Tiago Teixeira Resende

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.

Development of the Spittlebug Mahanarva fimbriolata under Varying Photophase Conditions

Abstract The effects of varying photophase conditions on biological parameters of Mahanarva fimbriolata (Stal) (Hemiptera: Cercopidae), nymphs and adults were evaluated. Eggs of a late developmental stage were placed near sugarcane roots (cultivar RB739735) maintained in a greenhouse (21 ± 7° C, 90 ± 10% RH). Nymphs and adults were exposed to the following photophase conditions: a) 13:11 L:D as nymphs and adults, b) 13:11 as nymphs and 12:12 as adults, c) 12:12 as nymphs and adults, and d) 12:12 as nymphs and 13:11 as adults. Exposure of nymphs to 13 hr of light significantly reduced the duration of the nymphal stage and the number of nymphs that matured to adults. The duration of the nymphal stage was longer in individuals developing into females than in those developing into males. There was an increase in the longevity of adults kept at 13 hr of light since the nymphal stage. The average longevity of adult males and females was approximately the same. The sex ratio was similar under all photophase conditions. The life cycle of insects kept at 12 and 13 hr of light during nymphal and adult stages respectively was extended. The total life cycle was significantly longer in M. fimbriolata females than males. The different photophase conditions did not affect the reproductive potential of M. fimbriolata. Females produced more diapausing than non-diapausing eggs, except when under 13- and 12-hr light conditions. There was no significant difference in the number of diapausing and non-diapausing eggs produced by females under the other photophase conditions.

Use of Chemical Inducers as a Resistance Trigger in Brachiaria Grasses and Sugarcane

Abstract Chemical inducers have relevant roles in activating the defense responses of plants to insects. The present research examines the defense mechanisms of Brachiaria (Poaceae) grasses and sugarcane cultivars exposed to exogenous of chemical inducers with and without injury due to Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae). Plants were subjected to herbivory by spittlebug nymphs and to 3 chemical inducers: salicylic acid, silicic acid, and nitric oxide. Dry matter was calculated at 15 d after induction, and extraction and quantification of phenolic compounds were performed. The phenolic content and percentage of dry matter of the plants was evaluated by analysis of variance, and means were compared by the Scott-Knott test (P < 0.005). Changes in dry matter were assessed with regard to interactions between inducers and Brachiaria roots and sugarcane shoots. Salicylic acid, silicic acid, and nitric oxide, as well as attack by M. spectabilis, triggered alterations in phenolic contents. The highest and lowest concentrations of phenolic compounds were found in the standard cultivar susceptible (cv. Basilik) and resistant to the insect pest (cv. Marandu), respectively. However, the results showed that inducers failed to impact the defense mechanism of Brachiaria cultivars and that assessment of total phenolic compounds is not the most adequate approach for measuring resistance in these cultivars. In sugarcane, inducers did not appear to act on defense mechanisms, though the resistant cultivar did exhibit a greater phenolic content. Hence, the use of the above chemical inducers is not useful for triggering resistance in Bracharia and sugarcane.

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.