Stimulatory sublethal response of a generalist predator to permethrin: hormesis, hormoligosis, or homeostatic regulation?

The assessment of pesticide effects in arthropods historically have relied heavily on acute lethal effects. Although the sublethal responses to such compounds are sometimes neglected, stimulatory effects associated with low doses of compounds toxic at higher doses, such as pesticides, have been widely reported in recent years and recognized as a general toxicological phenomenon. Evidence of such stimulatory response has also been reported among mites and a few insect pest-species exposed to pesticides and recognized as a one of the potential causes underlying pest resurgence and secondary pest outbreaks. However, fitness parameters and its implications were seldom considered in these studies and natural enemies are not usually target of attention. Here, we reported the stimulatory effect of sublethal doses (ranging from 0.02 to 172.00 ppb in addition to the control) of the pyrethroid permethrin topically applied to third instar nymphs of the spined soldier bug, Podisus distinctus (Stål) (Heteroptera: Pentatomidae). The parameters estimated from the fertility tables of insects exposed to the increasing doses of insecticide indicated a slight increase in the mean survival time for doses > or = 0.20 ppb and a peak in the net reproductive rate at 1.72 ppb. This trend is coincident and correlated with the intrinsic rate of population growth (n = 18, r = 0.78, P = 0.0001), which also shows a peak at 1.72 ppb, leading to higher reproductive values of insects exposed to this dose. The phenomenon is consistent with insecticide-induced hormesis, for which the potential implications are discussed.

Toxicidade de óleo de nim para pupas e adultos de chrysoperla externa (hagen) (neuroptera: chrysopidae)

ABSTRACT The objective of this work was to evaluate the effects of Nim-I-Go on pupae and adults of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae). The neem-based insecticide Nim-I-Go was used in the following concentrations (%) in the pupae trial: 0.5; 1.0; 2.0 and 5.0; equivalent to (in mg of azadirachtin/L of water) 5 mg/L, 10 mg/L, 20 mg/L and 50 mg/L, respectively. In the larvae trial the following concentrations were used: 0.25; 0.5; 0.75; 1.0 and 2.0; equivalent to (in mg of azadirachtin/L) 2.5 mg/L, 5.0 mg/L, 7.5 mg/L, 10 mg/L and 20 mg/L, respectively. Chlorpyrifos was used as a negative control (0.48 g a.i./L) in both trials, and water as a positive control. The bioassays were carried out at 25 ± 2o C, RH of 70 ± 10%, and 12-h of photophase. The sprayings were carried out using a Potters tower, ensuring the application of 1.5 ± 0.5 mg/cm2. Survival of pupae and adults, and the effects of the insecticides on the reproductive capacity of this predator were evaluated. The total toxic effect (E) of the insecticides was calculated according to the standard methodology established by IOBC. Nim-I-Go was harmless to pupae and adults of C. externa. Chlorpyrifos was harmful to this natural enemy.

RESUMO O objetivo do presente trabalho foi avaliar os efeitos do Nim-I-Go® sobre pupas e adultos de Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae). As concentrações (%) do Nim-I-Go® utilizadas no experimento com pupas foram as seguintes: 0,5; 1,0; 2,0 e 5,0; correspondendo a (mg de azadirachtina/L de água) 5 mg/L, 10 mg/L, 20 mg/L e 50 mg/L, respectivamente. No experimento com adultos foram utilizadas as seguintes concentrações: 0,25; 0,5; 0,75; 1,0 e 2,0; correspondendo a (mg de azadirachtina/L) 2,5 mg/L, 5,0 mg/L, 7,5 mg/L, 10 mg/L e 20 mg/L, respectivamente. Clorpirifós foi utilizado como testemunha negativa (0,48 g i.a./L) nos dois experimentos e água como testemunha positiva. Os bioensaios foram conduzidos a 25 ± 2 o C, UR de 70 ± 10% e fotofase de 12 horas. As pulverizações foram realizadas por meio de torre de Potter com aplicação de 1,5 ± 0,5 mg de calda química/cm2. Avaliaram-se a viabilidade dos ovos, a sobrevivência de pupas e adultos e o efeito dos inseticidas sobre a capacidade reprodutiva dos indivíduos. A toxicidade foi calculada em função do efeito total (E), conforme metodologia padrão estabelecida pela IOBC. Nim-I-Go® nas diversas concentrações foi inócuo a pupas e adultos do predador. Clorpirifós foi nocivo para pupas e adultos de C. externa.

Efeitos de inseticidas botânico e sintéticos sobre ovos e larvas de cycloneda sanguinea (linnaeus) (coleoptera: coccinellidae) em condições de laboratório

ABSTRACT The objective of this work was to evaluate the effects of azadirachtin and some synthetic insecticides used in the cotton crops on eggs and firstand fourth-instar larvae of Cycloneda sanguinea (Linnaeus). The neem-based insecticide Nim-I-Go was used in the following concentrations: 1% (10 mg of azadirachtin/L), 5% (50 mg of azadirachtin/L) and 10% (100 mg of azadirachtin/L). The synthetic insecticides teflubenzuron (Nomolt 150 SC) (0.15 g a.i./ L), lambdacyhalothrin (Karate Zeon 250 CS (0.08 g a.i./L) and chlorpyrifos (Vexter 480 CE) (1.6 g a.i./L) also were used in this study. Distilled water was used as control. A fully randomized experimental design was used, with seven treatments and six replicates, each one formed of three eggs or larvae of C. sanguinea. A manual sprayer was used to spew the solutions. The bioassays were kept in a room at 25±2oC, RH of 70±10% and 12h photophase. The insects were fed with Schizaphis graminum (Rondani). Lambdacyhalothrin and chlorpyrifos were harmful to all stages of C. sanguinea. Azadirachtin at 50 and 100 mg;L was toxic to fourth-instar larvae of C. sanguinea. Based in its low toxicity, azadirachtin 10 mg/L and teflubenzuron present favorable characteristics for use in the integrated pest management where C. sanguinea is an important factor of natural mortality of pests.

RESUMO Este trabalho objetivou avaliar os efeitos do azadirachtina e de alguns inseticidas sintéticos utilizados na cultura do algodoeiro sobre ovos e larvas de primeiro e quarto instares do predador Cycloneda sanguinea (Linnaeus). Nim-I-Go® (azadirachtina) foi utilizado nas concentrações de 1%, 5% e 10%, correspondendo a 10 mg/L, 50 mg/L e 100 mg/L de azadirachtina, respectivamente. Os inseticidas utilizados foram teflubenzurom (Nomolt 150 SC) (0,15 g i.a./L), lambdacialotrina (Karate Zeon 250 CS) (0,08 g i.a./L) e clorpirifós (Vexter 480 CE) (1,6 g i.a./L). O tratamento testemunha foi composto somente por água destilada. Utilizaram-se sete tratamentos com seis repetições, sendo cada parcela formada por três ovos ou larvas de C. sanguinea, sendo as aplicações realizadas com um pulverizador manual. Os bioensaios foram mantidos a 25 ± 2o C, UR de 70 ± 10% e fotofase de 12h. Os insetos foram alimentados ad libitum com o pulgão-verde-do-sorgo Schizaphis graminum (Rondani). Todos o compostos avaliados reduziram a viabilidade de ovos. Lambdacialotrina e clorpirifós foram altamente tóxicos para larvas de 1 o e 4o instar de C. sanguinea. Azadirachtina a 50 e 100 mg/L foi tóxico para larvas de quarto instar de C. sanguinea. Em função da baixa toxicidade apresentada, azadirachtina 10 mg/L e teflubenzuron apresentam as características mais favoráveis para uso em associação com C. sanguinea, para o controle de pragas na cultura algodoeira, dentre os compostos testados.