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The soybean stalk weevil, Sternechus subsignatus Boheman 1836 (Coleoptera: Curculionidae), is a very serious soybean pest in the Neotropical region. Both adults and larvae feed on soybean, causing significant yield losses. Adult survival was evaluated during three soybean growing seasons under controlled environmental conditions. A survival analysis was performed using a parametric survival fit approach in order to generate survival curves and obtain information that could help optimize integrated management strategies for this weevil pest. Sex of the weevils, crop season, fortnight in which weevils emerged, and their interaction were studied regarding their effect on adult survival. The results showed that females lived longer than males, but both genders were actually long-lived, reaching 224 and 176 d, respectively. Mean lifetime (l50) was 121.88±4.56 d for females and 89.58±2.72 d for males. Although variations were observed in adult longevities among emergence fortnights and soybean seasons, only in December and January fortnights of the 2007–2008 season and December fortnights of 2009–2010 did the statistically longest and shortest longevities occur, respectively. Survivorship data (lx) of adult females and males were fitted to the Weibull frequency distribution model. The survival curve was type I for both sexes, which indicated that mortality corresponded mostly to old individuals.
In this work, we report the effect of rainfall on Sternechus subsignatus Boheman, 1836, adult emergence after winter dormancy. This weevil is a univoltine soybean pest found in northwestern Argentina, a subtropical region with dry winters and rainy summers. Before harvest, fully grown larvae burrow into the soil where they overwinter. In the spring, they emerge as adults and recolonize the crop during its planting and early vegetative stages. Our study examines the seasonal timing of adult emergence with the aim of improving chemical control strategies and avoiding unnecessary pesticide applications. To do so, we developed a regression model to predict adult emergence onset as a function of cumulated rainfall after 1st November. The regression with the highest coefficient of determination between cumulated rainfall and adult emergence onset was Emergence onset (Julian day) = -7.98 Ln(cumulative rainfall) + 65.7. The negative relationship showed that adults emerged earlier in wet years than in dry years. Also it was observed that adults emerged from late November to mid-March, in pulses following periods of rainfall. Males were more abundant than females at first, but then the reverse was true toward the end of the period. In most cases, there was a suggestion of relationship (though not significantly) between peaks of adult emergence with peaks of rainfall 15 d before adult emergence. These results reveal that rainfall has a significant impact on the beginning and dynamics of adult emergence from the soil.
The locust species Schistocerca cancellata Serville, endemic to South America, is known for its ability to form dense swarms, which reach the status of agricultural pest for several crops in southern South America. This article aimed to gather more accurate information about the history, biology, ecology, and control of S. cancellata, because of the 2021 invasions, which threatened to invade the Brazilian territory. During outbreak periods, swarms consume any available vegetation in the occurrence areas of Argentina, Brazil, Paraguay, Uruguay, Chile, and Bolivia. These invasions have been well documented in history, since they left deep marks wherever they went, especially in Argentina, which to this day represents the country that most accounted for agricultural losses from outbreaks. economy’s main current means of control are based on pesticides, whose chemical composition induces a series of damages to health, the environment, and consequently the ecosystem. Knowing about the biological processes of this locust is an important factor in understanding how swarms form, as well as controlling them. The intergovernmental coalition shows positive results in monitoring and controlling the swarms, which, even demonstrating stability, remain under constant surveillance by competent bodies.
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