Finite Rate Of Increase Research Articles

Two-Sex Life Table Analysis of Phenacoccus solenopsis (Hemiptera: Pseudococcidae) on Lettuce, Parsley, and Rocket

Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), commonly known as the cotton mealybug, is a polyphagous pest causes significant economic losses worldwide. This study aimed to determine two-sex life table analysis of P. solenopsis on lettuce (Lactuca sativa), parsley (Petroselinum crispum), and rocket (Eruca sativa). Experiments were conducted under controlled conditions 26°C, 65 ± 10% relative humidity, and a 16:8 light-dark cycle. The results indicated that lettuce was more suitable for P. solenopsis development comparted to parsley and rocket. Total fecundity of P. solenopsis was recorded as 221.45, 158.00, and 121.64, on lettuce, parsley, and rocket respectively. In addition, ovipositon period of P. solenopsis was 14.00, 9.73, and 8.45 days on lettuce, parsley, and rocket respectively. The highest values of net reproductive rate (R0), intrinsic rate of increase (r), and finite rate of increase (λ) were obtained as 97.44 offspring female-1, 0.14 day-1, 1.16 day-1, respectively from lettuce in this present research. The results showed that lettuce was the better host plant for P. soleneopsis than parsley and rocket. However, further studies should be done about host plant pest interactions to provide successful control measures against P. solenopsis.

Sublethal effects of nanoformulated Mentha pulegium L. essential oil on the biological and population growth parameters of the greenhouse whitefly, Trialeurodes vaporariorum, (Hemiptera: Aleyrodidae)

We evaluated the toxicity and sublethal effects of essential oil (Mentha pulegium L.) and its nanoformulation against greenhouse whitefly, Trialeurodes vaporariorum, which is one of the most destructive pests of a wide range of crops. The essential oil was extracted from the plant by steam distillation using a Clevenger apparatus, and 14 chemical components of M. pulegium were identified using gas chromatography-mass spectrometry. The results illustrated that monoterpenoids were main characterized components including pulegone (%66), menthofren (%10.54), 1, 8 Cineole (%8.36), betapenin (%3.49) and limonene (%2.01). The nanoformulation was characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), revealing that the particles were spherical in shape with an average size of 156.40 nm. The leaf dipping was used for the bioassays. The obtained LC50 and LC25 values of treatments indicated that the nanoformulation of essential oil (LC50: 2418.96 and LC25: 1724. 25 ppm) was more toxic than the pure of M. pulegium oil (LC50: 3223.083 and LC25: 779.439 ppm ppm) against greenhouse whitefly adults after 24 h. The life table data were analyzed based on the age-stage, two-sex life table theory using computer program of TWOSEX–MSChart. Also, the sublethal concentration (LC25) of its nanoformulation led to delaying in preadult stage and decreased the adult longevity, and fecundity compared to treatments. Moreover, the sublethal concentration of either M. pulegium oil or its nanoformulation affected the population growth parameters of T.vaporariorum compared to the control. However, the net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), of adults who exposed to the nanoformulation was lower than the pure form of M. pulegium. The overall results demonstrated that the nanoformulation of M. pulegium has the most lethal and sublethal effects on greenhouse whitefly compared with the pure form of essential oil which can be consider in integrated pest management program (IPM) of this pest.

Demographic parameters of Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) reared on Drosophila suzukii (Diptera: Drosophilidae), Ceratitis capitata (Diptera: Tephritidae), and Anastrepha fraterculus (Diptera: Tephritidae) puparia.

Pachycrepoideus vindemiae (Rondani) is a solitary generalist pupal ectoparasitoid that parasitizes dipterans of various families and genera. This study aimed to evaluate Anastrepha fraterculus (Wiedemann), Ceratitis capitata (Wiedemann), and Drosophila suzukii (Matsumura) to determine the best host for the development and mass production of parasitoid P. vindemiae in the laboratory. The experiments were performed in air-conditioned rooms at a temperature of 25 ± 2 °C, relative humidity of 70% ± 10%, and photophase of 12h. Moreover, 24-h-old pupae of A. fraterculus, C. capitata, and D. suzukii were provided daily to 25 pairs of the parasitoid. The following parameters were determined: percentage of parasitism, percentage of emergence, hind tibia size, sex ratio, and longevity. A fertility life table was established using biological data. Notably, P. vindemiae parasitized the pupae of all 3 hosts but did not affect the sex ratio of the offspring. Parental parasitoids from the pupae of A. fraterculus and C. capitata lived longer than those from the pupae of D. suzukii. However, for all other parameters, parasitoids from D. suzukii showed better performance than those from other hosts, with shorter intervals between generations (T) and a higher net reproduction rate (Ro), intrinsic rate of increase (rm), and finite rate of increase (λ).

The Adaptability of Beet Webworm (Loxostege sticticalis) to Soybeans and Other Different Host Plants

The beet webworm Loxostege sticticalis has caused significant economic losses to the production of agriculture and animal husbandry in China. Preference testing of larva feeding and adult oviposition and flight capability tests were carried out on five host plants: soybean, pigweed, pea, broad bean, and alfalfa. An experimental population life table and population growth trends over the subsequent 200 days were constructed. The test results show that the larvae showed no significant preference among different plants. However, adults lay more eggs on soybeans. The pests failed to complete a generation when fed on broad beans and alfalfas. When fed on pigweed, they showed the shortest larvae development period, the heaviest pupal weight, the longest adult longevity, and the largest egg-laying amount. The net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), and simulated population growth trend of the pests fed on pigweed show the highest values, and those fed on peas showed the lowest values. The total flight distance and flight time of adults fed on pigweed and soybeans were significantly greater compared to those fed on peas. In summary, beet webworms fed on pigweed showed the fastest development and reproduction, the largest population, and the strongest flight capability.

Comparative demography of two wild cladoceran species, Alona quadrangularis and Scapholeberis mucronata, collected in western Washington state and reared under laboratory conditions

AbstractPopulations of two cladoceran species, Alona quadrangularis and Scapholeberis mucronata, were collected from a pond in Puyallup, Washington, and reared under controlled laboratory conditions. Life tables were developed for each species under the same environmental conditions and feeding regimen to develop basic demographic data. We also compared the major demographic parameters of these two wild species with those of several cladoceran species that are commonly used in laboratory research, Daphnia pulex, D. magna, and Ceriodaphnia dubia. Compared to A. quadrangularis, S. mucronata had a much higher net reproductive rate (R0), a longer generation time (T), but a similar intrinsic rate of increase (rm), similar finite rate of increase, similar doubling time (DT), and a lower birth rate (b). Both wild species had lower R0, shorter T, and higher b than in D. pulex, D. magna, and C. dubia. Results of this study showed that demographic rates differed between A. quadrangularis and S. mucronata, and differed from those reported for the other three laboratory species. These results suggest that data developed for commonly used cladoceran species in the laboratory should not be used to make generalizations about effects on wild species.

Biological performance of Bollgard II® Bt-resistant vs susceptible population of pink bollworm, Pectinophora gossypiella (Saunders) on non-toxic diet

BackgroundThe pink bollworm, Pectinophora gossypiella (Saunders), is a devastating global pest of cotton that has caused substantial economic damage to Bt Bollgard-II® cotton plants in recent years due to the evolution of Bt resistance. The associated fitness cost is assumed to be one of the factors delaying the development of resistance against Bt transgenic crops. Hence, the present study was undertaken to assess the biological performance of pink bollworms by comparing the life history and demographic parameters of a resistant (Field-R) and susceptible (Lab-S) population.ResultsProlonged larval duration (23.40 days in Field-R vs 18.80 days in Lab-S population), total life cycle (male = 50.00 vs 42.80 days; female = 53.60 vs 46.20 days), reduced fecundity (100.60 vs 154.20 eggs/female) and fertility (88.00 vs 138.00 fertile eggs/female) was observed. The demographic parameters indicated a significant reduction in the net reproductive rate (184.27 vs 276.72), innate capacity for increase in number (0.11 vs 0.15), finite rate of increase in number (1.12 vs 1.16 female progenies produced/female/day), weekly multiplication rate (2.16 vs 2.86), potential fecundity (545.06 vs 634.11 eggs), number of hypothetical F2 females (33 955.65 vs 76 572.41), but longer mean length of generation (47.54 vs 37.74 days) and population doubling time (6.30 vs 4.62 days) in Field-R compared with Lab-S population. A stage-specific life table demonstrated the differences in survival rates between susceptible and resistant populations at various life stages, with the resistant population having higher generation mortality (0.22 vs 0.19).ConclusionsThe study confirms the involvement of fitness costs associated with Bt resistance in P. gossypiella. Despite reduced reproductive fitness, the resistant population tried prolonging the larval stage as a compensatory mechanism to repair the damaged host tissues due to Bt intoxication and for accumulation of enough nutrient reserves for normal pupation and adult emergence. Presence of a high proportion of double Bt-resistant larvae in the field coupled with continued noncompliance with refug planting certainly favours the flaring up of this monophagous pest despite the observed fitness costs. The resistance cannot be effectively reversed unless suitable alternative management strategies are deployed.

Survival, development, and reproduction of Aulacorthum solani (Hemioptera: Aphididae) fed on Persicaria lapathifolia.

The foxglove aphid, Aulacorthum solani (Kaltenbach), is a polyphagous economic pest. In this study, A. solani were fed on detached leaves of dockleaf knotweed, Persicaria lapathifolia (L.) Delarbre. Survival, development, and reproduction were studied at constant temperatures of 17, 20, 23, 26, 29, and 32 °C. These data were compared with those of controls fed on Glycines max (L.) Merrill. At 17, 20, 23, and 26 °C, the survival rate of A. solani adults fed on P. lapathifolia were lower than those fed on G. max; the adult longevity, aphid total longevity, and reproduction period were shorter. At 20, 23, and 26 °C, the adult fecundity, intrinsic rate of increase, finite rate of increase, and net reproductive rate of A. solani fed on P. lapathifolia were smaller than those fed on G. max. At 29 °C, the survival rate of A. solani adults fed on P. lapathifolia were higher than those fed on G. max; the adult longevity and aphid total longevity were longer. These results are consistent with our finding that A. solani feed on P. lapathifolia, which is important for studying the host adaptability of A. solani.

A GIS-coupled thermal response model for predicting the population growth potential of the red cotton bug, Dysdercus koenigii (Fabricius) (Hemiptera: Pyrrhocoridae) in India under climate change conditions

Recently, the red cotton bug has become a significant menace to cotton in India. With the potential for increased habitat suitability due to predicted temperature rise of 2.5°C under future climate change in India, this pest could become even more severe in certain regions. Addressing the knowledge gap on the temperature-driven population growth of this pest is crucial for developing a climate-resilient pest management strategy. In this study, life history data gathered at various constant temperatures (15°C to 35°C) were used to estimate temperature thresholds and thermal requirements for the red cotton bug development. Stochastic estimation of life table parameters and validation with real-time weather data were performed. The phenology model, integrated into a geographic information system, projected the future pest status based on SSP126 temperature change scenarios for the year 2050. The temperatures between 8.35 – 10.83 °C were estimated as lower developmental thresholds for various immature life stages. The optimum and upper threshold temperatures estimated for different life stages ranged between 22.14 – 28.32°C and 35.80 – 39.08°C, respectively. Thermal requirements of 447.97 degree days for life cycle completion were estimated. The optimum immature survival rates (>70%) were observed at temperatures between 25-30°C. The temperature-dependent decrease in generation times from 90.45 days (15 °C) to 25.44 days (35°C) was observed, whereas maximum fecundity was recorded at 32°C. Simulation at fluctuating temperatures across different cotton growing locations provided reasonably similar results on potential population increase (finite rate of increase: 0.99 - 1.04 females/female/day and a generation time of 44.25 – 83.97 days). Risk mapping highlighted moderate to high suitability (ERI >0.4, GI > 6, and AI >4) of various cotton growing areas under current climate, and projected shifts in suitability under future climate change. The study has generated information valuable for implementing effective and timely pest management strategies for RCB. Integrating the field observations with model outputs can enhance a practical understanding of red cotton bug dynamics.

Life table and feeding behavior of Myzus persicae (Hemiptera: Aphididae) at sublethal concentrations of Afidopyropen, Spirotetramat and sulfoxaflor

AbstractThe green peach aphid Myzus persicae Sülzer is a major insect pest of cruciferous plants, including vegetables such as Chinese cabbage. The objective of the present study was to determine the effects of sublethal afidopyropen and spirotetramat concentrations on the survival and reproduction of M. persicae. In addition, we used an electrical penetration graph (EPG) to study the feeding behavior of M. persicae on Chinese cabbage leaves treated with various concentrations of afidopyropen, spirotetramat and sulfoxaflor. The results showed that sublethal concentrations (LC10 and LC30) of afidopyropen and spirotetramat significantly decreased adult longevity and fecundity. However, sulfoxaflor had no significant effects. Several population parameters, including the net reproductive rate (R0), intrinsic rate of increase (rm), mean generation time (T), finite rate of increase (λ), and doubling time (DT), were significantly decreased only at the LC30 of spirotetramat. According to the EPG feeding behavior analyses, when all three insecticides were applied at LC30, the nonpenetration (NP) waveform significantly increased. The above results can be used as basic data for the well‐planned use of insecticides.

Effect of Chlorantraniliprole on Life History Traits and Relative Fitness of Laboratory-Selected Resistant and Susceptible Populations of Spodoptera litura (Lepidoptera: Noctuidae).

Insecticides are widely used to control pests and improve agricultural yield. The use of indiscriminate amounts and persistent pesticides has not only resulted in insect pest resistance challenges but has also harmed non-target organisms and contaminated the environment. We assessed the cost-effectiveness of Spodoptera litura (Fabricius) resistance to chlorantraniliprole (CTPR) as part of insect resistance control programs. S. litura larvae were collected from the fields and treated with chlorantraniliprole for 15 generations. Compared to the unselected population (Unsel-Lab), the chlorantraniliprole-selected population (CTPR-Sel) of S. litura exhibited a resistance level of 98.23 times. The findings demonstrated that the chlorantraniliprole-resistant genotype had lower egg-to-adult survivability, longer egg-to-adult developing times, and lower fecundity than the chlorantraniliprole-susceptible genotype. Compared to the Unsel-Lab population, the CTPR-Sel population of S. litura had a poorer relative fitness (0.44) at LC30 and shorter male/female longevity. Demographic parameters, including net reproductive rate (R0) and intrinsic (rm) and finite rate of increase (λ), were lower in the CTPR-Sel strain than in Unsel-Lab S. litura. These findings demonstrate that chlorantraniliprole resistance in S. litura has fitness costs at the individual and population levels, implying that removing the selecting agent from the environment might result in less resistance and opportunities for susceptibility restoration. As a result, the current work could help to determine effective management strategies to prevent chlorantraniliprole resistance in S. litura.

Biological and population parameters of Telenomus remus and Trichogramma atopovirilia as biological control agents for Spodopterafrugiperda

Maize production faces a significant threat from Spodoptera frugiperda (J. E. Smith) worldwide; historically, Trichogramma pretiosum Riley has served as the primary augmentative egg parasitoid for its biological control. However, since 2004, Telenomus remus Nixon has emerged as a viable global alternative. On a regional scale, in Mexico, Trichogramma atopovirilia (Oatman & Platner) was theorized to outperform T. pretiosum, proving superior in both laboratory and field conditions in 2020. To further the field efficacy of the augmentative use of parasitoids as biological agents of S. frugiperda, we conducted comparisons of biological and population parameters under laboratory-controlled conditions to determine whether T. remus would be more effective than T. atopovirilia, the best Trichogramma parasitoid in Mexico for S. frugiperda. We found that the former parasitoid had statistically significant longer female and male longevity, as well as a higher proportion of female offspring, and greater numerical values in net reproduction rate, intrinsic rate of increase, and finite rate of increase, but no differences were found in the number of days required for both parasitoids to develop from egg to female or egg to male, as well as in the mean generation time and doubling time. Under the conditions of these trials, T. remus had a 47.02% greater intrinsic rate of increase (rm) and may thus be a more effective biological control agent for S. frugiperda than T. atopovirilia. However, these biological and population parameter comparisons are the first execution worldwide; further studies are needed to validate these promising T. remus results.

The impact of lethal and sub-lethal exposure of emamectin benzoate on populations of Spodoptera litura (Lepidoptera: Noctuidae) under laboratory conditions

Emamectin benzoate is an avermectin bio-insecticide commonly used for managing several insect pests including Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), a major polyphagous pest of many cultivated crops. The current study was conducted to evaluate the effects of emamectin benzoate on the fitness of S. litura populations exhibiting differential susceptibility to insecticide. The selection process and all the bioassays were carried out using 6-day-old 2nd instar larvae of S. litura. A field-collected population of S. litura was divided into two groups: one selected with emamectin benzoate for eight generations (EB-Sel) and the other kept unexposed (Unsel-Lab) to insecticide in the laboratory. An increase in resistance ratio from 1.71-fold in the F1 generation to 22.54-fold in the F8 generation of the EB-Sel population was observed compared to the Unsel-Lab (F8) population. The EB-Sel and Unsel-Lab populations were treated with their respective lethal and sub-lethal concentrations which resulted in an extended development period, decreased larval survival, and adult emergence along with increased morphological abnormalities in adults. Significant reductions were observed in both male and female longevity, fecundity, egg hatching, net reproductive rate (R0), intrinsic rate of increase (rm), and finite rate of increase (λ) in EB-Sel and Unsel-Lab populations. Higher concentrations of the insecticide also reduced the relative fitness (Rf) of S. litura larvae, with maximum effect at LC50 of the EB-Sel population where the Rf value was 0.32 compared to the Unsel-Lab population. Both populations have been affected by emamectin benzoate exposure, however, the impact was more pronounced in the EB-Sel population indicating fitness costs. Our results suggested the fitness cost linked to emamectin benzoate resistance in S. litura which might favor managing insecticide resistance by reducing the frequency of resistant alleles by removing selection pressure. Consequently, our research provides significant insights to devise better pest management strategies for S. litura.

Infection with pathogenic fungi is a major threat to the mass production of the parasitoid wasp Habrobracon hebetor: 20 generations under surveillance

Pathogen infection is one of the most important challenges threatening the success of mass rearing of natural enemies either in insectaries or in augmentative biological control programs. In this investigation, we studied the biological and population growth parameters of a naturally infected colony of the parasitoid wasp Habrobracon hebetor (Say) (Hymenoptera: Braconidae) over 20 generations (G1inf − G20inf) of rearing on Ephestia kuehniella (Zeller) (Pyralidae: Lepidoptera) under laboratory conditions. Based on morphological characteristics and ITS sequences, two types of fungal colonies were isolated from the diseased females and identified as Thermothielavioides terrestris and Aspergillus flavus. The results showed that although no significant differences were found in the female longevity and fecundity of H. hebetor on E. kuehniella up to G15inf, the duration of the immature period was extended as the number of generations increased. In addition, the intrinsic rate of increase (r) and finite rate of increase (λ) had no significant differences up to G8inf. The net reproductive rate (R0) of G15inf had no significant differences with G2inf, G8inf, and G10inf. On the other hand, in G15inf, R0 was significantly higher than G4inf, G6inf, and G20inf. The findings underscore the negative impact of fungal infection on population growth parameters compared with uninfected population. This study showed that naturally fungal infection of the parasitoid affected the population growth and life table parameters through mass rearing, compared and discussed with the healthy parasitoid.

Susceptibility of Capsicum varieties to Thaumatotibia leucotreta (Lepidoptera: Tortricidae) infestation for production optimization.

Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is a major threat to the production and marketing of pepper (Capsicum spp.) in Ghana. To reduce the damage of the pest on pepper farming, it is important to find appropriate control methods, which may include the use of resistant host plants. This study investigated the relative susceptibility of 6 pepper varieties commonly cultivated in Ghana: Legon 18, Bird's eye, Scotch bonnet, Cayenne, KA2, and sweet pepper (Yolo wonder+ variety). Choice and no-choice ovipositional preference tests were conducted and the population growth rate of T. leucotreta was determined by establishing life table parameters including the net reproductive rates (R0), the mean generation time (G), intrinsic rate of natural increase (rm), the population doubling time (T), and the finite rate of increase (λ). In the no-choice test, females exhibited oviposition preference for sweet pepper (12.08 eggs/fruit), while Bird's eye was the least preferred (5.00 eggs/fruit). The same results were observed in the choice test. However, the population growth rate of T. leucotreta was highest on the Scotch bonnet and Cayenne, with rm of 0.124 and 0.127, respectively, while the Bird's eye and sweet pepper recorded the least rm of 0.116. Thus, the tested varieties had varying levels of susceptibility to T. leucotreta infestation. Bird's eye was the least susceptible variety, while Cayenne and Scotch bonnet were the most susceptible varieties. These findings could direct farmers on the choices of pepper varieties for cultivation and proffer potential opportunities to breed new varieties resistant to T. leucotreta infestation.

Fitness and Survival of the Fall Armyworm, Spodoptera Frugiperda (Lepidoptera: Noctuidae) on Maize in West Java, Indonesia

An important pest of maize is a new invasive species called Spodoptera frugiperda, also known as the fall armyworm (FAW), causing a considerable economic impact in Indonesia since 2019. This insect has a large host range, a quick generation time at the right temperature, a high rate of reproduction, and a high dispersal capacity. In population ecology and pest management, fitness and survival are crucial. This research was aimed to determine some biological aspects and demographic statistics of three FAW populations (lowland, midland, and highland) in a laboratory setting with 25 ± 2 °C, 75 ± 5% relative humidity, and a 12:12 (L:D) hour photoperiod. Findings indicated no variation in the length of the FAW life stage or its reproductive capacity. Nonetheless, notable variations were noted in the average fecundity of females, with FAW of the highland population laying the most eggs (1242.1 eggs). FAW had the shortest mean generation time (T), the highest intrinsic rate of increase (rm), the finite rate of increase (λ), and the highest net reproductive rate (R0) of the highland population. Overall FAW collected from highland, midland, and lowland can adapt well when brought to a laboratory with a constant temperature at 25 ± 2 °C without detriment to the parameters of the life table. The knowledge gained from this study is crucial for managing FAW because it improves comprehension of its life cycle and adaptability to various altitudes, enabling us to take appropriate action to stop its spread.

Resistance Realized Heritability and Fitness Cost of Cyproflanilide in Rice Stem Borer, Chilo suppressalis (Lepidoptera: Pyralidae)

The rice stem borer (RSB) Chilo suppressalis is a devastating rice pest with resistance to a number of insecticides. Recently, the new meta-diamide insecticide cyproflanilide has been considered an effective insecticide to control RSB. However, its resistance risk has not been reported. In the present study, we aimed to assess the resistance risk and evaluate the fitness cost after the RSB was exposed to cyproflanilide. After five generations of selection, the resistance level of RSB increased by 1.5-fold. When h2 was 0.125, a 10-fold resistance increase in the LD50 values was expected in fourteen and thirty-one generations at the selection intensity of 90% and 50%, respectively. The selected population (RSB-SEL) had significant differences in the developmental duration of eggs, 1st, 2nd, 3rd, and 6th instar larvae, and female pupae compared to the unselected population (RSB-UNSEL). Besides, the adult longevity was shortened, and the average pupal weight of males, the emergence rate, the sex ratio, the oviposition, the mean fecundity, and the full life cycle rate were decreased in RSB-SEL. The intrinsic rate of increase (r), the net reproductive rate (R0), and the finite rate of increase (λ) of RSB-SEL were significantly lower than those of RSB-UNSEL, while the mean generation time (T) of RSB-SEL was significantly longer than that of RSB-UNSEL. Based on the results of the prediction of the generations required for a 10-fold resistance increase in the LD50, a potential risk of resistance development exists in RSB after continuous and excessive use of cyproflanilide. These results will be useful in designing the dose of cyproflanilide to control C. suppressalis in field.

Sublethal effect of emamectin benzoate on age-stage, two-sex life table and population projection of red palm weevil, Rhynchophorus ferrugineus

The red palm weevil (RPW), Rhynchophorus ferrugineus Olivier, is a devastating insect-pest of 29 plants including date palm. It feeds inside the tree bark thus it is difficult to manage using insecticides. Only a few insecticides have been found effective against RPW. Among these insecticide, emamectin benzoate (EMB) is widely used. This insecticide can pose threat human and environmental health as it is used in the form of tree injection. Thus, keeping in view its possible, its sublethal effect on RPW was studied using Age-stage, two sex life table. Life table parameters of the progeny of exposed larvae to LC10, LC25, and LC50 of EMB were computed. Statistically higher fecundity (161.12 per female) was observed in control treatment, while less fecundity was observed in LC50 treatment. Significantly higher values for intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (Ro) (0.0376, 1.0383, and 67.13 per day, respectively) were recorded for the control treatment. Contrarily, lower values for r, Ro, and λ i.e. 0.0318, 23.82, and 1.0324 per day, respectively were recorded in the LC50 treatment. Decreased population parameters suggest that EMB can be successfully used in for the management of RPW.

How does Neoseiulus californicus McGregor respond to sublethal doses of entomopathogenic fungus Beauveria bassiana (Hyp.: Cordycipitaceae)?

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Prostigmata), is one of the most economically important mite species, mainly controlled by chemical acaricides. Natural enemies have been assessed as reliable alternatives for management of this phytophagous mite. In the current project, demographic characteristics of Neoseiulus californicus McGregor (Acari: Phytoseiidae) to sublethal concentrations (LC10 = 6.76 × 102, LC20 = 8.74 × 103 and LC30 = 55.38 × 103 conidia ml-1) of entomopathogenic fungus, Beauveria bassiana (Bals.) Vuill. TV strain were investigated under laboratory conditions at 25 ± 2°C, 70 ± 5% RH and a photoperiod of 16:8 (L:D) h. Our results indicated that when adult predators were exposed to LC20 and LC30 of B. bassiana, the oviposition period was significantly reduced compared with other treatments. Neoseiulus californicus fecundity was significantly greater in the control (37 eggs) than in LC30 (24 eggs). Life table analysis revealed that the net reproductive rate (R0) declined as the sublethal concentrations of B. bassiana increased. The most striking result to emerge from the data is that not only intrinsic (r); but also, finite rate of increase (λ) was not significantly affected by different concentrations of B. bassiana. Our findings revealed some potential interactions of B. bassiana and N. californicus during their combinations for managing T. urticae that may be helpful for optimising control of this important pest.

Multigenerational hormetic effects of different insecticides on Spodoptera frugiperda (J.E. smith) (Lepidoptera: Noctuidae)

To protect crops from pest insects, farmers continuously use insecticides, which eventually degrade into residue due to abiotic or biotic factors. These residual effects of pesticides may cause low lethal and/or sublethal impacts on the exposed pest insect populations, leading to the induction of pest resurgence through hormesis and ultimately the development of resistance. Hormesis is a beneficial bi-phasic effect generally characterized by low-dose reproductive stimulation and high-dose inhibition. In the present study, we investigated the impact of low lethal and sublethal concentrations (LC10, LC20, and LC30) of spinetoram, chlorantraniliprole, and thiodicarb on the F0 generation as well as their multigenerational hormesis effects on the F1 and F2 generations of Fall Armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). The study focused on reproductive parameters, fecundity, fertility, and life index parameters such as net reproductive rate (R0), intrinsic rate of increase (rm), finite rate of increase (λ), mean length of generation (Tc), and gross reproductive rate (GRR). Fecundity of S. frugiperda increased by 4.82%, 4.63% and 4.58%, while eggs fertility improved by 7.77%, 6.78% and 6.52% at LC10 of thiodicarb, chlorantraniliprole and spinetoram, respectively, from the F1 to F2 generation. Further, interaction analysis (Concentration × Insecticidal treatments) revealed that important vital parameters like pre-oviposition period (POP), oviposition period (OP), post-oviposition period (PtOP), R0,rm,λ, Tc and GRR of F0 were negatively impacted by LC30 of all the tested insecticides and LC20 of only spinetoram. However, LC10 of any of the tested insecticides did not affect these parameters when compared with control. Furthermore, interactive analysis in multigenerational exposure experiments (Concentration × Insecticidal treatments × Generation(s)) showed hermetic effects of LC10 of all tested insecticides which is more positive in F2 as compared to F1 generation. These unwanted positive hermetic effects of low lethal concentrations (LC10) of tested insecticides in offspring of exposed parental population of S. frugiperda indicated its resistance and/or resurgence. Furthernore, present study emphasizes the necessity for additional research to elucidate the underlying mechanisms responsible for these effects.

Effects of Dietary Zinc Chloride and Zinc Sulfate on Life History Performance and Hemolymph Metabolism of Spodoptera litura (Lepidoptera: Noctuidae).

Zinc is an essential micronutrient crucial in various biological processes of an organism. However, the effects of zinc vary depending on its chemical form. Therefore, the aim of this study was to conduct a comparative analysis of the life history performances and hemolymph metabolism of Spodoptera litura exposed to different concentrations of dietary zinc chloride (ZnCl2) and zinc sulfate (ZnSO4), utilizing two-sex life tables and untargeted metabolomics. The preadult survival rate of S. litura significantly decreased, while the preadult developmental period of S. litura was prolonged as the dietary ZnCl2 concentration increased. However, the fecundity of S. litura at 50 mg/kg dietary ZnCl2 was significantly increased. The intrinsic rate of increase (r) and the finite rate of increase (λ) in S. litura in the control group (CK, no exogenous ZnCl2 or ZnSO4 added) and with 50 mg/kg dietary ZnCl2 were significantly higher than those at 100 mg/kg, 200 mg/kg, and 300 mg/kg. Dietary ZnSO4 exerts a devastating effect on the survival of S. litura. Even at the lowest concentration of 50 mg/kg dietary ZnSO4, only 1% of S. litura could complete the entire life cycle. Furthermore, as the dietary ZnSO4 concentration increased, the developmental stage achievable by the S. litura larvae declined. High-throughput untargeted metabolomics demonstrated that both 100 mg/kg dietary ZnCl2 and ZnSO4 decreased the hemolymph vitamins levels and increased the vitamin C content, thereby helping S. litura larvae to counteract the stress induced by ZnCl2 and ZnSO4. Simultaneously, dietary ZnCl2 obstructed the chitin synthesis pathway in the hemolymph of S. litura, thus extending the developmental period of S. litura larvae. These results indicate that low concentrations of Zn2+ positively impact populations of S. litura, but the effectiveness and toxicity of Zn depend on its chemical form and concentration.