Effects Of Host Plant Quality Research Articles

Sub-optimal host plants have developmental and thermal fitness costs to the invasive fall armyworm.

The fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) is a global invasive pest of cereals. Although this pest uses maize and sorghum as its main hosts, it is associated with a wide range of host plants due to its polyphagous nature. Despite the FAW's polyphagy being widely reported in literature, few studies have investigated the effects of the non-preferred conditions or forms (e.g., drought-stressed forms) of this pest's hosts on its physiological and ecological fitness. Thus, the interactive effects of biotic and abiotic stresses on FAW fitness costs or benefits have not been specifically investigated. We therefore assessed the effects of host plant quality on the developmental rates and thermal tolerance of the FAW. Specifically, we reared FAW neonates on three hosts (maize, cowpeas, and pearl millet) under two treatments per host plant [unstressed (well watered) and stressed (water deprived)] until the adult stage. Larval growth rates and pupal weights were determined. Thermal tolerance traits viz critical thermal maxima (CTmax), critical thermal minima (CTmin), heat knockdown time (HKDT), chill-coma recovery time (CCRT), and supercooling points (SCPs) were measured for the emerging adults from each treatment. The results showed that suboptimal diets significantly prolonged the developmental time of FAW larvae and reduced their growth rates and ultimate body weights, but did not impair their full development. Suboptimal diets (comprising non-cereal plants and drought-stressed cereal plants) increased the number of larval instars to eight compared to six for optimal natural diets (unstressed maize and pearl millet). Apart from direct effects, in all cases, suboptimal diets significantly reduced the heat tolerance of FAWs, but their effect on cold tolerance was recorded only in select cases (e.g., SCP). These results suggest host plant effects on the physical and thermal fitness of FAW, indicating a considerable degree of resilience against multiple stressors. This pest's resilience can present major drawbacks to its cultural management using suboptimal hosts (in crop rotations or intercrops) through its ability to survive on most host plants despite their water stress condition and gains in thermal fitness. The fate of FAW population persistence under multivariate environmental stresses is therefore not entirely subject to prior environmental host plant history or quality.

Enemy-free space is important in driving the host expansion of a generalist herbivore to an inferior exotic plant in a wetland of Yangtze Estuary

Novel interactions between exotic plants and native herbivores can be driven by multiple ecological and evolutionary processes, but the underlying mechanisms have rarely been explored from a multitrophic perspective. In this study, we examined the effects of host plant quality and natural enemies on the host plant use of a native generalist Laelia coenosa, which was recently known to expand its host range from indigenous Phragmites australis to invasive exotic Spartina alterniflora in the wetlands of Yangtze Estuary, China. A field population survey showed that larval density of L. coenosa was significantly higher in S. alterniflora monocultures (SM) than in P. australis monocultures (PM) and patches in S. alterniflora-dominated communities (PIS). Nonetheless, an indoor rearing experiment suggested feeding on S. alterniflora significantly reduced larval growth rate, cocoon weight, adult lifespan and female lifetime fecundity of L. coenosa in comparison with P. australis. Despite an induced feeding preference in 5th instar larvae, both 1st and 3rd instar larvae of L. coenosa significantly preferred leaves of P. australis over S. alterniflora. These results contradicted the field population survey. Subsequent field experiments showed larval mortality of L. coenosa significantly increased in habitats with SM < PIS < PM. The same trend was observed in the egg parasitism rate of L. coenosa by a specialized parasitoid Telenomus laelia. Generally, our study suggests that the enemy-free space provided by the invasive S. alterniflora is important in driving the host expansion of L. coenosa to this inferior exotic plant.

Plant-mediated vulnerability of an insect herbivore to Bacillus thuringiensis in a plant-herbivore-pathogen system

ABSTRACTLaboratory studies were performed to explore the effects of host-plant quality on the vulnerability of Plutella xylostella to Bacillus thuringiensis. P. xylostella were kept on different host plants, including Brassica pekinensis (Chinese cabbage) cv. Hero, Brassica oleracea var. botrytis (cauliflower) cv. Royal, and B. oleracea var. capitata (common cabbage) cv. Globe Master (white cabbage) and cv. Red Dynasty (red cabbage) for at least two generations. These host plants are considered as the high (Chinese cabbage), intermediate (cauliflower and white cabbage) and low-quality (red cabbage) hosts for P. xylostella. The vulnerability of the pest larvae was then tested using two formulation of B. thuringiensis var. kurstaki, including Biolarv® and Biolep®. The results demonstrated that the susceptibility of P. xylostella to B. thuringiensis was influenced by host-plant quality. Indeed, B. thuringiensis acted better on the pest fed on the low-quality host plant compared with that on the high-quality host plant. The interaction between the pathogen and plant quality/resistance resulted in more mortality of the pest larvae, implying a synergistic effect. From a pest management viewpoint, these findings may be promising for the integration of the pathogen and the low-quality/partially resistant host plants against P. xylostella in field studies.

Effect of host species on larval growth differs between instars: The case of a geometrid moth (Lepidoptera: Geometridae)

Although the effects of host plant quality on the performance of polyphagous herbivores are largely uniform across insect taxa, there are various exceptions to this rule. In particular, there are scattered reports of cases in which the relative quality of dif- ferent hosts differs among larval instars of a single insect species. Such cases are explained either in terms of differences in the sus- ceptibility of different aged larvae to plant defences or, alternatively, age-specific nutritional demands. Here we report the results of experiments that show that young larvae of the polyphagous common heath moth Ematurga atomaria (Lepidoptera: Geometridae) consistently attain higher weights on common heather Calluna vulgaris than bilberry Vaccinium myrtillus, whereas the rank order of these host plants is reversed in the final larval instar. Phytochemical analyses showed that differences in nutrient content of these plants are not likely to explain the observed pattern. Instead, the results are more consistent with the idea that the greater chemical defence of bilberry has a relatively stronger influence on young than old larvae.

Increased temperature reduces herbivore host‐plant quality

Globally increasing temperatures may strongly affect insect herbivore performance, as their growth and development is directly linked to ambient temperature as well as host-plant quality. In contrast to direct effects of temperature on herbivores, indirect effects mediated via thermal effects on host-plant quality are only poorly understood, despite having the potential to substantially impact performance and thereby to alter responses to the changing climatic conditions. We here use a full-factorial design to explore the direct (larvae were reared at 17°C or 25°C) and indirect effects (host plants were reared at 17°C or 25°C) of temperature on larval growth and life-history traits in the temperate-zone butterfly Pieris napi. Direct temperature effects reflected the common pattern of prolonged development and increased body mass at lower temperatures. At the higher temperature, efficiency of converting food into body matter was much reduced being accompanied by an increased food intake, suggesting compensatory feeding. Indirect temperature effects were apparent as reduced body mass, longer development time, an increased food intake, and a reduced efficiency of converting food into body matter in larvae feeding on plants grown at the higher temperature, thus indicating poor host-plant quality. The effects of host-plant quality were more pronounced at the higher temperature, at which compensatory feeding was much less efficient. Our results highlight that temperature-mediated changes in host-plant quality are a significant, but largely overlooked source of variation in herbivore performance. Such effects may exaggerate negative effects of global warming, which should be considered when trying to forecast species' responses to climate change.

The tri-trophic interactions hypothesis: interactive effects of host plant quality, diet breadth and natural enemies on herbivores.

Several influential hypotheses in plant-herbivore and herbivore-predator interactions consider the interactive effects of plant quality, herbivore diet breadth, and predation on herbivore performance. Yet individually and collectively, these hypotheses fail to address the simultaneous influence of all three factors. Here we review existing hypotheses, and propose the tri-trophic interactions (TTI) hypothesis to consolidate and integrate their predictions. The TTI hypothesis predicts that dietary specialist herbivores (as compared to generalists) should escape predators and be competitively dominant due to faster growth rates, and that such differences should be greater on low quality (as compared to high quality) host plants. To provide a preliminary test of these predictions, we conducted an empirical study comparing the effects of plant (Baccharis salicifolia) quality and predators between a specialist (Uroleucon macolai) and a generalist (Aphis gossypii) aphid herbivore. Consistent with predictions, these three factors interactively determine herbivore performance in ways not addressed by existing hypotheses. Compared to the specialist, the generalist was less fecund, competitively inferior, and more sensitive to low plant quality. Correspondingly, predator effects were contingent upon plant quality only for the generalist. Contrary to predictions, predator effects were weaker for the generalist and on low-quality plants, likely due to density-dependent benefits provided to the generalist by mutualist ants. Because the TTI hypothesis predicts the superior performance of specialists, mutualist ants may be critical to A. gossypii persistence under competition from U. macolai. In summary, the integrative nature of the TTI hypothesis offers novel insight into the determinants of plant-herbivore and herbivore-predator interactions and the coexistence of specialist and generalist herbivores.

Light environment and the impacts of foliage quality on herbivorous insect attack and bird predation

Theory predicts that variation in plant traits will modify both the direct interactions between plants and herbivores and the indirect impacts of predators of those herbivores. Light has strong effects on leaf quality, so the impacts of herbivores and predators may differ between plants grown in sun and shade. However, past experiments have often been unable to separate the effects of light environment on plant traits and herbivory from direct effects on herbivores and predators. We first manipulated light availability in an open habitat using a shade cloth pre-treatment to produce oak saplings with different leaf qualities. Leaves on plants exposed to high light were thicker and tougher and had lower nitrogen and water contents, and higher carbon and phenolic contents than leaves on plants under a shade cloth. Then, in the main experiment, we moved all plants to a common shade environment where bird predators were excluded in a factorial design. We measured insect herbivore abundance and leaf damage. Herbivores were significantly more abundant and caused greater leaf damage on sun trees, although these leaf characteristics are usually associated with low-quality food. Bird exclusion did not change herbivore abundance but did increase leaf damage. Contrary to our predictions, the effects of birds did not differ between trees grown in sun and shade conditions. Thus, differences in effects of predators on herbivores and plants between light habitats, when observed, might be due to variation in predator abundance and not bottom-up effects of host plant quality.

Influence of host-plant quality on the performance of Episimus unguiculus, a candidate biological control agent of Brazilian peppertree in Florida

Brazilian peppertree, Schinus terebinthifolius Raddi (Sapindales: Anacardiaceae), introduced from South America, invades a variety of habitats in Florida (e.g. disturbed sites, coastal mangrove forests). The objective of this study was to evaluate the effect of host-plant quality on the performance of Episimus unguiculus Clarke (=E. utilis Zimmerman) (Lepidoptera: Tortricidae), a potential biocontrol agent of Brazilian peppertree. Experiments were conducted in the laboratory using Brazilian peppertrees exposed either to different salinity levels (0, 6, 12 parts per thousand), or to different nutrient levels (low, medium, high). Higher survival (55%) and faster development (32 day) to adulthood was observed on plants grown in fresh-water environments (0 ppt) compared to low (6 ppt) or high-salinity environments (12 ppt). In addition, higher survival (40%), faster development (34 day) and higher fertility (88% eggs hatched) occurred in high-nutrient treatments. Based on these results, field releases should be conducted in favorable habitats (e.g., low salinity, high fertility soils) to maximize the possibility of establishment and population growth of E. unguiculus in Florida.

Combined Effects of Host Plant Quality and Predation on a Tropical Lepidopteran: A Comparison between Treefall Gaps and the Understory in Panama

ABSTRACTIn tropical forests, light‐gaps created from treefalls are a frequent source of habitat heterogeneity. The increase in productivity, through gap formation, can alter food quality, predation and their impact on insect herbivores. We hypothesized that in gaps, herbivores would be less resource‐limited and more predator limited, whereas in the understory, we predicted the reverse. In this study, we investigate the combined effects of food quality and predation on the lepidopteran larva Zunacetha annulata feeding on its host plant Hybanthus prunifolius in two habitats; sunny treefall gaps and the shaded understory in Panama. In bioassays, Z. annulata feeding on sun leaves ate 22 percent less leaf area, grew 25 percent faster, and had higher pupal weights than larvae feeding on shade leaves. However, shade leaves had higher nitrogen content and specific leaf area. In gaps, predation was 26.4 percent compared to 13.8 percent in the understory. Larvae on understory plants traveled greater distances and spent more time searching and traveling than larvae on gap plants. These differences in behavior are consistent with lower predation risk and lower quality food in the understory. Using data from bioassays and field experiments we calculated 0.22 percent and 1.02 percent survival to adulthood for larvae in gaps and the understory, respectively. In conclusion, although these habitats were in close proximity, we found that larvae in the understory are more resource‐limited and larvae in gaps are more predator limited.

Effects of Host Plant Quality and Ant Tending for Treehopper &lt;I&gt;Publilia concava&lt;/I&gt;

Few studies have evaluated the relative importance of bottom-up regulation for the population dynamics of mutualism. To address this, we tested the hypothesis that host plant quality affects the strength of the mutualism between Publilia concava (Say) (Hemiptera: Membracidae) treehoppers feeding on Solidago altissima L. and ants. P. concava is a phloem-feeding treehopper that excretes a sugary waste product called honeydew. Ants collect this honeydew as a food resource, and treehoppers benefit both directly (e.g., feeding facilitation) and indirectly (e.g., protection from predators). We evaluated the effect of host plant quality on both the direct and indirect effects of this mutualism by using a factorial design that manipulated N–P–K fertilizer level and ant presence. For the experiment that focused on the direct effects of ant tending, both body size and survivorship were monitored. For the experiment that included the indirect effects of ant tending, only survivorship was monitored. Both host plant quality and ant tending increased the performance (survivorship and size) of Publilia treehoppers. However, we find no support for the hypothesis that host plant quality influences the strength of the mutualism in this system—there was no significant interaction between ant tending and fertilization for any measure of treehopper performance considered. We suggest that this result is explained by the independence of per capita tending levels with both host plant quality and treehopper density in this experiment.

Variation in Egg Size Within and Among Generations of the Bean Weevil, Bruchidius dorsalis (Coleoptera, Bruchidae): Effects of Host Plant Quality and Paternal Nutritional Investment

Variation in Egg Size Within and Among Generations of the Bean Weevil, <i>Bruchidius dorsalis</i> (Coleoptera, Bruchidae): Effects of Host Plant Quality and Paternal Nutritional Investment

Variation in Egg Size Within and Among Generations of the Bean Weevil, &lt;I&gt;Bruchidius dorsalis&lt;/I&gt; (Coleoptera, Bruchidae): Effects of Host Plant Quality and Paternal Nutritional Investment

Abstract Factors affecting egg size variation and its fitness consequences were studied within and among generations of a multivoltine bean weevil, Bruchidius dorsalis (Fahraeus), which exhibits reversed courtship roles. Because the toughness of host plant (Gleditsia japonica Miquel) seed pods varies among weevil generations in the field and it was supposed that seed hardness varies as well, it was hypothesized that female weevils regulate egg size according to seed hardness. To test this hypothesis, egg size was compared among three generations. The overwintering generation of B. dorsalis laid significantly larger (≈ 40% greater volume) eggs than did the other two generations. To assess the effect of paternal nutritional investment on egg size, females were allowed to mate with either well-fed or poorly fed males. During the first half of the 20-d experiment, no significant effect was detected, but during the second half, females that had mated with well-fed males laid significantly and slightly larger (...

Effects of host plant quality on overwintering success of the leaf beetle Chrysomela lapponica (Coleoptera: Chrysomelidae)

I investigated effects of density-dependent variation in host plant quality on adult feeding and overwintering success of the leaf beetle Chrysomela lapponica L. During pre-overwintering period adult beetles were fed in the laboratory on host plants, Salix borealis, originating from (a) a site with low density population of C. lapponica, (b) a site with peak density of C. lapponica, and (c) a post-outbreak site. Beetles fed on plants from low density and peak density sites demonstrated similar performance, whereas on plants from post-outbreak site beetles fed longer, gained more weight, and experienced greater mortality during overwintering. Higher water content in these beetles suggests that the main reason for increased winter mortality is insufficient dehydration of the beetles' bodies, presumably due to low quality food. The total carbon concentration in host plant foliage explained variation in most beetle performance indices, while total nitrogen did not correlate with beetle performance. Damage-induced decrease in quality of host plants from post-outbreak sites (delayed inducible resistance, DIR), associated with increase in carbon-containing defensive compounds, was earlier found to increase larval mortality and thus contribute to the decline in population density of C. lapponica. Results of the current study suggest that DIR can also disturb pre-overwintering feeding and thus increase winter mortality of adult beetles, enhancing post-outbreak density decline.

Larval diet affects number of femoral 'brush' scales in male Helicoverpa punctigera moths (Lepidoptera: Noctuidae).

Males of Helicoverpa punctigera (Wallengren) show considerable variation in the number of femoral scales on the prothoracic legs. Such intraspecific variation in adult morphology could indicate the presence of undetected sibling species, or it may be related to larval diet. Helicoverpa punctigera is polyphagous, and different host plant species are likely to represent diets of different quality. Femoral lengths and the numbers of femoral scales on the prothoracic legs were therefore determined from: (i) individuals that had been collected as larvae from various host species in the field; and (ii) individuals that had been laboratory-reared, in split-family tests, on different diets, namely cotton, lucerne, sowthistle and artificial diet. Host plant species (and therefore presumably diet quality) influenced femoral length of H. punctigera males and, perhaps in conjunction with this, the number of femoral scales on the fore leg. The rearing experiment indicated, in addition, that the effect of host plant quality varies with larval stage, and that the pattern of this variation across the immature stages is dependent on host plant species. The recorded variation in the morphology of field-collected H. punctigera males is therefore most readily explained as a consequence of different individuals developing (at least for most of their larval life) on different host plant species, with diet quality varying significantly with species. The relevance of these results for insect developmental studies and evolutionary interpretations of host relationships is outlined.

Effect of Host Plant Quality on the Sex Ratio and Fitness of Female Wheat Stem Sawflies (Hymenoptera: Cephidae)

Larvae of the wheat stem sawfly, Cephus cinctus Norton, feed and complete their development within the lumen of wheat and other hollow-stemmed grasses. Stems with large diameters are preferred and are the most suitable hosts. The sex ratios of wasps are male-biased in small stems and female-biased in large stems. Sawfly fitness, as indicated by wasp size, fecundity, and longevity, increases with host stem size.

Effect of Host Plant Quality on the Sex Ratio and Fitness of Female Wheat Stem Sawflies (Hymenoptera: Cephidae)

Effect of Host Plant Quality on the Sex Ratio and Fitness of Female Wheat Stem Sawflies (Hymenoptera: Cephidae)

Induced resistance of host tree foliage during and after a natural insect outbreak

1. Plant resistance against insect herbivores often increases after experimental damage to foliage, but few studies have obtained field estimates of the effect of induced resistance on insect populations during and after a natural insect outbreak. 2. This study measured the effect of quality of the host tree, mountain birch (Betula pubescens ssp. czerepanovii), on the periodically fluctuating folivore Epirrita autumnata (Lepidoptera, Geometridae) during peak and postpeak years of an outbreak in Finnish Lapland. Comparisons were made both within and between study sites to assess host plant quality, and thereby the effect of delayed induced resistance (DIR). 3. In within‐site comparisons, a set of experimental trees was defoliated by wild larvae in the peak year of the outbreak, whereas control trees were protected from defoliation by spraying with an insecticide. The effect of host plant quality was quantified in the following year by measuring the pupal mass of E. autumnata larvae reared in enclosures on these trees. 4. In between‐site comparisons, the sizes of pheromone‐trapped males were measured at both outbreak and low density sites during the progress of the outbreak. The size of trapped males was subsequently used to estimate the corresponding fecundity of females at the same sites. 5. Pupal mass of E. autumnata reared on trees defoliated in the previous year was 0–10% lower than on those trees protected from defoliation by the insecticide. Field‐collected adults indicated a similar pattern: they were smaller at outbreak sites than at low‐density sites, and the size reached its minimum in the post‐peak year. However, the estimated loss of reproductive capacity of females resulting from DIR was too small to be the sole explanation for the termination of the outbreak. 6. Whether the weak DIR response in this system was a characteristic of the 1990s outbreak alone remains unclear, because different terminating agents may be important for different individual outbreak peaks. During this outbreak, larval parasitism and developmental asynchrony between larvae and birch were probably more important reasons for population collapse than DIR.

The relationships between host selection and subsequent larval performance in three free‐living graminivorous sawflies

1. Selection of host plants for oviposition by females of three graminivorous sawfly species, Doleruspuncticollis C. G. Thomson, Doleruspicipes Klug. and Pachynematusclitellatus Lepeletier, was investigated experimentally using three grass species, Loliumperenne L., Festucarubra L. and wheat, Triticum aestivum L. cv. Hunter.2. Both species of Dolerus showed significant preferences for one grass over the other two, D. puncticollis preferring L. perenne and D. picipes selecting F. rubra. P. clitellatus females used L. perenne and F. rubra equally for oviposition, but avoided wheat.3. The results correlated closely with larval performance trials, with D. puncticollis larvae having maximal survival and growth rates on L. perenne, and D. picipes larval performance being maximized on F. rubra. P. clitellatus larvae survived well on both grasses, but had a high level of mortality on wheat.4. P. clitellatus larval growth rates were significantly higher on L. perenne than on F. rubra. Individual P. clitellatus adult females developing from larvae reared on L. perenne reached a significantly greater dry weight than those reared on F. rubra, but there was no significant difference in weight between males reared on the two hosts. There was some evidence that this disproportionate effect of host plant quality on the weight gain of the two sexes was translated into a bias in sex ratio of the eggs laid towards a greater proportion of females on L. perenne than on F. rubra. This manipulation of sex ratio would have a potential benefit for ovipositing females through disproportionate fecundity gains for female offspring.

Effects of host-plant quality on male two-spotted spider mite (Acari: Tetranychidae) mate location and guarding behavior

Effects of host-plant quality on two-spotted spider mite,Tetranychus urticae Koch, mate location and guarding behaviors were described using a no-choice bioassay. Males and quiescent deutonymphs were collected from lima bean leaves of one of two host qualities. High-chlorophyll (HC) leaves had been infested with spider mites for 6–10 days, while low-chlorophyll (LC) leaves had been infested for>21 days. Three parameters of maleT. urticae guarding behavior were quantified: approach arrestment, and arrestment duration. HC males approached quiescent deutonymphs more often than did LC males, even though host quality of females had no effect on male approach frequency. HC males were arrested more frequently by HC quiescent deutonymphs than were LC males, while LC males were arrested more often by LC females than were HC males. However, a different pattern was observed for arrestment duration. HC males were arrested for twice as long by LC quiescent deutonymphs than by HC females, while the LC-male arrestment durations elicited by HC and LC females did not differ. These results show that host-plant quality affectsT. urticae intersexual communication, in terms of both the female signal and the male response. Whether the differing male responses observed in this study indicate alternativeT. urticae mating strategies or are incidental by-products of host-induced physiological changes remains to be determined.

Influence of Bean–Tomato Intercropping on Population Dynamics of the Potato Leafhopper (Homoptera: Cicadellidae)

This study describes the influence of tomato, Lycopersicon esculentum Mill, and bean plant, Phaseolus vulgaris L., intercropping on the potato leafhopper, Empoasca fabae (Harris). The field design consisted of a single density of snap bean plants intercropped with a gradient of tomato plant densities. Leafhopper oviposition, nymph and natural enemy populations, and plant growth were monitored throughout two seasons. A complementary laboratory study analyzed the potential influence of host plant quality upon its acceptability for oviposition by potato leafhopper. Leafhopper densities in medium to high density intercrop subplots were >25% of those populations on bean planted alone, during periods of high leafhopper population densities. Differences in nymphal counts between treatments were a function of oviposition, not differential nymphal mortality from natural enemies or host plant resistance. Differences in tomato plant density across treatments did not fully account for differences in leafhopper densities. Reduced bean host plant acceptability was observed when choice tests were conducted using beans grown under different fertilizer levels. Up to 76% of the eggs were laid in plants containing the greatest amount of total nitrogen. Although tomato is believed to have directly reduced leafhopper densities in the intercrop treatments, the additional effect of host plant quality was also shown to be a potentially important factor.