Evaluation of diets from various maize hybrids reveals potential tolerance traits against Spodoptera littoralis (Boisd) as measured by developmental and digestive performance.

Spodoptera littoralis (Boisd) (Lepidoptera: Noctuidae) is a highly polyphagous insect that significantly reduces agricultural production of several food staples. We evaluated performance of S. littoralis on several meridic diets based on various maize hybrids, including Oteel, Simon, Valbum, SC703, and SC704. Growth, feeding behaviours, and activity of digestive enzymes of S. littoralis were examined under laboratory conditions. In addition, selected biochemical characteristics of maize hybrid seeds were evaluated, including starch, protein, anthocyanin, as well as phenolic and flavonoid contents, to examine relationships between plant properties and digestive performance of S. littoralis. Performance of S. littoralis on maize hybrids, as measured by nutritional indices, was related to both proteolytic and amylolytic activities quantified using gut extracts. Larval S. littoralis reared on SC703 exhibited the highest efficiency of conversion of digested food, while the lowest was recorded in those fed on the Oteel hybrid. S. littoralis reared on SC703 and Oteel also exhibited the highest and lowest relative growth rates, respectively. The highest levels of proteolytic activity in S. littoralis were measured from larvae reared on the SC703 hybrid, while the lowest levels occurred on the Oteel and Valbum hybrids. Amylolytic activity was lowest in larvae reared on SC703 and Valbum hybrids and highest in larvae reared on the Oteel hybrid. Our results suggest that the SC703 hybrid was the most suitable host for S. littoralis, while the Oteel hybrid demonstrated the greatest level of tolerance against S. littoralis of those evaluated. We discuss the potential utility of maize hybrids exhibiting tolerance traits against this cosmopolitan pest with reference to cultivation of tolerant varieties and identification of specific tolerance traits.

Insecticidal Activity of Allium sativum Essential Oil-Based Nanoemulsion against Spodoptera littoralis.

Spodoptera littoralis, commonly known as the Egyptian or African cotton leafworm, is a significant agricultural threat. It is widely distributed in Africa, Mediterranean Europe, and Middle Eastern countries. This polyphagous pest infests numerous crop plants across 44 families, including cotton, soybeans, alfalfa, sweet potato, pepper, eggplant, tomato, maize, lettuce, strawberry, wheat, and hibiscus. The damage caused by S. littoralis on different plant organs, such as young leaves, shoots, stalks, bolls, buds, and fruits, often determines substantial product losses. Current control strategies predominantly rely on synthetic insecticides, which, despite their efficacy, have notable drawbacks, including insecticide resistance, environmental contamination, consumer concerns, and adverse effects on non-target organisms and beneficial insects. In response to these challenges, in this study, we developed and evaluated a garlic EO-based nanoemulsion with a high EO concentration (15%) and low surfactant content to mitigate the possible negative impact on plants and to enhance efficacy against S. littoralis larvae. Laboratory bioassays demonstrated promising larvicidal activity and reduced larval feeding, although some phytotoxicity symptoms were observed. This study underscores the potential of botanical insecticides as sustainable alternatives to synthetic chemicals, emphasizing the importance of balancing efficacy with environmental and ecological considerations in pest management strategies.

Insights into the toxicity, biochemical activity, and molecular docking of Cymbopogon citratus essential oils and citral on Spodoptera littoralis (Lepidoptera: Noctuidae).

Insecticide resistance is a significant problem in insect management that can result from several processes including target-site change and increased activity of detoxifying enzymes. Spodoptera littoralis is one of the most resistant insect pests. For more effective insect management, alternatives to synthetic pesticides are encouraged. One of these alternatives is essential oils (EOs). Cymbopogon citratus EO and its main constituent citral were, therefore, considered in this study. The results revealed that C. citratus EO and citral exhibited significant larvicidal activity against S. littoralis, and the former was insignificantly more toxic than the latter. Additionally, treatments significantly affected the activity of detoxification enzymes. Cytochrome P-450 and glutathione-S-transferase were inhibited, while carboxylesterases, a-esterase and ß-esterase, were induced. The molecular docking study indicated that citral bonded with the amino acids cysteine (CYS 345) and histidine (HIS 343) of cytochrome P-450. This result suggests that interaction with cytochrome P-450 enzyme is one key mechanism by which C. citratus EO and citral act in S. littoralis. The results of our study are hoped to contribute to a better understanding of the mechanism of action of essential oils at the biochemical and molecular levels and provide safer and more efficient pest management solutions for S. littoralis.

Feeding responses and digestive function of Spodoptera littoralis (Boisd) on various leafy vegetables exhibit possible tolerance traits.

Spodoptera littoralis is a highly polyphagous pest that attacks numerous important crops in the world and causes substantial economic losses to agricultural production. In the present study, the effects of different leafy vegetables, including Purslane, Chives, Parsley, Basil, Dill, Coriander, and Mint, were investigated on feeding responses and enzymatic activities of S. littoralis under laboratory conditions. Furthermore, the total contents of the three major secondary metabolites (phenolics, anthocyanins, and flavonoids) in the studied vegetables were determined. Our findings showed that the lowest and the highest approximate digestibility were on Basil and Purslane, respectively. The highest values of efficiency of conversion of ingested and digested food were achieved in larvae fed on Chives and Coriander, respectively, whereas the lowest values were recorded after feeding on Purslane. The highest and lowest relative growth rates were in larvae reared on Dill and Purslane, respectively. Furthermore, the highest amylolytic and proteolytic activities were in larvae fed with Coriander and Dill, respectively, while the lowest activities of these enzymes were on Purslane. In addition, correlation analysis revealed significant correlations between feeding characteristics and enzymatic activity of S. littoralis with biochemical compounds of the studied leafy vegetables. Our results suggest that Coriander is a suitable host, while Purslane displayed tolerance traits against S. littoralis, which can be used in sustainable management programs aiming to reduce chemical inputs.

Life Table Parameters and Digestive Enzyme Activity of Spodoptera littoralis (Boisd) (Lepidoptera: Noctuidae) on Selected Legume Cultivars.

Spodoptera littoralis (Boisd) is a highly destructive pest that attacks a large number of economically important crops. We examined life table parameters as well as activity of major digestive enzymes of S. littoralis larvae in response to protein and starch contents across 11 legume cultivars to identify potential resistance traits. The results showed that S. littoralis reared on the common bean, Arabi, displayed the highest intrinsic rate of increase (r), while the lowest was recorded on the cowpea, Mashhad. Also, the highest net reproductive rate (R0) was obtained in those insects reared on the Arabi cultivar. Larvae displayed the highest and lowest proteolytic activities when fed on Mashhad and Arabi cultivars, respectively. The highest amylolytic activity was quantified in larvae that fed on the Arabi and 1057 cultivars, while the lowest occurred in larvae feeding on Yaghout and Mashhad cultivars. Developmental time of S. littoralis larvae was negatively correlated with protein content, while amylolytic activity was positively correlated with starch content of legumes. Our findings indicate that Arabi was a susceptible cultivar, while Mashhad exhibited tolerance traits against S. littoralis. These results should facilitate selection of legume cultivars for production or breeding efforts that involve S. littoralis management.

Cloning and Characterization of 1,8-Cineole Synthase (SgCINS) Gene From the Leaves of Salvia guaranitica Plant.

Monoterpenes are one of the most common groups belonging to the terpenoid family, with a C10 structure comprising of two isoprene units. Most of monoterpenes are volatile plant compounds, and they act as signaling molecules between plants and the environment, particularly as defensive compounds against herbivores and pathogens. In this study, 1,8-cineole synthase (SgCINS) gene was identified and cloned from the leaves of Salvia guaranitica plant. To examine the role of SgCINS in insect resistance, we transformed and expressed this gene into tobacco leaves. The metabolic analysis revealed that the production of various types and amount of terpenoid was increased and decreased in SgCINS overexpression and control lines, respectively, suggesting that overexpressing SgCINS in transgenic tobacco plants lead to an increase in the production of various types of terpenoids and other phytochemical compounds. These results indicated why transgenic tobacco was highly resistant against cotton worm than the highly susceptible control plants. Our results demonstrate that the SgCINS gene can play an important role in plants against cotton worm insect attack, and pave the way for using terpenoids genes for improving resistance to insect attack in higher plants.

Susceptibility of Alabama argillacea and Chrysodeixis includens (Lepidoptera: Noctuidae) larvae to Beauveria bassiana associated with kaolin / Susceptibilidade de larvas de Alabama argillacea e Chrysodeixis includens (Lepidoptera: Noctuidae) a Beauveria bassiana associada com caulim

Abstract The mortality of the Alabama argillacea and Chrysodeixis includens (Lepidoptera: Noctuidae) larvae caused by the kaolin inert powder and the entomopathogenic fungus Beauveria bassiana were determined under laboratory conditions. Using the caterpillar submersion method, the CG 138 B. bassiana isolate was more pathogenic to A. argillacea than the CG 70, GC 82, ESALQ 634, and ESALQ 645. All five tested isolates caused similar mortality of C. includens. The mortality of first-instar larvae of A. argillacea and C. includens by feeding on leaf-disc impregnated with B. bassiana (CG 138) and kaolin was also determined. Higher A. argillacea mortalities were observed in the B. bassiana (CG 138) treatments, regardless of the presence of kaolin. However, the activity of kaolin + B. bassiana (CG 138) against C. includens was higher than each ingredient alone, indicating an additive action against C. includes larvae. The mortality of A. argillacea and C. includens larvae treated with kaolin + B. bassiana (CG 138) was similar, and the A. argillacea mortality was higher than that of C. includens with kaolin and B. bassiana (GC 138) separated. The treatment kaolin + B. bassiana (CG 138) is promising for the simultaneous management of these two defoliator pests, mainly A. includes. In addition, the monophagous A. argillacea is more susceptible to both kaolin and B. bassiana (GC 138) than the polyphagous C. includens, suggesting that the nutritional ecology plays an important role in the susceptibility of these defoliator species to alternative insecticides.

Resumo A mortalidade de larvas de Alabama argillacea e Chrysodeixis includens (Lepidoptera: Noctuidae), causada pelo pó inerte do caulim e pelo fungo entomopatogênico Beauveria bassiana, foi determinada em condições de laboratório. Usando o método de submersão da lagarta, o isolado CG 138 de B. bassiana foi mais patogênico para A. argillacea que os CG 70, GC 82, ESALQ 634 e ESALQ 645 desse fungo. Os cinco isolados testados causaram mortalidade semelhante de C. includens. A mortalidade de larvas de primeiro ínstar de A. argillacea e C. includens pelo método de alimentação em discos foliares impregnados com B. bassiana (CG 138) e caulim foi, também, determinada. A mortalidade de A. argillacea foi maior nos tratamentos com B. bassiana (CG 138), independentemente da presença do caulim. A atividade do caulim + B. bassiana (CG 138) contra C. includens foi maior que cada ingrediente isolado, indicando ação aditiva contra larvas desse Lepidoptera. A mortalidade de larvas de A. argillacea e C. includens, com caulim + B. bassiana (CG 138), foi semelhante e as de A. argillacea maiores que as de C. includens com caulim e B. bassiana (GC 138) isoladamente. O tratamento caulin + B. bassiana (CG 138) é promissor para o manejo simultâneo dessas duas pragas desfolhadoras, principalmente A. includens. Além disso, a monófaga, A. argilacea, é mais suscetível ao caulim e à B. bassiana (GC 138) que a polífaga, C. includens, sugerindo que a ecologia nutricional desempenha papel importante na suscetibilidade dessas espécies desfolhadoras a inseticidas alternativos.

Wild strawberry shows genetic variation in tolerance but not resistance to a generalist herbivore.

Plants' defenses against herbivores usually include both resistance and tolerance mechanisms. Their deployment has predominantly been studied in either single-plant genotypes or multiple genotypes exposed to single herbivores. In natural situations, however, most plants are attacked by multiple herbivores. Therefore, aims of this study were to assess and compare the effects of single and multiple herbivores on plant resistance and tolerance traits, and the consequences for overall plant performance. For this, we exposed multiple genotypes of wild woodland strawberry (Fragaria vesca) to jasmonic acid (JA), to mimic chewing herbivory and induce the plants' defense responses, and then introduced the generalist herbivore Spodoptera littoralis to feed on them. We found that woodland strawberry consistently showed resistance to S. littoralis herbivory, with no significant genetic variation between the genotypes. By contrast, the studied genotypes showed high variation in tolerance, suggesting evolutionary potential in this trait. Prior JA application did not alter these patterns, although it induced an even higher level of resistance in all tested genotypes. The study provides novel information that may be useful for breeders seeking to exploit tolerance and resistance mechanisms to improve strawberry crops' viability and yields, particularly when multiple herbivores pose significant threats.

Delving into the Causes and Effects of Entomopathogenic Endophytic Metarhizium brunneum Foliar Application-Related Mortality in Spodoptera littoralis Larvae.

The aim of the current study was to delve into the causes of mortality of Spodoptera littoralis larvae feeding on Metarhizium-colonized plants in the absence of fungal outgrowth on the cadavers as previous studies reported and to elucidate the possible indirect effects of this fungus-colonized diet. The effect was evaluated in experiments conducted using leaf discs of colonized plants and in planta using fungus-colonized whole plants. The mortality rates of larvae fed on Metarhizium-colonized melon leaves were 45.0% and 87.5%, and the average survival times were 6.6 and 3.1 days in experiments performed with discs and in planta, respectively. Notably, these mortality levels were not associated with observed apoptosis mediated by caspases 1, 3-7 and 8; thus, further investigation into the possible immune system reaction of the insect after the ingestion of colonized plants is required. The leaf consumption of S. littoralis larvae fed on melon-colonized leaves was lower than that on control plants in the disc experiments but not in experiments conducted in planta. In this regard, in experiments performed in planta, plant damage increased larval mortality in both fungally challenged and control larvae. There was also a meaningful effect of exposure to Metarhizium-colonized melon leaf discs on S. littoralis fitness, with significant reductions in 39.0% and 22.0% in female fecundity and egg fertility, respectively, detected in females emerging from pupae developing from larvae surviving exposure to colonized plant discs; all larvae died in the in planta experiments. Hence, the present work presents new findings revealing the high potential of endophytic entomopathogenic fungi to improve the outcome of foliar applications against chewing insects in the short, mid- and long term, by the reduction of the reproductive potential of surviving adults and reveals new insights into the development of bioassays with whole plants for more detailed evaluation of the impact of these fungi as endophytes used for plant protection.

Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis.

BACKGROUND: The cotton leafworm, Spodoptera littoralis, is one of the most destructive pests in the Mediterranean basin, being predominantly controlled using synthetic chemical pesticides. Strain EAMa 01/58-Su of the fungus Metarhizium brunneum and the parasitoid Hyposoter didymator are promising biological control agents for this pest. In this study, we assessed the compatibility between these two agents to control S. littoralis under joint attack scenarios. RESULTS: Firstly, the direct and indirect effects of the fungus towards parasitoid adults were studied. The fungus significantly decreased life expectancy of the parasitoid (mortality = 62.5%; mean lethal concentration = 1.85 × 106 conidia ml-1 ; average survival time = 92.2 h) when applied at high concentrations (108 conidia ml-1 ), whereas it did not affect the reproductive potential of the parasitoid females during the 3 days after treatment. Secondly, the combinations between the two agents to control S. littoralis under different simultaneous use scenarios (inoculation of S. littoralis larvae with the fungus before being exposed to parasitoid females and vice versa) were investigated, with additive effect in all cases. A significant effect on fitness (preimaginal development time and reproductive potential) of the F1 parasitoid generation were detected. Moreover, parasitization significantly reduced the total hemocytes in S. littoralis hemolymph compared with the control, promoting fungal infection. Finally, parasitoids showed a significant preference for non-inoculated S. littoralis larvae. CONCLUSIONS: We demonstrated compatibility (additive effect) between fungus and parasitoid under different joint attack scenarios to control S. littoralis in laboratory conditions. However, this will be supported by our ongoing greenhouse and field studies. © 2019 Society of Chemical Industry.

Toxicity of Fipronil and Emamectin Benzoate and Their Mixtures Against Cotton Leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae) With Relation to GABA Content.

Fipronil and emamectin benzoate (EMB) are effective insecticides for controlling cotton leafworm, Spodoptera littoralis. Fipronil works by blocking gamma-amino butyric acid (GABA) gated chloride. In contrast, EMB is activating GABA transporters. The objectives of our study were to assess relative toxicity of the technical fipronil and EMB alone and in mixture against S. littoralis. In addition, the GABA content was simultaneously determined using HPLC. Technical fipronil and EMB and their mixtures were applied topically to the fourth-instar larvae, and their LD50 values were estimated after 48 h. Results demonstrated that the LD50 for EMB applied alone was 0.751 ng/larva which was much less than for fipronil 7.271 ng/larva. Each of the two insecticides alone showed a significant decrease in GABA content at LD10, LD25, and LD50 doses, while their mixtures induced GABA levels. The highest potentiation was observed when both insecticides were in a mixture at the ratio of LD10:LD10 which was associated with higher increase in GABA levels. Moreover, the weight of the alive larvae was less than that was in the untreated control. However, all mixtures exhibited potentiation effect, except for the mixture of fipronil at LD50 with EMB at LD10, LD25, and LD50 that had antagonistic effect correlated with the lowest decrease in GABA level. Results suggested that lower doses of both insecticides in a binary mixture had potentiation effect against S. littoralis. This mixture could be used in combination as field application for successful and effective control of S. littoralis and would also help in managing insecticide resistance.

Ultrastructure of the antennal sensilla of Alabama argillacea (Hübner, 1823) (Lepidoptera: Erebidae)

Abstract Insects have several types of sensilla, the characterization of which has been fundamental to understanding the mechanisms of sensory perception in different species. This study aimed to describe the ultrastructure of the sensilla present on the antennae of Alabama argillacea (Hübner, 1823) (Lepidoptera: Erebidae), an important pest of cotton (Gossypium hirsutum L.) crops, as well as their possible variation between sexes. To do this, the antennae of males and females of A. argillacea were analyzed using scanning electron microscopy. Sensilla morphometry was assessed using photomicrographs, from which the lengths and basal and apical diameters of sensilla were measured using the ImageJ program. Seven types of sensilla were identified on the antennae of A. argillacea: sensilla trichodea, sensilla chaetica, sensilla auricillica, sensilla coeloconica, sensilla styloconica, sensilla basiconica, and sensilla Böhm bristles. Differences between the sensilla of males and females were found in their lengths and basal diameters in the distal and proximal regions. This suggests that sensilla functionality may not only vary from one species to another, but also between sexes within the same species. Thus, further transmission electron microscopy and single sensillum recording studies may provide more detailed information on the sensilla of A. argillacea and their functions.

Effect of caffeic acid on feeding, α-amylase and protease activities and allatostatin-A content of Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae).

Efficiency of caffeic acid (CA) on Spodoptera littoralis was investigated. CA was mixed with artificial diet, and feeding indices and allatostatin-A (AST-A) content of the midgut were measured 10 days later. α-Amylase and protease activities were evaluated for 10 days. CA significantly decreased feeding indices. Feeding on an artificial diet containing CA decreased protease and α-amylase activities in the midgut. The incubation of the dissected midgut with AST-A increased α-amylase and protease activities. The injection of AST-A into the hemolymph of larvae also increased protease and α-amylase activities. Competitive ELISA and immunohistochemistry results showed that starvation decreased the AST-A titer and AST-A immunoreactivity (AST-A-ir) cells in the midgut whereas refeeding increased it. Here, for the first time we showed that feeding on an artificial diet containing CA also caused the AST-A level to decrease in the midgut, which itself caused α-amylase and protease activities to decrease.

Effects of temperature on the feeding behavior of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) on Bt and non-Bt cotton plants

ABSTRACT The host acceptance behavior and environmental factors as temperature affect the feeding behavior of Lepidoptera pests. Thus, they must be considered in studies about the risk potential of resistance evolution. The current study sets the differences in the feeding behavior of neonate Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) larvae exposed to Bt and non-Bt cotton plants, under different temperatures and time gap after hatching. Two cotton cultivars were used: the Bt (DP 404 BG - bollgard) and the non-transformed isoline, DP 4049. We found that the feeding behavior of neonate A. argillacea is significantly different between Bt and non-Bt cotton. Based on the number of larvae with vegetal tissue in their gut found on the plant and in the organza as well as on the amount of vegetal tissue ingested by the larvae. A. argillacea shows feeding preference for non-Bt cotton plants, in comparison to that on the Bt. However, factors such as temperature and exposure time may affect detection capacity and plant abandonment by the larvae and it results in lower ingestion of vegetal tissue. Such results are relevant to handle the resistance of Bt cotton cultivars to A. argillacea and they also enable determining how the cotton seeds mix will be a feasible handling option to hold back resistance evolution in A. argillacea populations on Bt cotton, when it is compared to other refuge strategies. The results can also be useful to determine which refuge distribution of plants is more effective for handling Bt cotton resistance to A. argillacea.

Susceptibility of Alabama argillacea and Chrysodeixis includens (Lepidoptera: Noctuidae) larvae to Beauveria bassiana associated with kaolin

Abstract The mortality of the Alabama argillacea and Chrysodeixis includens (Lepidoptera: Noctuidae) larvae caused by the kaolin inert powder and the entomopathogenic fungus Beauveria bassiana were determined under laboratory conditions. Using the caterpillar submersion method, the CG 138 B. bassiana isolate was more pathogenic to A. argillacea than the CG 70, GC 82, ESALQ 634, and ESALQ 645. All five tested isolates caused similar mortality of C. includens. The mortality of first-instar larvae of A. argillacea and C. includens by feeding on leaf-disc impregnated with B. bassiana (CG 138) and kaolin was also determined. Higher A. argillacea mortalities were observed in the B. bassiana (CG 138) treatments, regardless of the presence of kaolin. However, the activity of kaolin + B. bassiana (CG 138) against C. includens was higher than each ingredient alone, indicating an additive action against C. includes larvae. The mortality of A. argillacea and C. includens larvae treated with kaolin + B. bassiana (CG 138) was similar, and the A. argillacea mortality was higher than that of C. includens with kaolin and B. bassiana (GC 138) separated. The treatment kaolin + B. bassiana (CG 138) is promising for the simultaneous management of these two defoliator pests, mainly A. includes. In addition, the monophagous A. argillacea is more susceptible to both kaolin and B. bassiana (GC 138) than the polyphagous C. includens, suggesting that the nutritional ecology plays an important role in the susceptibility of these defoliator species to alternative insecticides.

Resumo A mortalidade de larvas de Alabama argillacea e Chrysodeixis includens (Lepidoptera: Noctuidae), causada pelo pó inerte do caulim e pelo fungo entomopatogênico Beauveria bassiana, foi determinada em condições de laboratório. Usando o método de submersão da lagarta, o isolado CG 138 de B. bassiana foi mais patogênico para A. argillacea que os CG 70, GC 82, ESALQ 634 e ESALQ 645 desse fungo. Os cinco isolados testados causaram mortalidade semelhante de C. includens. A mortalidade de larvas de primeiro ínstar de A. argillacea e C. includens pelo método de alimentação em discos foliares impregnados com B. bassiana (CG 138) e caulim foi, também, determinada. A mortalidade de A. argillacea foi maior nos tratamentos com B. bassiana (CG 138), independentemente da presença do caulim. A atividade do caulim + B. bassiana (CG 138) contra C. includens foi maior que cada ingrediente isolado, indicando ação aditiva contra larvas desse Lepidoptera. A mortalidade de larvas de A. argillacea e C. includens, com caulim + B. bassiana (CG 138), foi semelhante e as de A. argillacea maiores que as de C. includens com caulim e B. bassiana (GC 138) isoladamente. O tratamento caulin + B. bassiana (CG 138) é promissor para o manejo simultâneo dessas duas pragas desfolhadoras, principalmente A. includens. Além disso, a monófaga, A. argilacea, é mais suscetível ao caulim e à B. bassiana (GC 138) que a polífaga, C. includens, sugerindo que a ecologia nutricional desempenha papel importante na suscetibilidade dessas espécies desfolhadoras a inseticidas alternativos.

Efeito do nível e da época de desfolha artificial sobre os componentes de produtividade de cultivares de algodoeiro / Effect of level and time defoliation on the agronomic traits of cotton cultivars

A substituição periódica de cultivares pelos produtores pode alterar os níveis de danos econômicos e de controle de pragas, e desta forma comprometer o sucesso no manejo do curuquerê-do-algodoeiro. O objetivo deste trabalho foi avaliar os efeitos dos desfolhamentos simulados em cultivares atualmente utilizadas. O ensaio foi realizado em área experimental do Polo Apta Centro Norte, em Pindorama, estado de São Paulo. Foram avaliados quatro níveis de desfolhamento (0%, 36,8%, 62,1% e 100%), realizados numa única operação, em três épocas (30, 60 e 90 dias após a emergência das plantas - DAE) e quatro cultivares de algodoeiro (IAC-25, DeltaOpal, Fibermax 966 e Fibermax 993). As desfolhas foram realizadas com o auxílio de tesoura, simulando o dano da lagarta. Foram avaliados o número de capulhos, peso de um capulho e de 100 sementes, percentagem de fibra e a produtividade (kg ha-1). As desfolhas afetaram negativamente todos os componentes de produtividade avaliados, exceto a percentagem de fibra. Os níveis mais prejudiciais foram 62,1 e 100% de retirada do limbo foliar. O período de maior suscetibilidade à desfolha ocorre dos 30 aos 60 dias após a emergência das plantas.

The periodic substitution of cotton cultivars for the farms can modify the levels of economic damages and control of pests, compromising the success in pest control. The objective of this work was to evaluate the effect of simulated defoliation levels in cotton cultivars actually used. The assay was carried out in experimental area of the Polo Apta Centro Norte, in Pindorama, São Paulo state. There were evaluated four defoliations levels (0%, 36.8%, 62.1% e 100%), done at a unique operation, in tree times (30, 60 and 90 days after plant emergence) and four cotton cultivars (IAC-25, DeltaOpal, Fibermax 966 and Fibermax 993). The defoliation was done with a scissor simulating the caterpillar damage. Evaluations included the number of open bolls, weight of one boll and 100 seeds, fiber percentage and productivity (kg ha-1). The defoliation negatively affected all components of agronomic traits, with the exception of percentage of fiber. The most damaging levels were 62.1 and 100% removal of the leaf blade. The period of higher susceptibility to defoliation occurs from 30 to 60 days after plant emergence.

Food extraction by the males of Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) from cotton leafworm larvae

In this work, the effect of different densities (1, 3, 5, 7 and 9) of 3rd instar Alabama argillacea (Huebner) larvae on food consumption by Podisus nigrispinus (Dallas) males was evaluated. The densities established were converted to weight of prey offered: 13.4 mg (one larva), 33.3 mg (three larvae), 54.3 mg (five larvae), 81.8 mg (seven larvae), and 110.34 mg (nine larvae). The quantity of food consumed by P. nigrispinus increased with the prey density. The density of preys did not affect the time spent by the predator to ingest the food. The quantity of food extracted per minute was always higher in smaller densities and lower in higher densities. Males mean body weight did not differ statistically between the treatments tested, and weight gain was smaller in the first two densities tested. Relative consumption rates increased with the quantity of larvae offered. P. nigrispinus males might change its predatory behavior as a function of the quantity of prey available.

O efeito de diferentes densidades (1, 3, 5, 7 e 9) de 3º lagartas do instar de Alabama argillacea (Huebner) no consumo de alimento por machos de Podisus nigrispinus (Dallas) foi avaliado em condições de laboratório. As densidades utilizadas foram convertidas a peso de presa oferecida: 13,40 mg (1 lagarta), 33.30 mg (3 lagartas), 54,30 mg (5 lagartas), 81,80 mg (7 lagartas) e 110,34 mg (9 lagartas). A quantidade de alimento consumido pelo macho de P. nigrispinus aumentou com a densidade da presa. A densidade da presa não afetou o tempo gasto pelo predador para ingerir o alimento. A quantidade de alimento extraído por minuto pelo predador foi sempre maior nas mais baixas densidades e menores nas mais altas densidades. O peso corpóreo médio dos machos de P. nigrispinus não difereriu entre os tratamentos testados e o seu ganho de peso foi menor nas duas primeiras densidades testadas. As taxas de consumo relativo aumentaram com a quantidade de lagartas oferecidas. Os machos de P. nigrispinus podem mudar seu comportamento predatório em função da quantidade de presas disponíveis.

Distribuição espacial de Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) em algodoeiro / Spatial distribution of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) on cotton crop

O conhecimento do modelo de distribuição espacial de pragas na cultura é fundamental para estabelecer um plano adequado de amostragem seqüencial e, assim, permitir a correta utilização das estratégias de controle e a otimização das técnicas de amostragem. Esta pesquisa objetivou estudar a distribuição espacial de lagartas de Alabama argillacea (Hübner) na cultura do algodoeiro, cultivar CNPA ITA-90. A coleta de dados ocorreu durante o ano agrícola de 1998/99 na Fazenda Itamarati Sul S.A., localizada no município de Ponta Porã, MS, em três diferentes áreas de 10.000 m² cada uma. Cada área amostral foi composta de 100 parcelas com 100 m² cada. Foi realizada semanalmente a contagem das lagartas pequenas, médias e grandes, encontradas em cinco plantas por parcela. Os índices de agregação (razão variância/média e índice de Morisita), o teste de qui-quadrado com o ajuste dos valores encontrados e esperados às distribuições teóricas de freqüência (Poisson, binomial positiva e binomial negativa), mostraram que todos os estádios das lagartas estão distribuídos de acordo com o modelo de distribuição contagiosa, ajustando-se ao padrão da Distribuição Binomial Negativa durante todo o período de infestação.

The knowledge of the dispersion pattern of the pests on a crop is fundamental for establishing an appropriated sequential sampling method. Also it permits the correct utilization of control strategies and optimization of sampling techniques. The objective of this research was to determine the spatial distribution of larvae of Alabama argillacea (Hübner) on cotton crop, CNPA ITA-90 cultivar. During the 1998/99 growing season a sampling system was applied in three experimental areas located at Itamarati Sul S.A. farm in the region of Ponta Porã, estate of Mato Grosso do Sul, Brazil. The areas measured 1 ha and contained 100 plots with 100 m². In a weekly basis the number of small, medium and large larvae were counted on five plants per plot. The aggregation indexes (variance/mean ratio and Morisita index), the chi-square test and the adjust of observed and expected values to theoretical distributions of frequencies (Poisson, positive binomial and negative binomial) showed that all stages of cotton leafworm larvae were distributed according to the contagious model, fitting the Negative Binomial Distribution during the whole period of infestation.

Amostragem seqüencial de Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) em algodoeiro / Sequential sampling of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) on cotton crop

Para implantar o manejo apropriado do curuquerê-do-algodoeiro, é necessário construir um plano de amostragem que permita estimar, de forma rápida e precisa, a densidade populacional da praga. Esta pesquisa objetivou determinar o plano de amostragem seqüencial de Alabama argillacea (Hübner) em algodoeiro, cultivar CNPA ITA-90. Os dados foram coletados no ano agrícola de 1998/99 na Fazenda Itamarati Sul S/A, localizada no município de Ponta Porã, MS, em três áreas de 10.000 m² cada. As áreas amostrais foram compostas de 100 parcelas de 100 m². O número de lagartas pequenas, médias e grandes foi determinado semanalmente em cinco plantas tomadas ao acaso por parcela. Após verificado que todos os instares das lagartas estavam distribuídos de acordo com o modelo de distribuição agregada, ajustando-se à Distribuição Binomial Negativa durante todo o período de infestação, construiu-se um plano de amostragem seqüencial de acordo com o Teste Seqüencial da Razão de Probabilidade (TSRP). Adotou-se o nível de controle de duas lagartas por planta para a construção do plano de amostragem. A análise dos dados indicou duas linhas de decisão: a superior, que representa a condição de que a adoção de um método de controle é recomendado, definida por S1= 4,8784+1,4227n; e a inferior representando que a adoção de algum método de controle não é necessário, definida por S0= -4,8784+1,4227n. A amostragem seqüencial estimou o número máximo esperado de 16 unidades amostrais para se definir a necessidade ou não do controle.

An appropriated management of the cotton leafworm on cotton crop demands a sampling plan that quantifies the population density of the pest in an accurate and fast form. The objective of this research was to determine the plan of sequential sampling of Alabama argillacea (Hübner) on cotton crop, CNPA ITA-90 cultivar. During the 1998/99 growing season a sampling system was applied in three experimental areas located at the Fazenda Itamarati Sul S/A in the region of Ponta Porã, state of Mato Grosso do Sul, Brazil. Each area measured 1 ha and was composed of 100 plots with 100 m². The number of small, medium and large larvae was counted on five plants per plot, in a weekly basis. After defined that all stages of cotton leafworm larvae were distributed according to the contagious model, fitting Negative Binomial Distribution during the whole period of infestation, a sequential sampling plan was provided, according to the Sequential Probability Ratio Test (SPRT). A threshold level of two larvae per plant was assumed to trigger the sampling plan. After the data were analyzed two decision lines were indicated: the superior one, which represents the condition that the adoption of some control method is recommended, and was defined as S1= 4.8784+1.4227n; and the inferior one, representing the situation where the adoption of some control method is not recommended, defined as S0= -4.8784+1.4227n. The sequential sampling plan indicated the expected maximum number of 16 samples to determine whether or not the pest control is necessary.

Efeito da Densidade de Presas e do Acasalamento na Taxa de Predação de Fêmeas de Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) em Condições de Laboratório e Campo / Effect of Prey Density and Mating Status on Predation Rate of Females of Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) in Laboratory and Field Conditions

The predation rate of unmated and mated females of Podisus nigrispinus (Dallas) was evaluated on different densities of Alabama argillacea (Huebner) caterpillars (50 ± 10 mg), in laboratory and field conditions. In the laboratory, the predator females were maintained in 500 ml plastic jars with five different densities of prey (one, two, four, eight, and 16). In the field, caterpillars at the same densities were caged on flowering cotton plants. Under both conditions, females gained weight and increased the predation rate when the availability of prey increased, although higher values were obtained for females kept in the laboratory. Weight gain and predation rate did not differ between unmated and mated females under both conditions. In the field, P. nigrispinus searched 94.7 percent of the available foliar area under low prey density, and 21.2 percent under high prey density. The estimated handling time and attack rate were, respectively, 3.37 ± 0,82h and 0.076 ± 0.013h-1 in the laboratory, and 3.33 ± 0.93h and 0.017 ± 0.003h-1 in the field. The functional response corresponded to a type II for both conditions. The number of killed caterpillars observed and estimated by the model were highly correlated for both laboratory (r = 0.78) and field (r = 0.70) conditions.

Avaliou-se a taxa de predação de fêmeas virgens ou acasaladas de Podisus nigrispinus (Dallas) em diferentes densidades de lagartas de Alabama argillacea (Huebner) em condições de laboratório e de campo. Em laboratório, empregaram-se potes plásticos de 500 ml contendo fêmeas do predador, uma folha de algodão e lagartas de A. argillacea (50 ± 10 mg) nas densidades de uma, duas, quatro, oito e 16 lagartas. No campo, algodoeiros na fase de florescimento foram engaiolados, sendo empregadas as mesmas densidades de lagartas que no laboratório. Em ambas as condições, as fêmeas de P. nigrispinus apresentaram ganho de peso e aumento de sua taxa de predação com o aumento da densidade de lagartas de A. argillacea, mas com valores maiores para fêmeas em laboratório. Nas duas condições, o ganho de peso e a taxa de predação foram semelhantes para fêmeas virgens ou acasaladas. No campo, P. nigrispinus explorou 94,7 por cento e 21,2 por cento da área foliar disponível na menor e maior densidade de presas, respectivamente. O tempo de manipulação e a taxa de ataque estimadas foram de 3,37 ± 0,82h e de 0,076 ± 0,013h-1 em laboratório, e de 3,33 ± 0,93h e de 0,017 ± 0,003h-1 em campo. A resposta funcional em laboratório e no campo foi caracterizada como do Tipo II. Os números observados e estimados de lagartas predadas pelo modelo foram significativamente correlacionados com as condições de laboratório (r = 0,78) e de campo (r = 0,70).