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The use of higher dosage and repeated applications of conventional pesticides have led to the rapid development of insect resistance to pesticide and adverse effects on human health and environment. Accordingly, researchers are prompted to identify an alternative entomotoxic agent for crop protection. Nanocides are being considered as alternatives to conventional insecticides because they are expected to lessen the application rate and reduce the chances of resistance development in pests. In this study, we evaluated the entomotoxic effects of nanosilica on larvae of Plutella xylostella, in a laboratory by using dust spray, larva dipping, leaf dipping, and solution spray methods. Dust treatment showed a more highly significant effect than the other three treatments. The mortality percentage increased up to 58% and 85% at 24 and 72 h after treatment, respectively, when nanosilica was applied at a rate of 1 mg cm−2. In all four bioassays, mortality rate increased with both increased time after nanosilica exposure and increased concentration. Light microscopy and scanning electron microscopy images showed that larval death was due to desiccation, body wall abrasion, and spiracle blockage. These results suggested that nanosilica can be an alternative to conventional pesticides if dust formulation would be properly used. [ABSTRACT FROM AUTHOR]

Most insects must accumulate certain metabolites before entering diapause by virtue of photoperiodic regulation. Photoperiods influence diapause beyond the maternal generation in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), which is one of the most important larval endoparasitoid of Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). The accumulation of metabolites in the non-diapausing prepupae, adults, and eggs (before and after oviposition) in progeny from C. vestalis cultures reared at 25°C under three photoperiods (8:16, 12:12, and 16:8 (L:D) hr), along with diapausing prepupae were measured to investigate the effects of photoperiod on the accumulation of metabolites during diapause induction. Compared with those of non-diapausing prepupae, free water, trehalose, total lipid titer, and total polyol contents in diapausing prepupae showed no significant differences; but weight, bound water, total sugar, glycogen, triglyceride, and protein contents were significantly higher. Under 8 hr short days, non-diapausing prepupae and adult females were significantly heavier, and held more bound water content, however, had less free water content than those under 16 hr long days; during diapause induction from maternal generation to progeny, the variation trends of triglyceride and protein contents were irregular, such as at one stage the contents under 8 hr short lights were higher, at another stage were lower, and there was even no difference at the other stage with those under long light. Total polyol (except at prepupal stage) increased with the increase of light period, but glycogen contents increased as the light period was reduced from prepupal, adult stages to egg stages (before and after oviposition) in progeny. These results revealed that in C. vestalis, the parasitoids might start accumulating glycogen, rather than other metabolites, before entering diapause, even at maternal generation influenced by short photoperiod. Meanwhile, lower total polyol content, and higher bound water content, dry weight under short light may be prepared for surviving adverse environments (desiccation and cold) after diapause. The condition experienced by maternal generation must be concerned during diapause induction. [ABSTRACT FROM AUTHOR]

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Most insects must accumulate glycogen before entering diapause. Photoperiod influences diapause beyond the maternal generation in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae). In this study, we measured glycogen content and the activity and messenger RNA (mRNA) expression of glycogen synthase and glycogen phosphorylase at different G (25 °C under light:dark photoperiods of 8L:16D, 12L:12D, and 16L:8D) and G life stages (13 °C under 8L:16D). Glycogen content in G and G increased with shorter light periods, except for G adult males, which showed no significant difference under the three photoperiods. Compared with those under 16 h, in those under 8 h light, glycogen synthase activity was significantly higher at all tested stages, except for G pupa and adult male, for which it was identical; mRNA expression was higher at G larva and prepupa, lower at pupa, and identical at rest stages. Glycogen phosphorylase activity was significantly higher for G egg, lower at G prepupa, and identical at all other stages; mRNA expression was higher at G and G larval stages, and similar at rest stages. These findings suggest that glycogen, being regulated by the two enzymes, may be a consequential factor in the transmission of maternal information and diapause induction of C. vestalis. [ABSTRACT FROM AUTHOR]

The article discusses a study on the signaling functions of hydrogen peroxide in diapause induction in the Cotesia vestalis wasp. It describes the measurement of hydrogen peroxide and activities of the antioxidant enzymes superoxide dismutase, peroxidase and catalase at diapause, as well as in maternal non-diapausing pre-pupa, adult and offspring egg stages. Maternal non-diapausing pre-pupae under eight hours of short light were found to have higher superoxide dismutase, lower catalase and similar peroxidase activities as diapausing pre-pupae.

Interspecific competition between Encarsia formosa and Encarsia sophia, two major parasitoids of Bemisia tabaci, and the influence of five tomato varieties on competition outcome were investigated under laboratory conditions. E. formosa parasitized more B. tabaci than E. sophia when in single wasp assays on any of the tomato varieties investigated. When B. tabaci nymphs were exposed to both wasp species (either simultaneously or sequentially), the number of B. tabaci nymphs parasitized by either wasp species was significantly decreased compared to the sole access condition. Total mortality of B. tabaci was increased when B. tabaci nymphs were exposed to both wasp species compared to only one wasp species. Thus competition between E. formosa and E. sophia apparently reduced parasitoid offspring numbers, but not the efficiency of biological control. In fact, control efficiency was enhanced in some cases, particularly on tomato variety Huangtuoyuan (HTY). When wasps were allowed sequential access to hosts, interference occurred through host feeding by the second wasp, especially if it was E. sophia. The effect of different tomato varieties was not significant. [ABSTRACT FROM AUTHOR]

Maximizing the contribution of endemic natural enemies to integrated pest management (IPM) programs requires a detailed knowledge of their interactions with the target pest. This experimental field study evaluated the impact of the endemic natural enemy complex of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) on pest populations in commercial cabbage crops in southeastern Queensland, Australia. Management data were used to score pest management practices at experimental sites on independent Brassica farms practicing a range of pest management strategies, and mechanical methods of natural enemy exclusion were used to assess the impact of natural enemies on introduced cohorts of P. xylostella at each site. Natural enemy impact was greatest at sites adopting IPM and least at sites practicing conventional pest management strategies. At IPM sites, the contribution of natural enemies to P. xylostella mortality permitted the cultivation of marketable crops with no yield loss but with a substantial reduction in insecticide inputs. Three species of larval parasitoids (Diadegma semiclausum Hellén [Hymenoptera: Ichneumonidae], Apanteles ippeus Nixon [Hymenoptera: Braconidae], and Oomyzus sokolowskii Kurdjumov [Hymenoptera: Eulophidae]) and one species of pupal parasitoid Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) attacked immature P. xylostella. The most abundant groups of predatory arthropods caught in pitfall traps were Araneae (Lycosidae) > Coleoptera (Carabidae, Coccinelidae, Staphylinidae) > Neuroptera (Chrysopidae) > Formicidae, whereas on crop foliage Araneae (Clubionidae, Oxyopidae) > Coleoptera (Coccinelidae) > Neuroptera (Chrysopidae) were most common. The abundance and diversity of natural enemies was greatest at sites that adopted IPM, correlating greater P. xylostella mortality at these sites. The efficacy of the natural enemy complex to pest mortality under different pest management regimes and appropriate... [ABSTRACT FROM AUTHOR]

1 Accurate assessment of the impact of natural enemies on pest populations is fundamental to the design of robust integrated pest management programmes. In most situations, diseases, predators and parasitoids act contemporaneously on insect pest populations and the impact of individual natural enemies, or specific groups of natural enemies, is difficult to interpret. These problems are exacerbated in agro-ecosystems that are frequently disrupted by the application of insecticides.2 A combination of life-table and natural enemy exclusion techniques was utilized to develop a method for the assessment of the impact of endemic natural enemies onPlutella xylostellapopulations on commercialBrassicafarms.3 At two of the experimental sites, natural enemies had no impact onP. xylostellasurvival, at two other sites, natural enemy impact was low but, at a fifth site, natural enemies drastically reduced theP. xylostellapopulation.4 The calculation of marginal death rates and associatedk-values allowed the comparison of mortality factors between experimental sites, and indicated that larval disappearance was consistently the most important mortality factor, followed by egg disappearance, larval parasitism and pupal parasitism. The appropriateness of the methods and assumptions made to calculate the marginal death rates are discussed.5 The technique represents a robust and easily repeatable method for the analysis of the activity of natural enemies ofP. xylostella, which could be adapted for the study of other phytophagous pests. [ABSTRACT FROM AUTHOR]

Diadromus collaris (Gravenhorst)(Hymenoptera: Ichneumonidae) has been recordedin many parts of the world as a major pupalendoparasitoid of the diamondback moth Plutella xylostella (Linnaeus) (Lepidoptera:Plutellidae). Experiments were conducted tocompare reproductive compatibility andperformance as affected by temperature betweentwo geographic populations of D.collaris, one from Hangzhou, Zhejiang and theother from Lishan, Taiwan, China. The numbersand sex ratio of progeny in all possiblecrosses and backcrosses were similar to thoseobtained within each of the populations,demonstrating complete reproductivecompatibility between the two populations. Thetwo populations showed similar responses totemperature with respect to development time,adult longevity and number of host pupaeparasitized per female. However, the populationfrom Hangzhou achieved higher rates of survivalfrom larva to adult emergence at hightemperatures and had higher proportions offemale progeny at some temperatures, than thepopulation from Lishan. The Hangzhou populationachieved higher intrinsic rates of increase atall temperatures tested from 15 to33.5 °C, and the differences weresignificant at 30 and 32 °C. Thedifferences between the two populations inability to survive high temperatures mayreflect their adaptation to local climates. Thesignificance of the intraspecific variationsrevealed is discussed with regard to the use ofgeographic populations of the parasitoid in thebiological control of P. xylostella. [ABSTRACT FROM AUTHOR]

The braconid Cotesia plutellae(Kurdjumov) (Hymenoptera: Braconidae) is amajor solitary, larval endoparasitoid of thediamondback moth, Plutella xylostella(L.) (Lepidoptera: Plutellidae). Parasitism oflarvae of different host instars and fourdevelopmental ages of the 4th instar ofthe pest was examined. The effects of hostinstar at initial parasitization on thedevelopment, survival, size and fecundity ofthe parasitoid were determined in thelaboratory at 25 °C. The effects ofparasitism on host development and foodconsumption were investigated at 28 °C. Cotesia plutellae could parasitize larvaeof all four instars of P. xylostella, butpreferred 2nd and 3rd instars. In achoice test, the relative parasitism indicesfor 2nd, 3rd and 4th instarswere 0.37, 0.39 and 0.24, respectively.Parasitism decreased sharply with increasinghost age in the 4th instar and approachedzero in host larvae that had gone beyond 37%of 4th stadium. The development time andthe final adult size of the parasitoid variedwith the host instar at initial parasitization.Parasitoids with initial parasitism in the4th instar hosts had the shortestdevelopment time, followed by those in the3rd instar, and then by those in the2nd instar. Parasitoids startingparasitism in 2nd instar hosts weresmaller in body size than those starting in the3rd or 4th instar. However, resultantfemales starting parasitism in 3rd instarhosts had the highest fecundity. Parasitizedlarvae exhibited longer development time andincreased food consumption compared withunparasitized ones. This study presents thefirst record that a solitary parasitoidregulates host behavior leading to an increasein food consumption by the host. [ABSTRACT FROM AUTHOR]

A correction to the article "Effects of Photoperiod on Body Size and Hormone Titres Relating to Diapause Regulation in Cotesia vestalis (Hymenoptera: Braconidae)" that was published in the August 2013 issue is presented.