Marcy das Graças Fonseca

Effect of Climate Change on Longevity and Reproduction of Sipha flava (Hemiptera: Aphididae)

ABSTRACT This study examined effects of elevated CO2 alone and in combination with elevated temperature on plant-aphid interactions. CO2 levels in which the host plants were grown affected the durations of some nymphal stadia, but not the survivorship within each instar or of all nymphal instarS. Sipha flava (Forbes) (Hemiptera: Aphididae) adults kept under a constant high CO2 environment (500 ppm) and fed on plants grown under fluctuating CO2 levels (avg. 440 ppm) in a greenhouse had significantly greater longevity and greater reproduction than aphids fed on plants grown either under a constant high CO2 level (500 ppm) or under fluctuating CO2 levels (avg. 368 ppm). Nevertheless, no significant differences were observed in these biological parameters of S. flava that were kept individually in a greenhouse, regardless of the CO2 and temperatures under which the plants used to feed them were grown. However, populations of aphids kept and fed on plants grown in the greenhouse produced significantly more nymphs and adults than did those fed plants grown in a climate-controlled chamber under a constant high CO2 level (500 ppm). The combination of elevated CO2 and high temperature significantly decreased the duration of nymphal stadia, the longevity and reproductive success of S. flava but not nymphal survival. Adults produced fewer nymphs in an environment with elevated CO2 and high temperature than an environment with elevated CO2 and lower fluctuating temperatures. Based on these results, we concluded that S. flava populations will significantly decrease under future climatic conditions when both the concentration of atmospheric CO2 and temperature are projected to increase.

Hymenoptera (Insecta: Hymenoptera) associated with silvopastoral systems

The objective of this work was to estimate the abundance, diversity and constancy of families from the order Hymenoptera, such as the seasonality of those through a survey on the insect population in a silvopastoral system. We installed a Malaise-type trap in a Brachiaria decumbens area managed by a silvopastoral system in Coronel Pacheco, MG, from August 2006 to July 2008. The trapped insects were screened, and those of the order Hymenoptera were classified into their respective family categories and quantified. We adopted the methodology of Bodenheimer to calculate the indices of constancy, while other indices were estimated PAST program. We sampled 5841 specimens in total, which included 549 morphospecies and were distributed among 11 families. Of the total specimens sampled, 80% were Formicidae, which besides being the most abundant, was also the most diverse and constant family. When entomophagous insects were analyzed, the highest values for these indices were recorded for the families Ichneumonidae, Braconidae, and Vespidae. Pollinators were less prevalent compared to the total number of sampled individuals. The population density in the Hymenoptera was not correlated between the two sampling years and climate factors.

Aspects of the Biology of the Lady Beetle Diomus seminulus (Coleoptera: Coccinellidae): A Potential Biocontrol Agent Against the Yellow Sugarcane Aphid in Brazil

ABSTRACT The predator Diomus seminulus (Mulsant) has been found frequently on forage grasses feeding of Sipha flava (Forbes), suggesting that it is a natural predator of this aphid and has potential as a biological control agent for this pest in Brazil. The objectives of this study were to evaluate the effect of temperature on biological aspects of D. seminulus and to determine whether odor is used by this predator to locate prey on forage grass infested with S. flava. We performed daily evaluations of the viability and duration of each instar of the larval and pupal stages at 16, 20, 24, and 28°C. The reproductive capacity and longevity of adults were estimated at 24°C. The use of odor by D. seminulus to search for aphids was evaluated using a Y-tube olfactometer. The average duration of the embryonic period, each instar, larval, and pupal stages decreased significantly with increasing temperatures from 16 to 24°C. Eggs were blackened and parched, leading to low viability at 16 and 28°C. However, viability of the instars and larvae were not significantly affected by temperature. Adults of D. seminulus survived for >135 d; however, peak oviposition occurred 20–50 d after emergence, suggesting that this is the ideal duration of adult maintenance in laboratory culture. The predator D. seminulus used the odors from aphid prey or volatile compounds released from attacked plants to locate their prey. These results provide support for the use of D. seminulus as a successful biological control for aphids.

Impact of the Spittlebug Mahanarva spectabilis on Signal Grass

The aim of this study was to determine the damage in Brachiaria ruziziensis (Germain & Edvard) according to the density of and exposure time to adults of Mahanarva spectabilis (Distant, 1909) (Hemiptera:Cercopidae). Each plant was kept with 0, 12, 18, or 24 adults of M. spectabilis for five or ten days. Then, the insects were removed from the plant, and the following parameters were evaluated: content and loss of chlorophyll, visual damage score, shoot dry mass, and the capability for regrowth. In fact, plants exposed to the highest level of infestation for 10 days showed an 80.97% loss of chlorophyll, which is 25% higher than that shown by the plants exposed for five days. The damage score also increased with infestation levels. In the levels of 12 and 18 adults per plant, the damage score increased with increasing time of exposure. The dry mass content was higher in plants exposed to 24 insects for 10 days, suggesting that the attack of spittlebugs caused premature drying of the plant. These effects caused significant reduction in the number of tillers of infested plants. Our results indicate that exposure to adults of M. spectabilis causes significant damage and affects the development and persistence of B. ruziziensis plants.

How will Mahanarva spectabilis (Hemiptera: Cercopidae) Respond to Global Warming?

The aim of this study was to determine the favorable constant temperature range for Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae) development as well as to generate geographic distribution maps of this insect pest for future climate scenarios. M. spectabilis eggs were reared on two host plants (Brachiaria ruziziensis (Germain and Edvard) and Pennisetum purpureum (Schumach)), with individual plants kept at temperatures of 16, 20, 24, 28, and 32°C. Nymphal stage duration, nymphal survival, adult longevity, and egg production were recorded for each temperature*host plant combination. Using the favorable temperature ranges for M. spectabilis development, it was possible to generate geographic distribution. Nymphal survival was highest at 24.4°C, with estimates of 44 and 8% on Pennisetum and Brachiaria, respectively. Nymphal stage duration was greater on Brachiaria than on Pennisetum at 20 and 24°C but equal at 28°C. Egg production was higher on Pennisetum at 24 and 28°C than at 20°C, and adult longevity on Pennisetum was higher at 28°C than at 20°C, whereas adult longevity at 24°C did not differ from that at 20 and 28°C. With these results, it was possible to predict a reduction in M. spectabilis densities in most regions of Brazil in future climate scenarios.

How Many Adults of Mahanarva spectabilis (Hemiptera: Cercopidae) Should be Used for Screening Brachiaria ruziziensis (Poales: Poaceae) Resistance?

ABSTRACT This study determined the number of spittlebug adults, Mahanarva spectabilis Distant (Hemiptera: Cercopidae), that should be used in selection tests of the forage grass, Brachiaria ruziziensis (Germain and Evrard). In this study, 0, 1, 2, 4, or 8 M. spectabilis adults were kept in plants for 4 or 8 d per experimental plot. After these periods, the insects were removed from the plants and chlorophyll content, damage score, dry weight, fresh weight, and percent dry matter of shoots were evaluated. Chlorophyll content decreased significantly with higher density of M. spectabilis in plants exposed to the pest for 4 or 8 d. Plants that were exposed to eight spittlebugs for 8 d showed a ≈60% loss of chlorophyll content. When the forage was infested with eight adults for 4 d, the average damage score was 3 (50% of the leaf area was affected). The damage score and fresh and dry weights of the forage did not change depending on the exposure time of the plants to the spittlebugs. The percentage of dry matter of the plants infested was higher with the increase insect density and exposure time for all densities. Thus, the minimum recommended number is eight M. spectabilis adults for 4 d in resistance tests of B. ruziziensis to this pest species.

Brachiaria ruziziensis Responses to Different Fertilization Doses and to the Attack of Mahanarva spectabilis (Hemiptera: Cercopidae) Nymphs and Adults

Cropping practices are necessary in order to help reduce the population of pest insect, such as the induction of resistance through fertilization. Therefore, this study aimed to assess alterations on the production and quality of Brachiaria ruziziensis when receiving the fertilization composed by the macronutrients NPK and/or exposed to the attack of Mahanarva spectabilis nymphs and adults. B. ruziziensis plants were fertilized according to the recommendation (R), half of the recommended fertilization (H), or non-fertilization (C). They were also exposed to different M. spectabilis nymph and adult densities. The damage, regrowth, and bromatological components were evaluated. The fertilization treatment promoted a higher M. spectabilis nymph survival on B. ruziziensis; however, it reduced the damage caused by the forage exposed to nymphs and adults of pest insect, and it did not alter the quality of the signal grass. Moreover, the fertilization treatment enabled forage recovery, even when exposed to 5 nymphs or 10 spittlebug adults.

Effects of Temperature on Development and Survival of Harmonia axyridis (Coleoptera: Coccinellidae) and Chrysoperla externa (Neuroptera: Chrysopidae) Fed on Rhopalosiphum padi (Hemiptera: Aphididae)

Abstract The effects of various temperatures on the development and survival of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) fed on Rhopalosiphum padi (Linnaeus) (Hemiptera: Aphididae) were studied, and some biological aspects among these predators were compared. On average, 70 nymphs of R. padi were added to each experimental unit with predator larvae and maintained at 12, 16, 20, 24, 28, or 32 °C. The duration (days) and survival (%) were measured for each immature stage of the two predator species. The developmental durations of all H. axyridis larval instars, the total larval stage, the pupal stage and total preimaginal stage were very long at 16 °C but shortest at 24 °C for the first, second and third larval instars and at 28 C for the fourth larval instar, the total larval stage and the total pre-imaginal stage. Both at 24 °C and 28 °C, 92% of H. axyridis completed the larva to adult cycle, whereas survival was significantly reduced in the 16 to 20 °C range. At the highest temperature (32 °C), 70% of H. axyridis did not reach adulthood. In the case of C. externa, the durations of development of all larval instars and the total larval stage became progressively shorter as the temperature increased from 12 to 20 °C. At still higher temperatures the developmental duration this insect remained almost constant. The predator completed the larval stage at all temperatures from 12 to 32 °C. However, at 12 and 16 °C, mortality of the larvae was greater than 88%, and 100% of the pupae perished. Although the lower threshold temperatures estimated for both predator species were very similar, the development period from larva to adult of H. axyridis was only 59% as long as that of C. externa. By comparing certain biological parameters including durations of development and survival rates of the two predator species, it is suggested that H. axyridis has intrinsic advantages over C. externa; however, additional factors must be considered when choosing the species of predator for biological control of R. padi on grass pastures in Brazil.

Does the Silvopastoral System Alter Hymenopteran Fauna (Insecta: Hymenoptera) in Brachiaria decumbens Monocultures?

ABSTRACT The aim of this study was to evaluate whether environmental changes promoted by the conversion from a Brachiaria decumbens monoculture to a silvopastoral system can be measured by the diversity, richness, abundance, and constancy of insects of the order Hymenoptera. A Malaise trap for collecting insects was installed in a B. decumbens area managed as a silvopastoral system, and another was installed in a monoculture system. Hymenoptera richness and abundance were determined based on the number of morphospecies and specimens, respectively. The diversity and constancy indices were calculated using the Shannon-Wiener and Bodenheimer methodologies. Fifteen families of Hymenoptera were collected, seven of which were unique to the monoculture system. The samples from the silvopastoral system were significantly more abundant (3,889) and rich (305) compared with those from the monoculture system, which were much less abundant (1,473) and rich (173). Similar trends were noted for the families Formicidae, Ichneumonidae, and Braconidae. Additionally, these families and Sphecidae showed significantly greater diversity in the silvopastoral system. Formicidae and Braconidae were constant in both systems, while Ichneumonidae was constant only in the silvopastoral system. The families Vespidae, Pompilidae, and Apidae were more diverse; Chalcididae, Pompilidae, Sphecidae, Halictidae, Evaniidae, and Gasteruptiidae were more abundant; and Vespidae had more richness in the monoculture system. The conversion from the monoculture system to the silvopastoral system can be measured by the occurrence of Hymenoptera, especially the families Formicidae, Ichneumonidae, and Braconidae, which can be used as potential bioindicators.