Hideki Kagata

Bottom-up trophic cascades and material transfer in terrestrial food webs

In contrast to top-down trophic cascades, few reviews have appeared of bottom-up trophic cascades. We review the recent development of research on bottom-up cascades in terrestrial food webs, focusing on tritrophic systems consisting of plants, herbivorous insects, and natural enemies, and attempt to integrate bottom-up cascade and material transfer among trophic levels. Bottom-up cascades are frequently reported in various tritrophic systems, and are important to determine community structure, population dynamics, and individual performance of higher trophic levels. In addition, we highlight several features of bottom-up cascades. Accumulation or dilution of plant nutritional and defensive materials by herbivorous insects provides a mechanistic base for several bottom-up cascades. Such a stoichiometric approach has the potential to improve our understanding of bottom-up cascading effects in terrestrial food webs. We suggest a future direction for research by integration of bottom-up cascades and material transfer among trophic levels.

Bottom-up cascade in a tri-trophic system: different impacts of host-plant regeneration on performance of a willow leaf beetle and its natural enemy

Abstract.  1. Plant quality can directly and indirectly affect the third trophic level. However, little attention has been paid to how changes in plant quality affect the performance of predators through trophic levels, and which herbivores or predators are affected more strongly by host‐plant quality. The present study examined the effects of artificial cutting of willows on the performance of a willow leaf beetle (Plagiodera versicolora Laicharting) and its predatory ladybird beetle (Aiolocaria hexaspilota Hope).

Positive and negative impacts of insect frass quality on soil nitrogen availability and plant growth

Frass deposition to soil is an important pathway by which herbivorous insects impact decomposition and soil nutrient availability. However, little is known about how frass quality influences ecosystem properties. Here, we examined the effects of frass quality on the decomposition process, soil nitrogen (N) availability, and plant growth, using frass of Mamestra brassicae (L.) that fed on fertilized or unfertilized Brassica rapa L. var. perviridis Bailey. The frass quality was largely dependent on the host plant quality. Frass excreted by larvae that fed on the fertilized plants had higher N than that of larvae that fed on the unfertilized plants. The decomposition rate of the frass did not differ between N-rich and N-poor frass, except during the early decomposition period. The inorganic N concentration decreased during decomposition in both frass types. However, difference in the initial inorganic N concentration led to different consequences regarding soil N availability. Furthermore, addition of frass to the soil differently influenced the growth of B. rapa plants depending on the frass quality: plant biomass was increased by N-rich frass addition but decreased by N-poor frass addition, compared to the biomass without frass addition. These results indicate that frass quality is an important factor in determining the impact of herbivorous insects on nutrient dynamics, and that frass positively or negatively influences soil N availability and plant growth, depending on its quality.

Clutch Size Adjustment of a Leaf-Mining Moth (Lyonetiidae: Lepidoptera) in Response to Resource Availability

Abstract Clutch size variation of a leaf mining moth Paraleucoptera sinuella Reutti was investigated on two host plants, Populus sieboldii Miquel and Salix miyabeana Seemen. We found that female moths oviposited egg clutches with different size on the two host plants and that clutch size was correlated with leaf area between host species. Therefore, we concluded that females are adjusting clutch size in response to variation in resource availability for offspring. Positive correlation was also found between clutch size and leaf area within host species, however, the relationship was weak. Expected clutch size was determined from estimates of leaf area consumed by a larva until pupation. Females laid significantly smaller clutches than the expected size that could be supported by a single leaf on both host plants. We discussed how the females determined clutch 2size in response to resource availability.

Carbon–nitrogen stoichiometry in the tritrophic food chain willow, leaf beetle, and predatory ladybird beetle

Although plant quality can indirectly increase the performance of the third trophic level by bottom-up cascading effects, the mechanisms of this indirect effect are still unclear. In this study the carbon–nitrogen stoichiometry in a tri-trophic system consisting of the willow, a leaf beetle, and a predatory ladybird beetle were examined to determine the mechanisms of the bottom-up cascading effect. The bottom-up cascade is initiated by increasing leaf nitrogen, because of artificial cutting of willow trees. The relative growth rate (RGR) of the leaf beetle increased when fed on cut willow leaves, because of the high leaf nitrogen in the cut willows. Ladybird beetle RGR also increased when fed on leaf beetles fed on cut willow leaves. The increased RGR of the ladybirds cannot be explained by the quality of the prey, however, because leaf beetle nitrogen was not affected by host plant quality. Thus, the carbon–nitrogen stoichiometry could not be a mechanism of the bottom-up cascade through multiple trophic levels.

Leaf Miner as a Physical Ecosystem Engineer: Secondary Use of Vacant Leaf Mines by Other Arthropods

Abstract We have documented the secondary use of vacant leaf mines of a lepidopteran leaf miner, Phyllonorycter pastorella (Zellar), by other arthropods. At least six species were identified as secondary users of the vacant mines. Among secondary users, aphids and springtails were most abundant. Distribution patterns of these two insects showed that aphids used vacant mines by chance and that springtails used them selectively as feeding and reproductive sites. Hole diameter of mines did not affect the use of vacant leaf mines by aphids and springtails. We believe this is the first report on leaf miners as physical ecosystem engineers that provide modified habitats to other organisms.

Does nitrogen limitation promote intraguild predation in an aphidophagous ladybird

Reciprocal intraguild predation occurs between the two aphidophagous ladybird beetles Coccinella septempunctata L. and Harmonia axyridis Pallas (Coleoptera: Coccinellidae). However, its direction is asymmetrical; H. axyridis generally acts as an intraguild predator, and C. septempunctata as an intraguild prey. According to Denno and Fagans prediction that nitrogen shortages in predators may promote intraguild predation, it was hypothesized that growth of intraguild predator H. axyridis is more limited by nitrogen than that of intraguild prey C. septempunctata, and that H. axyridis growth is enhanced by feeding on C. septempunctata compared to feeding on aphids.

Nitrogen homeostasis in a willow leaf beetle, Plagiodera versicolora, is independent of host plant quality

While foliar nitrogen (N) content of host plants depends on environmental conditions, N content of herbivorous insects may remain relatively constant due to homeostasis. However, it is unknown to what extent insects can maintain their body elemental composition against natural variation in host plant quality. The present study examined the performance and N content of a willow leaf beetle, Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae), when fed leaves of host willow, Salix eriocarpa Franchet et Savatier (Salicaceae), with varying nutritional status.

Conflict between optimal clutch size for mothers and offspring in the leaf miner, Leucoptera sinuella

Abstract.  1. Clutch size in a leaf‐mining moth, Leucoptera sinuella (Reutti), was examined to determine whether the clutch size in natural populations meets the prediction of an optimal strategy, through comparisons between the optimal clutch sizes for offspring and for a mother.

Ecosystem consequences of selective feeding of an insect herbivore: palatability–decomposability relationship revisited

1. The relationship between leaf palatability and litter decomposability is critical to understanding the effects of selective feeding by herbivores on decomposition processes, and several studies have reported that there is a positive relationship between them.