Free-choice Assays Research Articles

Antifeedant activity of guayule resin and its compounds against the agricultural pest Labidostomis lusitanica

The economic sustainability of guayule (Parthenium argentatum A. Gray) cultivation will largely depend on its profitability, which drives strategies for the integral utilization of its biomass. Because guayule resin has been proposed as a broad-spectrum biopesticide, the aim of the present study was to test and compare its bioactivity against the agricultural pest Labidostomis lusitanica (Coleoptera: Chrysomelidae) Germar, with essential oils (EOs) from thyme (Thymus vulgaris L.), savory (Satureja montana L.), and oregano (Origanum vulgare L.). Repellency, oviposition and feeding inhibition activity were measured using free choice assays under controlled conditions, and minimal inhibitory concentrations of guayule resin fractions and isolated compounds were determined. Finally, guayule resin was tested under simulated field conditions. Results showed that the solvent used to dissolve and apply the resin had a great impact on its performance. Guayule crude resin was more active than tested EOs, particularly as an antifeedant. However, its activity did not seem to be concentration dependent, and was effective within a narrow range. In contrast to low molecular-weight rubber (LMWR), which acted as attractant, the refined resin was repellent. Nevertheless, the two different enriched resin fractions, with sesquiterpene bioactive compounds acted as attractants and feeding stimulants, as well as the isolated compounds. In the semi-field trial, crude guayule resin again showed repellency and feeding deterrence, with no mortality, overall suggesting that while guayule resin is active against L. lusitanica, the compounds responsible for this activity are likely not the sesquiterpenes.

Metabolic engineering of a 1,8-cineole synthase enhances aphid repellence and increases trichome density in transgenic tobacco (Nicotiana tabacum L.).

The green peach aphid (Myzus persicae Sulzer) is a harmful agricultural pest that causes severe crop damage by directly feeding or indirectly vectoring viruses. 1,8-cineole synthase (CINS) is a multiproduct enzyme that synthesizes monoterpenes, with 1,8-cineole dominating the volatile organic compound profile. However, the relationship between aphid preference and CINS remains elusive. Here, we present evidence that SoCINS, a protein from garden sage (Salvia officinalis), enhanced aphid repellence and increased trichome density in transgenic tobacco. Our results demonstrated that overexpression of SoCINS (SoCINS-OE) led to the emission of 1,8-cineole at a level of up to 181.5 ng per g fresh leaf. Subcellular localization assay showed that SoCINS localized to chloroplasts. A Y-tube olfactometer assay and free-choice assays revealed that SoCINS-OE plants had a repellent effect on aphids, without incurring developmental or fecundity-related penalties. Intriguingly, the SoCINS-OE plants displayed an altered trichome morphology, showing increases in trichome density and in the relative proportion of glandular trichomes, as well as enlarged glandular cells. We also found that SoCINS-OE plants had significantly higher jasmonic acid (JA) levels than wild-type plants. Furthermore, application of 1,8-cineole elicited increased JA content and trichome density. Our results demonstrate that SoCINS-OE plants have a repellent effect on aphids, and suggest an apparent link between 1,8-cineole, JA and trichome density. This study presents a viable and sustainable approach for aphid management by engineering the expression of 1,8-cineole synthase gene in plants, and underscores the potential usefulness of monoterpene synthase for pest control. © 2023 Society of Chemical Industry.

Physicochemical Properties of Sugarcane Cultivars Affected Life History and Population Growth Parameters of Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae).

Simple SummaryThe sugarcane stem borer, Sesamia nonagrioides (Lefebvre), is the most important pest of sugarcane in Iran and some other regions of the world. Variation in the resistance of six commercial sugarcane cultivars to S. nonagrioides was investigated using the oviposition preference, life history, and population growth parameters. Moreover, the physical and biochemical properties of the tested sugarcane cultivars were estimated to understand any possible correlation between the insect’s parameters and the physiochemical features of the cultivars tested. The physicochemical properties of sugarcane cultivars significantly affected S. nonagrioides oviposition behavior, life history, and population parameters. Based on the obtained results, the resistant cultivar, SP70-1143, could be recommended for cultivation in sugarcane fields where the risk of S. nonagrioides damage is usually high.The use of resistant cultivars is an efficient management strategy against S. nonagrioides. The effects of different sugarcane cultivars, CP48-103, CP57-614, CP69-1062, CP73-21, SP70-1143, and IRC99-02 were evaluated on the oviposition preference (free-choice assay), life history, and life table parameters of S. nonagrioides at 27 ± 1 °C, 60 ± 5% RH and a photoperiod of 16: 8 (L: D) h. The longest and shortest developmental times were on cultivars SP70-1143 and CP48-103, respectively. The oviposition preference of S. nonagrioides was the highest on cultivars CP48-103 and CP69-1062, and negatively correlated with the shoot trichome density and shoot rind hardness of the cultivars. The highest intrinsic rate of increase of S. nonagrioides was on cultivar CP48-103 and the lowest was on cultivar SP70-1143. The shortest mean generation time was on CP48-103 and the longest was on SP70-1143. The results indicate that cultivars CP48-103 and CP69-1062 were susceptible, and cultivar SP70-1143 was partially resistant against S. nonagrioides. This information could be useful for developing integrated management programs of S. nonagrioides, such as the use of resistant cultivars to reduce the damage caused by this pest in sugarcane fields.

Induced Tomato Resistance Against Bemisia tabaci Triggered by Salicylic Acid, β-Aminobutyric Acid, and Trichoderma.

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) biotype B is a key pest of Solanum lycopersicum L. (Solanaceae) throughout the world. In this study, we examined the induction of resistance on tomato plants treated with SA, BABA, and Trichoderma either individually or in combination against B. tabaci biotype B through the assessment of some biological and behavioral aspects of this insect pest. Also, to understand the mode of action of these inducers, we correlated and analyzed the biochemical basis of plant resistance, by measuring levels of polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), and phenolic content in leaves of treated tomato plants. The longest development time of whitefly immature stages was recorded for plants treated with root β-aminobutyric acid application (RBABA) + root Trichoderma application (RT), root salicylic acid application (RSA) + RT, and RT. In a free-choice assay, B. tabaci adults showed a significantly lower preference for settling and oviposition in RBABA + RT, RSA + RT, and RT in comparison with control. In a no-choice assay, B. tabaci females laid significantly fewer eggs on treatments than those in control, with better results observed in RBABA + RT. Plants responded to different treatments and showed higher induction of PPO, POD, and PAL activities, besides the higher accumulation of phenols in RBABA + RT, RSA + RT, and RT treatments. These results suggest that RBABA + RT, RSA + RT, and RT could be utilized for the induction of effective plant defense against B. tabaci.

Screening chilli genotypes for whitefly (<em>Bemisia tabaci </em>Genn.) resistance: A vector for chilli leaf curl virus

Whiteflies (Bemisia tabaci) are one of the most important insect-pests of chilli worldwide mainly due to their role in transmission of Begomoviruses like Chilli Leaf Curl Virus (ChL CV). In this study, selected chilli genotypes (N = 125) including wild and cultivated species were evaluated against whitefly using free choice assays and parameters like number of whiteflies settled and nymphal population (both early and late stage) were considered to identify less preferred genotypes. The genotypes were also evaluated for plant traits namely trichome density, leaf colour and biochemical content (phenols and flavonoids). The results showed that the whitefly population and nymphal density were significantly different among the genotypes evaluated. Whitefly settlers and their nymphal density were positively correlated with the leaf non-glandular trichomes. The chilli genotypes viz., IHR 4283, IHR 4329, IHR 4300, IHR 4321, IHR 4338 recorded the less numbers of whiteflies as well as nymphs and grouped as the least preferred genotypes. On the contrary, the genotypes IHR 4586 A-1, IHR 4588 and IHR 4330 recorded the highest numbers of whiteflies. The role of plant traits in whitefly resistance in chilli was discussed in detail.

Pectin Methylesterases Modulate Plant Homogalacturonan Status in Defenses against the Aphid Myzus persicae.

Because they suck phloem sap and act as vectors for phytopathogenic viruses, aphids pose a threat to crop yields worldwide. Pectic homogalacturonan (HG) has been described as a defensive element for plants during infections with phytopathogens. However, its role during aphid infestation remains unexplored. Using immunofluorescence assays and biochemical approaches, the HG methylesterification status and associated modifying enzymes during the early stage of Arabidopsis (Arabidopsis thaliana) infestation with the green peach aphid (Myzus persicae) were analyzed. Additionally, the influence of pectin methylesterase (PME) activity on aphid settling and feeding behavior was evaluated by free choice assays and the Electrical Penetration Graph technique, respectively. Our results revealed that HG status and HG-modifying enzymes are significantly altered during the early stage of the plant-aphid interaction. Aphid infestation induced a significant increase in total PME activity and methanol emissions, concomitant with a decrease in the degree of HG methylesterification. Conversely, inhibition of PME activity led to a significant decrease in the settling and feeding preference of aphids. Furthermore, we demonstrate that the PME inhibitor AtPMEI13 has a defensive role during aphid infestation, since pmei13 mutants are significantly more susceptible to M. persicae in terms of settling preference, phloem access, and phloem sap drainage.

Effect of Eugenia winzerlingii Extracts on Bemisia tabaci and Evaluation of its Nursery Propagation

The development of natural alternatives to control Bemisia tabaci Genn. (Hemiptera: Aleyrodidae), such as the use of plant derivatives, is a preponderant need in horticultural production systems. Plant extracts and essential oils of several species of the genus Eugenia (Myrtaceae) have shown insecticidal activity. In southern Mexico, leaf extracts from Eugenia winzerlingii showed nematicidal effect but its insecticidal properties have not been explored. Therefore, the objective of this study was to evaluate the insecticidal effect of aqueous and organic extracts from E. winzerlingii leaves on B. tabaci egg, nymph and adult stages, and else to explore its nursery propagation. Then, extracts of this species were obtained by maceration with different polarity solvents. Bioassays were carried out on Capsicum chinense leaves. Mortality assays showed that aqueous and total crude ethanol (TCE) extracts necrosed the eggs (LC50=4.68 mg/mL and 0.21% w/v) whereas hexane, ethyl acetate (ETA), residual ethanol and TCE extracts affected the nymphs (LC50=0.25 - 4.85 mg/mL). In adults, oviposition inhibition by free choice assay indicated that TCE and ETA extracts had major activity (EC50=14.62 and 27.9 µg/cm2, respectively). On other hand, the sexual and vegetative propagation of E. winzerlingii showed that this species can be easily cultivated by seeds. In conclusion, extracts of E. winzerlingii leaves are highly effective in controlling B. tabaci. TCE extract, in particular, was toxic to three stages of B. tabaci. This plant could be a potential alternative to develop a novel botanical insecticide to manage this destructive pest.

Bactericera cockerelliSulc Oviposition Preference and Development on Three Tomato Varieties

Interactions between plants and insects have been widely studied. Plants develop numerous strategies to avoid establishment and/or feeding by insects. The aim of this research was to evaluate oviposition preference, nymphal development, and survival of Bactericera cockerelli Sulc on ‘Floradade’, ‘Micro-Tom’, and ‘Wild’ varieties of tomato (Solanum lycopersicum L.). Free-choice assays showed B. cockerelli oviposited twice more on ‘Floradade’ than ‘Micro-Tom’ with 1,000 and 479 eggs, respectively. Nymphal stages as well as adults of the pest developed much better on Floradade’ variety to emerge 3 days earlier than in ‘Micro-Tom’ and ‘Wild’ varieties. Adult emergence percentage was 52, 36, and 18% for ‘Floradade’, ‘Micro-Tom’, and ‘Wild’. Results in a greenhouse showed the degree of domestication of tomato varieties affected oviposition preference and survival of the insect.

Identification and Characterization of Resistance to Soybean Aphid (Hemiptera: Aphididae) in Plant Introductions of Wild Soybean

The soybean aphid, Aphis glycines Matsumura, is a serious pest of soybean [Glycine max (L.) Merr.] in the USA and Canada, and a sporadic pest of soybean in Asia. Infestations by soybean aphid cause economic loss to soybean through reductions in seed yield and oil concentration. Aphid-resistant soybean lines are needed to supplant insecticides for managing soybean aphid, and resistant lines may be developed from both domesticated and wild soybean lines. Free-choice assays of 42 lines of wild soybean (Glycine soja Siebold and Zucc.) in this study identified line 99PI522233 as resistant to soybean-aphid biotype 1. That line was advanced for follow-up assays with wild soybean lines PI 469399 B, PI 507825, PI 507840 and PI 507843, which had previously been screened as aphid resistant. Line 99PI522233 had significantly fewer soybean aphids than other lines except the resistant check in the second and third weeks of a no-choice assay, but the four other putatively resistant lines did not show resistance in the no-choice assay. Thus, line PI99522233 may be advanced for genetic characterization of its resistance, and it should be tested for resistance against virulent soybean aphid biotypes.

Establishing alighting preferences and species transmission differences for Pea seed-borne mosaic virus aphid vectors

Pea seed-borne mosaic virus (PSbMV) infection causes a serious disease of field pea (Pisum sativum) crops worldwide. The PSbMV transmission efficiencies of five aphid species previously found landing in south-west Australian pea crops in which PSbMV was spreading were studied. With plants of susceptible pea cv. Kaspa, the transmission efficiencies of Aphis craccivora, Myzus persicae, Acyrthosiphon kondoi and Rhopalosiphum padi were 27%, 26%, 6% and 3%, respectively. Lipaphis erysimi did not transmit PSbMV in these experiments. The transmission efficiencies found for M. persicae and A. craccivora resembled earlier findings, but PSbMV vector transmission efficiency data were unavailable for A. kondoi, R. padi and L. erysimi. With plants of partially PSbMV resistant pea cv. PBA Twilight, transmission efficiencies of M. persicae, A. craccivora and R. padi were 16%, 12% and 1%, respectively, reflecting putative partial resistance to aphid inoculation. To examine aphid alighting preferences over time, free-choice assays were conducted with two aphid species representing efficient (M. persicae) and inefficient (R. padi) vector species. For this, alatae were set free on multiple occasions (10–15 repetitions each) amongst PSbMV-infected and mock-inoculated pea or faba bean (Vicia faba) plants. Following release, non-viruliferous R. padi alatae exhibited a general preference for PSbMV-infected pea and faba bean plants after 30min–4h, but preferred mock-inoculated plants after 24h. In contrast, non-viruliferous M. persicae alatae alighted on mock-inoculated pea plants preferentially for up to 48h following their release. With faba bean, M. persicae preferred infected plants at the front of assay cages, but mock-inoculated ones their backs, apparently due to increased levels of natural light there. When preliminary analyses were performed to detect PSbMV-induced changes in the volatile organic compound profiles of pea and faba bean plants, higher numbers of volatiles representing a range of compound groups (such as aldehydes, ketones and esters) were found in the headspaces of PSbMV-infected than of mock-inoculated pea or faba bean plants. This indicates PSbMV induces physiological changes in these hosts which manifest as altered volatile emissions. These alterations could be responsible for the differences in alighting preferences. Information from this study enhances understanding of virus-vector relationships in the PSbMV-pea and faba bean pathosystems.

Decreased rates of operant food self-administration are associated with reward deficits in high-fat feeding mice.

Highly palatable foods behave as appetitive reinforcers and tend to be consumed compulsively. Nevertheless, the motivation for this kind of diets in experimental diet-induced obesity models has not been well established. Our hypothesis is that obesity caused by a regular consumption of high-fat diet (HFD) occurs concomitantly with the inhibition of food reward. The ultimate goal of our study was to further analyze the extent to which the perception of food as an appetitive reinforcer is a necessary condition for obesity. We have evaluated the influence of HFD on operant food self-administration (FSA) during a whole light-dark (12-12-h) cycle in mice that consumed HFD either during 1, 4 or 8weeks. The study has been complemented by a two-bottle free-choice assay between tap water and sweetened drinks. These data show that both 4- and 8-week HFD treatments induced a significant decrease in operant FSA rate. Moreover, HFD impaired the sweetened-conditioned flavor preference in the two-bottle choice assay. Our results, showing a reduction in how hard an animal is willing to work for food reinforcers, provide evidence that chronic consumption of HFD negatively contributes to the incentive motivation to acquire food/drink reinforcers. We demonstrate that energy homeostasis imbalance triggered by HFD is associated with the inhibition of hedonic feeding.

Population parameters of Tetranychus turkestani (Acari: Prostigmata: Tetranychidae) on fourteen melon genotypes

The antixenosis effects of Galia, CMD-158, CMC-132, CMI-157, CMI-167, CMI-175, Ananasi, Yellow Canary, Samsoori, Honey Dew, Bargney, CM-170, Khaghani and Garmsari, and the life table parameters of T. turkestani on CMC-132, CMI-167, Ananasi, Samsoori, Honey Dew and Bargney, were examined at 28 ± 1°C, 65 ± 10 % RH and a photoperiod of 16:8 L:D. In free-choice assay, the lowest preferences by adults were observed on CMI-167, Samsoori and Ananasi opposed to Honey Dew and Bargney were preferred the highest by adults of T. turkestani . The longest developmental times for both sexes were observed on CMC-132 and Ananasi, while the shortest developmental times were obtained on Honey Dew, Samsoori for females. The lowest total fecundity was observed on CMC-132 whereas the maximum was on Honey Dew. In addition, the highest value of intrinsic rate of increase ( r m ), net reproductive rate ( R 0 ), finite rate of increase ( l ) of T. turkestani were observed on the Honey Dew. The Weibull and Enkegaard models were used to fit survivorship ( l x ) and age specific fecundity ( m x ) data, respectively. The comparison and cluster analysis of biological parameters of T. turkestani on different melon genotypes demonstrated that CMC-132, Ananasi and CMI-167 were the most resistant genotypes to this pest.

Triple monoamine uptake inhibitors demonstrate a pharmacologic association between excessive drinking and impulsivity in high-alcohol-preferring (HAP) mice.

Approximately 30% of current drinkers in the United States drink excessively, and are referred to as problem/hazardous drinkers. These individuals, who may not meet criteria for alcohol abuse or dependence, comprise binge, heavy drinkers, or both. Given their high prevalence, interventions that reduce the risk of binge and heavy drinking have important public health implications. Impulsivity has been repeatedly associated with excessive drinking in the clinical literature. As impulsivity is correlated with, and may play a critical role in, the initiation and maintenance of excessive drinking, this behavior may be an important target for therapeutic intervention. Hence, a better understanding of pharmacological treatments capable of attenuating excessive drinking and impulsivity may markedly improve clinical outcomes. The high-alcohol-preferring (HAP) mice represent a strong rodent model to study the relationship between impulsivity and excessive alcohol drinking, as recent evidence indicates they consume high levels of alcohol throughout their active cycle and are innately impulsive. Using this model, the present study demonstrates that the triple monoamine uptake inhibitors (TUIs) amitifadine and DOV 102, 677 effectively attenuate binge drinking, heavy drinking assessed via a 24-hour free-choice assay, and impulsivity measured by the delay discounting procedure. In contrast, 3-PBC, a GABA-A α1 preferring ligand with mixed agonist-antagonist properties, attenuates excessive drinking without affecting impulsivity. These findings suggest that in HAP mice, monoamine pathways may predominate as a common mechanism underlying impulsivity and excessive drinking, while the GABAergic system may be more salient in regulating excessive drinking. We further propose that TUIs such as amitifadine and DOV 102, 677 may be used to treat the co-occurrence of impulsivity and excessive drinking.

Resposta à mosca-branca (Bemisia tabaci) e ao Tomato severe rugose virus de acessos de Solanum subgênero Leptostemonum

A mosca-branca (Bemisia tabaci) e a infecção por espécies de Begomovirus são dois graves problemas fitossanitários que afetam a produção e qualidade do tomateiro (Solanum lycopersicum) e de outras solanáceas de importância econômica. O presente trabalho foi conduzido sob condições controladas, em casa de vegetação, visando avaliar a resposta ao Tomato severe rugose virus (ToSRV) e à mosca-branca (B. tabaci biótipo B) de 36 acessos de espécies relacionadas ao gênero Solanum subgênero Leptostemonum (= grupo das solanáceas providas de espinhos). A inoculação de ToSRV foi realizada em mudas (43 dias após o semeio) utilizando-se um colônia virulífera de B. tabaci biótipo B. Duas cultivares de tomateiro foram incluídas como testemunhas suscetíveis. A avaliação ao ToSRV foi feita de acordo com uma escala de severidade de sintomas e a presença de infecção sistêmica foi verificada via reação em cadeia da polimerase (PCR) com 'primers' universais para espécies de Begomovirus. A maioria dos acessos apresentou uma resposta do tipo resistência ou quase imunidade ao ToSRV, não apresentando sintomas evidentes e nenhum indício de infecção sistêmica ou acumulação viral. Um grupo reduzido de acessos de S. stramonifolium, S. asperolanatum e S. jamaiscense apresentou uma resposta do tipo tolerância, caracterizada por baixa acumulação viral e sintomas suaves. O acesso S. mammosum 'CNPH 035', embora tolerante, foi o único que apresentou sintomas mais evidentes de infecção viral e acumulação de ToSRV. O mesmo grupo de 36 acessos foi avaliado em relação à colonização por B. tabaci em testes de livre escolha. Diferenças significativas foram observadas entre acessos para oviposição e o número de ninfas no quarto instar, indicando a presença de fatores de resistência ao inseto. Dez acessos de S. asperolanatum, S. stramonifolium, S. paniculatum e S. syssimbriifolium se mostraram completamente livres de oviposição. Desta forma, esses acessos do subgênero Leptostemonum podem ser considerados potenciais fontes de genes de resistência tanto para B. tabaci quanto para ToSRV. Essa diversidade genética pode ser transferida para outras espécies do gênero Solanum via técnicas de biologia celular e/ou isolamento e mobilização desses genes via transgenia. Os resultados também sugerem que, em condições naturais, espécies do subgênero Leptostemonum não representam importantes fontes de inóculo de ToSRV e/ou hospedeiras alternativas para B. tabaci.

Resistance of tomato genotypes to the greenhouse whitefly Trialeurodes vaporariorum (West.) (Hemiptera: Aleyrodidae)

The greenhouse whitefly, Trialeurodes vaporariorum Westwood, is the most common and abundant whitefly in Argentine horticultural greenhouse crops, especially in tomato (Solanum lycopersicum). Resistance in some wild tomato relatives, such as S. peruvianum, S. habrochaites and S. pennellii to the greenhouse whitefly has been described. The Mi gene confers effective resistance against several species of insects, among them the sweet potato whitefly, Bemisia tabaci Gennadius. Resistance to T. vaporariorum was found in the prebreeding line FCN 93-6-2, derived from a cross between S. lycopersicum cultivar Uco Plata INTA (MiMi) and the wild line FCN 3-5 S. habrochaites. The purpose of this study was to evaluate resistance to T. vaporariorum in tomato genotypes and to study the relationship between this resistance and the presence of the REX-1 marker, which is linked to the Mi gene. In a free-choice assay, the average number of adults per leaf and the number of immatures on the middle and basal plant parts were analyzed. In a no-choice assay, the oviposition rate and adult survival rate were calculated. For all variables analyzed, FCN 3-5 was the most resistant strain. Variations were found in the F2 progeny between the prebreeding line FCN 13-1-6-1 and cv. Uco Plata INTA. Results from the F2 progeny indicate that resistance to T. vaporariorum may be polygenic with transgressive segregation. Whitefly resistance was found to be independent of the REX-1 marker.

Benzothiadiazole Induces Local Resistance to Bemisia tabaci (Hemiptera: Aleyrodidae) in Tomato Plants

Plant resistance to the B and Q biotypes of sweetpotato whitefly, Bemisa tabaci (Gennadius), induced by benzo [1,2,3] thiadiazole-7-carbothioic acid-S-methyl ester (BTH or acibenzolar-S-methyl) in tomato 'Marmande' plants was evaluated in free-choice and no-choice assays under different conditions. BTH is the active ingredient of the Syngenta plant activator Bion. BTH treatment affected host preference of B. tabaci (B and Q biotypes) adults on plants sprayed with Bion at 0.2 and 0.4 g/liter during the earlier days of free-choice assays. As a consequence, a decrease in the total number of eggs (although female fecundity was not affected) and in the final number of pupae and empty pupal cases was observed. The effect produced by BTH applied at 0.1 g/liter Bion was not significant. In no-choice assays, a reduction of the numbers of first-stage larvae and total individuals and a delay in insect development were observed when local treatment was restricted to one leaflet per plant, 5 d before B. tabaci (biotype B) infestation. This acquired resistance induced by BTH seemed to be locally expressed because of the differences between treated and nontreated leaflets in the same plants, whereas no differences in nontreated leaflets were observed between BTH-treated and control plants.

Oviposição dos curculionídeos-das-raízes dos citros (Coleoptera: Curculionidae)

A oviposição dos curculionídeos-das-raízes dos citros das espécies Naupactus cervinus Boheman, Naupactus versatilis Hustache, Naupactus tarsalis Boheman, Parapantomorus fluctuosus Boheman e Teratopactus nodicollis Boheman foi estudada neste trabalho. Os insetos e os substratos vegetais (frutos, folhas, ramos, solo e resíduos) foram coletados em pomares de laranja, em Itapetininga, SP, e, no laboratório, foram montados seis experimentos, em caixas plásticas, com dimensões de 10,0 x 20,0 x 30,0cm, mantidas à temperatura do ar de 25 ± 1ºC, 60 ± 10 % de UR e fotofase de 14h. Foi avaliada a preferência de oviposição por folhas, frutos ou papel parafinado, com livre escolha no experimento A e sem chance de escolha no experimento B; preferência por três colorações de frutos (verde, verde amarelado e amarelo) no experimento C; três distâncias da casca ao cálice [aderido, intermediário (= 1,5mm) e distante (> 1,5mm)] no experimento D; e por folhas, frutos, solo umedecido ou resíduos vegetais de gramíneas no experimento E. As espécies de curculionídeos-das-raízes dos citros apresentaram diferenças nas características de oviposição. Os curculionídeos-das-raízes dos citros ovipositam em frutos, independentes de sua cor, e em papel parafinado sanfonado. O papel parafinado constitui-se em alternativa para a coleta de ovos em laboratório. Algumas espécies de curculionídeos ovipositam no solo ou em resíduos presentes na superfície do solo.

Sensibilite des bois de construction des greniers traditionnels aux attaques de Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Various wood species used for granary or crib construction were tested for their susceptibility to Prostephanus truncatus (Horn), a new stored grain pest in Benin found in 1984. Ten of the widely used wood species were chosen after survey in infested zones. Wood samples were dried in the oven (60°, 72 hr). They were reduced to 20 cm length, with diameter 2.0–2.6 cm and moisture content varying from 11.1–12.7%, respectively. Wood densities ranged from 0.455–0.999 g/cm−3. Fifty adult insects (<7 days old) were released into the middle of a sample made up of the 10 wood species for free-choice assays and 20 insects per wood species in no-choice tests. Four replicates were set up for each category. After 45 days of exposure at a temperature of 20–35°C and 60–90% r.h., data related to number of Insects that had penetrated each wood, number of larvae, and length of tunnelling were assessed. From the overall data analysis, Elaeis guineensis Jacq. and Holarrhena floribunda (G. Don) appeared least susceptible. Tectona grandis L., Fagara xanthoxyloides Lam., Azadirachta indica A. Juss and Mallotus oppositifolius (Geisel). Mull. Arg. were the more susceptible wood species.