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

Effect of temperature on the life cycle of Harmonia axyridis (Pallas), and its predation rate on the Spodoptera litura (Fabricius) eggs

Biological control is one of the strategies of pest control which is determined by the biological fitness and metabolic rates of the predator species used. Temperature and resource are important factors which influence the role of insects as biocontrol agents. Harmonia axyridis is a cosmopolitan and non-specific polyphagous predator. It can survive ecologically diverse environments and exploit multiple preys. This study investigated the effects of temperature on the population parameters of H. axyridis and its predation on the eggs of prey Spodoptera litura. For this purpose, an age-stage, two-sex life table of the predator was constructed at four constant temperatures, i.e. 15, 20, 25 and 30 °C, under laboratory settings of: 70 ± 5% RH, and 16:8 h (L: D) photoperiod. A computer simulation was then used to project the population and predation responses with respect to temperatures tested. We found that the development of larvae and adult (male/female) stages of H. axyridis decreased with colder temperatures (i.e., 15 and 20 °C) but increased with warmer temperatures (25 and 30 °C). The intrinsic rate of increase (r) and mean generation time (T) were 0.0662 d^-1 and 79.84 d at 15 °C, 0.0843 d^-1 and 64.90 d at 20 °C, 0.1067 d^-1 and 48.89 d at 25 °C, and 0.1378 d^-1 and 35.55 d at 30 °C, respectively. The mean duration of the total pre-adult stage was 44.26, 32.91, 20.63, and 15.39 d at 15, 20, 25, and 30 °C, respectively. At 30 °C. the finite rate of increase (1.1477 d^-1) was the highest and the mean generation time (35.55 d) was the shortest. The net predation rate (C₀) was 7935.54, 10,466.28, 10,139.38, and 7126.36 eggs at 15, 20, 25, and 30 °C, respectively. Population and predation projections were proportional to temperature. These findings are important for modelling the population responses of H. axyridis to climate change and tailoring integrated pest management strategies to altered climates.

Resistance to Spinetoram Affects Host Adaptability of Frankliniella occidentalis (Thysanoptera: Thripidae) Based on Detoxifying Enzyme Activities and an Age-Stage-Two-Sex Life Table

The western flower thrip (WFT) Frankliniella occidentalis (Pergande) is a serious agricultural pest with a wide host range which has developed resistance to several groups of insecticides. In this study, the effect of insecticide resistance on WFT host adaptability was explored by examining changes in detoxification enzyme activities and thrip development, and reproduction on preferred and less preferred host plants, eggplant Solanum melongena L. and broad bean Vicia faba L., respectively. Thrips were screened with spinetoram on kidney bean for six generations. Activities of glutathione S-transferase (GST), mixed function oxidases (MFOs), and cytochrome P450 enzyme (P450) in a resistant strain (RS) reared on broad bean were significantly higher than those in a sensitive strain (SS), and only carboxylesterase (CarE) increased in the RS when reared on eggplant, compared with the SS. Activities of the four detoxification enzymes in the RS reared on broad bean were significantly higher than in those reared-on eggplant. On broad bean, RS adult longevity was lower and developmental duration of offspring was shorter than those of the SS, but fecundity increased. On eggplant, RS fecundity was lower and developmental duration of offspring was shorter than those of the SS. In addition, fecundity was higher and developmental duration was longer in the RS reared on broad bean than in those reared-on eggplant. The results indicated that spinetoram resistance could change WFT host preference and that those changes might be associated with detoxification enzyme activities. Thus, it was hypothesized that adaptability of the RS to the less preferred host broad bean increased, whereas adaptability to the preferred host eggplant decreased.

Demography and Fitness of Anastatus japonicus Reared from Antheraea pernyi as a Biological Control Agent of Caligula japonica

Japanese giant silkworm (JGS), Caligula japonica Moore, is an emerging defoliator pest of forest and fruit trees in East Asia, causing severe economic losses. To develop a cost-effective biological control program against JGS, we used eggs of the Chinese oak silkworm (COS) Antheraea pernyi Guérin-Méneville as an alternative host to rear the most dominant JGS egg parasitoid Anastatus japonicus Ashmead. We compared the demographic parameters and total parasitism (killing) rates of A. japonicus parasitizing JGS and COS eggs using an age-stage, two-sex life table method. The results showed that A. japonicus performed differently on these two different hosts. Anastatus japonicus reared from COS eggs had a higher fecundity (369.7 eggs per female) and a longer oviposition period (35.9 days) on the COS than JGS eggs (180.9 eggs; 24.0 days). Consequently, A. japonicus parasitizing COS eggs had a higher intrinsic rate of increase (r = 0.1466 d−1), finite rate of increase (λ = 1.1579 d−1) and net reproductive rate (R0 = 284.9 offspring) than those parasitizing JGS eggs (r = 0.1419 d−1, λ = 1.1525 d−1, R0 = 150.0 offspring). The total net parasitism rate (the number of parasitized hosts in which the parasitoids successfully developed) of A. japonicus parasitizing COS eggs was 284.9, significantly higher than that of A. japonicus parasitizing JGS eggs (150.0), while the net non-effective parasitism rate (the number of parasitized hosts in which the parasitoids failed to develop) of the former (0.0) was significantly lower than that of the latter (9.6). These results suggest that A. japonicus can be efficiently reared on the alternative (or factitious) COS eggs, and the reared parasitoids have a high biological control potential against the target JGS.

Compatibility of six reduced-risk insecticides with Orius strigicollis (Heteroptera: Anthocoridae) predators for controlling Thrips hawaiiensis (Thysanoptera: Thripidae) pests

Contact toxicity assessments of six reduced risk insecticides were carried out to compare their selectivity and sensitivity toward the minute pirate bug Orius strigicollis and its prey Thrips hawaiiensis. Additionally, and their potential exposure risk were evaluated for O. strigicollis. The LR₅₀ value of acetamiprid, emamectin benzoate, cyetpyrafen, and indoxacarb to T. hawaiiensis were 0.126, 2.093, 7.486, and 2.264 g a.i. ha^-1, respectively, far less than the maximum field recommended rate (MFRR) for each. These four insecticides showed higher selectivity for predator and prey with selectivity ratio values of 37.3, 14.8, 22.1, and 119.3, respectively. However, the LR₅₀ value of acetamiprid and emamectin benzoate were lower than MFRR, and unacceptable (approximately unacceptable for emamectin benzoate) risk to O. strigicollis in in-field, and the opposite results were shown in cyetpyrafen and indoxacarb. Although T. hawaiiensis was more sensitive to abamectin than O. strigicollis, the insecticide had poor selectivity for both test insects. The LR₅₀ value of spirotetramat was more than 3 fold MFRR for T. hawaiiensis and O. strigicollis, showing extremely low contact toxicity and selectivity. In general, acetamiprid, emamectin benzoate, cyetpyrafen, and indoxacarb showed high bioactivity against T. hawaiiensis, but only cyetpyrafen and indoxacarb could be well compatible with O. strigicollis, the combination of two insecticides with O. strigicollis indicated a potential strategy for the efficient and safe control of T. hawaiiensis.

Temperature-Dependent Functional Response of Harmonia axyridis (Coleoptera: Coccinellidae) on the Eggs of Spodoptera litura (Lepidoptera: Noctuidae) in Laboratory

Simple Summary

Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is a notorious and polyphagous pest of several economically important agricultural crops. It is worldwide in distribution and primarily managed through typical dependence on insecticides, which resulted in health and the environmental challenges and selected for resistance development in S. litura field populations. Resistance caused chemical control failures and S. litura outbreaks around the world. This necessitated development of eco-friendly alternative approaches such as biological control. With this view, current study investigated the functional response of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) at various growth stages (i.e., 1st, 2nd, 3rd and 4th instars, and male and female stages) and temperatures (i.e., 15, 20, 25, 30 and 35 °C) against S. litura eggs to enable the recognition of efficient biocontrol stages that could be utilized to suppress S. litura populations. In our findings, egg consumption depended on the growth stage of the predator as well as temperature. All stages consumed S. litura eggs, but more promising stages with active egg consumption were the 4th instar and adults (male and female) typically at higher temperatures (25–35 °C). We conclude that these stages may be exploited to suppress S. litura populations in fields and greenhouses.

Abstract

Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is a major pest of several economically important crops with worldwide distribution. Use of insecticides is the principal strategy for its management, which has subsequently led to insecticide resistance and control failures. Functional response of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) at larval and adult stages was evaluated in this study, using S. litura eggs as the prey at various temperatures varying between 15 and 35 °C. Based on logistic model findings, linear parameters of various predatory stages of H. axyridis at various temperatures were significantly negative, which indicate a type II functional response. The theoretical maximum number (T/T_h) of eggs consumed increased with increasing temperature across all predatory stages. According to the random predator equation, the coefficients of attack rate increased and that of handling time decreased as the temperature increased. The 4th instar and adult stages were superior candidates for biocontrol of the target prey, typically at higher temperatures. The maximum attack rate (0.546 ± 0.058 h⁻¹) and lowest handling time (0.189 ± 0.004 h) were exhibited by the females at 30 and 35 °C, respectively, whereas these parameters were inferior for early instars. These findings clearly depict that the 4th instar and adult predators are efficient egg consumers and can serve as potential suppressors of S. litura field populations. The limitations of the predictions formulated by functional response trials are also discussed.

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

Background

Pink bollworm (Pectinophora gossypiella) is a destructive insect pest of cotton crops in China and globally, which is actively predated on by Orius strigicollis. Studies on the fitness or survival of O. strigicollis fed on P. gossypiella at different temperatures have not been reported. The fitness of O. strigicollis may be well explained using two-sex life table parameters. Thus, the present study provides important insights for the effective biocontrol of P. gossypiella.

Methodology

Considering the importance of fitness parameters and biocontrol, the present study explores the feeding potential and age-stage, two-sex life table traits of O. strigicollis on P. gossypiella eggs at different temperatures (24, 28 and 32 °C) in the laboratory.

Results

The intrinsic rate of increase (r) was higher at 28 °C (0.14 d⁻¹) than at 24 °C (0.0052 d⁻¹) and 32 °C (0.12 d⁻¹). Similarly, the net reproductive rate (R₀) was higher at 28 °C (17.63 offspring) than at 24 °C (1.13 offspring) and 32 °C (10.23 offspring). This concluded that the maximum feeding potential and growth capacity of O. strigicollis could be attained at 28 °C when fed on P. gossypiella eggs. O. strigicollis adults preferred to feed on P. gossypiella eggs compared with first instar larvae. Based on these results, the present study suggests that O. strigicollis represents a promising biological control agent against P. gossypiella eggs in cotton fields.

Lethal and Sublethal Effects of Chlorpyrifos on Biological Traits and Feeding of the Aphidophagous Predator Harmonia axyridis

Except of pest control, insecticides have shown adverse effects on natural enemies as well. Thus, risk assessment of pesticides for biological control agents is critical for effective use in integrated pest management (IPM) schemes. In the present study, the lethal and sublethal effects of chlorpyrifos, a commonly used insecticide that may negatively affect biological control agents, were evaluated on a non-target predator, the Asian ladybeetle Harmonia axyridis. Previous studies have reported on lethal concentrations, but the effects of sublethal concentrations remain unclear. Lethal and sublethal concentrations of chlorpyrifos were applied to third instar larvae of H. axyridis, and different growth and developmental parameters were measured. Treatment with LC10 (4.62 mg a.i. L-1) significantly shortened the developmental period of third instar larvae, whereas it significantly prolonged those of fourth instar larvae and pupa. Treatment with LC30 (9.59 mg a.i. L-1) significantly increased the larval and pupal developmental period compared with that of the control, whereas feeding potential, female fecundity, and adult longevity significantly decreased after LC10 and LC30 treatment. The pre-oviposition period significantly increased compared with that of the control. Population growth parameters, the finite (λ) and intrinsic rate of increase (r) and the net reproductive rate (R0), decreased following exposure to sublethal concentrations of chlorpyrifos. According to the results, the use of chlorpyrifos in IPM schemes requires further research because even sublethal concentrations of this insecticide were harmful to H. axyridis population growth.