Interaction between Short-Term Heat Pretreatment and Fipronil on 2 Instar Larvae of Diamondback Moth, Plutella Xylostella (Linn)

Demography and predatory potential of Orius strigicollis on eggs of Plutella xylostella at two temperatures

Background

The polyphagous predatory bug Orius strigicollis Poppius (Heteroptera: Anthocoridae) is an active predator used to control many insect pests of agricultural crops. Orius species are significantly affected by the type of food and temperature.

Method

A study of O. strigicollis feeding on Plutella xylostella L. (Lepidoptera: Plutellidae) eggs in climate chambers at 28 and 32 °C, 70 ± 5% relative humidity, 16:8 photoperiod, was conducted to determine the effects of different temperatures on the predation activity, biological characteristics and demographic parameters of O. strigicollis. Twosex-MS Charts were used to determine the age-stages and characteristics of this species.

Results

The results showed that the daily consumption of pre-adults on eggs of P. xylostella was highest at 28 °C, and at this temperature, there was a greater probability that O. strigicollis would survive to adulthood (42.5%) than at 32 °C (25.0%). It has also been found that at 28 °C there was a long oviposition period (9.38 days) and the greatest female fecundity (44.2 eggs/female) In addition to the highest life expectancy of O. strigicollis (16.96 days) at 28 °C, the intrinsic rate of increase (0.087 d-1) was also highest. According to our results, O. strigicollis has the potential to grow and develop on the eggs of P. xylostella at 28 °C and, therefore, could potentially be used as a biological control agent in integrated pest management (IPM) programs.

Cross-protection interactions in insect pests: Implications for pest management in a changing climate

Agricultural insect pests display an exceptional ability to adapt quickly to natural and anthropogenic stressors. Emerging evidence suggests that frequent and varied sources of stress play an important role in driving protective physiological responses; therefore, intensively managed agroecosystems combined with climatic shifts might be an ideal crucible for stress adaptation. Cross-protection, where responses to one stressor offers protection against another type of stressor, has been well documented in many insect species, yet the molecular and epigenetic underpinnings that drive overlapping protective responses in insect pests remain unclear. In this perspective, we discuss cross-protection mechanisms and provide an argument for its potential role in increasing tolerance to a wide range of natural and anthropogenic stressors in agricultural insect pests. By drawing from existing literature on single and multiple stressor studies, we outline the processes that facilitate cross-protective interactions, including epigenetic modifications, which are understudied in insect stress responses. Finally, we discuss the implications of cross-protection for insect pest management, focusing on the consequences of cross-protection between insecticides and elevated temperatures associated with climate change. Given the multiple ways that insect pests are intensively managed in agroecosystems, we suggest that examining the role of multiple stressors can be important in understanding the wide adaptability of agricultural insect pests. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Insecticidal activity of the extract, fractions, and pure steroidal saponins of Trillium govanianum Wall. ex D. Don for the control of diamondback moth (Plutella xylostella L.) and aphid (Aphis craccivora Koch)

BACKGROUND

Plutella xylostella L. is the major pest of crucifers globally, causing significant yield loss. Aphis craccivora Koch is the main sucking pest of legumes that transmit viral diseases, leading to economic yield reduction. To minimize loss due to pests, farmers/growers use synthetic insecticides frequently for their control, which led to insecticide resistance, detrimental to natural enemies of pest, environment, etc. Therefore, in this study, the insecticidal activity of plant extract, fractions, and pure steroidal saponins from Trillium govanianum was evaluated for their bio-efficacy against targeted pests.

RESULTS

Parent extract was found more effective (LC₅₀ = 1541.2 mg L^-1 ) against larvae of P. xylostella after 96 h than n-butanol, n-hexane, and ethyl acetate fractions (LC₅₀ = 3030, 3578 and 3878.1 mg L^-1 , respectively). For A. craccivora, ethyl acetate fraction (LC₅₀ = 2186.3 mg L^-1 ) was most effective after 96 h than n-hexane fraction (LC₅₀ = 2234.6 mg L^-1 ), n-butanol fraction (LC₅₀ = 2696.3 mg L^-1 ) and parent extract (LC₅₀ = 3709.1 mg L^-1 ). Among pure molecules, govanoside B was found more effective (76% mortality, LC₅₀ = 3279.5 mg L^-1 ) followed by borassoside E (74%, LC₅₀ = 3467.1 mg L^-1 ) against A. craccivora after 96 h.

CONCLUSION

Parent extract/fractions of T. govanianum showed promising efficacy against larvae of P. xylostella and A. craccivora. Further, field study is required for its bio-efficacy against targeted pests for validation and formulation development.

Fitness parameters of Plutella xylostella (L.) (Lepidoptera; Plutellidae) at four constant temperatures by using age-stage, two-sex life tables

Different temperature zones have significant impact on the population dynamics of Plutella xylostella. Effective management of P. xylostella requires the knowledge of temperature tolerance by different life stages. In the current study, fitness parameters of diamondback moth were reported by using age-stage, two-sex life table traits at four constant temperatures (15, 20, 25 and 30 °C). The life cycle of P. xylostella was significantly longer at 15 °C. The 20 °C level of temperature was found optimal for fecundity, gross reproductive rate (51.74 offspring) and net reproductive rate (44.35 offspring per individual). The adult pre-oviposition period was statistically at par at all four level of temperatures. However, the survival was maximum at 20 °C as compared to other three temperature ranges. Based on the current study, it was concluded that temperature has a great role in population build-up of P. xylostella and effective management tactics should be applied to prevent significant damage to cabbage and other cruciferous crops when the temperature in the field is near 20 °C.

Does Resistance to Buprofezin Improve Heat and Cold Tolerance of Laodelphax striatellus (Hemiptera: Delphacidae)?

There is ample evidence that insecticide resistance causes fitness costs and benefits in pests, while the impact of insecticide resistance on thermotolerance of pests is mostly unclear. The Laodelphax striatellus (Fallén), is an important rice insect pest, which has developed resistance to buprofezin in China. Here, we investigated differences in heat tolerance and cold tolerance among L. striatellus lines with variable buprofezin resistance. The lethal time for 50% of the individuals to die (LT50) at 40 °C increased with an increase in buprofezin resistance level, whereas both the survival rate under -22 °C and the supercooling point of planthoppers did not differ significantly between resistant and susceptible strains. The metabolic enzyme carboxylesterase was found to have an association with buprofezin resistance. Our research showed that buprofezin resistance was positively related with heat tolerance in L. striatellus, but it had no effect on cold tolerance. Insecticide resistance in L. striatellus may therefore have broader implications for the ecology of L. striatellus, and the management of buprofezin resistance in this pest may be challenging.

Larvicidal activity and structure activity relationship of cinnamoyl amides from Zanthoxylum armatum and their synthetic analogues against diamondback moth, Plutella xylostella

Cinnamoyl amides isolated from Zanthoxylum armatum (Rutaceae) and their synthetic analogues were tested for their insecticidal activity against the second instar larvae of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) to determine the promising structures with insecticidal activity. Most of the test compounds showed promising activity against larvae of P. xylostella. However, the activities of different compounds varied depending on the presence of different substituents at various positions of both the aromatic rings A and B. Among the tested compounds, 8, N-(3-bromo-4-methoxyphenethyl)cinnamamide showed best larvicidal activity with an LC50 = 62.13 mg/L followed by 6, N-(3׳-bromophenethyl)cinnamamide (LC50=128.49 mg/L) and 2 N-(4׳-methoxyphenylethyl)cinnamamide (LC50 = 225.65 mg/L).

Chemical composition and larvicidal activities of the Himalayan cedar, Cedrus deodara essential oil and its fractions against the diamondback moth, Plutella xylostella

Plants and plant-derived materials play an extremely important role in pest management programs. Essential oil from wood chips of Himalayan Cedar, Cedrus deodara (Roxburgh) Don (Pinales: Pinaceae), was obtained by hydrodistillation and fractionated to pentane and acetonitrile from which himachalenes and atlantones enriched fractions were isolated. A total of forty compounds were identified from these fractions using GC and GC-MS analyses. Essential oils and fractions were evaluated for insecticidal activities against second instars of the diamondback moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae), using a leaf dip method. All samples showed promising larvicidal activity against larvae of P. xylostella. The pentane fraction was the most toxic with a LC₅₀ value of 287 µg/ml. The himachalenes enriched fraction was more toxic (LC₅₀ = 362 µg/ml) than the atlantones enriched fraction (LC₅₀ = 365 µg/ml). LC₅₀ of crude oil was 425 µg/ml and acetonitrile fraction was LC₅₀ = 815 µg/ml. The major constituents, himachalenes and atlantones, likely accounted for the insecticidal action. Present bioassay results revealed the potential for essential oil and different constituents of C. deodara as botanical larvicides for their use in pest management.