Parasitismo de traça-das-crucíferas por Oomyzus sokolowskii

Abstract

Resumo -O objetivo deste trabalho foi avaliar a capacidade de parasitismo do parasitoide larval-pupal Oomyzus sokolowskii, submetido a diferentes densidades do hospedeiro traça-das-crucíferas (Plutella xylostella), em laboratório, casa telada e campo. Em laboratório e campo, O. sokolowskii foi exposto às densidades de 2, 4, 8 e 16 lagartas. Em laboratório, empregaram-se recipientes de 300 mL e, em campo, plantas de couve foram confinadas em gaiolas de organza (30x50 cm). Em casa telada, foram utilizadas microparcelas compostas por seis plantas de repolho infestadas com 25, 50, 85 ou 100 lagartas. O número de lagartas parasitadas aumentou de acordo com a densidade do hospedeiro e variou de 1,7 a 10,4, em laboratório, e de 0,61 a 7,0, em campo. Em casa telada, a maior taxa de parasitismo foi observada nas microparcelas com densidades mais elevadas do hospedeiro. O tempo de exposição aos parasitoides proporcionou maior taxa de parasitismo após 72 horas (24 horas, 52,4% e 72 horas, 80,7%) independentemente da densidade. Oomyzus sokolowskii responde positivamente ao incremento na densidade de P. xylostella, embora a taxa de parasitismo permaneça constante independentemente da disponibilidade do hospedeiro.Termos para indexação: Plutella xylostella, controle biológico, densidade do hospedeiro, reposta funcional. Parasitism of diamondback moth by Oomyzus sokolowskiiAbstract -The objective of this work was to evaluate the parasitism capacity of the larval-pupal parasitoid Oomyzus sokolowskii submitted to different densities of the host diamondback moth, Plutella xylostella, in the laboratory, greenhouse and field. In the laboratory and in the field, O. sokolowskii was exposed to densities of 2, 4, 8 or 16 larvae. In the laboratory, 300 mL recipient were used, and in the field kale plants were placed in cages (30x50 cm). In the greenhouse, microparcels consisted of six cabbage plants each infested with 25, 50, 85 or 100 larvae. The number of parasitized larvae increased with host density and varied from 1.7 to 10.4 (laboratory) and from 0.61 to 7.0 (field). In the greenhouse, parasitism rate was higher in microparcels with higher host infestation. The time of exposition was significant, with higher parasitism rate at 72 hours after host exposure (24 hour, 52.4%; and 72 hour, 80.7%), irrespective of host density. Oomyzus sokolowskii responds to increases in host density, but maintains the parasitism rate unchanged irrespective of variations in the host availability.

Tetrastichus howardi(Hymenoptera: Eulophidae) in Different Densities and Periods of Parasitism onDiatraea saccharalis(Lepidoptera: Crambidae) Caterpillars

“…However, the development and progeny (Barbosa et al 2008(Barbosa et al , 2010 of the parasitoids depends on the resources available and the host quality in addition to the length of parasitism period. These data concur with reports regarding Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae), with the parasitism rate approximately doubling from 40% after 24 h to 80% after 72 h of exposure to third-instar Plutella xylostella (L.) (Lepidoptera: Plutellidae) (da Silva-Torres et al 2010). Thus, the longer exposure period to the parasitoid host may stimulate a higher parasitism rate, as observed in T. howardi females.…”

“…The parasitoid density and length of exposure to the host may affect the successful of parasitism (Sagarra et al 2000, da Silva-Torres et al 2010, progeny production (Chong and Oetting 2006), offspring sex ratio (Choi et al 2001), life cycle length (egg to adult; Barbosa et al 2008Barbosa et al , 2010, and adult longevity in T. howardi. Thus, adequate parasitoid densities per host and exposure times can enhance the quality and number of individuals produced.…”

Behavioral Studies of the Parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae)

“…Differences appeared only when we considered clutch size per parasitized larva, within host density, and number of pupae formed and adults emerged; with lower means for 3 and 24 hosts offered, and highest means for intermediate values (6 and 12 hosts offered). This result suggests possible clutch size adjustment by the parasitoid females, reported for other parasitoid wasps (Bezemer and Mills 2003;Silva-Torres et al 2010).…”

Behavioral response and adaptive cost in resistant and susceptiblePlutella xylostellato Chlorantraniliprole

“…Each strain was reared separately in the laboratory. Both susceptible and resistant DBM strains were maintained on organic kale leaves offered daily to adults for oviposition and larvae as food, according to Silva-Torres et al , (2010), but the resistant DBM strain was kept under selection pressure by exposure to kale leaves treated with the LC 50 of chlorantraniliprole estimated from the concentration-response curve. After consumption, untreated kale leaves were used to feed the resistant larvae until the end of the cycle and for adult oviposition.…”