Backward Bifurcation and Optimal Control Analysis of a Trypanosoma brucei rhodesiense Model

In this paper, a mathematical model for the transmission dynamics of Trypanosoma brucei rhodesiense that incorporates three species—namely, human, animal and vector—is formulated and analyzed. Two controls representing awareness campaigns and insecticide use are investigated in order to minimize the number of infected hosts in the population and the cost of implementation. Qualitative analysis of the model showed that it exhibited backward bifurcation generated by awareness campaigns. From the optimal control analysis we observed that optimal awareness and insecticide use could lead to effective control of the disease even when they were implemented at low intensities. In addition, it was noted that insecticide control had a greater impact on minimizing the spread of the disease compared to awareness campaigns.

Efficacy of Insecticides Against Spodoptera frugiperda (Smith, 1797)

The Brazil’s economy is supported by agribusiness, however, the continuous cycle of food production and favorable climate contributes to the incidence of pest insects all year round. The fall armyworm Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) is considered the main insect in the corn crop, due to voracity of the caterpillars and occurrence throughout the crop cycle. Therefore, the chemical control has been demanded considerably, causing emergence of populations resistant to the different products, as well as implications in the environment. Thus, studies are needed to evaluate the efficiency of chemical insecticide control according to the susceptibility and the stages of biological development of the pest. The objective of this work was to evaluate the performance of isolated and combined insecticides for the control of S. frugiperda caterpillars under laboratory conditions. In the residual and direct contact bioassays, 8 treatments with 5 replications were used in a completely randomized design, performed with 2nd and 5th instar. The results showed that by residual contact after 72 hours, clofenapir + zeta-cypermethrin treatment had 100% efficacy in the mortality of both instars. When applied via direct contact 72 hours later, the combined treatments showed an efficiency above 80%. However, for an integrated pest management program, where it was recommended the association of different control tactics, the management of insecticides with clofenapir + zeta-cypermethrin was effective with 100% control efficiency in both instars.

Assessment of nocturnal insects in desert locust habitat after the application of insecticides against Desert Locust in Sub-Zoba Shieb, Eritrea

The study on the impact of insecticide nocturnal insects used to control desert locust was conducted at Shelshela, sub-region Shieb from November 2015 to February 2016. Its aim was to assess the impact of Desert Locust control insecticides spray on non-target arthropods. The experiment was carried out in RCBD using three treatments of fenitrothion 96% ULV, chlorpyrifos 45% ULV and control with three replications. It was replicated three times. Each plot had a size of 1 ha with a buffer zone among plots and blocks were 100 m. Data were recorded two times at pre-sprays and five times at post-sprays. During study period 4 insect families were observed and data were analyzed. These were Calliphoridae, Elateridae, Scarabidae, and Pselaphidae. In pre-spray, data did not show significant difference among treatments used. After 48 hrs of post-spray result showed significant difference among treatments. Both insecticides treated plots showed significantly lower population count than control plot. Between the treatments used fenitrothion treated plots generally showed more reduction in population count than chlorpyrifos. From the study it is observed that Elateridae can be used as bio-indicator during insecticide control of desert locust in the study areas.