The temperature is among the abiotic factors that directly affect the developmental time and behavior of insects. The adaptability to climatic conditions is a key point for the success of mass-rearing and establishment of parasitoids in biological control programs. The objective of this study was to evaluate the developmental time and parasitism of Lysiphlebus testaceipes (Cresson) on Aphis gossypii Glover as host in different temperatures. The tests were carried out in climatic chambers at 15, 20, 25 and 30 ± 1°C, 60 ± 10% RH and 10h photophase. Parasitized nymphs of A. gossypii were kept individualized in petri dishes (6 cm of diameter) on a leaf disk (2 cm diameter) of chrysanthemum (Dendranthema grandiflorum Tzvelev) 'Yellow Snowdon' cultivar on a layer of agar. The developmental time of L. testaceipes was 26.9, 14.8, 11.3 and 12.2 days at 15, 20, 25 and 30ºC, respectively. Parasitism rates were 76, 68, 65 and 40% at 15, 20, 25 and 30°C, and emergence rates were 80, 61, 62 and 14% at these temperatures. The combination of a low developmental time (11.3 days) and parasitism and emergency higher than 60% occurred at 25ºC, indicating that this temperature could be the most adequate for reproduction and establishment of L. testaceipes as a biological control agent of A. gossypii in protected cultivation.
ABSTRACT. Fertility life table of Lysiphlebus testaceipes (Cresson, 1880) (Hymenoptera, Aphidiidae) on Schizaphis graminum (Rondani, 1852) (Hemipera, Aphididae). Life table analyses have been developed to understanding the impact of various sources of intrinsic and extrinsic mortalities on the rate of population growth. The understanding of the population increase of the parasitoids related to their hosts is important in biological control programs. This work had as objective to evaluate the survival and fertility of the parasitoid Lysiphlebus testaceipes (Cresson, 1880) on Schizaphis graminum (Rondani, 1852) as a host under fertility life table. The experiment were carried out in a climatic chamber at 25 ± 1°C, RH 60 ± 10% and 10h photophase. To determine the immature mortality, the development time and the sex ratio of the parasitoid, 12 females of the parasitoid (less than one day old) and 240 nymphs of S. graminum (3 days old) were used. To evaluate the longevity and fertility of L. testaceipes, 15 females (less than one day old) were used. Nymphs of S. graminum (3 days old) were offered for each parasitoid female daily, until the female died, being in the 1 st day -300 nymphs; 2 nd day -250 nymphs; 3 rd day -200 nymphs; 4 th day -150 and in the other days a number of 50 nymphs. L. testaceipes had an immature mortality of 22,2%, and a development time of males and females of 9.0 and 9.1 days, respectively. The females of L. testaceipes laid, in it first life day, 257.8 eggs, and they survived up until seven days. The net reproduction rate (R o ) and the intrinsic rate of increase (r m ) were respectively, 301.9 and 0.513. The finite rate of increase (l) was 1.67 females per day, the mean length of a generation (T) was 11.13 days and the time to duplicate the population (TD) was 1.35 weeks. The parasitoid L. testaceipes have a high potential of population growth on S. graminum as a host under the analyzed conditions.
ABSTRACT. Response to temperature of Aphidius colemani Viereck (Hymenoptera, Braconidae, Aphidiinae) from three climatic regions of Minas Gerais state, Brazil. The parasitoid Aphidius colemani Viereck, 1912 presents higher mortality at constant temperatures above 25°C, and probably it is the cause of the failure on the biological control of Aphis gossypii Glover, 1877 when this parasitoid is used at higher temperatures in greenhouses. The aim of this work was to evaluate the influence of different temperatures on individuals of A. colemani from different climatic regions of Minas Gerais state, Brazil. Individuals of A. colemani were collected in the localities of Juramento, Lavras and São Gotardo, and reared in laboratory (22±2°C, 70±10% RH and 12h photophase) for three generations in the host A. gossypii, on cucumber plants. One mated female of A. colemani, 24-48 h old, was released for one hour, in a Petri dish (15cm) with 20 nymphs of 2 nd instar of A. gossypii on a leaf disk of cucumber (4 cm of diameter) laid on a layer of agar-water (1%). The parasitized aphids were kept at 16, 19, 22, 25 and 28±1°C, 70±10% RH and 12h photophase. The emergence rates of individuals from Juramento (65.9 and 35.4%) and São Gotardo (71.4 and 47.6%) were lower compared to those from Lavras (87.1 and 80.9%) at 16 and 28°C. The more suitable temperature for the development of A. colemani from Lavras was higher than those for individuals from Juramento and São Gotardo. The individuals from Lavras showed highest emergence at 28°C, and this demonstrated the existence of individuals of A. colemani with tolerance to higher temperatures. These results open news perspectives on the use of different strains of A. colemani on biological control of A. gossypii in protected cultivation.
ABSTRACT. Fecundity and longevity of Aphis gossypii Glover, 1877 (Hemiptera, Aphididae) at different temperatures and commercial chrysanthemum cultivars (Dendranthema grandiflora Tzvelev). The aphid A. gossypii is one of the main pests in a number of crops both under field and protected conditions. The objective of the present study was to evaluate the fecundity and longevity of A. gossypii under different temperatures and commercial chrysanthemum cultivars (Yellow Snowdon, White Reagan and Dark Splendid Reagan) with different trichomes densities (11.3; 16.6 and 21.6 trichome/mm 2 of the leaf, respectively) The trials were carried out in climatic chambers, at four temperatures (15, 20, 25 and 30 ±1 °C), 70 ± 10% RH and photophase 10h. The reproductive period significantly decreased with increase of temperature in the three cultivars. In Yellow Snowdon cultivar average duration of the reproductive period was 14.3 days at 25 °C. The maximum fecundity was obtained at the temperature of 25 o C with 3,1; 2,8 and 3,6 nymphs/female/day in the Yellow Snowdon, White Reagan and Dark S. Reagan cultivars, respectively. The total fecundity was reduced by extreme temperatures (15 and 30 °C), and was obtained at 25 °C with 35,9 nymphs/female. Females maintained in Yellow Snowdon cultivar significantly showed superiority (30,7 nymphs/female) in total fecundity in relation to White Reagan (22,1 nymphs/ female) and Dark S. Reagan (22,9 nymphs/female). The Yellow Snowdon cultivar (with a lower trichome density) had a significant influence in daily and total capacity of nymphs production, showing a higher fecundity of A. gossypii females. The aphid's longevity was affected by cultivars and temperature, and this longevity decreased whit increase of temperature. The results showed that there was an interaction between the temperature and host plant on reproductive parameters of A. gossypii. KEYWORDS. Aphis gossypii; biology; reproduction; trichome. INTRODUÇÃOAphis gossypii Glover, 1877 (Hemiptera, Aphididae), apresenta ampla distribuição mundial e encontra-se associado a culturas de grande importância econômica. Constiui-se numa das principais pragas em ambientes protegidos tanto nas regiões de clima temperado como nas de clima tropicais. É uma espécie polífaga, capaz de transmitir mais de 50 viroses de plantas (BLACKMAN & EASTOP 1984). Esta espécie, assim como Myzus persicae (Sulzer, 1776) é praga primária em cultivos de crisântemo em casas-de-vegetação no Brasil (BUENO 1999).O aumento da área de produção intensiva da cultura de crisântemo, principalmente no interior de casas-de-vegetação, tem favorecido o aparecimento desses insetos em níveis populacionais capazes de provocar prejuízos econômicos à cultura (BERGMANN et al. 1996). Os pulgões são conhecidos como "estrategistas r", isto é, são muito bem adaptados para explorar temporariamente um novo habitat, através de um rápido aumento da população. RABASSE (1980)
Taxas de Parasitismo de Lysiphlebus testaceipes (Cresson) (Hym.: Aphidiidae) emSchizaphis graminum (Rond.) e Aphis gossypii Glover (Hem.: Aphididae)
This study aimed to evaluate the importance of wild bee and feral honeybee visits for cotton production on conventional and organic farms. Experiments were conducted in Brazil, on a conventional cotton farm in Mato Grosso state in the Amazon biome and on an organic farm in Paraíba state in the Caatinga biome. On the conventional farm, bee assemblage and cotton production were measured near to and far from natural vegetation. Bee richness, fibre fraction, seed number and yield (Kg/ha) were higher by 57.14, 1.95, 17.77 and 18.44% respectively in plots near natural vegetation, but bee abundance did not vary with distance to natural vegetation. On the organic farm, because the cropping area is surrounded by natural vegetation, pollination deficit was evaluated using an exclusion experiment where cotton production of flowers bagged to prevent bee visitation (spontaneous self-pollination) was compared to production of flowers open to bee visitation (open pollination). Open pollinated flowers had higher average boll weight, fibre weight and seed number. Although cotton is not directly dependent on bee pollination, bees increased cotton production on the organic farm by more than 12% for fibre weight and over 17% for seed number. Our data confirm the importance of maintaining communities of pollinators on cotton farms, especially for organic production.
Development and Parasitism of Lysiphlebus testaceipes (Cresson) and Aphidius colemani Viereck (Hymenoptera: Braconidae) on Aphis gossypii Glover (Hemiptera: Aphididae) on Two Chrysanthemum Cultivars
Helicoverpa armigera (Hübner) is part of an important complex of insects-pests that attack the cotton crop. This study aimed to identify the preferential plant parts for the oviposition of moths, as well as the movement and feeding behavior of caterpillars, in the vegetative phase of the cotton cultivar BRS 369 RF. Plants emitting floral buds were used to study the oviposition behavior of moths. For this, a completely randomized design, with three treatments (adaxial and abaxial sides of the leaf and floral buds) and twenty replications (plants in pots), was used. In order to evaluate the behavior of the caterpillars in the cotton vegetative phase, another 3 × 5 factorial design, with nine replications, was used. The treatments were three ages (first, second and third instars) combined with five behaviors (walking, resting, waving, eating and drop-off). In this trial, the period of the day when caterpillars are more active was also evaluated. It was observed that H. armigera moths prefer to lay their eggs on the adaxial leaf side and on the last two nodes of the plant, in a descending direction. The adaxial leaf side is also the part of the plant preferred by caterpillars for walking, eating and resting, being this last behavior the most frequent in all instars. In general, the caterpillars walk more in the morning.
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