experimental

Three main causes to population synchrony are proposed: exogenous factors, dispersal and inter-specific interactions. This paper had as main goal to test the influence of the exogenous factors in the synchrony in spatially isolated (i.e., no dispersal) populations of Sitophilus zeamais (Mots.) (Coleoptera: Curculionidae), in microcosms with different environmental conditions (humidity, temperature and light intensity). Twelve populations of 20 individuals each, were randomly assigned between two treatment conditions: with or without light. Population size and environmental factors (temperature and relative humidity) were weekly assessed for seven months. Temporal trend in populations increase was eliminated adjusting autoregressive models. Population synchrony, detected by means of Pearson's and Spearman's correlation coefficients, was higher within than between treatments, although the populations kept without lamp were more synchronized than populations with lamp. Besides demonstrating the influence of environment on population fluctuations, these results suggest that metabolism and intra-specific interactions are important factors in population dynamic. Organisms exposed to unsuitable environmental conditions may have abnormal metabolic rates, which negatively influences the population grow. Thus, small populations are more likely to suffer from demographic stochasticity, decreasing the probability of the synchrony among populations. On the other hand, in more suitable environments, individuals are expected to have normal metabolic functions, and so, to achieve higher rates of population grow. In this case, the demographic stochasticity has smaller influence, leading populations without lamp to fluctuate synchronously.

Malathion resistance inSitophilus zeamais(mostch) in Zimbabwe

Abstract Varying levels of resistance were detected in populations of Sitophilus zeamais (Mostch) collected from small farmers’ stores in Zimbabwe. Some populations showed 4–6‐fold resistance levels to malathion compared to a susceptible laboratory strain.

The growth of single and mixed laboratory populations of Sitophilus zeamais Motschulsky and Sitotroga cerealella (Olivier) on stored maize

The growth of single and mixed laboratory populations of <i>Sitophilus zeamais</i> Motschulsky and <i>Sitotroga cerealella</i> (Olivier) on stored maize