Efficacy of Citrullus colocynthis seed extract on Earias vittella, Fabricius, (Lepidoptera: Noctuidae): environment sustainable approach

Earias vittellaFabricius, 1794 (Noctuidae: Lepidoptera) is deliberated to be one of the most destructive pests of cotton and okra vegetation in the world including Asia. The pest has established resistance to various synthetic insecticides. The use of bio-pesticide is one of the unconventional approaches to develop a vigorous ecosystem without harming non- target pests and beneficial natural insect fauna. In the present study, the toxicity levels of Citrullus colocynthis seed extract have been evaluated against the populations of E. vittellaunder standardized laboratory conditions. The toxic effects of C. colocynthis on development periods, protein contents and esterase activity of the life stages of E. vittella were also evaluated. The toxicity levels of methanol, ethanol, hexane, water and profenofos were evaluated on the 1st instar larvae of E. vittella. LC30 and LC80 concentrations exhibited the effectiveness of methanol-based C. colocynthis seed extract against 1st instar larvae of E. vitella. The enhanced larval and pupal periods were revealed in treated samples during the comparison with untreated samples. The intrinsic rate of increase, net reproductive rate in the LC30 and LC80 concentrations exposed larvae remained less than the control treatment. Fecundity, the esterase activity and protein contents were declined in LC30 and LC80 treated samples as compared to the control. The present findings suggest that C. colosynthis extracts based botanical insecticides are beneficial, ecosystem sustainable and can be integrated with insect management programs from environment safety perspective.

Effects of Acetamiprid at Low and Median Lethal Concentrations on the Development and Reproduction of the Soybean Aphid Aphis glycines

The soybean aphid Aphis glycines Matsumura (Hemiptera: Aphididae) is a major pest of soybean and poses a serious threat to soybean production. Studies on the effect of acetamiprid on the life table parameters of A. glycines, provide important information for the effective management of this pest. We found that exposure to acetamiprid at LC50 significantly extended the mean generation time, adult pre-reproductive period, and total pre-reproduction period compared with the control, whereas exposure to acetamiprid at LC30 significantly shortened these periods. Exposure to acetamiprid at both LC30 and LC50 significantly decreased the fecundity of the female adult, net reproductive rate, intrinsic rate of increase, and finite rate of increase compared with the control. The probability of attaining the adult stage was 0.51, 0.38, and 0.86 for a newly born nymph from the LC30 acetamiprid treatment group, LC50 acetamiprid treatment group, and control group, respectively. Acetamiprid at both LC50 and LC30 exerted stress effects on A. glycines, with the LC50 treatment significantly decreased the growth rate compared with the LC30 treatment. The present study provides reference data that could facilitate the exploration of the effects of acetamiprid on A. glycines in the field.

Impact of citrus species on the biological characteristics and life table parameters of Eutetranychus orientalis (Klein) (Acari: Tetranychidae)

Biological characteristics and life table parameters of Eutetranychus orientalis (Klein) were revealed on four different citrus species: grapefruit (Citrus paradisi Macf. cv. Star Ruby), lemon (C. limon (L.) Burm. f. cv. Meyer), mandarin (C. reticulata Blanco cv. Okitsu) and orange (C. sinensis L. cv. Washington Navel) under laboratory conditions. Results show that oviposition period, fecundity, and life table parameters varied significantly depending on the host plant species. Furthermore, host plant species had little effect on immature development, except for the teleiochrysalis and total developmental period, which was significantly shorter on lemon (13.77 days for females, 12.67 days for males). Total mean numbers of eggs laid by E. orientalis was 15.92 on mandarin and 29.78 on lemon. In addition, intrinsic rate of increase (rm), net reproductive rate (R0), finite rate of increase (λ) and doubling time (DT) are 0.12 day–1, 10.41 ♀/♀, 1.13 day–1 and 5.59 days for lemon, 0.17 day–1, 22.36 ♀/♀, 1.19 day–1 and 4.04 days for grapefruit, respectively. However, shortest and longest mean generation times (To) were obtained at 18.26 days on orange and 19.37 days on grapefruit. Our results demonstrate that intergeneric differences of Citrus should be considered when determining E. orientalis population abundance and dynamics in field conditions.

Improvement of Bemisia tabaci (Hemiptera: Aleyrodidae) Fitness on Chinese Kale upon Simultaneous Herbivory by Plutella xylostella (Lepidoptera: Plutellidae)

Bemisia tabaci and the diamondback moth (DBM), Plutella xylostella, are two major cosmopolitan pests that often occur together and cause severe economic losses to cruciferous crops. However, little is known about how they interact with each other. To determine the effects of defense responses induced by the two pests on the biology and population dynamics of the herbivores, we studied the performance and fitness of B. tabaci and DBM when they damaged Chinese kale simultaneously and in different orders. The results showed that DBM pre-infestation shortened the developmental duration, increased longevity, oviposition days, and fecundity of B. tabaci. Meanwhile, the intrinsic rate of increase (r), net reproductive rate (R0) and finite rate of increase (λ) of B. tabaci increased significantly with dual infection as compared with only B. tabaci infestation. In contrast, B. tabaci pre-infestation reduced the longevity and oviposition days of DBM, but the population parameters r, R0, and λ did not vary significantly compared with only DBM infestation. Thus, co-infestation of B. tabaci and DBM was beneficial to the performance of the B. tabaci population. The present findings highlight that B. tabaci has become a dominant competitor when mixing with DBM on the same host plant.

The Combination of Bacillus Thuringiensis and Its Engineered Strain Expressing dsRNA Increases the Toxicity against Plutella Xylostella

RNA interference (RNAi) has been developed and used as an emerging strategy for pest management. Here, an entomopathogen Bacillus thuringiensis (Bt) was used to express the dsRNA for the control of Plutella xylostella. A vector containing a 325-bp fragment of the conserved region of P. xylostella arginine kinase gene (PxAK) flanking in two ends with the promoter Pro3α was developed and transferred into Bt 8010 and BMB171, and consequently engineered Bt strains 8010AKi and BMB171AKi expressing dsRNA of PxAK were developed. The two engineered Bt strains were separately mixed with Bt 8010 in a series of ratios, and then fed to the P. xylostella larvae. We found that 8010:8010AKi of 9:1 and 8010:BMB171AKi of 7:3 caused a higher mortality than Bt 8010. PxAK expression levels in the individuals treated with the mixtures, 8010AKi and BMB171Aki, were lower than that in the control. The intrinsic rate of increase (r) and net reproductive rate (R0) of the population treated with 8010:8010AKi of 9:1 were lower than those of the population treated with Bt 8010 or 8010AKi. We developed a Bt-mediated insect RNAi for the control of P. xylostella and demonstrated a practical approach to integrating the entomopathogen with RNAi technique for the pest management.

Identification of Tetranychus neocaledonicus (Acari: Tetranychidae) resistant genotypes in Phaseolus lunatus

The spider mite Tetranychus neocaledonicus André (Acari: Tetranychidae) is a potential threat to the cultivation of lima bean (Phaseolus lunatus L.). In many countries, lima beans are grown by small-holder farmers with limited access to inputs and technologies. In such systems, the implementation of control practices, such as chemical treatments that require costly equipment and supplies, becomes unviable. Therefore, the development and use of resistant plant genotypes could provide a promising alternative for small producers. Accordingly, the present study aimed to identify and evaluate T. neocaledonicus-resistant genotypes of lima bean. A total of 30 lima bean genotypes were evaluated using the instantaneous increase rate (ri) of T. neocaledonicus reared on individual host genotypes, and T. neocaledonicus fertility life tables were generating by rearing mites on host genotypes with the two highest ri values (IFCE-085 and IFCE-091, considered highly susceptible) and two lowest ri values (IFCE-084 and IFCE-090, considered resistant). Only the IFCE-090 genotype adversely affected immature T. neocaledonicus individuals, by reducing their survival rate, net reproductive rate (Ro), finite rate of increase (λ), and intrinsic rate of increase (rm) and by increasing their mean generation time (T) and time to reach adulthood. The results demonstrate the variation in the susceptibility of lima bean genotypes to T. neocaledonicus and identify the IFCE-090 genotype as a potential source of mite resistance.

Sub-lethal doses of Nucleopolyhedrosis Virus and synthetic ınsecticides alter the biological parameters of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Resistance management is very important for devising control strategies of polyphagous insect-pests like Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). Considering the importance of resistance management, demographic features of selected and unselected populations of H. armigera were studied in 6 different treatments viz. emamectin benzoate, Helicoverpa armigera Nucleopolyhedrosis Virus (HaNPV), emamectin benzoate+HaNPV, spinetoram, spinetoram+HaNPV and control. Higher values for fecundity, intrinsic rate, the finite rate of increase (λ) were recorded in the control of selected as compared to the rest of treatment. Similarly, higher values for these population parameters viz. oviposition days, fecundity, intrinsic rate, the finite rate of increase were calculated in the unselected control. Similarly, net reproductive rate (R0) for selected and unselected control was higher as compared to the rest of the treatments. It may happen because these kinds of selection pressures can result in decreased fitness of the test insect thus decreased fitness of H. armigera in different treatments was observed as compared to the control. Additionally, quicker development of susceptible insects was observed because susceptible insects were growing without any stressor (xenobiotics) as compared to the rest which contributed to their faster development.

Active and frozen host mite Tyrophagus putrescentiae (Acari: Acaridae) influence the mass production of the predatory mite Blattisocius mali (Acari: Blattisociidae): life table analysis

Blattisocius mali (Oudemans) is a candidate predatory mite on some astigmatid mite pests like Tyrophagus putrescentiae (Schrank). In current study, life table parameters of B. mali were comparatively evaluated when fed on mixed life stages, frozen (one day at -20°C) and cold stored (90 days at -20°C and 4°C) eggs of T. putrescentiae. The highest and lowest values of fecundity, total longevity, oviposition period, life span and adult longevity of B. mali were observed when the predator provided with one-day and 90-days frozen eggs (stored at 4°C) of T. putrescentiae, respectively. Moreover, the highest values of net reproductive rate (R0), intrinsic rate of increase (r) and finite rate of increase (λ) of B. mali were obtained by feeding on one-day frozen eggs (23.94 offspring/individual, 0.332 day-1, 1.39 day-1, respectively), without significant differences from the predators reared on alive mixed stages of T. putrescentiae. However, the lowest values of R0 (1.54 offspring/individual), r (0.058 day-1) and λ (1.06 day-1) were recorded when B. mali was reared on 90-days frozen eggs (stored at 4°C). The results, as first evidence of life-history of B. mali, represent not only the potential of the predator as suitable biological control agent against T. putrescentiae, but also the possibility of its mass production by frozen host stages. Provision of one-day frozen eggs of T. putrescentiae were the best choice for B. mali survival and reproduction with no harmful effects of living stages (direct damage, frass and exuviae) on crop.

Temperature based phenology model for predicting establishment and survival of Spodoptera litura (Fab.) on groundnut during climate change scenario in India

Studies were conducted to develop temperature-based phenology model for Spodoptera litura on groundnut, at both constant and fluctuating temperatures and to predict the possibility of pest risk in future climate change scenarios of India using ‘stochastic simulation tool’ in Insect Life Cycle Modelling (ILCYM) software ,which is based on rate summation and cohort up-dating approach. Phenology model predicted temperatures between 25oC and 30oC as the favourable range for S. litura development, survival and reproduction. The intrinsic rate of increase (rm), and finite rate of increase (») increased with increase in temperature from 15oC to 30oC and decreased with increase in temperature. Intrinsic rate of increase (rm), varied from 0.05 females/female/day at 15oC to 0.17 females/female/day at 30oC. S. litura population attained a maximum net reproductive rate ‘Ro’ (334.09 females/female/generation) and total fecundity (1041.88 individuals/ female/generation) at 27°C temperature. Simulated life table parameters were used to determine indices such as the establishment risk index (ERI), the generation index (GI), and activity index (AI) by using the ‘Population distribution and risk mapping’ module of software during present and future climatic scenarios and significant increase in AI and ERI with higher GI at future (2050) climatic conditions compared to current (2000) climatic conditions indicating the strong suitability for establishment and survival of S.litura in India.

Sublethal effects of bifenazate on biological traits and enzymatic properties in the Panonychus citri (Acari: Tetranychidae)

Panonychus citri, a major citrus pest. In pest management, bifenazate is a novel acaricide with high biological activity against red mites, such as Tetranychus urticae Koch. However, in the field, pests are frequently exposed to sublethal or lethal concentrations of pesticides. At present, its sublethal effects on P. citri have not been reported. Therefore, in order to investigate sublethal effect of bifenazate on biological traits and enzymatic properties of P. citri. The newly emerged females were treated with two concentrations of bifenazate: LC10 and LC30, the development and fecundity were observed. The results showed that female adult duration, fecundity, oviposition days, longevity were decrease compared with control, but pre-oviposition period was longer, net reproductive rate (R0), mean generation (T) were decreased, intrinsic rate of increase (rm), finite rate (λ) were decreased in LC30, however, doubling time was increased. Enzymatic tests showed that CAT, POD, CarE activities were higher in treatments than control. The SOD and GST activities were lower in LC30 than control and LC10, the CYP450 activity was decreased with the increasing concentrations. This study demonstrated that low lethal concentrations of bifenazate adversely affected life table parameters, enzymatic properties in P. citri. Therefore, bifenazate has the potential to control this pest.