Mortality factors affecting Bemisia tabaci populations on cotton in Turkey

Cohort‐based, partial life tables were constructed to determine the sources and rates of mortality factors affecting Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on cotton in the eastern Mediterranean region of Turkey over a two year period. Mortality factors were recorded as due to predation, parasitism, dislodgement and unknown for five developmental stages. Across 10 independent cohorts, the highest median rate of marginal mortality pooled over all stages was attributed to parasitism (0.69) followed by predation (0.67). The key factor was hypothesized to be parasitism based on graphical and regression‐based comparison of individual factor k‐values to total generational mortality. The greatest amount of marginal immature mortality occurred during the fourth nymphal stadium (median = 0.77) and mortality during this stage was also most predictive of variation in total mortality. Pooled over all developmental stages, the highest rates of irreplaceable mortality were associated with parasitism (median: 0.112), followed by predation (0.088), dislodgement (0.020) and unknown (0.017). Although crawler mortality was not explicitly measured, sensitivity analyses indicated that mortality during this stage would have changed total mortality by only 0.45–1.21% and had no effect on identification of key factors. There was no significant effect of cotton cultivar on any mortality factor or total mortality over the two years of study. Results suggest that conservation of natural enemies, particularly parasitoids, may provide for more sustainable management of B. tabaci on cotton in Turkey.     

Intraguild predation on Eretmocerus sp. nr. emiratus,a parasitoid of Bemisia tabaci,by three generalist predators with implications for estimating the level and impact of parasitism

Intraguild predation (IGP) is pervasive in many managed and unmanaged ecosystems and may have negative, neutral or positive effects on the biological control of pest insects. Both generalist predators and aphelinid parasitoids attack Bemisia tabaci (Gennadius) Biotype B (=B. argentifolii Perring & Bellows) on cotton in the southwestern USA. Free-choice and no-choice laboratory assays were conducted to quantify prey consumption patterns and preference by three representative generalist predators, Geocoris punctipes (Say), Orius insidiosus (Say), and Hippodamia convergens Guérin-Méneville, offered fourth instar B. tabaci nymphs and nymphs parasitized by Eretmocerus sp. nr. emiratus. All three predators showed a significant preference for larval and pupal stage parasitoids over early fourth instar nymphs, but G. punctipes and O. insidiosus were non-discriminating when offered a choice of larval parasitoids and late fourth instar nymphs. The potential implications of these observed patterns for the field were examined through sensitivity analyses of existing field life table data. First, preference for parasitized hosts alters the methods required for calculating marginal rates of parasitism. Incorporating a preference variable in the estimation procedure had a very small positive effect (0.02–1.13% change) on total generational mortalities observed in previous life table studies. However, further hypothetical analyses suggested that under circumstances of lower generational mortality and higher levels of either apparent parasitism or predation, high levels of predator preference for parasitized prey could alter estimates of total mortality as much as 14%. Second, although intraguild predation was demonstrated, the implications for biological control are unclear. Based on field life table data the rate of IGP ranged from 0.019 to 0.126 depending on predator species and prey comparison, but accounting for these levels of IGP had only small negative effects on total generational mortalities (0.193–1.278% change).     

Size-dependent survivorship in the web-building spiderAgelena limbata

Summary Stage-specific mortality rates and mortality factors for the web-building spiderAgelena limbata, which is suggested to be food-limited, were studied, and the relationship between body size of spiders and survivorship for instar 3 to adults was examined. The mortality rate of the egg sac stage including eggs, deutova (prenymphal stage), and overwintering instar 1 nymphs was low. The low mortality of this stage was partly due to maternal care that reduced the mortality caused by predation and/or abiotic factors. From emergence of instar 1 nymphs from egg sacs to reproduction, the stagespecific mortality rates were almost constant, 32–47%, and the time-specific mortality rates were also constant. These results suggest a Deevey (1947) type II survivorship curve inA. limbata, in contrast to other reports on the wandering or burrowing spiders which suggested type III curves. Important mortality factors for nymphs and adults were parasitism by an ichneumonid wasp and predation by spiders. There were great variations in body size (carapace width) ofA. limbata in the field. Smaller individuals survived at a lower rate to the next stage than larger individuals. This tendency was clearer for the population living under poorer prey availability.A. limbata was unlikely to starve to death in the field because every stage ofA. limbata could survive starvation for a long time in the laboratory, 22–65 days on average. I suggest that the size-dependent survivorship of this spider is associated with vulnerability of smaller individuals to parasitism and predation.     

Constructing life-tables for the invasive maize pest Diabrotica virgifera virgifera (Col.; Chrysomelidae) in Europe

Abstract: The western corn rootworm (Diabrotica virgifera virgifera LeConte, Col.; Chrysomelidae) is an alien invasive species in Europe. It is a univoltine species with eggs that overwinter in the soil and larvae that hatch in spring. Three larval instars feed on maize roots, which can cause plant lodging and yield loss of economic importance. Adults emerge between mid‐June and early August and can reduce yields through intensive silk feeding. In order to provide a thorough understanding of the population dynamics of this invasive pest species in the invaded European region, complete age specific life‐tables were constructed in two maize fields in southern Hungary assessing the significance of natural mortality factors acting on D. v. virgifera populations. This information provides a rational basis for devising sustainable integrated pest management programmes, in particular, by enabling the identification of vulnerable pest age intervals for the timely application of various management tools. The life‐table for D. v. virgifera in Europe resulted in a total mortality of about 99% from the egg stage in the autumn to the emergence of adult females in the following year (K_Total = 2.48), which is comparable with North America. The highest reduction of D. v. virgifera numbers resulted from the mortality in first instar larvae (94% marginal death rate) and from the unrealized fecundity (80%). However, only the variation in mortality between years can change the generational mortality and thus influence population growth. High variation in the marginal death rate between fields and years was found in the second and third instar larval stages, and in the overwintering egg stage. These mortality factors therefore have the potential to cause changes in the total generational mortality. Furthermore, the life‐table suggested that a high fecundity could compensate for a high generational mortality and would lead to population increase.     

Life‐history parameters and predation capacity of Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae) on eggs of Plutella xylostella (Lepidoptera: Plutellidae)

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Mortality Dynamics of Spodoptera frugiperda (Lepidoptera: Noctuidae) Immatures in Maize

We characterized the dynamics of mortality factors affecting immature developmental stages of the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). Multiple decrement life tables for egg and early larval stages of S. frugiperda in maize (Zea mays L.) fields were developed with and without augmentative releases of Telenomus remus Nixon (Hymenoptera: Platygastridae) from 2009 to 2011. Total egg mortality ranged from 73 to 81% and the greatest egg mortality was due to inviability, dislodgement, and predation. Parasitoids did not cause significant mortality in egg or early larval stages and the releases of T. remus did not increase egg mortality. Greater than 95% of early larvae died from predation, drowning, and dislodgment by rainfall. Total mortality due to these factors was largely irreplaceable. Results indicate that a greater effect in reducing generational survival may be achieved by adding mortality to the early larval stage of S. frugiperda.     

The effect of temperature on the behaviour and development of Triatoma brasiliensis

Abstract. The effects of temperature on the development of early stages and the thermopreference of nymphs and adults were analysed in the haematophagous bug Triatoma brasiliensis Neiva, 1911 (Hemiptera, Reduviidae). Egg hatching, mortality of nymphs, feeding and moulting success of the early stages of T. brasiliensis were all affected by temperature. While high rates of egg hatching were observed between 25 and 27 °C, no hatching occurred at 12, 19 and 38 °C. The mortality of first‐instar nymphs was highest at 38 °C, at which no insects survived after 10 days of exposure. Feeding success was only affected at the lowest temperature (12 °C). No ecdysis was observed in the groups exposed to 12, 19 and 21 °C. Recently fed fourth‐instar nymphs preferred to stay at a temperature of approximately 30 °C. The preferred temperature began to decline gradually to approximately 27 °C during ecdysis, reaching 26 °C at 30 days after ecdysis. After a second blood meal, the insects' preferred temperature was again approximately 30 °C. The thermopreference pattern of females was similar to that of nymphs. Nymphs and females showed a daily fluctuation in their preferred temperature, moving towards higher values at the beginning of the dark phase, and choosing lower ones after this time interval, at which they remained until the end of the light phase. The females laid their eggs in all sectors of the arena, although the largest numbers of eggs were found between 28 and 32 °C.     

不同虫态叉角厉蝽对草地贪夜蛾幼虫的室内捕食作用

为了明确叉角厉蝽 Eocanthecona furcellate (Wolff)对草地贪夜蛾 Spodoptera frugiperda (J.E.Smith)幼虫的控制作用,在实验室条件下测定了叉角厉蝽不同虫态对草地贪夜蛾不同龄期幼虫的捕食能力,研究了该蝽捕食功能反应、搜寻效应以及种内干扰作用。结果表明,叉角厉蝽3龄若虫、5龄若虫、成虫均可捕食草地贪夜蛾幼虫,总体呈现叉角厉蝽低龄若虫捕食草地贪夜蛾低龄幼虫的数量较多,高龄若虫和成虫捕食中间龄期幼虫数量较多的规律;叉角厉蝽3个虫态对草地贪夜蛾2~3龄幼虫的捕食功能反应均符合Holling II方程和HollingⅢ型功能反应新模型;5龄若虫对草地贪夜蛾2~3龄幼虫的捕食效能(a/Th)最强（214.0）、日最大捕食量(1/Th)最大（256.4头）。不同虫态叉角厉蝽的搜寻效应与草地贪夜蛾密度均呈负相关。建立了叉角厉蝽成虫密度、草地贪夜蛾4龄幼虫密度对捕食作用的干扰反应方程,干扰作用发生后该蝽的平均捕食量和捕食作用率均逐渐下降。本研究结果可为田间释放叉角厉蝽防治草地贪夜蛾提供依据。     

小黑瓢虫对高氏瘤粉虱捕食作用的研究

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Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.