Bioassay method for toxicity studies of insecticide formulations to Tuta absoluta (meyrick, 1917)

Abstract

Chemical control is the main method for controlling the tomato leafminer, Tuta absoluta (MEYRICK, 1917) (Lepidoptera: Gelechiidae). Reported techniques for the evaluation of insecticide toxicity to the tomato leafminer are not in agreement with field conditions and do not allow us to verify whether doses used in the field are efficient for control. Thus, the objective of this work was to develop a bioassay methodology to study the toxicity of insecticide formulations to T. absoluta that represent field conditions for fast-acting insecticides (neurotoxics and inhibitors of respiration) and slow-acting insecticides (Bacillus thuringiensis and insect growth regulators). The leaf-dip method was the most efficient method for toxicity studies of insecticides formulations to T. absoluta. We verified that bioassays with fast-acting insecticides should be performed with glass Petri dishes containing one tomato foliole from the 4 th leaf from the plant apex infested with 10 larvae of 3 rd instar and these bioassays can last 48 hours. Conversely, bioassays with slow-acting insecticides should be performed with two-liter transparent PET bottles containing the 4 th leaf from the plant apex, with their petioles immersed in a glass bottle containing 120 mL of water, and this leaf should be infested with 10 larvae of 2 nd instar and this bioassays can last seven days.Index terms: Susceptibility, tomato leafminer, chemical control, bioassay standardization, resistance survey. RESUMOO principal método utilizado no controle da traça-do-tomateiro Tuta absoluta (MEYRICK, 1917) (Lepidoptera: Gelechiidae) é a aplicação de inseticidas. As técnicas atuais de avaliação da toxicidade de inseticidas sobre essa praga não simulam a situação de campo e não possibilitam a verificação se as doses usadas no campo são eficientes no seu controle. Assim, neste trabalho, objetivouse desenvolver uma metodologia que represente as condições de campo para inseticidas de ação rápida (neurotóxicos e inibidores respiratórios) e de ação lenta (Bacillus thuringiensis e reguladores de crescimento. A metodologia mais eficiente para estudos de toxicidade de formulações comerciais a T. absoluta foi a imersão de folhas em calda inseticida. Para os bioensaios de inseticidas de ação rápida, sugere-se que estes sejam realizados em placas de Petri, contendo folíolos de tomate da 4ª folha a partir do ápice da planta, infestados com 10 larvas de 3º ínstar e eles podem durar 48 horas. Quanto aos bioensaios de toxicidade de inseticidas de ação lenta, sugere-se que sejam realizados em garrafas PET transparentes, de dois litros, contendo a 4ª folha de tomate a partir do ápice da planta infestada com 10 larvas de 2º ínstar e seu pecíolo inserido em vidro de 120 mL contendo água. Nesse caso, o bioensaio pode durar sete dias sem prejuízo na eficiência.Termos para indexação: Suscetibilidade, traça-do-tomateiro, controle químico, padronização de bioensaio, levantamento de resistência.

Insecticide toxicity and walking response of three pirate bug predators of the tomato leaf miner Tuta absoluta

“…tristicolor , A. constrictus and B. pallescens ) collected from tomato crops in Viçosa county (20°48′45″S, 42°56′15″W, 600 m a.s.l., and tropical climate), Minas Gerais, Brazil. Individuals of T. absoluta were established and maintained on tomato leaves in a laboratory that included four cages (45 × 45 × 45 cm) according to the life cycle stages of this species (egg, larva, pupa and adult), as described previously by Galdino et al () and Silva et al (). This population of T. absoluta exhibited low levels of resistance to different insecticides and moderate resistance (approximately 50‐fold) to the growth regulator teflubenzuron (Silva et al , ; Gontijo et al , ).…”

“…Because these adjuvants do not exhibit toxic effect to the insects based on preliminary bioassays, the control treatment was established by immersing the tomato leaves only in water. After drying, the leaves were placed in a Petri dish (90 × 20 mm) and 10 larvae (third instar) of the tomato leaf miner were placed in each Petri dish for a period of 48 h for mortality assessment (Galdino et al , ). The bioassays were completely randomized with five or six treatments (concentrations) and four replicates for each treatment.…”

Life history and life table parameters of the Tuta absoluta (Lepidoptera: Gelechiidae) on twelve commercial tomato cultivars under laboratory conditions

“…Currently, chemical control methods are used for T. absoluta control (Siqueira et al, 2001;Galdino et al, 2011). However, to control the pest several insecticide applications are needed in a single growing season that substantially increases production costs and leads to the development of insecticide resistant populations of the insect.…”

Toxicity of insecticides to Chrysodeixis includens and their direct and indirect effects on the predator Blaptostethus pallescens

“…These pest outbreaks can cause economic damage to crops if they are not controlled immediately (Lima et al 2014). In this situation, we must apply fast-acting insecticides of control (Galdino et al 2011;Silva et al 2011). In this context, we note that all insecticides tested in this study (except acephate) caused high toxicity to C. includens less than 48 h after exposure of larvae to insecticides.…”