Effects of temperature on baseline susceptibility and stability of insecticide resistance against Plutella xylostella (Lepidoptera: Plutellidae) in the absence of selection pressure

Abstract

Plutella xylostella L. (Lepidoptera: Plutellidae) is an important pest causing significant losses to vegetables worldwide. Insecticides resistance in P. xylostella is a serious issue for scientists since last 30 years. However, deltamethrin and Bt Cry1Ac are commonly used insecticides against P. xylostella but studies involving development of resistance in P. xylostella against these two insecticides at different temperatures are lacking. The current study was aimed to find out the toxicity of deltamethrin and Bt Cry1Ac, and resistance development in P. xylostella. Results showed that the positive correlation between the temperature and toxicities of deltamethrin and Bt Cry1Ac. The results indicated −0.051, −0.049, −0.047, and −0.046 folds of deltamethrin resistance at 15 °C, 20 °C, 25 °C, and 30 °C temperatures, respectively from 1st to 12th generations. The toxicity of Bt Cry1Ac after 24 h was 2.2 and 4.8 folds on 1st generation at 20 °C and 25 °C temperatures, respectively compared to the toxicity recorded at 15 °C (non-overlapping of 95% confidence limits). Based on the results of this study, it is concluded that the temperature has a positive correlation with the toxicity of deltamethrin and Bt Cry1Ac against the larvae of P. xylostella. This study suggests that deltamethrin and Bt Cry1Ac can be included in the management program of P. xylostella on many vegetable crops. The baseline susceptibility data might be helpful to understand the resistance mechanisms in P. xylostella.

Using a Two-Sex Life Table Tool to Calculate the Fitness of Orius strigicollis as a Predator of Pectinophora gossypiella

“…An early oviposition (egg laying) period under the selection pressures of a specific diet, may result in an increased metabolic rate, as reported in previous investigations [10,21,61,91]. The highest lifetime fecundity (overall oviposition per female) was observed with 10 eggs of P. gossypiella in our study (Table 3), which showed the egg laying potential of O. strigicollis with specific diets, in correlation to previous studies [14,17,18,30,33,49,54,81,92].…”

“…This showed that O. strigicollis had greater reproduction potentials on the higher prey densities (10 and 15 eggs of P. gossypiella), enabling it to complete its development faster. Previous studies on the dipteran and lepidopteran insects have shown the same trends of results [11,61,76], that the reproduction rate and expectancy of the individuals was affected by the availability of the prey pressure and environmental factors, e.g., temperature.…”

“…The consumed or damaged eggs of the P. gossypiella were counted and replaced with fresh eggs daily. The stems with eggs laid by the O. strigicollis female were kept in plastic containers and were placed in a chamber as described above, to check their biological or fitness parameters after each treatment following previously described methods [30,[61][62][63]. These parameters were greatly influenced by the selection pressures on the predators, to continue the next generation or suppress the pest population dynamics successfully [10][11][12][13]59,64].…”

Determination of fitness traits of Orius strigicollis Poppius (Hemiptera: Anthocoridae) on Pectinophora gossypiella (Lepidoptera: Gelechiidae) using two-sex life table analysis

“…Culture was maintained on P. gossypiella eggs in the laboratory according to a previously described method ( Zhou et al, 2006 ). The population of O. strigicollis was maintained on the P. gossypiella eggs at three temperatures (24, 28 and 32 °C) to acclimatize for at least two generations before the experiments ( Jaleel et al, 2020 ). The reason for the selection of three temperatures (24, 28 and 32 °C) was that many Orius spp.…”

“…The biology of predators and parasitoids is greatly influenced by environmental factors ( Jaleel et al, 2019 ; Ali et al, 2020 ). Temperature is one of the most important abiotic environmental factors ( Saleh & Sengonca, 2003 ; Jaleel et al, 2020 ). The development time of insect pests is greatly affected by variable temperature ( Barbosa et al, 2019 ).…”