Abstract
Exposure of Helicoverpa armigera to sublethal concentrations of insecticides can cause physiological deficiencies manifested by reduced longevity, development, fertility and fecundity. Research on the sub-lethal effects, to identify the non-lethal negative impacts of insecticides on pests can provide practical information for integrated management. The objective of this study was to determine the lethal concentrations and sublethal effects of insecticides on larval development and reproduction of H. armigera. The insecticides were diluted in water and applied via immersion of soybean leaf discs directly in the solution for three second, subsequently provided to the larvae maintained under controlled conditions for a period of 48 h. For surviving larvae, artificial diet was provided with daily evaluation until pupation. The pupae obtained were weighed after 24 h and transferred to Petri dishes, covered with filter paper until the adult phase, to evaluate longevity and pupal viability. For the assessments related to oviposition, couples were separated in polyvinyl chloride (PVC) cages and fed with 10% honey solution; the counting of eggs was done every two days, until the end of the oviposition period. All of the insecticides tested presented lethal and sublethal effects on the parameters weight, mortality and pupal viability and reduced oviposition and can be used in pest management, representing an alternative in the product rotation for the control of the third instar of H. armigera. Key words: Management, chemical control, lethal concentration.
Highlights
Brazil is one of the largest global producers of grains, with production of 206.33 million tons in the 2014/2015 crop (Conab, 2015)
For the assessments related to oviposition, couples were separated in polyvinyl chloride (PVC) cages and fed with 10% honey solution; the counting of eggs was done every two days, until the end of the oviposition period
For LC50, the best result was obtained for the spinosad treatment that resulted in 36.25% mortality followed by chlorantraniliprole with 25% (Table 3)
Summary
Brazil is one of the largest global producers of grains, with production of 206.33 million tons in the 2014/2015 crop (Conab, 2015). The Brazilian grain production systems are characterized by being intensive, while cultural practices are extensive in relation to planted areas These facts, coupled with inadequate farming practices, characterized by the successive planting of host plant species in contiguous areas and inappropriate handling of pesticides, have made agricultural ecosystems susceptible to attack by insect pests, due to the constant availability of food, shelter and breeding sites (Embrapa, 2013). The H. armigera caterpillar is a major pest of cultivated plants, having as hosts more than 181 plant species belonging to 45 families (Rajapakse and Walter, 2007) It feeds on leaves and stems, but preferably shoots, inflorescences, fruits and pods, being able to adapt to various cropping systems. In Bahia, the costs of infestation of the pest were estimated at about US $ 2 billion in crops such as soybeans, corn and cotton due to the increase in the number of applications of insecticides and reduced productivity (Adab, 2013)
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