Simulated climate change: a field manipulation study of polar microarthropod community response to global warming

Passive cloches were deployed at three altitudinally distinct sites on Signy Island, maritime Antarctica, to investigate the effect of ameliorated thermal environment upon fellfield microarthropod communities Temperature was monitored at 1 5 m height, at ground surface level, and at 5 cm depth in cloche and control plots During summer (December - March), cloches elevated monthly mean temperatures by up to 2 46°C at the soil surface and 2 20°C at 5 cm depth Integrated air temperatures over consecutive 10 d periods were up to 4 65°C wanner in cloches than controls During winter (April - November), snow cover of the fellfield sites buffered temperature variation and reduced the treatment effect After eight years of these manipulations, sampling of the upper 50 mm of soil revealed consistently greater microarthropod populations within cloches than in controls (treatment effect p<0.05) Maximum difference occurred at high altitude where thermal amelioration was greatest (site effect p<0.05) Cloche populations of the numerically dominant collembolan Cryptopygus antarcticus Willem contained an increased proportion of small (length < 750 μm) individuals No species new to Signy Island were recorded Relating these microarthropod populations to the ameliorated thermal environment suggests that Antarctic invertebrate communities may respond to global warming, as predicted by global circulation models, with an increase in abundance with little increase in diversity However, this response could be indirect, the intermediate controlling factor being the percentage cover of the soil surface by vegetation, itself a function of climate change     

The utilization of heather moorland by territorial Red Grouse Lagopus lagopus scoticus

Although the breeding density of Red Grouse Lagopus lagopus scoticus is related to the density of burned patches of heather Calluna vulgaris , territories appear to offer surplus food, and other factors, especially the risk of predation, may be important. In order to determine how Red Grouse make use of heather moorland, an individually marked population was studied on a moor in northeast Scotland from 1992 to 1994. Territorial birds preferred stands of tall heather during the daytime in autumn and winter, but in spring they increased their use of heterogeneous heather/grass mixtures. Furthermore, in spring, females showed a very strong affinity for edges between heather stands of different ages, where they had easy access to nutritious young heather and good cover. When near the vegetation edge, territorial birds spent most time on the side of the edge providing greater cover. Broods occupied ranges in areas with rather more old heather and with more edge than was available over the entire study site. Within their ranges though, broods clearly preferred heterogeneous areas during the first month after hatching, and showed a further preference for vegetation edge. Their behaviour changed during the second month after hatching, when they utilized tall heather to a greater extent, but edge remained important.     

Influence of larvae of Gastrophysa viridula on the distribution of conspecific adults in the field

1. Previous laboratory bioassays indicate that exocrine glandular secretions of larvae of Gastrophysa viridula repel conspecific adults and deter them from feeding and oviposition. The present study was conducted to investigate the influence of larvae of G. viridula on conspecific adults in the field.
2. Within the G. viridula population studied, two generations were observed in a year. Occurrence of the different developmental stages overlapped temporally.
3. Some individual plants of Rumex obtusifolius , the host of the G. viridula population studied, grew so close to each other that they were considered as a plant group. When investigating the spatial distribution of larvae and adults within such plant groups, larvae were rarely found on plant groups on which adults were feeding.
4. A field experiment revealed that adults avoided plants of R. obtusifolius infested by conspecific larvae of the second and third instar. Adults still avoided these damaged plants when larvae had left them for pupation.
5. Gastrophysa viridula avoided oviposition on leaves and plants infested by conspecific larvae. Larvae of the second instar significantly deterred oviposition when present at a high density (33.3 larvae/dm²), whereas larvae of the first instar did not deter oviposition of conspecifics at either density tested. The oviposition deterring effect was also observed when just exocrine glandular secretion of larvae of the second instar was applied to the leaves in amounts equivalent to a density of 33.3 larvae/dm².
6. Availability of food ( R. obtusifolius ) largely exceeded its exploitation in each group of plants examined. This may be due to either the spatial separation of adults and larvae or the low population density observed on these plant groups.     

Pollen-feeding and the host specificity and fecundity of flower thrips (Thysanoptera)

Abstract. 1. Flower thrips could feed on pollen of a wide range of sizes and were unaffected by exine spines. One species of thrips was unable to feed on very adhesive grains.
2. The proportion of time spent feeding on each species of pollen (in seconds per minute of exposure) reflected the known host specificities. Host-specific thrips could distinguish their host pollen, apparently without probing.
3. Kakothrips pisivorus (Westwood) appeared to have a higher rate of ingestion of a host pollen than of four non-host pollens.
4. In cages in the laboratory, Thrips fuscipennis Haliday laid significantly more eggs over 48h when given pollen than when given other floral tissues or no food. K. pisivonis and Ceratothrips ericae (Haliday) also laid significantly more eggs over 48h in the presence of pollen than in its absence.
5. In comparisons between pollen diets, T. fuscipennis, a generalist, laid similar numbers of eggs with each species of pollen, but K. pisivorus and C. ericae laid significantly more eggs with their respective host pollens. The differences in oviposition rate between pollen diets reflected the differences in the proportion of time spent feeding.     

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。     

Effects of environmental change, including drought, on water use by competing Calluna vulgaris (heather) and Pteridium aquilinum (bracken)

1. Competition for water between Calluna vulgaris (heather) and Pteridium aquilinum (bracken) was studied in conditions of increased temperature, drought and increased nitrogen supply. All these factors increased the intensity of competition for water, with the combination of drought and increased nitrogen having the greatest effect on water use.
2. Both species increased water-use efficiency in response to increased nitrogen and drought. The effects of temperature were however, equivocal. Calluna had a greater water demand than Pteridium but acclimated to water stress more readily.
3. Calluna was the superior competitor for water; its water-use efficiency was reduced as a consequence of its roots depleting water from the Pteridium rooting zone. Pteridium , the poorer competitor, increased water-use efficiency to cope with reduced water availability owing to competition.
4. There was a strong relationship between carbon isotope discrimination (Δ) and instantaneous water-use efficiency for both species, but discrimination provided a more sensitive measure of seasonal water-use efficiency. Reconstruction of the plant's history of water-use efficiency by retrospective measurement of Δ proved a useful technique for Calluna leaves but was inappropriate for Pteridium rhizome.     

The Lepidoptera fauna associated with Calluna vulgaris: effects of plant architecture on abundance and diversity

Abstract .1. The effects of plant architecture on the Lepidoptera assemblage associated with heather Calluna vulgaris were studied at four locations in northern England and southern Scotland in 1992 and 1993. The study areas were Calluna vulgaris – Vaccinium myrtillus heaths, where management by rotational burning had created a mosaic of stands of different-aged Calluna . Lepidoptera were sampled in the larval stage.
2. Larval abundance was considered in relation to Calluna age, height, cover, green shoot density, and flower density. For most study areas and species, multiple regression selected Calluna height as the variable that explained most variation in larval density, although the explanatory variables were intercorrelated.
3. After compensating for the effects of different study locations, the slope of the regression between the logarithm of larval density and the logarithm of Calluna height was common to the macrolepidoptera, microlepidoptera, geometrid, and noctuid larval groups.
4. There was a significant progressive increase in larval diversity with increase in Calluna height, due to the presence of uncommon moth species in the samples from taller Calluna, and a change in the contribution of common species to the community in different height zones.
5. The significance of these results is discussed in relation to other heathland invertebrate studies and management practices.     

Experimental demography of rhizome populations of establishing clones of Solidago altissima

1 Solidago altissima forms large compact below-ground rhizome systems. The rhizome systems of 30 genets in a population that had colonized an old-field in 1984 were mapped yearly in situ from 1988 to 1992. Branching angles, lengths and survival of rhizomes, and production of daughter rhizomes, were calculated from digitized maps.
2 We hypothesized that genets of S. altissima would prevent intraclonal crowding by producing longer but fewer rhizomes as they increased in size. In addition, we tested the effects of environmental factors on rhizome dynamics by (i) mowing in late summer, (ii) cutting of rhizome connections, and (iii) removal of close neighbour plants.
3 Most rhizomes were initiated at an angle of 60°−65° relative to the parent rhizome. Subsequent growth tended towards the parent axis and towards more centrifugal growth. Rhizome angles were not influenced by any treatment.
4 In control genets, rhizome density increased 1.3-fold from March 1988 to March 1992. The number of newly produced rhizomes per genet decreased and their length increased from 1988 to 1992. Longer rhizomes had a higher survival probability than shorter rhizomes did. The number of newly produced rhizomes per parent rhizome was positively correlated with mean rhizome length per genet.
5 Mowing strongly decreased rhizome density from 1988 to 1992, mainly due to reduced production of new rhizomes.
6 Rhizome cutting led to a slight decline in the rhizome population and to shorter lengths of rhizomes in their second year compared with controls.
7 The removal of close neighbour plants led to increased rhizome densities. These rhizomes grew longer than controls in unmown plots and shorter in mown plots and had higher probabilities of surviving into their second year.
8 Yearly mowing could successfully prevent the further spread of S. altissima because it acts on rhizome and shoot dynamics as well as on seed output.     

Change in the distribution of a member of the strand line community: the seaweed fly (Diptera: Coelopidae)

Abstract.  1. Coastal organisms are predicted to be particularly susceptible to the impact of global warming. In this study the distribution and relative abundance of two coastal invertebrates, Coelopa frigida (Fabricius) and C. pilipes are investigated.
2.  Coelopa pilipes has a more southerly distribution than C. frigida , and prefers a warmer climate. Coelopa pilipes is less resistant to sub-zero temperatures than C. frigida and its northerly distribution is probably limited by cold winter days.
3. The most recent distribution map of C. frigida and C. pilipes in northern Europe was published a decade ago and showed the northerly extent of the distribution of C. pilipes reaching the north coast of mainland Scotland but its complete absence from the Western and Northern Isles.
4.  C. pilipes has now spread throughout the Western Isles and the Orkney Islands but is still absent from Shetland. There has also been an increase in the relative frequency of C. pilipes at sites harbouring coelopids on the British mainland. A similar pattern of distribution change along the west coast of Sweden is reported.
5. It is proposed that these changes have occurred primarily as a result of global warming and in particular due to the recent increase in winter temperatures. A number of other indirect effects may have also contributed to these changes, including a probable change in macroalgae distribution. The implications of these changes for the wrack bed ecosystem and at higher trophic levels are considered.     

Density-dependent melanism in sub-arctic populations of winter moth larvae (Operophtera brumata)

Abstract.  1. The aim of this 4-year observational study was to test for the presence of direct and delayed density-dependent larval melanism in the geometrid moth species Operophtera brumata (winter moth) in northern Norway.
2. Data from many populations with a wide range of population densities in time and space facilitated statistical analyses that could separate the effects of current and past density. The data also included different phases of the 10-year population cycle of this species so that eventual non-linear density effects due to population phase could be detected.
3. The results showed that the prevalence of melanism had a strong positive, linear relation to population density within years, whereas there was no evidence for a delayed effect from the year before or dependency on the phase of the population cycle.
4. In combination, these results limit the range of possible explanations of larval melanism in this outbreaking species. The possible reasons why winter moth larvae might benefit from crowding-induced melanism are discussed.     

Factors affecting the abundance of introduced hedgehogs (Erinaceus europaeus) to the Hebridean island of South Uist in the absence of natural predators and implications for nesting birds

Introduced hedgehogs Erinaceus europaeus are a known threat to ground-nesting birds on many islands. Spring hedgehog density and sex ratio were measured over a 5-year period at four plots on the 315 km² Hebridean island of South Uist. The mean instantaneous density on the sandy-soiled machair plots (31.8 hedgehogs km⁻², se 2.95) was over twice that on the peaty-soiled blackland plots (15.4 hedgehogs km⁻², se 3.46), a difference reflecting the amount of preferred foraging habitat (mainly pasture). Plot population densities fluctuated approximately in unison. Year-to-year density changes were strongly correlated with temperature in the preceding winter and previous year's spring/summer, indicating that warmer conditions promote both survival and breeding success. The mean spring sex ratio of sub-adults (animals born in the previous calendar year) was not significantly different from 1M:1F. However, the 1.8M:1F ratio observed for adults was significantly male biased, probably a result of female mortality associated with rearing young. The study estimates that in an average year the South Uist hedgehog population numbers c . 2750 (95% confidence limit±800) adults and sub-adults and these produce around 3000 young. Compared with the native range, hedgehog densities on South Uist are shown to be unusually high, probably because their natural predators are absent. High hedgehog densities have led directly to high rates of egg predation of ground-nesting shorebirds and subsequent declines in bird populations. The results suggest that over the past 20 years egg losses have become more severe and control of hedgehogs more difficult because climate warming has resulted in generally more favourable conditions for hedgehogs on the islands.     

Steinernema carpocapsae (Rhabditida: Steinernematidae) as a biological control agent against the fungus Gnat Bradysia agrestis (Diptera: Sciaridae) in propagation houses

A recently introduced fungus gnat, Bradysia agrestis, has caused serious problems in Korean propagation houses where vegetable seedlings are produced for transplant into the fields. Although chemical insecticides are available against this pest, alternate control measures are needed. A Korean isolate of the entomopathogenic nematode, Steinernema carpocapsae Pocheon strain, was tested against this insect in the laboratory and propagation house. In the laboratory, S. carpocapsae affected oviposition, with the untreated females laying an average of 121±25 eggs, whereas the treated females averaged 7±2 eggs. The infectivity of S. carpocapsae to the fungus gnat was affected by the developmental stage and temperature, with highest mortality observed with the third and fourth instars and pupal stage. Nematode mortality in the second instar fungus gnat ranged between 23 and 35%, but showed no significant differences among the temperatures tested. The egg and first instar were not infected by the nematode. In nematode dispersal studies, adult female fungus gnats alone dispersed S. carpocapsae from the nematode-treated area to the control area at a higher rate than male and female gnats or male gnats alone. In the propagation house experiments with watermelon seedlings, no significant difference was observed in fungus gnat larval reduction at S. carpocapsae concentrations of 5, 10, or 20 infective juveniles (IJs)/g of soil at 7, 14, and 21 days after treatment. In comparison with the control, the S. carpocapsae treatments significantly reduced B. agrestis larval numbers. When the watermelon seed was treated with S. carpocapsae at sowing, the larval density of B. agrestis was significantly reduced, that is, the number of B. agrestis larvae ranged from four to eight and from five to eight in the nematode-treated plots compared with 26 and 30 in the control plots on the 17th and 34th day post-treatment, respectively. In the chemical insecticide treatments, diflubenzuron and chlorpyrifos were significantly more effective than S. carpocapsae and diazinon in reducing larval populations of the fungus gnat. Our data show that, although some of the chemical insecticides were more effective than S. carpocapsae Pocheon strain, the nematode was still an effective tool for management of the fungus gnat larvae and in protecting seedlings from damage in propagation houses.     

Natural enemy ravine revisited: the importance of sample size for determining population growth

Abstract. 1. The population growth of three aphid species, Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.), and Sitobion avenae (F.), on winter wheat, was analysed by regression. The calculations were based on censuses of aphids made in 268 plots at 3- or 7-day intervals for 10 years on leaves and 6 years on ears. The calculations were made separately for each plot each year, then repeated on the pooled data from all plots monitored in a year.
2. At the level of individual plots, no population growth was detected at very low densities. At high densities, the populations grew exponentially and the growth rates did not decrease with increasing aphid density.
3. Significant growth was always detected in the pooled data. These growth rates decreased significantly at the highest densities. Field estimates of the intrinsic rate of increase derived from these data ranged from 0.010 to 0.026 for M. dirhodum , 0.0071–0.011 for R. padi , and 0.00078–0.0061 and 0.0015–0.13 for S. avenae , on leaves and ears respectively .
4. The apparent lack of growth in the individual plots at low densities is attributable to small sample size. It is concluded that the natural enemy ravine in the population dynamics of cereal aphids, identified by Southwood and Comins (1976), is a consequence of low population densities at which population increase is undetectable unless very large samples are taken.     

The life cycle and growth of Sialis lutaria L. (Megaloptera) in a drainage channel under different methods of plant management

Abstract. 1. The life cycle of Sialis lutaria in two experimental reaches, one treated with the herbicides dalapon and 2,4-D (Chemical) and the other subjected to a conventional method of plant control (Hand), of a drainage channel in Essex took about 2 years.
2. A maximum density of 815 m^-2 was recorded and the density of each year class in both reaches generally decreased exponentially with age.
3. At certain times of the year the mean individual weight of each year class increased exponentially with age. Annual production was estimated to be 985 (Hand) and 1171 (Chemical) mg dry weight m^-2, with ratios of annual production to mean standing crop (P: ) of 1.6 and 1.8 respectively.
4. There was no evidence that the use of herbicides had any discernible effect on the mortality, growth or production of S.lutaria.     

Responses of bracken to increased temperature and nitrogen availability

In 1993 a project was set up at Upper Teesdale to investigate some of the effects of predicted increased temperatures and increased nutrient availability resulting from increased litter decomposition rates, and atmospheric deposition of nitrogen, on the interaction between bracken and heather, two species which cover large areas globally. 32 2 × 2 m plots were laid out on a hillside on, and just below, the interface between the two species. Half of the plots were placed on pure bracken, and the other half on the boundary. Within each vegetation type half of the plots were covered with open-topped polythene tents to simulate climate warming, while the other plots remained open. The second treatment consisted of additional fertilizer at 50 kg N ha⁻¹ y⁻¹ simulating increased decomposition rates at higher temperatures and increased atmospheric nitrogen deposition. The two treatments and their controls were combined in a 2 × 2 factorial design, with two replicates in each of two blocks. Results obtained in the first two summers indicated that fronds emerged earlier in spring and senesced later in autumn inside the tents, effectively lengthening the growing season. Fronds were taller when growing in warmer conditions, and carried more pinnae. In addition, the frond density was higher inside the tents, and together these effects contributed to greatly enhanced vigour of bracken in some of the conditions predicted by General Circulation Models. It seems likely that bracken will be more competitive, and have the potential to further encroach into heather dominated areas under these conditions.     

Control of the flexible annual/biennial life cycle of the heather psyllid Strophingia ericae

Abstract. Strophingia ericae (Curtis) (Homoptera: Psylloidea) takes one or two years to complete its life cycle. In both cases eggs hatch over a prolonged period from midsummer, possibly extending into the following spring at high altitude, and instars overlap in time. Instar III is the predominant overwintering stage in the lowland, annual cycle, whereas in the upland, biennial cycle most first-year nymphs overwinter in instars I and II and most second-year nymphs in instar V. When moved to the laboratory, instars IV and V from a predominantly annual population showed accelerated development in response to elevated temperatures and to long days in both mid-winter and early spring. In the biennial life cycle, short autumn days retard instar V development but the response to photoperiod disappears by the end of winter. Exposure to LD 18 : 6 h retarded development of early instars in the annual population, resulting in an accumulation in instar III. The proportion of overwintering instars I and II rises with increase in altitude and moult to instar III becomes progressively delayed. Nymphs that reach instar III under long daylengths in the year following hatching are channelled towards the biennial cycle. Exposure of a predominantly biennial population to 15 °C and LD 18 : 6 h after midsummer, thus avoiding autumn conditions, promoted the rapid development of overwintered nymphs, switching the cycle from biennial to annual.     

Winter warming effects on overwinter survival,energy use,and spring emergence of Cerotoma trifurcata (Coleoptera: Chrysomelidae)

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Studies on the biology of Chaoborus flavicans (Meigen) (Diptera: Chaoboridae) in a fish-free eutrophic pond,Japan

Population dynamics of Chaoborus flavicans larvae of various instars was studied from November 1986 to December 1987 in a eutrophic, fish-free pond, Japan. First and 2nd instar larvae were observed from late April to late October, indicating a reproductive period of about half a year. C. flavicans overwintered in the 4th instar larvae. In water column samples, total density of all instars was 680–23680 m^-2, and pupal density 0–2600 m^-2; larvae of the 1st, 2nd, and 3rd instars showed 5–6 density peaks in 1987, suggesting that 5–6 generations occur during a year (peaks of the 4th instar larvae were not clear, probably due to their longer development than those of younger instars). In sediment samples, no 1st and 2nd instar larvae were found, 3rd instar larvae were found occasionally but density of the 4th instar larvae was 280–18600 m^-2, and pupal density varied between 0–502 m^-2. Fouth instar larvae accumulated in sediment in the cold season and in the water column in the warm season; high temperature and low oxygen concentration were the most important factors limiting the distribution of larvae in the sediment in summer in the NIES pond. The dry weight of total C. flavicans larvae was 0.08–4.2 g m^-2 in sediment samples and 24–599 μg l^-1 (0.10–2.40 g m^-2) in water column samples. Comparisons of maximum densities in the NIES pond in different years and in waters of different trophic status show that density is generally higher in eutrophic than in oligotrophic habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Demographic responses of adult Mesocyclops thermocyclopoides (Copepoda, Cyclopoida) to different plant and animal diets

1. We studied the effects of food type on adult females of the cyclopoid copepod Mesocyclops thermocyclopoides.
2. The test diets, covering a size range of 5–1250 μm, included a toxic strain of Microcystis aeruginosa , three algae (i.e. Chlorella vulgaris, Scenedesmus acutus and Chlorogonium elongatum ), three ciliates (i.e. Tetrahymena pyriformis, Stylonychia notophora and S. mytilus ), two rotifers (i.e. Brachionus angularis and B. calyciflorus ) and two cladocerans (i.e. Ceriodaphnia cornuta and Moina macrocopa ), and a selected subset of them in a second experiment.
3. Experimental diets were started with the last juvenile instar (C5) and data were collected on the newly moulted adult females. The survival of the copepod was less affected by food type than its reproductive output. Net reproductive rate was significantly higher with animal than with plant food. Algal diets enriched with organic extracts supported higher reproductive rates than unenriched diets of the same algal species. The large and motile alga Chlorogonium gave performances which approached those of ciliate diets.
4. The pre-reproductive period of M. thermocyclopoides was shorter and its post-reproductive period longer with animal than with plant diets, the latter being chiefly caused by a briefer period between clutches.
5. The frequency of infertile clutches increased in later clutches, indicating possible sperm limitation in females which have mated only once.
6. There was a significant, positive correlation between the size of food particles and the lifetime reproductive output of M. thermocyclopoides , with more than an order of magnitude difference in the total fecundity between the largest and the smallest food items.
7. Mesocyclops thermocyclopoides achieved the highest total fecundity with 'mixed' food, and thus, reflected the adaptive value of omnivory for this species.     

Factors affecting the rate of attack by Cotesia rubecula (Hymenoptera: Braconidae)

Abstract. 1. The relationship between responses of the insect parasitoid Cotesia rubecula (Marshall) to kairomones produced by the feeding activities of its host, Pieris rapae (L.), and patterns of parasitism were investigated under field conditions.
2. Parasitoid adults aggregated in patches with the highest densities of host larvae but there was no commensurate increase in the rate of attack in these patches.
3. The rate of attack was not limited by the availability of eggs.
4. The rate of parasitoid attack was highest where feeding damage by the host was highest, irrespective of current host density.
5. The rate of parasitoid attack was further influenced by host age distribution. Late instar larvae were less susceptible to parasitism than were early instar larvae. The rate of attack on early instar larvae occupying the same plants as late instar larvae was reduced. This reduction in rate of attack was due to limitations on parasitoid search time imposed by the increased feeding damage associated with large host larvae and by the increased time the parasitoid required to recover from an attack on these large host larvae.