Behavioral Response of Bemisia tabaci (Hemiptera: Aleyrodidae) to 20 Plant Extracts

Essential oils of plants and their combinations as an alternative adulticides against Anopheles gambiae (Diptera: Culicidae) populations

The persistence of malaria and the increasing of resistance of Anopheles gambiae species to chemicals remain major public health concerns in sub-Saharan Africa. Faced to these concerns, the search for alternative vector control strategies as use of essential oils (EOs) need to be implemented. Here, the five EOs from Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora, Ocimum americanum obtained by hydro distillation were tested according to World Health Organization procedures on An. gambiae "Kisumu" and field strains collected in "Vallée du Kou". Also, the binary combinations of C. nardus (Cn) and O. americanum (Oa) were examined. As results, among the EOs tested, L. multiflora was the most efficient on both An. gambiae strains regarding KDT₅₀ (50% of mosquitoes knock down time) and KDT₉₅ and rate of morality values. Our current study showed that C8 (Cn 80%: Oa 20%) and C9 (Cn 90%: Oa 10%), were the most toxic to An. gambiae strain "Vallée de Kou" (VK) with the mortality rates reaching 80.7 and 100% at 1% concentration, respectively. These two binary combinations shown a synergistic effect on the susceptible population. However, only C9 gave a synergistic effect on VK population. The bioactivity of the two EOs, C. nardus and O. americanum, was improved by the combinations at certain proportions. The resistance ratios of all EOs and of the combinations were low (< 5). The combinations of C. nardus and O. americanum EOs at 90: 10 ratio and to a lesser extent L. multiflora EO, could be used as alternative bio-insecticides against malaria vectors resistant to pyrethroids in vector control programmes.

Characterization of Zanthoxylum rhoifolium (Sapindales: Rutaceae) Essential Oil Nanospheres and Insecticidal Effects to Bemisia tabaci (Sternorrhyncha: Aleyrodidae)

Encapsulation via nanotechnology offers a potential method to overcome limited thermal and photo-stability of botanical pesticides. In this study, nanospheres of essential oils (NSEO) derived from Zanthoxylum rhoifolium Lam. fruit were characterized and evaluated for their photostability and insecticidal activity against Bemisia tabaci. Three major compounds of Z. rhoifolium fruits were detected by CG-MS: β-phellandrene (76.8%), β-myrcene (9.6%), and germacrene D (8.3%). The nanoprecipitation method was used to obtain homogeneous spherical NSEO, with ≥98% encapsulation efficiency. Tests with UV/Vis spectrophotometry showed significantly reduced photodegradation from exposed NSEO samples when compared with essential oil (EO) controls. Whitefly screenhouses bioassays with bean plants treated with 0.25, 0.5, 1 and 1.5% suspensions showed EO treatments in both free and nanoencapsulated forms reduced adult whitefly oviposition by up to 71%. In further tests, applications at 1.5% caused ≥64% mortality of second instar nymphs. When the test was conducted under high temperature and light radiation conditions, the insecticidal effect of NSEO treatments was improved (i.e., 84.3% mortality) when compared to the free form (64.8%). Our results indicate the insecticidal potential of EO-derived from Z. rhoifolium fruits with further formulation as nanospheres providing greater photostability and enhanced insecticidal activity against B. tabaci under adverse environmental conditions.

Repellency of Wild Oregano Plant Volatiles, Plectranthus Amboinicus, and Their Essential Oils to the Silverleaf Whitefly, Bemisia Tabaci, on Tomato

The Bemisia tabaci (Gennadius) whitefly is a major economically damaging pest of many crops such as tomato (Solanum lycopersicum L.). Pesticides are widely used to control B. tabaci while the use of aromatic plants is an alternative control method. The aim of this study was to assess the B.tabaci repellent effect of wild oregano, Plectranthus amboinicus (Lour.) Spreng, a widespread aromatic plant in the West Indies. We tested three origins of wild oregano, including northern, central, and southern Martinique (French West Indies). Our results showed that all essential oils of wild oregano had either masking properties or were true repellents-the mean percentage of whiteflies present in the upper part of the still-air olfactometer was 1.3- to 1.9-fold lower than in the controls. The ethanolic solution of volatile organic compounds of wild oregano from southern Martinique also had a true repellent effect-the mean percentage of whiteflies present in the upper part of the still-air olfactometer was 1.3-fold lower than in the controls. Moreover, in a greenhouse insect-proof cage, there were 1.5 fewer adult whiteflies on tomato intercropped with wild oregano from southern Martinique than on tomato alone after 96 h exposure. Our study generated further insight into the potential of P. amboinicus for B. tabaci biocontrol on tomato crops. Wild oregano extracts were repellent to B. tabaci and could be used as a companion plant to prevent whitefly infestations on tomato crops. However, the B. tabaci behavior depends on the plant origin.

Influence of Olfaction in Host-Selection Behavior of the Cassava Whitefly Bemisia tabaci

Cassava is a vital food-security crop in Sub-Saharan Africa. Cassava crops are, however, severely affected by viral diseases transmitted by members of the whitefly species complex Bemisia tabaci. We have here investigated the role of olfaction in host selection behavior of the cassava whitefly B. tabaci SSA-ESA biotype. Surprisingly, we find that the whiteflies appear to make little use of olfaction to find their favored host. The cassava whitely shows a highly reduced olfactory system, both at the morphological and molecular level. Whitefly antennae possess only 15 sensilla with possible olfactory function, and from the genome we identified just a handful of candidate chemoreceptors, including nine tuning odorant receptors, which would afford the whitefly with one of the smallest olfactomes identified from any insect to date. Behavioral experiments with host and non-host plants, as well as with identified specific volatiles from these sources, suggest that the few input channels present are primarily tuned toward the identification of unwanted features, rather than favored ones, a strategy quite unlike most other insects. The demonstrated repellence effect of specific volatile chemicals produced by certain plants unflavored by whiteflies suggests that intercropping with these plants could be a viable strategy to reduce whitefly infestations in cassava fields.

Avocado kernels, an industrial residue: a source of compounds with insecticidal activity against silverleaf whitefly

Fruit processing waste, such as kernels (endocarp + seed) of avocado [Persea americana Mill. (Lauraceae)], could be used as raw material in the preparation of botanical insecticides. In light of this potential, this study assessed the insecticidal action of extracts and fractions from kernels of two avocado cultivars (Breda and Margarida) on Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, an important pest species in tropical conditions. Ethanolic and aqueous extracts prepared from kernels of P. americana, regardless of the plant cultivar used, caused promising insecticidal activity to whitefly nymphs. Based on yield in crude extracts [10.32 and 9.85% (w/w), respectively, for cultivars Breda and Margarida], on the bioassay results with crude extracts and on the chemical profiles, the ethanolic extract of kernels of P. americana cv. Breda was chose for the continuation of the study. Thus, the ethanolic extract of kernels of cv. Breda (LC₅₀ = 197.84 ppm and LC₉₀ = 567.19 ppm) was selected and subjected to fractionation by the liquid-liquid partition technique. The hexane and dichloromethane fractions of this extract caused significant mortality of nymphs. The analysis using the ultraviolet (UV) and hydrogen nuclear magnetic resonance (¹H NMR) showed the presence of long-chain aliphatic compounds (alkanols or acetogenins of Lauraceae), alkylfurans (or avocadofurans), and unsaturated fatty acids in these fractions, which are possibly related to bioactivity observed in B. tabaci, besides saccharides. The results show that kernels of P. americana are promising sources of compounds with insecticidal action for the control of B. tabaci biotype B, a great opportunity to transform environmental problems into eco-friendly solutions to agriculture.

Insecticidal activity of marigold Tagetes patula plants and foliar extracts against the hemipteran pests, Lygus hesperus and Bemisia tabaci

The western tarnished plant bug, Lygus hesperus Knight (Hemiptera: Miridae) and the whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) are key hemipteran pests of numerous crop plants throughout the western United States and Mexico. Management in the U.S. currently relies on only a few insecticides and is threatened by the evolution of resistance. New chemistries or alternative management strategies are needed to reduce selection pressure on current insecticides and enhance control. Here, we investigated the bio-insecticidal toxicity of the French marigold, Tagetes patula Linnaeus (Asterales: Asteraceae), against both L. hesperus and B. tabaci. Assays indicated significantly reduced survival of both pest species on T. patula plants, and in diet incorporation assays containing aqueous and methanolic marigold foliar extracts. Mortality was concentration-dependent, indicating the presence of one or more extractable toxicants. These data suggest that T. patula plants have insecticidal constituents that might be identified and developed as novel alternatives to conventional chemical treatments.

TRPA1 modulates noxious odor responses in Lygus hesperus

Lygus hesperus isa key pest of many economically important crops across western North America. Central to many aspects of the lives of these insects is chemical signalling, with identified roles in host plant selection, aggregation and passive mate guarding. The development of novel monitoring and control approaches for this insect will rely on a sound understanding of how these cues are perceived and processed, and their impact on behavior. Towards this end, we investigated allyl isothiocyanate, cinnamaldehyde and citronellal, compounds that are noxious repellents to other insects. We found that L. hesperus avoided areas containing the three compounds and that exposure induced increases in movement velocity and duration in both nymphs and adults. This suggests these compounds may work as repellents. To better understand the underlying physiology of this response, RNA interference by dsRNA injection was used to inhibit the expression of two chemosensory-associated proteins, the odorant receptor co-receptor (Orco) and the transient receptor potential A (TRPA1) channel. While knockdown of Orco did not change the reaction of adult females to citronellal, TRPA1 silencing effectively eliminated the induced increase to movement, suggesting a chemoperceptory role in citronellal detection.

Citrullus ecirrhosus: Wild Source of Resistance Against Bemisia tabaci (Hemiptera: Aleyrodidae) for Cultivated Watermelon

Members of the highly polyphagous Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) species complex cause major crop damage by feeding and by transmitting plant viruses. The Middle East-Asia Minor 1 (MEAM1) of the B. tabaci complex is by far the most problematic whitefly affecting crops including cultivated watermelon (Citrullus lanatus; Cucurbitaceae: Cucurbitales). Watermelon cultivars share a narrow genetic base and are highly susceptible to whiteflies. We studied the potential of C. ecirrhosus, a perennial desert species that can be hybridized with C. lanatus, as a source of whitefly resistance for cultivated watermelon. The results of this study indicate that C. ecirrhosus offers resistance (although not total) against the MEAM1 B. tabaci based on, at least, antibiosis and antixenosis. Whitefly performance concerning developmental survival, body size attainment, and nonpreference were suppressed on C. ecirrhosus compared with the watermelon cultivar 'Sugar Baby'. Also, our olfactometer results indicated that the adults were less attracted to leaf volatiles of C. ecirrhosus. Although there is a pungent odor associated with the leaves of C. ecirrhosus, the leaf volatiles had no toxic effect on adult whitefly survival as compared with cultivated watermelon. We also demonstrated that plants of C. ecirrhosus can be clonally propagated from vine cuttings of the parent plant. Using traditional breeding procedures, C. ecirrhosus was hybridized with C. lanatus and viable F1 and F2 seeds were produced. This is the first report of pest resistance in C. ecirrhosus. This wild species offers a source of resistance against whiteflies for the improvement of cultivated watermelon.

Rosemary-Whitefly Interaction: A Continuum of Repellency and Volatile Combinations

The sweet potato whitefly Bemisia tabaci Genn (Hemiptera: Aleyrodidae) has been recorded to differentially prefer rosemary (Rosmarinus officinalis) varieties in commercial fields in Israel. As chemical signaling is a significant component in plant-insect interaction, the present study examined the involvement of rosemary essential oil volatiles in this differential colonization to elucidate the rosemary-whitefly ecological interaction. Thirty-two rosemary varieties with different chemical profiles were used. The average whitefly preference was 25.1% with a significant variation of 51.4%, partitioning the sampled varieties into five preference groups, hence suggesting rosemary as a non-preferred host for the insect. All relations between preference and the major volatiles 1,8-cineole, camphor, linalool, verbenone, bornyl acetate and borneol were significantly (P ≤ 0.05) or notably (0.05 < P ≤ 0.09) negative (r < 1). Therefore, revealing that whitefly preference for rosemary is based on a continuum of repellency rather than attraction. 'Choice' bioassays with a range of the major volatile concentrations and gas chromatography-mass spectrometry (GC-MS) volatile blends (fractions) validated this observation. Principle component analysis of the entire chemical profile of two extreme varieties, representing high and low preferences, identified that approximately 43% of the volatiles in the essential oil were directly associated with repellency. Keeping in mind the remaining 57% of the compounds, this myriad of volatiles exhibit the ecological complexity of the rosemary-whitefly eco-system, explaining that whitefly preference to rosemary is repellency based.

Methyl benzoate exhibits insecticidal and repellent activities against Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)

Methyl benzoate (MB) is a plant-derived volatile organic compound with insecticidal properties, but such activity has not been evaluated against the sweetpotato whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), a major crop pest. In this study, we tested methyl benzoate control efficacy on B. tabaci infecting tomato plants in a greenhouse, specifically measuring contact and fumigant toxicity, as well as repellent activity. For direct spray applications of 0% (control), 0.1%, 0.25%, 0.5%, 1%, 2% MB onto tomato leaves infested with adults of B. tabaci (< 5-d-old), 2% MB showed the highest corrected mortality (100%) at 24 h post-treatment. For residual toxicity in which the same MB solutions were sprayed onto tomato leaves and allowed to dry for 2 h before < 5-d-old adults were released, the 2% MB also showed the highest corrected mortality (100%) at 48 h post-treatment. The lethal median concentration (LC50) for eggs, fourth-instar nymphs, and adults were 0.3%, 0.2%, and 0.2%, respectively. In pot culture experiments, 1% MB concentration was found more effective at killing nymphs and preventing adult eclosion than all other concentrations, and gave 100 percent population reduction compared with the control. MB repelled adult whiteflies and caused 96.5% fumigant toxicity within 10 h post-treatment. Repellency and anti-oviposition rates against B. tabaci had median effective doses of 0.24% and 0.16%, respectively. Our results suggest that MB has strong potential as an environmentally friendly biopesticide for control of B. tabaci but field trials and further greenhouse studies are required to establish efficacy under more natural conditions.

Characterization of Nanospheres Containing Zanthoxylum riedelianum Fruit Essential Oil and Their Insecticidal and Deterrent Activities against Bemisia tabaci (Hemiptera: Aleyrodidae)

The aim of our study was to produce and characterize poly-ε-caprolactone (PCL) nanospheres containing essential oils from Zanthoxylum riedelianum fruit and to evaluate their stability gains as well as their insecticidal and deterrent activities against whitefly (Bemisia tabaci). The PCL nanospheres exhibited a homogeneous spherical morphology, with particle diameters between 106.7 nm and 129.2 nm, pH of approximately 6, zeta potential (ZP) lower than −19.0 mV and encapsulation efficiency higher than 98%. Only 43% of the nanoencapsulated essential oil (NSEO) was degraded in response to ultraviolet light, whereas the essential oil (EO) degraded by 76% over the same period. In a free-choice test, the NSEO and EO reduced the number of whitefly eggs by approximately 70%. NSEO and EO at 1.5% killed 82.87% and 91.23% of 2nd-instar nymphs of whitefly, respectively. Although NSEO displayed lower insecticidal activity, it offers a greater advantage over the free EO, due to protection conferred by polymer against photodegradation. Therefore, its usage may optimize the maintenance of essential oils in the field through photoprotection and controlled release. Our results suggest that the EO of Z. riedelianum fruit can be used for B. tabaci management strategy; nevertheless, the benefits of NSEO require further evaluation at the field level.

Toxic effects of Solanum xanthocarpum Sch &Wendle against Helicoverpa armigera (Hub.), Culex quinquefasciatus (Say.) and Eisenia fetida (Savigny, 1826)

Many commercially available agro and household chemicals are used as pesticides, repellents, and growth inhibitors against insect pests. The repeated uses of these chemicals against insect pests have caused the development of resistance in them; they also cause ill effects on nontarget organisms. The present study was aimed to evaluate the antifeedant, larvicidal, pupicidal, and biochemical effects of the solvent extracts of Solanum xanthocarpum against third instar larvae of Helicoverpa armigera. Hexane, chloroform and ethyl acetate extracts were subjected to phytochemical analysis. The results revealed the presence of terpenoids, flavonoid, and quinone. Maximum antifeedant activity of 72.30% was recorded in chloroform extract followed by hexane (69.02%) and ethyl acetate (57.40%) extracts against H. armigera. Chloroform extracts of S. xanthocarpum showed more than 60% larvicidal and pupicidal activity against H. armigera. The effective chloroform extract was fractionated with increasing polarity of solvent system (hexane, chloroform, and ethyl acetate extracts). Based on the TLC profile, nine major fractions were isolated. The fourth fraction showed higher antifeedant, larvicidal, and pupicidal activity against H. armigera. The effective fraction reduced the hemolymph and gut protein concentration in a concentration-dependent manner (r ² 0.99). The effective fraction 4 showed 100% larvicidal activity at 500 ppm concentration with LC₅₀ value of 227.95 ppm. The fourth fraction did not show any toxic symptom or mortality of earthworm. Based on these results, this effective fraction could be used in the development of a pesticide formulation to control insect.

Susceptibility of MED-Q1 and MED-Q3 Biotypes of Bemisia tabaci (Hemiptera: Aleyrodidae) Populations to Essential and Seed Oils

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a major pest of many agricultural and ornamental crops in tropical and subtropical regions causing damages that result in important economic losses. Insecticides are commonly used in greenhouses or fields to control B. tabaci populations leading to rapid evolution of resistance that render treatments inefficient. Therefore, and for environmental and human health concerns, other approaches must be developed for this pest management. In the present study, we compare, using the leaf dip method, the toxicity of three essential oils (Cymbopogon citratus, Ocimum americanum, and Hyptis spicigera) and three seed oils (Lannea microcarpa, Lannea acida, and Carapa procera) with three chemical insecticides (acetamiprid, deltamethrin, and chlorpyrifos-ethyl) on adults. Two B. tabaci biotypes (MED-Q1 and MED-Q3) belonging to the Mediterranean species and collected in Burkina Faso were used. Essential oils were analyzed by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector. We showed that these two biotypes have different levels of resistance to the three insecticides, MED-Q3 being more sensitive than MED-Q1. Moreover, they differ in the frequency of resistance alleles to insecticides, especially for organophosphates, as these alleles are almost fixed in MED-Q1. On the other hand, the two biotypes prove to be more susceptible to the plant extracts than to insecticides except for chlorpyrifos-ethyl, with essential oils that showed the highest insecticidal activities. Monoterpenes content were the most abundant and showed the highest insecticidal activities. Our results indicated that essential oils, but also seed oils, have the potential to constitute an alternative strategy of pest management.

Repellent Effects of Different Celery Varieties in Bemisia tabaci (Hemiptera: Aleyrodidae) Biotype Q

Y-tube olfactometer and net cages experiments were used to investigate the repellent effects of different celery varieties in biotype Q of sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), on cucumber, Cucumis sativus L. (Cucurbitaceae). Y-tube olfactometer tests showed that whiteflies have strong repellent behavior to different celery varieties. Intercropping different celery varieties with cucumbers had significant repellent effects and oviposition deterrent effects in whiteflies. Results obtained demonstrated that the Western Europe celery varieties, Juventus and Ventura, and the Chinese celery variety, Jinnan, had good repellent efficacy against the whitefly. D-Limonene, β-myrcene, and (E)-β-ocimene might be the main active components in celery that affected the selection behavior of B. tabaci. In Western Europe celery varieties, D-limonene was the main volatile component for the repellent effects in B. tabaci; however, the two Chinese celery varieties that showed repellent effects had relatively higher volatilization quantities of β-myrcene than of D-limonene.

Repellency of Plant Extracts against the Legume Flower Thrips Megalurothrips sjostedti (Thysanoptera: Thripidae)

Megalurothrips sjostedti Trybom is an important pest of cowpea (Vigna unguiculata L.) in Africa. To propose an alternative to chemical control, the repellency of 24 plant extracts was evaluated against adult female thrips of M. sjostedti in the laboratory. Plant extracts in ethanol were separately applied on a filter paper disk in a still air visual cue olfactometer. The results showed highly significant differences in repellency among extract type, concentration and their interactions. We classified the level of repellency into four categories as strong, good, moderate and weak or non- repellent based on hierarchical ascendant classification. We identified Piper nigrum, Cinnamomum zeylanicum, Cinnamomum cassia as strong repellents. Five extracts were classified as good, eight as moderate and the remaining eight extracts were weak or non-repellent. Repellency of the extracts increased with the concentration suggesting that the behavioral response of M. sjostedti was dose-dependent. Mono- and sesquiterpene hydrocarbon compounds from seven highly repellent extracts were identified by gas chromatography-mass spectrometry (GC/MS). The use of repellent extracts could be useful in developing integrated pest management strategies for thrips on legume crops. In this regard, the specific modes of action of the identified compounds need to be investigated to incorporate them into the existing crop protection strategies.