Ethological aspects of Helicoverpa armigera in the reproductive phase of cotton

Pest behavior studies are important to inform the periods when the pest is more exposed to pesticide. This study aimed to evaluate the movement and feeding of Helicoverpa armigera larvae in the first three instars during the reproductive phase of cotton. First, larval behavior was evaluated with a completely randomized design in a 3 × 5 factorial design with eight replications. The treatments were the instars versus behaviors (crawling, resting, waving, eating and dropping-off). In addition, another 3 × 6 factorial design with eight replications was performed to evaluate the plant region most preferred by the caterpillars. The treatments were the instars versus six parts of the plant (abaxial surface, adaxial surface, on floral bud, internal surface of bract, petiole, and terminal growth). Then, the period of the day when caterpillars are more active was also evaluated by a 3 × 2 factorial essay. The treatments were the instars versus periods of the day. Eating and resting are the most frequent behaviors for all instars. The plant regions preferred by the caterpillars for crawling are on the floral bud and the adaxial face of the leaf. There is no preferred period of the day for eating, resting, waving or dropping-off. Caterpillars (until the third instar) prefer to walk in the morning and other behaviors can occur at any period. Therefore, sprays should preferably occur in the morning, and the insecticide drops/spray should reach the flower buds and the adaxial surface of the leaves to contaminate the larvae.

Phytophagy of the predator Podisus nigrispinus (Dallas, 1851) (Hemiptera: Pentatomidae) fed on prey and Brassicaceae / Fitofagia do predador Podisus nigrispinus (Dallas, 1851) (Hemiptera: Pentatomidae) em diferentes brassicáceas

Abstract The purpose of this study was to investigate the development and reproduction of the zoophytophagous predator Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) fed kale, broccoli and cabbage affects its. Nymphs and adults of this predator were fed on larvae of Plutella xylostella (L.) (Lepidoptera: Plutellidae) as prey with kale, cabbage, or broccoli. In the nymph period, the duration and prey consumption were similar with all the Brassicacea cultivar. However, nymph viability was higher for predators with broccoli leaves. The mean weight of 5th-instar nymphs, newly emerged females and the sex ratio were similar among the Brassicacea cultivars, while newly emerged males were heavier with kale and broccoli leaves. The supply of broccoli leaves resulted in greater oviposition, higher number of eggs per egg mass and longer longevity of P. nigrispinus males and females. Furthermore, the consumption of P. xylostella larvae by adult predators was higher with these cultivars. The net reproductive rate (R0) and mean generation time (T) were highest for predators with prey and broccoli leaves. The reproductive parameters of P. nigrispinus were enhanced when fed on P. xylostella larvae with and broccoli leaves, which can be an alternative diet in laboratory rearing of this predator.

Resumo O objetivo deste estudo foi verificar o desenvolvimento e reprodução do zoofitófago Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) em couve, brócolis e repolho. Ninfas e adultos deste predador foram alimentados com lagartas de Plutella xylostella (L.) (Lepidoptera: Plutellidae) como presa e receberam folhas de couve, repolho ou brócolis. Durante o período ninfal, a duração do período e o consumo de presas foram semelhantes com as diferentes cultivares de brassicácea. Porém, a viabilidade ninfal foi maior para predadores com folhas de brócolis. O peso de ninfas de quinto instar e de fêmeas recém-emergidas e a razão sexual de P. nigrispinus foram semelhantes entre as cultivares de brassicáceas, enquanto que o peso de machos recém-emergidos foi maior com folhas de couve e brócolis. Folhas de brócolis proporcionaram maiores número de oviposições, ovos por postura e longevidade de machos e fêmeas de P. nigrispinus. Além disso, o consumo de lagartas de P. xylostella por adultos desse predador fora maiores com esta cultivar. A taxa líquida de reprodução (R0) e o tempo médio de geração (T) foram maiores para predadores com presa e folhas de brócolis. Podisus nigrispinus alimentados com lagartas de P. xylostella e folhas de brócolis apresentaram melhores parâmetros reprodutivos, podendo ser uma alternativa para a criação deste predador em laboratório.

Lipophilic metabolite profiling of maize and sorghum seeds and seedlings, and their pest spotted stem borer larvae: A standardized GC-MS based approach.

In order to better understand the biochemical interactions and to identify new biomarkers for plant resistance against insects, we proposed a suitable lipophilic profiling method for insects and their host plants. The critical components of GC-MS based analysis are: sample amount, extraction, derivatization, temperature gradient, run time, and identification of peaks. For lipophilic metabolite profiling of maize and sorghum, and their insect pest, spotted stem borer larvae, we recommend 100 mg sample weight for seeds and insect samples (whole insect body), and 200 mg for seedlings. Maize and sorghum seeds required less time for fat extraction in comparison to their seedlings and the pest fed on these seedlings. GC-MS was standardized for better separation and intensity of peaks using different temperature gradients in the range of 180-300 C. A total of 48 lipophilic compounds encompassing various classes based on their functional groups such as fatty acids, fatty alcohols, hydrocarbons, sterols and terpenoids, vitamin derivative, etc. were separated in the seedlings (30), seeds (14), and the pest (26) in the retention time range of 3.22 to 29.41 min. This method could be useful to study nutritional aspects of different field crops in relation to various stresses apart from the analysis of lipophilic compounds for better understanding of insect-plant interactions.

Development and survival of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) as a function of temperature: effect on the number of generations in tropical and subtropical regions

The diamondback moth, Plutella xylostella (L.), is the most important pest of brassicaceous crops worldwide. Since temperature is the major abiotic factor influencing insect development and thermal requirements may vary among insect populations, it is important to know the effect of temperature on development and survival of a subtropical strain of P. xylostella. Development and survival of the diamondback moth was evaluated under seven constant temperatures ranging from 10°C to 35°C. Development was completed between 10°C and 32.5°C, but at 35°C all individuals died in the larval stage. Data were fitted to one linear and five nonlinear models. Considering as criteria the goodness of fit and the ability to estimate parameters of biological significance, the models Briere-1 and Briere-2 were the most adequate to describe the relationship between temperature and development of P. xylostella. The linear model demonstrated that P. xylostella required 312.5 degree-days above a lower threshold of 6.3°C to complete development. The degree-day model showed that the number of diamondback moth generations in the tropical region of Brazil is nearly twice the number in the subtropical region of the country. This result explains, at least in part, the higher population levels of this species in the tropical region of Brazil, and also demonstrates that P. xylostella is tolerant to a wide range of temperatures (6.1-32.5°C). Therefore, temperature cannot be considered a limiting factor for the occurrence of diamondback moth throughout the year in most regions of Brazil.

Using energy budget data to assess the most damaging life-stage of an agricultural pest Mocis latipes (Guenèe, 1982) (Lepidoptera - Noctuidae) / Utilizando o balanço energético de Mocis latipes (Guenèe, 1982) (Lepidoptera - Noctuidae) para identificar o estágio do ciclo de vida mais perigoso de uma praga de pastos

There is much evidence to support that Mocis latipes larvae (Guenèe, 1852) are the most dangerous pasture pest and usually cause large environmental losses. However, no studies have been carried out to identify the instars during which this moth causes the most damage to the environment. Here we calculate M. latipes larval energy budget to assess its consumption across all instars and estimate the consumption/amount of plant biomass required to complete its larval development. Assimilation, respiration, consumption, excretion, gross growth efficiency and net growth efficiency were calculated. Pearson correlations were used to identify the best predictors that influenced larval growth and weight. Across all instars consumption increased exponentially, especially during the last phase. M. latipes larvae consumed ca 13.8 percent of total food from the first to the fifth instar, whereas during the sixth instars these larvae consumed ca 72.6 percent. Results also show that the best gross growth and net growth efficiency were obtained when larvae reached the fifth instar. The results also show that one larva of Mocis latipes consumes 1.02 g (dry weight) of Paspalum maritimum (Trin) in 19 days. Overall, our results indentified the sixth instar as the most destructive instar of this insect. Thus, once we know the most destructive instars of this pest, measures can be taken to disable M. latipes larval development and consequently stop their increase in plant consumption, reducing ecological and economic damage. This knowledge may eventually lead to reduced agricultural damage and contribute to sustainable farming strategies.

Inúmeras evidências indicam a larva de Mocis latipes (Guenèe, 1852) como uma das pragas de pastagem mais perigosas e que comumente causam grandes perdas ambientais. Entretanto, nenhum estudo foi feito para identificar qual a fase de desenvolvimento em que o dano ao ambiente é maior. Neste trabalho, nós calculamos o balanço energético larval de M. latipes para descobrir o consumo em cada instar e estimar o consumo requerido para completar o desenvolvimento larval. A assimilação, respiração, excreção, consumo e os coeficientes, bruto e líquido, do crescimento foram calculados. Correlações de Pearson foram usadas para identificar os preditores que mais influenciavam o crescimento da larva. Resultados indicaram que o consumo aumentou exponencialmente durante os instares, especialmente durante o último instar. Larvas de M. latipes consumiram aproximadamente 13,8 por cento do recurso alimentar total entre o primeiro e o quinto instar, enquanto que no sexto instar consumiram 72,6 por cento. Os resultados também indicaram que o consumo bruto e o consumo líquido foram maiores nos últimos instares. Também se verificou que apenas uma larva consumiu 1,02 g de Paspalum maritimum (Poaceae) em 19 dias. Em resumo, nossos resultados identificaram o sexto instar como o mais destrutivo. Uma vez que se conheça o instar mais destrutivo, medidas mais eficazes podem ser tomadas para inibir o desenvolvimento larval de M. Latipes e o crescimento significativo do seu consumo e, consequentemente, reduzir danos ao ambiente. Este conhecimento pode, eventualmente, contribuir para reduzir danos à agricultura e contribuir para seu desenvolvimento sustentável.

Impact of differential feeding on the growth and development of Helicoverpa armigera (Hubner).

The growth and development of Helicoverpa armigera was observed in the laboratory by feeding them on different foods viz; leaf, flower and fruit of lady finger, cotton, pigeon pea and chick pea. Based on the food ingested, food digested and food excreted as well as on weight and size of the larvae and the duration of larval period, the fruit of chick pea was found to be the most suitable food for H. armigera development, as the food ingesta and food digesta of the larvae on pigeon pea were more than on the other plants. On the pigeon pea pod the larval growth and development was fast and larval duration was short. Next to the fruit, the larvae preferred the leaf of lady finger and cotton and flower of pigeon pea. The results suggested that the larval growth and development was dependent on the feed i.e. both on the part and the type of the plant.

Influência do substrato alimentar sobre o desenvolvimento de Diaphania hyalinata L. (Lepidoptera: Crambidae) / Influence of nutritional substrates on the development of Diaphania hyalinata L. (Lepidoptera: Crambidae)

Aspectos biológicos de Diaphania hyalinata L. foram estudados quando as lagartas foram criadas em dietas natural e artificial em condições de laboratório, a 25 ± 1ºC, umidade relativa de 70 ± 10 por cento e fotofase de 14h. Como dieta natural foi utilizada abóbora jacaré, pepino e abobrinha caserda e uma dieta artificial utilizada em criações de Diatraea saccharalis (Fabr.), desenvolvida por Hensley & Hammond. As lagartas de D. hyalinata foram colocadas nos diferentes substratos e criadas por todo o ciclo. Observaram-se diferenças na duração do período larval, sobrevivência das larvas e pupas, longevidade do adulto e número de ovos entre os substratos. A dieta artificial a que mostrou de modo geral, mais adequada para a criação de D. hyalinata. Entre as dietas naturais, o pepino foi o que se apresentou mais adequado para criação desta praga.

The aim of this research was to evaluate the biological behaviour of melonworm at different natural and artificial diets. Squash cultivar jacaré, cucumber, summer squash and an artificial diets developed by Hensley & Hammond for the sugarcane borer were tried. The research was carried out in the Laboratório de Entomologia do Centro de Ciências Agrárias of the Universidade Federal do Espírito Santo, in climatized room at 25 ± 1ºC, relative humidity of 70 ± 10 percent and 14h photofase. The caterpillars fed on each substrate during the whole life cycle. Differences in duration of the larval period, larvae and pupae survival, adult longevity and number of eggs were registered between the substrates. The results show that the best diet for rearing is the artificial one. Between the natural diets the cucumber showed the best results.

Photoperiodism and seasonality in neotropical population of Plutella xylostella L. (Lepidoptera: Yponomeutidae) / Fotoperiodismo e sazonalidade em população neotropical de Plutella xylostella L. (Lepidoptera: Yponomeutidae)

Neotropical populations of the diamondback moth Plutella xylostella L. have seasonal cycles of growth and decrease, and moth migration plays a fundamental role in generating such population dynamics. Since the oscillation of these populations is predictable, photoperiod might operate as a signal that triggers the migratory behaviour of the insect. Migration in insects is usually preceded by reproductive diapause, a photoperiodic response that can be characterised by morphological, physiological and behavioural alterations that permit to discriminate between migratory and non-migratory forms. In this study, I tested whether the pre-imaginal and reproductive development of P. xylostella from Minas Gerais (Brazil) is affected by artificial day-lengths that are equivalent to the periods of natural population growth or decrease. No evidence of photoperiodic response was found for the insect reared in laboratory on five different constant photoperiods, from 8h to 16h of light per day. There was no significant variation in survival and duration of egg, larva, and pupa stages or in pupal weight, adult size (forewing length), fecundity, and longevity. Although some species have geographically distinct photoperiodic responses, previous assumptions that cosmopolitan P. xylostella responds to photoperiod in temperate regions was questioned. Migratory and population seasonality among neotropical populations of P. xylostella certainly occurs independently of the photoperiodic announcement of seasonal changes in habitat quality.

Populações neotropicais de Plutella xylostella L. possuem ciclos sazonais de crescimento e declíneo e a migração é um fator-chave na geração da dinâmica populacional. Devido à previsibilidade sazonal das oscilações populacionais, o fotoperíodo poderia agir como o sinal que desencadea o comportamento migratório do inseto. Migrações de insetos são geralmente precedidas por diapausa reprodutiva, uma típica resposta fotoperiódica caracterizada por alterações morfológicas, fisiológicas e comportamentais que possibilitam discriminar as formas migratórias das não-migratórias. Neste estudo, foi testado se o desenvolvimento pré-imaginal e reprodutivo de P. xylostella, proveniente de Minas Gerais, é inibido por fotoperíodos equivalentes aos comprimentos de dias em que ocorrem as fases de crescimento ou de declínio das populações naturais. Nenhuma evidencia de resposta fotoperiódica foi encontrada para os insetos criados em laboratório sob cinco regimes constantes de fotoperíodos, variando de oito a dezesseis horas-luz-dia. Não houve variação significativa na sobrevivência e na duração dos estágios de ovo, larva e pupa. O peso das pupas também não foi afetado, assim como o tamanho, a fecundidade e a longevidade dos adultos. Embora algumas espécies de insetos possuam respostas fotoperiódicas geograficamente diferenciadas, a sugestão de alguns autores de que a cosmopolita P. xylostella responde ao fotoperíodo em regiões de clima temperado foi questionada. Os dados experimentais não suportaram a hipótese de que a sazonalidade migratória e populacional de P. xylostella dependem do fotoperíodo como sinal de anúncio de mudanças temporais na qualidade do habitat.

Platynota rostrana (Walker) (Tortricidae) and Phidotricha erigens Raganot (Pyralidae): artificial diet effects on biological cycle

The lepidopterans Platynota rostrana (Walker) (Tortricidae) and Phidotricha erigens Raganot (Pyralidae) have been found frequently in citrus groves in São Paulo State in recent years. Since in Brazil, the fertility cycle of these two species is largely unknown, as are details of the damage wrought by them in crops, this research studied these aspects of the two species, which were kept under laboratory conditions (temperature 25 ± 2 °C, 70 ± 10 percent RH, 14 h photophase) and on an artificial diet. The duration of the biological cycle (egg-adult) for P. rostrana was 38.3 days and total viability was 44.0 percent; for P. erigens these values were 32.5 days and 63.6 percent, respectively. Both species showed five larval instars. Females of P. rostrana laid an average of 308 eggs, whereas those of P. erigens laid an average of 106 eggs. In both species, female pupae were heavier than males. Male and female longevity for both species was nearly 10 days. Based on the data obtained, the artificial diet produced better results in P. rostrana than in P. erigens. If these species, which have the potential to reach pest status in the citrus groves of São Paulo State, could be reared on an artificial diet, research on their control by alternative methods would be easier.

Os lepidópteros Platynota rostrana (Walker) (Tortricidae) e Phidotricha erigens Raganot (Pyralidae) têm sido constatados com freqüência nos pomares cítricos do Estado de São Paulo, nos últimos anos. O objetivo deste trabalho foi estudar a biologia das duas espécies, em condições de laboratório (temperatura 25 ± 2 °C, UR. 70 ± 10 por cento e fotofase de 14 h) em dieta artificial, elaborar uma tabela de vida de fertilidade e descrever os danos causados no campo, devido ao desconhecimento destes aspectos biológicos dos referidos insetos no Brasil. A duração do ciclo biológico (ovo-adulto) de P. rostrana foi de 38,3 dias e a viabilidade total de 44,0 por cento, enquanto para P. erigens foi de 32,5 dias e 63,6 por cento, respectivamente. Ambas as espécies apresentaram cinco ínstares e as pupas de fêmeas foram mais pesadas do que as de machos. As fêmeas de P. rostrana colocaram, em média, 308 ovos e as de P. erigens 106 ovos. A longevidade de machos e fêmeas das duas espécies foi próxima de 10 dias. Pela tabela de vida de fertilidade concluiu-se que P. rostrana tem melhor desempenho em dieta artificial que P. erigens. É possível criar estas espécies em dieta artificial, facilitando o desenvolvimento de pesquisas relacionadas ao seu controle por métodos alternativos, caso elas assumam o status de pragas nos pomares de São Paulo.

Heterochrony in cotton bollworm, Earias vitella (Fb) following ethoxyprecocene administration.

Administration of a synthetic precocene analogue, 7-ethoxy-6-methoxy-2,2-dimethyl chromene to fourth and last instar larvae of E. vitella results into heterochrony, viz. prothetely and metathetely. These disturbances are due to interference with the endocrine system and application of juvenile hormone to treated larvae abolishes the effect of ethoxyprecocene.

Mass production of polyhedral occlusion bodies of NPV of Helicoverpa armigera in relation to dose, age and larval weight.

A significant difference was noticed in the yield of polyhedral occlusion bodies (POBs) in various larval instars of H. armigera when three different doses of the nuclear polyhedrosis virus (NPV) were administered. The yield of POBs from a single larva ranged from 0.35 x 10(6) to 25033.33 x 10(6) with a mean of 18422.33 x 10(6) for fourth instar inoculated. Positive correlation existed between larval weight and number of POBs recovered. The regression analysis indicated POBs recovered responded with predictable manner to the weight of different larval instars and the various concentration of virus administered. The medium lethal time increased in the instars of the larva advanced with a minimum of 3.5 and maximum of 8 days in the first and fifth instars respectively.

Effect of sublethal concentration of Bacillus thuringiensis var. kurstaki on food and developmental needs of the american bollworm, Helicoverpa armigera (Hübner).

Effect of sublethal concentration of B. thuringiensis on the first, third, fourth and fifth instar larvae of the American bollworm, H. armigera was investigated to study their response to food consumption, digestion, utilization, and their development till adult formation. The young larvae surviving B. thuringiensis treatment in their first instar and third instar delayed larval period by two to three days, but did not consume more food as compared to control. However, they showed higher digestibility of food as compared to control, which was compensated by their reduced ability to utilize the digested food for body substance. Contrary to the effect on first and third instar larvae, the fifth instar larvae surviving B. thuringiensis treatment in its fourth instar consumed less food, showed less absorption efficiency in digesting food, but compensated by increase in the utilization of ingested and digested food into body substance. Insects surviving B. thuringiensis HD-1 sublethal toxicity adapted to normal larval growth when fed on untreated food, depending upon insect growth prior to treatment. The moths emerging from B.thuringiensis treated larvae had sex ratio favouring females, and adult pairs laid less fertile eggs than those from the untreated ones. The response of B. thuringiensis treated larvae to their food and developmental needs is discussed.