Christian S. A. Silva-Torres

Superparasitism and host size effects in Oomyzus sokolowskii, a parasitoid of diamondback moth.

Many aspects of a parasitoid’s biology may be affected by its host. Host size, for example, could affect parasitoid fitness, especially in gregarious parasitoids, in which the resource is used by multiple siblings. Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae) is a gregarious larval–pupal endoparasitoid of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), a major pest of crucifers worldwide, and is able to superparasitize the host. This study focuses on the hypothesis that because resource availability is higher in larger hosts, parasitoids developing in larger hosts will fare better. However, superparasitized hosts are expected to yield larger numbers of parasitoid offspring of smaller body size. Results showed that superparasitism increased the number of parasitoid offspring produced per host and increased offspring longevity, but decreased offspring body size. However, developmental time and sex ratio of parasitoid offspring was similar among hosts parasitized once, twice, or three times. Regardless of superparasitism, parasitoids emerging from larger hosts that were fed honey solution lived longer than similarly fed progeny from smaller hosts (36.4 vs. 22.1 days). The results partially support the hypothesis that Oomyzus gained fitness from an increase in host size; moreover, superparasitism seems advantageous for Oomyzus due to increased offspring numbers and longevity.

Compatibilidade de inseticidas e acaricidas com o percevejo predador Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) em algodoeiro

The objectives of this work were to study the insecticides espinosad, lambdacyhalothrin and monocrotophos on the control of Alabama argillacea (Hubner), the compatibility of these insecticides with the predatory stinkbug Podisus nigrispinus (Dallas), and the effects of the insecticides and acaricides methiocarb, pymetrozine, thiamethoxam, abamectin, diafenthiuron, dicofol and propargite on the predatory stinkbug behavior preying upon A. argillacea under field conditions. More than 90% of cotton leafworm control was obtained at the day 0 of application with all insecticides. Control of A. argillacea by lambdacyhalothrin (20 g a.i./ha) and monocrotophos (240 and 320 g a.i./ha) was observed up to day 3 after application; while spinosad (30 and 60 g a.i./ha) prolonged control up to day 5. Monocrotophos and lambdacyhalothrin were significantly more toxic to P. nigrispinus compared to spinosad. Toxicity of monocrotophos and lambdacyhalothrin to P. nigrispinus was evident up to day 3 after application. Survival of P. nigrispinus was affected by methiocarb, thiamethoxam, diafenthiuron, abamectin and sulfur one day after application and only under thiamethoxam treatment after three days. Pymetrozine, dicofol and propargite did not affect P. nigrispinus survival compared to untreated plants. Podisus nigrispinus at the day of application did not prey on A. argillacea under methiocarb treatment, and the predation rate was affected under thiamethoxam, abamectin, diafenthiuron and sulfur treatments at the day of application and after three days. The insecticides pymetrozine and spinosad, and the acaricides dicofol and propargite were compatible to P. nigrispinus and should be considered within a cotton pest management program.

New records of natural enemies of Plutella xylostella (L.) (Lepidoptera: Plutellidae) in Pernambuco, Brazil

We report the occurrence of natural enemies of Plutella xylostela (L.) in organically farmed kale in Pernambuco, Brazil. Seven natural enemies were observed parasitizing or preying on larvae and pupae of P. xylostella--three parasitoids: Cotesia plutellae Kurdjumov (Hym.: Braconidae), Conura pseudofulvovariegata (Becker) (Hym.: Chalcididae) and Tetrastichus howardi (Olliff) (Hym.: Eulophidae), and four predators: Cheiracanthium inclusum (Hentz) (Araneae: Miturgidae), Pheidole sp.Westwood (Hym.: Formicidae), nymphs and adults of Podisus nigrispinus (Dallas) (Hem.: Pentatomidae), and one unidentified species of solitary wasp. Beyond recording these natural enemies, data on predation of P. xylostella larvae in the field and laboratory by C. inclusum are presented.

Effect of two prey types on life-history characteristics and predation rate of Geocoris floridanus (Heteroptera: Geocoridae)

Abstract The predator Geocoris floridanus Blatchley has become more common in row crop systems in Georgia, but its ecology is unknown. We studied selected life-history characteristics of G. floridanus in the laboratory. Two prey treatments were evaluated for nymphs and adults of G. floridanus: 1) eggs of the corn earworm, Helicoverpa zea (Boddie), and (2) young larvae of the beet armyworm, Spodoptera exigua (Hübner). G. floridanus nymphs were reared on the prey, and predator development and prey consumption were monitored; predation rates, longevity, and fecundity of adults were evaluated. Nymphal development times and number of prey consumed by predators fed corn earworm eggs were similar for females and males. Nymphal development of predators fed beet armyworm larvae was prolonged compared with predators reared on corn earworm eggs. Nymphal survival was unaffected by prey type. Nymphs reared on corn earworm eggs required fewer prey to complete nymphal development and produced larger adults. Females fed corn earworm eggs had shorter preoviposition periods, and greater fecundity and longevity than females fed beet armyworms. Females consumed more beet armyworms than corn earworm eggs, but produced fewer eggs per unit prey. Female predators fed beet armyworms while nymphs and switched to corn earworm eggs when adult partially recovered their fecundity, and exhibited life-history characteristics equal to those of females fed corn earworm eggs throughout their lives. Thus, G. floridanus can feed, develop, and reproduce on both prey species, and its performance increases when switched from beet armyworm larvae to corn earworm eggs.

Efeito da idade, fotoperíodo e disponibilidade de hospedeiro no comportamento de parasitismo de Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae)

The high reproduction rate, potential to cause damage, wide geographic distribution and resistance to insecticides of Plutella xylostella (L.) makes difficult its efficient control. However, larvae and pupae of this pest are naturally parasitized by Oomyzus sokolowskii (Kurdjumov), providing opportunities to improve the natural parasitism. This study investigated the effects of the age of adult parasitoids, host availability and time of exposure on O. sokolowskii parasitism behavior. The number of larvae encounters by parasitoid females and the parasitism rate increased with parasitoid age up to 96h. The parasitization was higher when wasps received a constant number of hosts daily in comparison with a random number (13.3 versus 8.9 larvae parasitized). Female parasitization activity was maintained up to the age of 20 days in both treatments and exhibited similar longevity (constant host = 33.5 d; and random host = 34.7 d). The progeny produced per female and the number of parasitoids emerged per host significantly decreased as wasps aged. There was no significant effect of the light regime (12h darkness or 12h light exposure) on the parasitization, although parasitoid was more active after 3h of light exposure. Therefore, further studies on field application of O. sokolowskii should consider the release of 48 h- to 72 h-old parasitoids at dawn as a way to increase the success of host parasitization.

Predatory behavior and life history of Tenuisvalvae notata (Coleoptera: Coccinellidae) under variable prey availability conditions

Abstract Prey availability for predaceous insects can be uncertain in row crop ecosystems, requiring predators to employ flexible reproductive strategies to maintain their populations. In this study, we examined life history parameters and predatory behavior of the ladybeetle, Tenuisvalvae notata (Mulsant) (Coleoptera: Coccinellidae) under different conditions of prey availability. Females of T. notata exhibited a type III functional response when preying upon neonate striped mealybug [Ferrisia virgata Cockerell (Hemiptera: Pseudococcidae)] nymphs and a type II response when preying upon third instars and female adults. On average, T. notata females consumed 157.9 neonate nymphs, 3.6 third-instar nymphs and 2.2 adult females of F. virgata per day. When subjected to a one-day period of prey deprivation, T. notata females exhibited significant reductions in reproduction and survivorship. After 150 days of exposure 47, 13 and 20% of females were alive when fed daily or subjected to repeated one- or 2-day periods of prey deprivation, respectively. Prey consumption increased as a function of prey availability. Daily oviposition was observed for females fed daily, but a sharp reduction in egg production was observed under conditions of prey scarcity. These findings show that T. notata exhibits a positive response to prey availability preying upon the striped mealybug F. virgata.

Toxicidade de lufenurom para Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae)

This work investigated the susceptibility of the predatory stinkbug Podisus nigrispinus (Dallas) to lufenuron using different insecticide concentrations and exposure methods. In laboratory, 5th-instar nymphs and adults were exposed to 0, 25, 50, 100, 150 and 200 mg a.i./l of lufenuron by topical exposure and by ingestion exposure through treated drinking water. In open-sided greenhouse, 5th-instar nymphs and adults were caged on cotton plants treated with lufenuron at the lowest and the highest recommended doses (10 and 50 g a.i./ha). Ingestion exposure was set up by providing the predator during five days a cotton leafworm caterpillar Alabama argillacea (Hubner), previously fed on treated cotton leaves. Ingestion and topical exposure caused severe mortality to nymphs at concentration over 50 and 150 mg a.i./l, respectively. In general, adults of the predator were not susceptible to the lufenuron. On the other hand, egg viability was significantly reduced at concentrations over 100 mg a.i./l. Nymphs caged on treated plants and fed on treated caterpillars did not reach adult stage, while nymphs exposed to residual contact were not affected. Three-day old females exposed to residual contact and to residual contact ingestion of lufenuron through contaminated caterpillars (10 g a.i./ha) restored their egg viability between the 3rd- and 4th-week of adult lifetime, while, females fed with treated caterpillars (50 g a.i./ha) showed egg viability lower than 10% during lifetime. These results show the importance of using lufenuron at the lowest recommended dose, as a conservation strategy for P. nigrispinus.

Polyandry and Male Mating History Affect the Reproductive Performance of Eriopis connexa (Coleoptera: Coccinellidae)

ABSTRACT Insect polyandry often selects for increased male investment in ejaculates as it generates both sperm competition and the potential for cryptic (postcopulatory) female choice, a process males will seek to influence. Among the Coccinellidae, allomonal factors in male ejaculates are known to stimulate female fecundity and fertility and confer positive effects on the developmental phenotypes of progeny. We used the subtropical species Eriopis connexa (Germar) to test the hypothesis that male epigenetic factors will be diminished by sexual activity. We subjected virgin females to either a single mating, or 10 daily matings with the same male or different ones, either virgin or previously mated. There was no effect of male mating status or male novelty on female fecundity or fertility, but multiple matings with different virgin males resulted in faster production of clutches during the first 10 d of oviposition. When females were permitted only a single mating, their mean clutch size was diminished by males that had been previously mated two or more times and they took longer to produce 10 clutches, although egg viability was unaffected. Paternal effects did not vary with paternal mating history and progeny development was similar between first and tenth clutches, indicating an absence of the age-specific maternal effects observed in certain other species. The habitats occupied by this subtropical species provide prey for reproduction throughout the year and lack the strong seasonal patterns of prey availability that have been hypothesized to drive the evolution of age-specific maternal effects observed in some temperate species.

Life‐history costs associated with resistance to lambda‐cyhalothrin in the predatory ladybird beetle Eriopis connexa

1 The present study assessed the fitness of a lambda‐cyhalothrin‐resistant population of Eriopis connexa (Germar) with respect to development, reproduction, survival under prey scarcity and prey consumption. 2 Nontreated resistant females (R0) and females recovered after the topical application of 0.05, 0.10 and 0.25 mg active ingredient/mL of lambda‐cyhalothrin (R0.05, R0.10 and R0.25) produced, on average, 50% less eggs than susceptible females (S0), irrespective of the applied dose. All of the other traits evaluated remained similar. With respect to developmental characteristics, the larval viability and weight of adult male R0.25 progeny were statistically lower compared with the R0 and S0 progenies. Prey scarcity between days 3 and 13 of adulthood did not affect R0 and R0.25 survival, although egg production was significantly lower for R0 females, followed by R0.25 females, compared with S0 females. 3 The mean consumption of cotton aphids Aphis gossypii Glover over 5 consecutive days was significantly higher for S0, followed by R0 and R0.25, up to day 3 of observation. However, after day 4, prey consumption was similar among the three populations. 4 The results obtained in the present study show that resistant females have a lower reproductive output than susceptible females and that this is not related to the knockdown effect; however, the costs of recovering from knockdown interfere with the survival of offspring and also slightly with prey consumption. Thus, we conclude that the lambda‐cyhalothrin‐resistant E. connexa population exhibits an egg production disadvantage relative to the susceptible population and that this is increased when the population is subjected to prey scarcity.

Interação entre inseticidas e umidade do solo no controle do pulgão e da mosca-branca em algodoeiro

O objetivo deste trabalho foi avaliar o controle exercido por tiametoxam e pimetrozine, em aplicacao foliar ou ao solo, sobre Bemisia tabaci e Aphis gossypii, em algodoeiro, e determinar a interacao entre formas de aplicacao e a umidade do solo, em diferentes intervalos apos a aplicacao. Foram aplicados inseticidas via pulverizacao ou esguicho ao solo, em plantas de algodoeiro submetidas a tres faixas de umidade do solo. Os inseticidas foram testados separadamente, em arranjos fatoriais, com formas de aplicacao (tiametoxam), pragas (pimetrozine) e teores de umidade no solo como fatores de variacao, com as avaliacoes repetidas no tempo. Foram realizadas avaliacoes apos 3 horas e aos 3, 6, 12, 24 e 32 dias apos a aplicacao. Os inseticidas, em pulverizacao, apresentaram controle superior a 80%, ate 6 dias depois da aplicacao, para mosca-branca e pulgao. O uso de tiametoxam com esguicho, na menor faixa de umidade, propiciou controle inferior a 60%, no dia da aplicacao, superior a 90%, aos 3 e 6 dias, e superior a 80%, aos 12 dias apos aplicacao. O grau de estresse hidrico em que se encontra a planta e importante para a escolha do inseticida e da modalidade de aplicacao mais adequados ao controle das pragas avaliadas.