Leaf-dip Bioassay Research Articles

Chemical Profiling and Pharmaceutical and Biological Activities of Methanolic Extract of Citrullus colocynthis L. Seeds Collected from the Arid Zone of Qassim, Saudi Arabia against Aphis craccivora

Background: Citrullus colocynthis L. (C. colocynthis) is a medicinal plant with a long history of traditional usage in Saudi Arabia, particularly for the treatment of digestive issues such as indigestion and stomach pain.Methods: C. colocynthis seeds were examined using qualitative and quantitative phytochemical methods. Antioxidant testing was conducted using DPPH assay and the reducing power test. Antibacterial properties were evaluated using the well-diffusion test, minimum inhibitory concentration (MIC) test, and minimum bactericidal concentration (MBC) test. The effectiveness of the extract against Aphis craccivora (A. craccivora) was assessed using a leaf-dip bioassay, measuring generation time (GT), net reproduction rate (R0), intrinsic rate of increase (rm), doubling time (DT), and finite rate of growth (λ).Results: The methanolic extract of C. colocynthis seeds included diverse bioactive compounds, a good quantity of phenolic content (60.45 mg GAE/g) and flavonoid content (46.66 mg/g). The antibacterial tests showed that the extract was effective only against Staphylococcus aureus and Proteus mirabilis. The extract recorded inhibition zones of 14.5 ± 0.7 mm and 10.5 ± 0.5 mm for Staphylococcus aureus and Proteus mirabilis, respectively. Staphylococcus aureus showed the greatest sensitivity, with MIC of 6.25 mg/mL and MBC of 25.0 mg/mL. The extract was found to have a fatal concentration (LC50) of 9.02% and a lethal concentration (LC95) of 20.50% against A. craccivora aphid.Conclusions: The current vitro study on C. colocynthis reported that the seeds are effective as antioxidants, antibacterial agents (only against Gram-positive bacteria), and aphicidal agents against aphids. More investigations are recommended to examine the possible toxicity and biochemical interactions in vivo.Keywords: Plants; Biological activity; In vitro study; Citrullus colocynthis; Aphis craccivora; Aphicidal

Insecticidal and Anti-Feedant Activity of Clerodendrum Extracts on Growth and Development of Castor Spiny Caterpillar, Ariadne merione

The castor spiny caterpillar Ariadne merione (F.) is a major lepidopteran pest affecting castor (Ricinus communis) crops mainly by causing defoliation which in turn reduces the photosynthesis and yield. The conventional pest control methods have been based on chemical control which although has been effective, has its drawbacks of being hazardous to the environment and human health besides leading to resistance by the pests. The present work aims at investigating the possibility of using Clerodendrum inerme, a plant belonging to the Lamiaceae family, as an eco-friendly solution for pest management. Insecticidal and anti-feedant efficacy of C. inerme leaf extracts, which were prepared using solvents hexane, acetone, and petroleum ether, was tested against A. merione larvae using leaf dip bioassay under no-choice situation. The findings showed that the hexane extract had the highest insecticidal (73%) and anti-feedent (97%) action. The petroleum ether extract also showed moderate insecticidal (50%) and anti-feedant activity (48%) but not as potent as the acetone extract having insecticidal and anti-feedant action of 60 and 74 per cent respectively. The results imply that C. inerme extracts, especially the hexane extract, could be used as botanical insecticides in IPM programs as a natural replacement for chemical insecticides.

Novel transinfections of Rickettsiella do not affect insecticide tolerance in Myzus persicae, Rhopalosiphum padi, or Diuraphis noxia (Hemiptera: Aphididae).

Aphids (Hemiptera: Aphidoidea) are economically important crop pests worldwide. Because of growing issues with insecticide resistance and environmental contamination by insecticides, alternate methods are being explored to provide aphid control. Aphids contain endosymbiotic bacteria that affect host fitness and could be targeted as potential biocontrol agents, but such novel strategies should not impact the effectiveness of traditional chemical control. In this work, we used a novel endosymbiont transinfection to examine the impact of the endosymbiont Rickettsiella viridis on chemical tolerance in 3 important agricultural pest species of aphid: Myzus persicae (Sulzer) (Hemiptera: Aphididae), Rhopalosiphum padi (Linnaeus) (Hemiptera: Aphididae), and Diuraphis noxia (Mordvilko ex Kurdjumov) (Hemiptera: Aphididae). We tested tolerance to the commonly used insecticides alpha-cypermethrin, bifenthrin, and pirimicarb using a leaf-dip bioassay. We found no observed effect of this novel endosymbiont transinfection on chemical tolerance, suggesting that the strain of Rickettsiella tested here could be used as a biocontrol agent without affecting sensitivity to insecticides. This may allow Rickettsiella transinfections to be used in combination with chemical applications for pest control. The impacts of other endosymbionts on insecticide tolerance should be considered, along with tests on multiple aphid clones with different inherent levels of chemical tolerance.

Green chemistry approach for rapid synthesis of indol-3-yl-4H-pyran derivatives, biological assessments, and toxicological activities against Cowpea aphid (Aphis craccivora)

From diverse or indole-3-carbaldehyde, certain unique indol-3-yl-4H-pyran derivatives were generated by condensing with different nucleophiles. IR, 1HNMR, and elemental studies have all confirmed their chemical structures. The green catalyst for the formation of indol-3-yl-4H-pyran derivatives is a zinc-linked amino acid complex [Zn(L-proline)2]. Furthermore, the environmental friendliness of this synthetic technique was investigated by assessing the reusability of the Zn(L-proline)2 complex over five consecutive cycles with no significant loss of catalytic activity. This novel process has showed substantial advantages in terms of safety, simplicity, stability, mild conditions, a short reaction time, excellent yields, and good purity without the use of organic solvents. The antibacterial properties of the compounds produced were investigated and discovered to be promising. To determine whether compounds are appropriate as possible insecticidal agents, the toxicological activity of the synthesized compounds against Cowpea aphid, Aphis craccivora, was tested using leaf dip bioassay technique toxicity studies performed in the laboratory. KEY WORDS: One pot synthesis, Zn(L-proline)2, Indole-3-carbaldehyde, Aqueous media, Microwave irradiation, Cowpea aphid, toxicological activity Bull. Chem. Soc. Ethiop. 2024, 38(4), 1077-1090. DOI: https://dx.doi.org/10.4314/bcse.v38i4.21

Toxicity Bioassays of Essential Oils against Hadda Beetle <i>Henosepilachna vigintioctopunctata</i> (F)

Contact, repellent and antifeedant bioassays of essential oils (EO’s) viz., basil oil and citronella oil were evaluated against hadda beetle Henosepilachna vigintioctopunctata (F) in brinjal. Based on the results of leaf dip bioassay, the LC50 and LC90 values of basil oil and citronella oil were 1.25% and 2.85%, 0.93% and 1.52%, respectively at 24 hrs after treatment (HAT). While the corresponding LC50 and LC90 values at 48 HAT were 0.85% and 1.70%, 0.63% and 1.14%, respectively. Repellent and antifeedant effect of the chosen essential oils were also evaluated by modified preference method and no choice method, respectively. At 0.5 to 1% concentration, both basil and citronella oil showed 90-100% repellence at 30 and 60 min of treatment. 100% antifeedant effect was also observed at the same concentration (0.5 to 1%) for both the EO’s at 24 HAT. GC-FID/GC-MS analysis of basil and citronella oil revealed that the predominant component of basil oil was methyl chavicol (75.73%), followed by linalool (18.21%) and cuprenene (1.58%); in citronella oil, geranial (64.77%) was the most predominant component followed by citronellyl acetate (7.92%), geraniol (7.08%), (Z) iso citral (5.29%) and neral (3.60%).

Why does identification matter? Thrips species (Thysanoptera: Thripidae) found in soybean in southern Brazil show great geographical and interspecific variation in susceptibility to insecticides

Thrips have historically been considered secondary soybean pests in Brazil and neighboring countries. However, since the 2010s they have gained importance in soybean in central and northern Brazil. From 2017 onwards, high infestations of thrips have also been detected in soybean in southern Brazil. Here, we collected and identified thrips species from soybean fields in southern Brazil throughout the 2022/2023 season and conducted laboratory bioassays to assess their susceptibility to selected insecticides. Thrips were exposed to the field concentrations of selected insecticides in leaf-dip bioassays using soybean leaves. Our results indicated that Frankliniella schultzei (Trybom, 1910) and Caliothrips phaseoli (Hood, 1912) are the major thrips species found in soybean in southern Brazil. These species exhibited high mortality and relatively low geographic and interspecific variation in susceptibility to the field concentrations of spinetoram, methomyl, spinetoram + methoxyfenozide and profenofos + cypermethrin. In general, most populations of C. phaseoli were more susceptible to acephate, chlorfenapyr and abamectin than F. schultzei, whereas bifenthrin + carbosulfan showed high lethality against most populations of F. schultzei, however, both species had wide geographic variation in susceptibility to these chemistries. In contrast, populations of both species have low mortality when exposed to the field concentrations of imidacloprid, lambda-cyhalothrin and lambda-cyhalothrin + sulfoxaflor. In summary, our study documents significant variations in the susceptibility of F. schultzei and C. phaseoli to selected insecticides, both among species and among geographical areas across southern Brazil. These results highlight the importance of species identification for the effective control of thrips in soybean in Brazil and other South American countries.

Comprehensive comparative toxicity study on tomato (Solanum lycopersicum) and brinjal (Solanum melongena) using green labelled insecticides against Bemisia tabaci

Bemisia tabaci a serious sucking pest of tomato (Solanum lycopersicum L.) and brinjal (Solanum melongena L.), is mostly managed using high-dose conventional insecticides, which are harmful for end-users and the environment. Target-insect is also known to exhibit host-dependent variation in insecticidal toxicities; therefore an experiment was conducted during 2020–22 at ICAR-Indian Agricultural Research Institute, New Delhi, to study the host-specific toxicity relationships on tomato and brinjal using market-available safer insecticides with green labels in the Indian context. Bioefficacy evaluated on eggs, nymphs, and adults using leaf-dip bioassay (IRAC) recorded higher LC50 for candidate insecticides (clothianidin, spinetoram and cyantraniliprole), but lower toxicities for azadirachtin and novaluron for test-insects reared on brinjal. The possible role of test-leaf on LC50 was evaluated in a reciprocal way, i.e. test-populations grown in tomato were subjected to brinjal leaf bioassay and vice versa. This resulted to no significant change in LC50 and implies no effect of the test leaf. Feeding (honeydew excretion) and oviposition studies showed higher honeydew excretion (76.4 mm2) and egg-laying (43.6 eggs) per 20 adults on brinjal. Detoxification enzymatic activities in control showed the test enzymes, viz. carboxylesterase, glutathion S-transferase and cytochrome P450 monooxygenase, were at higher concentrations in the brinjal population, i.e. 1.75, 1.43 µ mol/min/mg, and 3.10 n mol/min/mg of protein. Results showed that brinjal is the preferred host for B. tabaci, on which it develops healthier and resulting in a higher insecticide dose to arrive at the desired lethal effect.

Protocol for Temperature Toxicity Investigation on Whitefly <i>Bemisia tabaci</i> (Gennadius)

A cost-effective laboratory protocol was perfected for investigating temperature toxicity against whitefly Bemisia tabaci (Genn.) on tomato. Understanding temperature toxicity relationship will aid in strategization of pest management. The experiments conducted to develop the current protocol used B. tabaci Asia II-1 as test insect. Essentially this protocol consist of three steps which are: (1) Temperature incubation of test insects: includes three hour starvation period and temperature treatment of B. tabaci; (2) Preparatory steps of leaf-dip bioassay: suggests use of agar cube method (reduces agar usage by 70%) to maintain green and turgid test leaves during post-exposure period of bioassay; (3) Release of temperature treated insects and mortality counting: test insect release, securing petri plates, recording observations, etc. all are deliberated in detail. This protocol facilitates economical, convenient and easy-to-handle experimentation to study temperature toxicity relationship in B. tabaci.

Studies on biology and preference of Helicoverpa armigera (Hubner) on different host plants and evaluation of botanicals for its management

The biology and fitness of Helicoverpa armigera (Hubner) was studied on bottle gourd, lady’s finger, chilli and tomato. The total larval duration was found to be 20, 22.5, 20.3 and 18.3 days on tomato, chilli, lady’s finger and bottle gourd respectively. The total life cycle was of 35.25, 40.7, 34.2 and 31.3 days on tomato, chilli, lady finger and bottle gourd respectively. Shortest life cycle was observed on bottle gourd and longest on chilli. Feeding preference and fitness of H. armigera revealed that it preferred bottle gourd over other host plants. On bottle gourd, the pest recorded highest mean larval weight gain (0.112g/ day), while the lowest was on chilli (0.090g/ day). The feeding period was 8.073 days on bottle gourd and 8.266 days on chilli. Average food ingested on bottle gourd, lady finger, chilli and tomato were 3.083, 2.347, 2.076 and 1.988g respectively. Bioefficacy of botanicals (5 % aqueous extracts of periwinkle, giloy, tulsi and lantana) against H. armigera by leaf dip bioassay using leaves of tomato showed that the average food ingested in periwinkle, giloy, tulsi, lantana and control was 0.644, 0.944, 1.038, 0.985 and 2.297g respectively. This is the first report evidencing the insecticidal properties of aqueous extracts of giloy against H. armigera.

English

Whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is a notorious sucking insect pest of cotton and many other crops worldwide. It acts as a vector of various diseases and responsible for causing destruction to economy by damaging major crops. In order to determine, the resistance ratio and efficacy of insecticides against whitefly, field populations of B. tabaci were collected from four districts (Multan, Bahawalpur, Jhang and Toba Tek Singh) of Punjab, Pakistan, during 2020 to 2022. After collection, leaf-dip bioassay method was used to measure resistance level in whitefly populations by insecticides (spirotetramat, buprofezin, pyriproxyfen, diafenthiuron, and bifenthrin). The results showed that B. tabaci developed high to very high resistance against buprofezin (97.26-108.41 fold), high resistance level against bifenthrin (70.65-95.30 fold), moderate to high resistance against pyriproxyfen (35.68-80.46 fold), moderate level of resistance against diafenthiuron (20.72- 30.77 fold), low level of resistance against spirotetramat (11.66-18.60 fold), while comparing with susceptible population. The results of present study i.e., spirotetramat and diafenthiuron may be used as wise choices regarding the selection of insecticides against B. tabaci and delay insecticide resistance

Managing sucking pests biorationally considering bean aphid, Aphis craccivora Koch. as an example

Conventional control of sucking pests infesting various vegetables has several drawbacks. Biorational insecticides are increasingly used for pest management due to their limited side effects. A study involving several biorational compounds, viz. spinosad, buprofezin, Beauveria bassiana, Lecanicillium muscarium and a chemical insecticide, fenitrothion was performed by leaf-dip bioassay to measure their efficacy against the bean aphid, A. craccivora Koch. as a representative of sucking pests. Mortality of aphids against treatment with biorational insecticides was recorded in three replicates under laboratory conditions. The lethal concentration (LC50 and LC90) of the treatments were calculated by probit analysis. Efficacy was concentration and time dependent. Spinosad has been found to be more effective than buprofezin. The spinosad (LC50 = 2582.04 ppm) and buprofezin (LC50 = 543.03 ppm) were found to be approximately 88 and 52 times less toxic than fenitrothion. At 48 h post-treatment (HPT), the highest mortality for spinosad and buprofezin was 66.67 and 60.00%, respectively, and reached 93.33% at 72 HPT. Among the two fungal biopesticides, L. muscarium was more effective than B. bassiana. For both, mortality (80–100%) at the higher concentrations was statistically different than others at 144 and 168 HPT. Thus, biorational compounds, particularly spinosad and L. muscarium, are useful for controlling bean aphids.

Myzus persicae (Sulzer, 1776) (Hemiptera: Aphididae) popülasyonlarında neonikotinoid ve sentetik piretroid insektisitlerin tekli ve karışımlarına karşı direnç durumu

The peach potato aphid, Myzus persicae (Sulzer, 1776) (Hemiptera: Aphididae), a vector of many plant virus diseases, causes damage to its wide range of hosts by direct feeding. Chemical control has been the primary method to control this species, and the intensive use of insecticides has led to the development of resistance. In this study, conducted between the years 2017-2019, firstly resistance ratio of five M. persicae populations from Antalya, Türkiye were determined by leaf-dip bioassay method. The field populations showed significant resistance to thiamethoxam (between 201-332 fold) and lambda-cyhalothrin (between 50-103 fold) when compared to susceptible population. To identify whether resistance mediated by mutations in sodium channel and nicotinic acetylcholine receptor, DNA regions that encompass “mutation hot-spot” were sequenced. This revealed no population contained R81T mutation that has been previously linked with neonicotinoid resistance. As to synthetic pyrethroid resistance, the L1014F kdr mutation was fixed in all field populations. This study is the first description of kdr mutation in M. persicae populations from Türkiye. Bioassay results also indicated that the toxicity of thiamethoxam and lambda-cyhalothrin mixture was higher than that of lambda-cyhalothrin alone. Our findings can make significant contributions to M. persicae resistance management.

Sublethal Effects of Flonicamid on Life Table of Myzus persicae (Sulzer)

The green peach aphid, Myzus persicae (Sulzer) (Aphididae: Hemiptera) is a cosmopolitan polyphagous pest of more than five hundred plant species belonging to at least forty different plant families including several economically important agricultural crops. The sublethal effect of LC25 concentration of flonicamid on M. persicae was assessed by using an age-stage two-sex life table approach for integrated management of this pest. A leaf-dip bioassay showed that flonicamid was very toxic to the adults of M. persicae at 48 h with the calculated LC25 concentration value of 0.0115 g a.i./L. The adults (parental generation) of M. persicae exposed to the LC25 concentration (sublethal dose) of flonicamid showed inhibitory effects on the life history traits across its generations such as reduction in adult longevity and fecundity of parental generation (F0); shortening the durations of fifth instar nymphs, adult female longevity, oviposition period, total longevity and fecundity of F1 & F2 generations. On the other hand, stimulatory effects were observed on the duration of first, second, third, and fourth instar nymphs; and pre-adults in F2 generation in the flonicamid-treated aphids. Consistently with the effects on individual traits, a higher mean generation time (T) and shorter intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R0) of F2 generation were observed in the flonicamid treated aphids, although r, λ, R0, T, and gross reproductive rate (GRR) of F1 generation were not significantly affected. The findings revealed the exposure of parental adults of M. persicae to sublethal concentration of flonicamid could induce hormetic (both inhibitory and stimulatory) effects on their succeeding generations. This study is useful for assessing the overall effects of flonicamid on M. persicae. The hormetic effects should be considered when it used flonicamid in the integrated management of M. persicae in crop fields.

Biochemical alterations in cotton leafworm, Spodoptera littoralis (Boisd.) related to emamectin benzoate and fipronil compared to their joint action

Cotton leafworm, Spodoptera littoralis (Boisduval), is one of the major destructive pests of ornamental, industrial, and vegetable crops. The efficacy of technical emamectin benzoate (EMB) and fipronil (FPR) was assessed against the 4th larval instar using leaf-dip bioassay method. EMB was more efficient than FPR based on 96 h LC50 values of 0.004 and 0.023 μg/ml, respectively. Joint toxic action of the dual exposure in sequence with time interval 24 h and in mix were evaluated at LC10:LC10, LC25:LC25 and LC50:LC50 after 96 h posttreatment, as well. Their impacts on detoxification enzymes, esterases (ESTs); alkaline phosphatase (ALP); and glutathione S-transferase (GST) as well as acetylcholine esterase (AChE) were also determined. The sequential exposure of EMB after FPR (S1) produced antagonism, potentiation, and potentiation effects, respectively while sequential exposure of FPR after EMB (S2) interacted as addition, potentiation, and potentiation respectively. The rest of binary mixtures (Mix) revealed antagonistic effect regardless of concentration. Orthogonal contrast analysis showed that the highest elevations of AChE, α-EST, β- EST and ALP enzymes were obtained from Mix at LC50:LC50 (181.6%, 288.4, 229.2 and 460.9%, respectively), LC25:LC25 (131.5%, 252.8, 205.60 and 252.0, respectively) and LC10:LC10 (106.6%, 215.6%, 201.8% and 170.0%, respectively). Differently, the greatest elevation of GST activity (157.7%) resulted from S1 at LC50:LC50, while it was significantly lower at LC25:LC25 and LC10:LC10 as well as Mix and S2 at all concentrations than corresponding concentrations of FPR. These findings shed some light on the role of GST in FPR toxicity and clarified the risk of these dual exposures in elevating detoxification enzymes dangerously compared to their individual insecticides. These dual exposures should be carefully handled. Although rotational exposure at low concentrations may enhance performance and mitigate resistance risk, rotational exposure at high concentrations and Mix may indirectly contribute to the evolution of cross-resistance to other insecticides.

Determining Field Insecticide Efficacy on Whiteflies with Maximum Dose Bioassays.

We conducted a rapid bioassay method to assess insecticide efficacy for controlling adult sweetpotato whitefly Bemisia tabaci in squash and cucumber crops before insecticide applications. The study aimed to evaluate the accuracy of a 24-hour laboratory bioassay in determining maximum dose insecticide efficacy in the field. Ten insecticides were evaluated using leaf-dip bioassays, and their effectiveness was tested across eight cucurbit field experiments in Georgia, USA, during the 2021 and 2022 field seasons. The maximum dose, defined as the highest labeled rate of an insecticide diluted in the equivalent of 935 L ha-1 of water, was used for all bioassays. Adult survival observed in the bioassay was compared to adult field count-based survival 24 h after treatment. A low concentration (1/10 rate) was used for imidacloprid, flupyradifurone, pyriproxyfen, and cyantraniliprole to assess insecticide tolerance in the whitefly population. Overall, significant positive correlation between laboratory bioassay and field efficacy was reported, explaining 50-91% of the observed variation. The addition of the low dosage was helpful, indicating that no rate response was consistent with susceptibility to the tested insecticide, while a rate response was associated with a loss of susceptibility between 2021 and 2022.

Development of Insecticide Resistance in Field Populations of Onion Thrips, Thrips tabaci (Thysanoptera: Thripidae).

The present study evaluated insecticide resistance in field populations of onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), collected from eight different onion-growing regions of Punjab, Pakistan. These field-collected populations were assessed for resistance development against eight commonly used active ingredients including deltamethrin, lambda-cyhalothrin, imidacloprid, acetamiprid, spinosad, spinetoram, cypermethrin, and abamectin. In leaf dip bioassays, T. tabaci adults showed varied levels of resistance towards different insecticides. Moderate or high levels of resistance to deltamethrin (58-86 fold), lambda-cyhalothrin (20-63 fold), and cypermethrin (22-54 fold) were observed in T. tabaci field populations. There were very low to moderate resistance levels to imidacloprid (10-38 fold), acetamiprid (5-29 fold), and abamectin (10-30 fold). The lowest levels of resistance were detected in thrips exposed to spinosad (3-13 fold) and spinetoram (3-8 fold). Insecticide resistance levels varied among populations collected from various geographic locations, but all populations exhibited elevated levels of resistance to deltamethrin. Thrips tabaci populations with higher resistance levels were most commonly found from the southern part of Punjab, Pakistan. Our findings revealed that spinosyns could be used as alternatives to conventional insecticides for the successful management of T. tabaci in onion fields.

Insecticidal activity and changes in midgut histology of the generalist herbivore, Spodoptera litura F. (Lepidoptera: Noctuidae) in response to seed extract of Annona squamosa Linn.

The tobacco caterpillar, Spodoptera litura F., is one of the most devastating, cosmopolitan polyphagous pests affecting major crops that significantly impact agricultural productivity. The present study aimed to evaluate the toxicological effect of seed extract of the medicinal plant, Annona squamosa L. and the histological effect on the midgut of Spodoptera litura F., under laboratory conditions. The crude methanolic extract of A. squamosa seed was tested against the third instar larvae of S. litura at five different concentrations viz., 0.5%, 1.0%, 1.5%, 2.0% and 2.5 % by leaf dip bioassay method. The seed extract exhibited larval mortality of 96.67%, 83.37 %,70%, 53.33% and 40 % at the concentrations 2.5 %, 2.0%, 1.5%, 1.0% and 0.5%, respectively.The results indicated that the response of larval mortality to the seed extract was dose-dependent. The dose of 0.5% showed the lowest mortality (40.00%), while the dose of 2.5 % showed maximum larval mortality (96.67%). Hence they were subjected to histological analysis. The anatomical sectioning of S. litura larval midgut treated with 0.5% concentration showed disruption in the peritrophic membrane and striated border of epithelial cells. The midgut of larvae treated with 2.5 % concentration showed an irregular epithelium and high vacuolization in the cytoplasmic cells. The results indicated that methanol extract of A. squamosa seed extract has the ability to cause changes in the midgut region, thereby affecting the digestion and nutrient absorption of S. litura larvae, which will lead to a debilitating effect on the development of larvae. Based on the present study A. squamosa seed extract will be a potential biopesticide for managing S. litura.

Baseline susceptibility of cabbage butterfly, Pieris brassicae (Linnaeus) (Lepidoptera: Pieridae) to Bacillus thuringiensis (Berliner) Cry toxins in Meghalaya

BackgroundCabbage butterfly, Pieris brassicae (Linnaeus) (Lepidoptera: Pieridae), is one of the most important pests of cabbage and other cruciferous crops and accounts for > 40% yield reduction in the crops. An investigation on the baseline susceptibility of P. brassicae to Bacillus thuringiensis (Bt) Cry toxins in Meghalaya was evaluated for future exploitation in Bt resistance monitoring. Two different Cry toxins, Bt Cry1C and Cry2Ab, were screened against 11 different field populations of P. brassicae from the state of Meghalaya. LC50 was evaluated based on the response of larval mortality of P. brassicae using the leaf-dip bioassay method.ResultsThe baseline-susceptibility tests conducted on P. brassicae in 11 different field populations from Meghalaya revealed that Smit population strains seemed to show less tolerance to both the Bt Cry toxins (Cry1C and Cry2Ab). Compared to the Cry1C toxin, Cry2Ab was found more potent against P. brassicae. The median lethal concentrations, LC50 72 h, varied from 0.535 to 1.725 µg/ml for Cry2Ab and 0.546–1.803 µg/ml for Cry1C toxin. The screening using leaf-dip bioassay resulted in a tolerance ratio of 3.3-fold and 3.2-fold for Cry1C and Cry2Ab, respectively. The most tolerant strains of P. brassicae from Umiam and Pepbah regions were observed to show discriminating concentrations of 19.30 µg/ml for Cry1C and 24.03 µg/ml for Cry2Ab (LC99, 72 h).ConclusionsThe Cry2Ab toxin was found to be more virulent than Cry1C toxin for P. brassicae. Certain candidate discriminating concentrations for Cry1C and Cry2Ab can be used as benchmarks for future resistance monitoring of P. brassicae to Bt Cry toxins.

Screening of the Acaricidal Activity of Essential Oils against Panonychus citri (McGregor) (Acari: Tetranychidae)

The citrus red mite, Panonychus citri (McGregor), is an important pest of citrus in China, where pesticides are commonly used in citrus orchards. In order to reduce the use of chemical pesticides against P. citri and the development of resistance, the screening of biological control agents has attracted the attention of students. In this study, seven plant essential oils with high toxicity were selected from 40 plant essential oils by the leaf-dip bioassay, including plant essential oils of lemongrass, patchouli, juniper berry, sage, clove, frankincense, and citrus. The LC50 after 72 h treatment were 3.198 μL/mL, 8.312 μL/mL, 3.244 μL/mL, 6.701 μL/mL, 8.350 μL/mL, 21.953 μL/mL, and 8.788 μL/mL, respectively. According to the LT50, the essential oils’ acute toxicity to P. citri from high to low were lemongrass, juniper berry, patchouli, citrus, sage, vetiver, and frankincense essential oils. In general, lemongrass and juniper berry essential oils have the best acaricidal effect and have high application value for the biological control of P. citri, which provides a basis for the development of botanical acaricides.

Baseline Susceptibility and Evidence of Resistance to Acetamiprid in Gill's Mealybug, Ferrisia gilli Gullan (Hemiptera: Pseudococcidae).

Gill's mealybug, Ferrisia gilli (Gullan) (Hemiptera: Pseudococcidae), is a major pest of pistachio in California. Insecticide treatment is the primary control method and acetamiprid is widely used to control this pest. However, there have been numerous reports of control failures for F. gilli after field applications of recommended insecticides in recent years. The purpose of this study was to develop a method for routine monitoring of F. gilli susceptibility and quantify current levels of F. gilli susceptibility to acetamiprid. A leaf-dip bioassay method using lima bean leaves was established and baseline susceptibility responses of 5 field populations were determined. Lethal concentrations to kill 50% of population (LC50) for second instar nymphs at 48 h ranged from 0.367 to 2.398 µg(AI)ml-1 of acetamiprid. Similarly, lethal concentrations to kill 90% of population (LC90) for second instar nymphs at 48 h ranged from 2.887 to 10.752 µg(AI)ml-1 of acetamiprid. The F. gilli population collected from Hanford area showed up to 6.5-fold significantly decreased mortality to acetamiprid compared to other populations. The resistance identified in this study, although relatively low, indicates that there has been repeated pressure to select for acetamiprid resistance and resistance levels can further magnify if effective management steps are not taken. The baseline susceptibility established in this study can be used to investigate potential cause of recent acetamiprid failures against F. gilli. In the long-term, results of this study will support the development of resistance management strategies by monitoring shifts in the susceptibility of F. gilli populations.