Food Plant Quality Research Articles

Genetics of fluctuating asymmetry in pupal traits of the speckled wood butterfly (Pararge aegeria).

Fluctuating asymmetry (FA), small random differences between left and right, has been extensively used as a measure of individual quality, though its usefulness in that respect is controversial. Whether FA is heritable has implications for sexual selection theory and for its usefulness as an indicator of stress. Heritability (h(2)) of FA is, however, difficult to estimate precisely and reliably. Here we report h(2)s of FA for two pupal traits in the speckled wood butterfly (Pararge aegeria). We used a restriction error maximum likelihood (REML) analysis in combination with a jackknife procedure to analyse a large mixed offspring-parent/half-sib/full sib data set. A five-generation selection experiment provided a second set of narrow sense h(2)s. Narrow sense h(2)s were not significant and on average -0.029 (REML-analysis) and 0.031 (selection experiment) for the pupal segment covering the fore leg (LEG) and 0.057 and 0.004 for a SPOT on that segment. Estimated percentage dominance variances were 0.057 (LEG) and 0.027 (SPOT) and not significantly different from 0. The h(2) estimates had been slightly increased by cage effects. Average FA for LEG after five generations of selection were higher in the high lines than in the low lines, and the control lines were in between. No difference in FA between lines was found for SPOT. Although differences between lines were not significant, a slight h(2) (<3%) for LEG could not be excluded. The genetic effect was, however, small compared with the effect of foodplant quality. Larvae grown on foodplants that were not watered enough for good growth showed significantly higher FA for LEG, but not for SPOT, compared with larvae grown on good foodplants.

Cascading effects of variation in plant vigour on the relative performance of insect herbivores and their parasitoids

Abstract1. Consequences of variation in food plant quality were estimated for a system consisting of two monophagous noctuid herbivores and three ichneumonid parasitoids.2. In a natural population, pupal weights of the herbivores in this system,Nonagria typhaeandArchanara sparganii, were found to be highly variable. Pupal weights increased strongly and consistently with the increase in the vigour of the host plant,Typha latifolia, providing support for the plant vigour hypothesis. Correspondingly, as the moths do not feed as adults, a strong, positive correlation between host vigour and fecundity of the herbivores would be expected.3. There were strong and positive relationships between adult body sizes of the parasitoids and the sizes of their lepidopteran hosts. Moreover, a direct, positive link between plant quality and parasitoid size was documented.4. For all three parasitoids, cascading effects of plant quality on body size were weaker than for the herbivores. Differences in the importance of adult feeding and oviposition behaviour suggest that dependence of fitness on body size is also weaker in the parasitoids than in the moths. It is therefore concluded that the numerical response of the herbivore population to a change in plant quality should exceed the corresponding response in the parasitoids.5. The results of this work imply that variation in plant variables may affect performance of different trophic levels to a different extent. It is suggested that the importance of adult feeding for the reproductive success (capital vs. income breeding strategies) in both herbivores and parasitoids is an essential aspect to consider when predicting responses of such a system to changes in plant quality.

Response of a herbivore community to increased food quality and quantity: an experiment with nitrogen fertilizer in a boreal forest

Summary 1. Herbivores make decisions at different spatial levels in response to food plant quality and quantity. Although experiments have examined the responses of herbivores at lower levels, few have examined how herbivores respond to such variation at the stand level. We assessed the response of a herbivore community in a boreal forest to manipulations of food resources at the stand level by performing a large replicated experiment where we fertilized young forest stands and then followed their use by herbivores during the subsequent year. 2. We used stands at 25 sites in an area 35 × 45 km. At each site we had one fertilized plot, a close control (100 m away) and a distant control (300 m away), all 50 × 50 m. 3. Before the growing season we fertilized treatment plots with calcium–ammonium–nitrate at 600 kg ha−1 (200 kg N ha−1). Fertilization significantly improved browse quality (nitrogen concentration) in both downy birch Betula pubescens and Scots pine Pinus sylvestris. Furthermore, the amount of browse significantly increased for birch, and Scots pine showed a similar trend. 4. Considering the animal community as a whole, we found that 10 of 13 animal species/groups made more tracks during winter in fertilized than in control plots. The total number of tracks was greater in fertilized plots, followed by close and then distant controls. 5. In the summer following fertilization, moose Alces alces strongly selected fertilized plots over controls. Furthermore, during the following winter moose again selected fertilized plots over controls. Hares Lepus timidus similarly left more pellets in the fertilized plots. Other mammals used the fertilized and the close controls similarly, and both were used more than distant controls. The number of grouse pellets did not differ among the treatments, although they followed a similar trend. 6. Several lines of evidence suggest that moose browsed fertilized plots more. Although not statistically significant, both heavy and light browsing were more common in fertilized than in control plots. Trees with the top shoot removed, or with bark stripped from the stem, did not differ significantly, but once again fertilized plots were browsed more than controls. 7. Our results are discussed in light of understanding both how herbivores in general respond to changes in food quality and quantity, and if fertilization may be a useful tool in modern forestry to manage herbivores. 8. Fertilization might be useful as a tool to alter the location of herbivore feeding, but buffer strips around any fertilized areas appear necessary, and other potential environmental effects should be evaluated.

Performance of moth larvae on birch in relation to altitude, climate, host quality and parasitoids.

We studied topographical and year-to-year variation in the performance (pupal weights, survival) and larval parasitism of Epirrita autumnata larvae feeding on mountain birch in northernmost Finland in 1993-1996. We found differences in both food plant quality and parasitism between sites ranging from 80 m to 320 m above sea level. Variation in food plant quality had particularly marked effects on larval survival. The advanced phenology of the birches in relation to the start of the larval period reduced pupal weights. Parasitism rates were different between years and between sites. The clearest site differences were in the proportions of different parasitoid species: Eulophus larvarum was most abundant at the lowest-altitude sites, and Cotesia jucunda at the highest. Differences in the performance of E. autumnata were related to temperature conditions: at higher temperatures, survival and the egg production index were lower, and larval parasitism was higher than at lower temperatures. The higher parasitism at higher temperatures was probably due to greater parasitoid activity during warmer days. In the comparison of different sources of spatial and annual variation in the performance of E. autumnata, the most important factor appeared to be egg mortality related to minimum winter temperature, followed by parasitism and, finally, the variation in food plant quality. If, as predicted, the climate gradually warms up, the effects of warmer summers on the outbreaks of E. autumnata suggest a decrease in outbreak intensity.

Foodplant effects on colour morphs of Eumorpha fasciata caterpillars (Lepidoptera: Sphingidae)

Abstract Caterpillars of the hawkmothEumorpha fasciataare highly polymorphic for colour, with green, pink, and pink-and-yellow forms in the second through fourth instars, and green and multicoloured forms in the fifth instar. Four years of field censuses on four foodplant species determined that all morphs were found on all plant species; morph frequencies were homogeneous on each plant species over time; and morph frequencies differed consistently among plant species. When larvae were reared from eggs on three of the hostplant species in the laboratory, differences in morph frequencies paralleled the census results. Thus foodplant quality is one factor affecting larval colour inE. fasciata. A literature survey reveals that foodplant effects on larval colouration may be widespread in the family Sphingidae, but most reports are anecdotal rather than experimental. The implications of this mechanism of colour determination are discussed.

Foodplant effects on colour morphs of Eumorpha fasciata caterpillars (Lepidoptera: Sphingidae)

Caterpillars of the hawkmoth Eumorpha fasciata are highly polymorphic for colour, with green, pink, and pink-and-yellow forms in the second through fourth instars, and green and multicoloured forms in the fifth instar. Four years of field censuses on four foodplant species determined that all morphs were found on all plant species; morph frequencies were homogeneous on each plant species over time; and morph frequencies differed consistently among plant species. When larvae were reared from eggs on three of the hostplant species in the laboratory, differences in morph frequencies paralleled the census results. Thus foodplant quality is one factor affecting larval colour in E. fasciata. A literature survey reveals that foodplant effects on larval colouration may be widespread in the family Sphingidae, but most reports are anecdotal rather than experimental. The implications of this mechanism of colour determination are discussed.

Effects of clear-cutting and selective felling in Swedish Boreal coniferous forest: response of invertebrate taxa eaten by birds

Our aim was to analyse the short-term effects (0-4 years) of selective felling and clear-cutting on the food resources of insectivorous birds. Literature data on bird diets showed that herbivorous larvae (Lepidoptera and Hymenoptera: Symphyta) and spiders (Araneae) were used by 81 and 50%, respectively, of 16 bird species breeding in the Swedish boreal coniferous forest. A field study comparing selective fellings, clear-cuttings and uncut controls showed considerable effects of clear-cutting on both terricolous and field layer invertebrates. Clear-cuttings had significantly lower abundance and biomass, and a different composition of herbivorous larvae and spiders, as well as a lower total biomass of invertebrates in the field layer than controls. Drastic changes of abiotic factors (like increased temperature range) following clear-cutting may directly affect the occurrence of invertebrates. However, indirect effects (like increased sun exposure, affecting food plant quality for herbivorous larvae) are probably also responsible. Selective fellings did not differ from controls in the occurrence of herbivorous larvae and spiders. Therefore, over the four-year term of our study, selective felling seems to provide birds with conditions similar to uncut forest for invertebrates used by birds.

The Ecology of the Chequered Skipper Butterfly Carterocephalus palaemon in Scotland. II. Foodplant Quality and Population Range

The Ecology of the Chequered Skipper Butterfly Carterocephalus palaemon in Scotland. II. Foodplant Quality and Population Range

Potential Benefits of Herbivore Behaviour Inducing Amelioration of Food-Plant Quality

Herbivore damage can elicit various kinds of responses in the host plant. The responses range from a deterioration (inducible resistance) to an improvement of foliage quality as a food resource of herbivores (inducible amelioration). Inducible resistance may well have an adaptive significance for the host plant, while the status of inducible amelioration is far less obvious. Inducible amelioration may, for instance, result from chemical changes associated with compensatory regrowth after physical damage. However, it may well be advantageous for a herbivore to ameliorate the host plant. This is especially so if amelioration does not imply a fitness cost for the herbivore, or if amelioration occurs rapidly after damage and the inducer itself gains the benefit (...)

Population Cycles of Forest Lepidoptera: A Maternal Effect Hypothesis

Many species of forest Lepidoptera have cyclic population dynamics. Although there are numerous potential causes, including interactions with predators, parasitoids, pathogens, and food-plant quality, strongly density-dependent interactions are often difficult to demonstrate. Both autocorrelation analysis and attractor-reconstruction methods have recently been applied to a number of species' time series. Results suggest that complex dynamics, i.e. cycles or deterministic chaos, may be more prevalent than once thought, and that higher-dimensioned models are necessary. We develop a two-dimensional difference equation model that relates the average quality of individuals to patterns of abundance

Food Plant Quality of Cynoglossum Officinale and Herbivory By Ethmia Bipunctella (Lepidoptera, Ethmiidae)

The oligophagous lepidoptcran Ethmia bipunctella F. (Lepidoptera: Ethmiidae) occurs in low numbers in Meijendel, the Netherlands, in spite of the great abundance of its host plant Cynoglossum officinale L. In this study, we examine the importance of food plant quality on individual performance of E. bipunctella, and discuss the impact on its population density. Grazing by E. bipunctella reduced the growth of plants in a growth room. In the field, flowering plants rather than rosettes were chosen for oviposition. In a choice experiment, larvae preferred undamaged rather than damaged leaves, suggesting that herbivory causes a rapid fall in plant acceptability. However, the larvae grew equally well on damaged and undamaged leaves. Our observations imply a role for alkaloids: flowering plants have a much lower alkaloid content than rosettes; and plants with eggs in the field had a lower alkaloid content than plants without eggs.

Synchronous short‐term population fluctuations of some birds and mammals in Fennoscandia ‐ occurrence and distribution

We examined population fluctuations of the voles Microtus agrestis L. and Clethrionomys glareolus Schreb. by biannual trapping; black grouse Tetrao tetrix L., mountain hare Lepus timidus L., and red fox Vulpes vulpes L. by using bag records from all over Sweden, questionnaires from south‐central Sweden, and population indices from Grimsö Wildlife Research Area in south‐central Sweden. Synchronous population fluctuations between voles as a group and the other species conformed to a 3–4 year periodic pattern in both autumn and spring populations only in northern and central Sweden (the boreal forest region). Spring populations of boreal forest grouse, hare, and probably also fox, lagged one year behind the voles. The northerly areas also formed geographical units of co‐fluctuation within each game species. Using our own data as well as reviewing previous studies in Fennoscandia, we conclude that synchronized 3–4 year population fluctuations of voles and medium‐sized herbivores are confined to the central and northern part of Fennoscandia, although voles may exhibit short‐term population fluctuations further south. The synchronizing link between the herbivores could be (1) food plant quality and/or quantity and/or (2) predation. We could not reject either of these two plausible mechanisms as a cause of interspecifically synchronous fluctuations.

Interactions Between Western Tent Caterpillars and Wild Rose: A Test of Some General Plant Herbivore Hypotheses

SUMMARY (1) Tent caterpillars which hatch from eggs early in April are less successful than those which hatch late in April; those fed on developing leaves grew more slowly than those fed on mature leaves. Therefore, early emergence of caterpillars does not seem to be associated with better food quality early in the season. Parasitization of late developing larvae seems to exert a stronger selection pressure for early emergence from eggs. (2) To determine if tent caterpillars induce deterioration of food plant quality by defoliation in the previous year, the survival of caterpillars feeding on previously defoliated vegetation was compared with that on protected plants. Caterpillars on rose bushes which had been protected from caterpillar feeding 1-3 yr before, survived no better than those on plants which had been defoliated the previous spring or subjected to control feeding levels.

Photoperiodism in the cabbage whitefly, Aleyrodes brassicae

ABSTRACT. Reproductive diapause was induced in A. brassicae by short photo‐period at 15 and 20°C but was almost prevented at 25°C. The critical photoperiod was LD 153/4: 81/4 at 15°C, giving 60% diapause. Photoperiodic sensitivity was confined to the early immature stages. Food plant quality appeared not to influence the induction or prevention of diapause. Chilling facilitated diapause termination. Overwintering females brought into the laboratory as adults or pupae from the field from September to December took longer before laying their first eggs than females collected in January and February.