The behavior of Aphis gossypii and Aphis craccivora (Hemiptera: Aphididae) and of their predator Cycloneda sanguinea (Coleoptera: Coccinellidae) in cotton-cowpea intercropping systems

ABSTRACT The intercropping is an important cultural practice commonly used in pest management. It is based on the principle that increased plant diversity in the agro-ecosystem can lead to reductions of pest populations in the crop. The current study aimed to assess the impact the colored fiber cotton-cowpea intercropped systems on Aphis gossypii and Aphis craccivora and on their predator Cycloneda sanguinea and the losses and the dispersion behavior of these aphids and their predator in these cropping systems. The experiment had a randomized block experimental design with two bioassays and four treatments. The number of apterous and alate aphids (A. gossypii) per cotton plant was 1.46 and 1.73 or 1.97 and 2.19 times highest in the solid cotton system than that found in the cotton-cowpea intercropped systems (S1) and (S2), respectively. On the other hand, the cotton-cowpea intercropped systems (S1 and S2) reduced, respectively, in 43% and 31% the number of apterousA. gossypiiper cotton plant compared to the control. Implementing cotton-cowpea intercropped system in the S1 scheme reduced A. gossypii infestation, favored the multiplication of C. sanguinea, and allowed obtaining heavier open bolls.

Population dynamics of Aphis gossypii Glover and in sole and intercropping systems of cotton and cowpea

ABSTRACT Population dynamics of aphids have been studied in sole and intercropping systems. These studies have required the use of more precise analytical tools in order to better understand patterns in quantitative data. Mathematical models are among the most important tools to explain the dynamics of insect populations. This study investigated the population dynamics of aphids Aphis gossypii and Aphis craccivora over time, using mathematical models composed of a set of differential equations as a helpful analytical tool to understand the population dynamics of aphids in arrangements of cotton and cowpea. The treatments were sole cotton, sole cowpea, and three arrangements of cotton intercropped with cowpea (t1, t2 and t3). The plants were infested with two aphid species and were evaluated at 7, 14, 28, 35, 42, and 49 days after the infestations. Mathematical models were used to fit the population dynamics of two aphid species. There were good fits for aphid dynamics by mathematical model over time. The highest population peak of both species A. gossypii and A. craccivora was found in the sole crops, and the lowest population peak was found in crop system t2. These results are important for integrated management programs of aphids in cotton and cowpea.

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.

Effect of temperature on the reproduction of Bracon vulgaris Ashmead (Hymenoptera: Braconidae), a parasitoid of the cotton boll weevil

Estudamos os efeitos da temperatura na reprodução de Bracon vulgaris Ashmead, ectoparasitóide do bicudo-do-algodoeiro, Anthonomus grandis Boheman, em câmaras climatizadas, em temperaturas constantes de 20, 25 and 30ºC, umidade relativa do ar de 70 ± 10 por cento e fotofase de 14 h. As fêmeas do parasitóide produziram mais ovos a 25ºC (124,65 ovos) do que aquelas expostas a 20 (43,40 ovos) e a 30ºC (49,60 ovos). O número médio de larvas parasitadas por fêmea de B. vulgaris a 25ºC(71,75 larvas) foi maior do que a 20ºC (31,40 larvas) e 30ºC (25,15 larvas). As taxas diárias de aumento (r m) foram -0,007 a 20ºC, 0,07 a 25ºC e 0,03 a 30ºC, indicando que a temperatura de 25ºC produziu aumento de 1100 e 133 por cento no valor de r m em relação às temperaturas de 20 e 30ºC, respectivamente. Nos programas de controle biológico do bicudo-do-algodoeiro, usando liberações inoculativas deve-se utilizar fêmeas adultasde B. vulgaris com aproximadamente 5 dias (a 25 ou 30ºC) ou 20 dias de idade (a 20ºC); quando usando liberações inundativas, utilizar fêmeas adultas de B. vulgaris , com idade entre 11 e 31 dias (a 20ºC); 9 e 29 dias (a 25ºC) ou 3 e 14 dias (a 30ºC).

This research studied the effect of temperature on the reproduction of Bracon vulgaris Ashmead, an ectoparasitoid of cotton boll weevil ( Anthonomus grandis Boheman) at constant temperatures of 20, 25 and 30ºC, 70 ± 10 percent RH and a photophase of 14 h. Females of the parasitoid produced a greater number of eggs when exposed to 25ºC (124.65 eggs) in relation to those exposed to 20 (43.40 eggs) and 30ºC (49.60 eggs). The number of parasitized larvae per female of B. vulgaris at 25ºC (71.75) was greater than at 20ºC (31.40) and 30ºC (25.15). The daily intrinsic rates of increase (r m) were - 0.007 at 20ºC, 0.07 at 25ºC and 0.03 at 30ºC, revealing that the temperature of 25ºC produced increases of 1,100 and 133 percent in the value r m in relation to temperatures of 20 and 30ºC, respectively. In programs of biological control of the boll weevil using innoculative releases, adult females of B. vulgaris with approximately five (at 25 or 30ºC) or 20 day old (at 20ºC) should be used; when using innundative releases, adult females of B. vulgaris , with ages between 11 and 31; 9 and 29 or 3 and 14 days, respectively, at 20, 25 or 30ºC should be used.

Mortality of the defoliator Euselasia eucerus (Lepidoptera: Riodinidae) by biotic factors in an Eucalyptus urophylla plantation in Minas Gerais State, Brazil

Euselasia eucerus (Hewitson, 1872) (Lepidoptera: Riodinidae) is a Brazilian native species commonly found in Eucalyptus plantations. Biotic mortality factors of this defoliator were studied in a Eucalyptus urophylla plantation in Minas Gerais State, Brazil aiming to identify natural enemies and their impact on this insect. Euselasia eucerus had biotic mortality factors during all development stages. The most important were Trichogramma maxacalii Voegelé and Pointel, 1980 (Hymenoptera: Trichogrammatidae) during egg stage (48.9 percent), a tachinid fly (Diptera: Tachinidae) during larval stages (10 percent) and Itoplectis sp. (Hymenoptera: Ichneumonidae) during pupal stage (52.2 percent). The parasitism rate was higher in the basal part of the plant canopy (37.8 percent).

Euselasia eucerus (Hewitson, 1872) (Lepidoptera: Riodinidae) é uma espécie brasileira nativa, comumente encontrada em plantios de Eucalyptus. Um estudo da mortalidade por fatores bióticos desse desfolhador foi feito em um plantio de Eucalyptus urophylla no Estado de Minas Gerais, Brasil, com o objetivo de identificar os inimigos naturais e seu impacto sobre esse lepidóptero. Euselasia eucerus possui fatores bióticos de mortalidade durante todas as suas fases de desenvolvimento. Os mais importantes foram Trichogramma maxacalii Voegelé e Pointel, 1980 (Hymenoptera: Trichogrammatidae) durante a fase de ovo (48,9 por cento), um Diptera: Tachinidae durante a fase de larva (10 por cento) e Itoplectis sp. (Hymenoptera: Ichneumonidae) durante a fase pupal (52,2 por cento). A taxa de parasitismo foi mais elevada na parte basal de plantas de eucalipto (37,8 por cento).

Estimative of Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) development time with non linear models / Estimativa do tempo de desenvolvimento de Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) através de modelos não lineares

The objective of this study was to evaluate the precision of the non linear models of Davidson (1942, 1944), Stinner et al. (1974), Sharpe & DeMichele (1977), and Lactin et al. (1995) to describe relationship between developmental rate of different stages of Podisus nigrispinus (Dallas) and temperature. Lower values of R² for the models of Davidson (0.1593 to 0.2672, and 0.1406 to 0.2804 for males and females, respectively) and of Stinner et al. (0.2136 to 0.6389, and 0.1417 to 0.3045 for males and females, respectively) showed that these models were not adequate to estimate developmental rate of P. nigrispinus as function of temperature. However, high values of R² for the models of Sharpe & DeMichele (0.9226 to 0.9893, and 0.8818 to 0.9914 for males and females, respectively), and of Lactin et al. (0.9485 to 0.9997, and 0.8961 to 0.9997 for males and females, respectively) showed that these models are suitable to estimate developmental rate of P. nigrispinus as function of temperature. Females of P. nigrispinus showed high tolerance to high temperature which is represented by high values of H H for immature stage of this insect obtained with the Sharpe & DeMichele model. According to this model females of P. nigrispinus present thermal stress at 33.3°C, which indicates that maximum thermal estimated by this model was close to the real one.

O objetivo deste estudo foi avaliar a precisão dos modelos não lineares de Davidson (1942, 1944), Stinner et al. (1974), Sharpe & DeMichele (1977) e Lactin et al. (1995) no estudo da relação entre as taxas de desenvolvimento das diferentes fases de Podisus nigrispinus (Dallas) e a temperatura. Os menores valores de R² para os modelos de Davidson (0,1593 a 0,2672, e de 0,1406 a 0,2804 para machos e fêmeas, respectivamente) e de Stinner et al. (0,2136 a 0,6389, e de 0,1417 a 0,3045 para machos e fêmeas, respectivamente), indicaram que esses modelos não são adequados para a estimativa do tempo de desenvolvimento de P. nigrispinus, em função da temperatura. Entretanto, os altos valores de R² para os modelos de Sharpe & DeMichele (0,9226 a 0,9893, e de 0,8818 a 0,9914 para machos e fêmeas, respectivamente), e de Lactin et al. (0,9485 a 0,9997, e de 0,8961 a 0,9997 para machos e fêmeas, respectivamente), indicaram que esses modelos são adequados para a estimativa do tempo de desenvolvimento de P. nigrispinus, em função da temperatura. Fêmeas de P. nigrispinus, na fase imatura, mostraram maior tolerância à alta temperatura, a qual é representada pelo parâmetro H H obtido do modelo de Sharpe & DeMichele. De acordo com este modelo, fêmeas de P. nigrispinus na fase imatura apresentam estresse térmico a 33,3°C, indicando que a estimativa da ação térmica máxima foi bastante realista.

Efeitos de hospedeiros alternativos na biologia de Catolaccus grandis (Burks) (Hymenoptera: Pteromalidae), parasitóide de Anthonomus grandis Boheman (Coleoptera: Curculionidae) / Effects of factitious hosts on biology of Catolaccus grandis (Burks) (Hymenoptera: Pteromalidae), a parasitoid of Anthonomus grandis boheman (Coleoptera: Curculionidae)

Foram estudados, em câmara climatizada, a 30°C, umidade relativa de 60 ± 10 por cento e fotofase de 14h, os efeitos dos hospedeiros alternativos Euscepes postfasciatus (Fairmaire) e Callosobruchus maculatus (Fabricius) na reprodução e ataque de Catolaccus grandis (Burks), parasitóide do bicudo-do-algodoeiro. Os hospedeiros alternativos C. maculatus e E. postfasciatus, proporcionaram ao parasitóide, taxas de desenvolvimento superiores às apresentadas por A. grandis. As taxas de parasitismo variaram de 44,3 por cento no hospedeiro alternativo E. postfasciatus a 39,9 por cento em A. grandis. O hospedeiro natural (bicudo) foi o que originou a maior porcentagem de pupas fêmeas (73,7 por cento). C. grandis apresentou a mesma aceitação para oviposição em ambos hospedeiros alternativos, porém a maior produção de ovos foi obtida sobre E. postfasciatus. A oogênese do parasitóide foi estimulada de forma semelhante na presença dos hospedeiros A. grandis e E. postfasciatus, e ambos superaram o hospedeiro alternativo C. maculatus em número de ovos depositados nos cinco primeiros dias. A qualidade do hospedeiro afetou o período de oviposição e a longevidade do parasitóide, sendo o hospedeiro A. grandis responsável por menor expectativa de vida e menor período de oviposição. Larvas de E. postfasciatus ou C. maculatus podem ser usadas como hospedeiros alternativos de C. grandis e estimulam a oogênese em fêmeas de C. grandis.

The effects of the factitious hosts Euscepes postfasciatus (Fairmaire) and Callosobruchus maculatus (Fabricius) on the reproduction and attack rates of Catolaccus grandis (Burks), parasitoid of the cotton boll weevil, were studied in bioclimate chambers, at 30°C, relative humidity of 60 ± 10 percent, and a 14L:10D photoperiod. The factitious hosts C. maculatus and E. postfasciatus provided higher development rates than A. grandis. The parasitism rates ranged from 44.3 percent in E. postfasciatus to 39.9 percent in A. grandis. The natural host (cotton boll weevil) originated the highest female pupae percentage (73.7 percent). C. grandis showed the same acceptance for oviposition in both factitious hosts; however, the highest production of eggs was obtained on E. postfasciatus. The parasitoid oogenesis was stimulated in a similar way in the presence of the host A. grandis and factitious host E. postfasciatus, and both overcame the factitious host C. maculatus in number of eggs deposited in the first five days. The host quality affected the oviposition period and the longevity of the parasitoid, being the host A. grandis responsible for smallest life expectation and oviposition period. Larvae of E. postfasciatus and C. maculatus might be used as factitious hosts of C. grandis. These factitious hosts serve as hosts for parasitoid females of C. grandis to stimulate oogenesis.

Influência de cultivares de batata-doce resistentes e suscetíveis a Euscepes postfasciatus Fairmaire (Coleoptera: Curculionidae) sobre o parasitismo, sobrevivência e a biologia de Catolaccus grandis Burks (Hymenoptera: Pteromalidae) / Influence of resistant and susceptible sweet potato cultivars to Euscepes postfasciatus (Coleoptera: Curculionidae) on parasitism, survival and biology of Catolaccus grandis (Hymenoptera: Pteromalidae)

Avaliou-se em laboratório a influência de quatro cultivares de batata-doce resistentes a Euscepes postfasciatus Fairmaire e duas suscetíveis, sobre o parasitismo e a biologia de Catolaccus grandis Burks. Seis raízes tuberosas de batata-doce de cada cultivar foram infestadas com adultos de E. postfasciatus durante 40 dias. Após esse período as larvas foram retiradas, pesadas e encapsuladas em parafilme e oferecidas em grupos de cinco, com chance e sem chance de escolha, a fêmeas grávidas de C. grandis por 12h. Foram feitas cinco repetições. Larvas parasitadas e os ovos do parasitóide sobre as mesmas foram contados. Em seguida as larvas foram colocadas em copos descartáveis de 500 ml. Diariamente foram efetuadas três observações para se determinar a duração de desenvolvimento das fases do parasitóide e sua sobrevivência. As fêmeas de C. grandis conseguiram distinguir as larvas de E. postfasciatus criadas em raízes tuberosas suscetíveis e resistentes, preferindo parasitar aquelas criadas sobre raízes tuberosas de cultivares suscetíveis. A sobrevivência de C. grandis foi maior em larvas de E. postfasciatus provenientes de genótipos suscetíveis e o número de fêmeas emergidas do parasitóide foi maior quando as larvas hospedeiras provieram de raízes tuberosas dessas cultivares.

The influence of four resistant and two susceptible genotypes of sweet potato to Euscepes postfasciatus Fairmaire on parasitism and biology of Catolaccus grandis Burks were evaluated under laboratory conditions. Six sweet potato roots of each genotype were infested with E. postfasciatus adults during 40 days. After this period the larvae were taken, weighted and encapsulated in parafilm. Five larvae were offered in free choice and no choice tests to C. grandis pregnant females for 12h. Five replications were used. The parasitized larvae and the eggs of the parasitoid were counted. Three daily observations were made to determine the developmental time of phases and parasitoid survival. C. grandis females can distinguish E. postfasciatus larvae reared on susceptible and resistant roots, prefering to parasitize larvae reared on susceptible roots. C. grandis survival was higher when the parasitoid was reared on larvae originated from susceptible roots and the number of emerged females was higher on larvae reared on hosts originated from susceptible roots.