Keiko Kishimoto-Yamada

How much have we learned about seasonality in tropical insect abundance since Wolda (1988)

Seasonal patterns in climatic conditions affect the life cycles and temporal patterns in the abundance of most temperate insect species. In tropical regions where there is no winter season, the situation may be different. For a better understanding of the evolution of seasonal life cycles, and the dynamics affecting temporal patterns in abundance of tropical insect populations and assemblages, it is important to study the life cycles of tropical insects and the presence or absence of seasonality in relation to climatic conditions. By reviewing studies on temporal patterns of abundance, this article examines the patterns of seasonality in adult tropical forest insects and discusses the variation in such patterns in various forest types. Seasonal and aseasonal patterns were found to be common in tropical dry and wet regions, respectively. In wet regions, which lack a distinctive dry season, there exists a wide variety of temporal patterns in addition to aseasonal patterns: distinctively seasonal and supra‐annual fluctuations in some insect species. Some of the problems of hidden ecological mechanisms underlying seasonal patterns in abundance are discussed, and the definition of seasonality in temporal patterns of insect abundance at a particular stage in the life cycle is considered. Methodological problems are also discussed.

Wide Host Ranges of Herbivorous Beetles? Insights from DNA Bar Coding

There are very few studies that have investigated host-specificity among tropical herbivorous insects. Indeed, most of the trophic interactions of herbivorous insects in Southeast Asian tropical rainforests remain unknown, and whether polyphagous feeding is common in the herbivores of this ecosystem has not been determined. The present study employed DNA bar coding to reveal the trophic associations of adult leaf-chewing chrysomelid beetles in a Bornean rainforest. Plant material ingested by the adults was retrieved from the bodies of the insects, and a portion of the chloroplast rbcL sequence was then amplified from this material. The plants were identified at the family level using an existing reference database of chloroplast DNA. Our DNA-based diet analysis of eleven chrysomelid species successfully identified their host plant families and indicated that five beetle species fed on more than two families within the angiosperms, and four species fed on several families of gymnosperms and/or ferns together with multiple angiosperm families. These findings suggest that generalist chrysomelid beetles associated with ecologically and taxonomically distant plants constitute a part of the plant-insect network of the Bornean rainforest.

Seasonality in light-attracted chrysomelid populations in a Bornean rainforest

Abstract.  1. Seasonal or annual population fluctuations have been reported for various tropical insect species, exhibiting one or more peaks in abundance at certain times of the year. Such fluctuations have mostly been observed in areas that experience annual wet and dry seasons, and not in areas where climatic fluctuations are unpredictable on an annual basis.

Population fluctuations of light-attracted chrysomelid beetles in relation to supra-annual environmental changes in a Bornean rainforest.

In Southeast Asian tropical rainforests, two events, severe droughts associated with the El Niño-Southern Oscillation and general flowering, a type of community-wide mass flowering, occur at irregular, supra-annual intervals. The relationship between these two supra-annual events and patterns of insect population fluctuations has yet to be clearly elucidated. Leaf beetles (Chrysomelidae) are major herbivores and flower-visitors of canopy trees, affecting their growth and reproduction and, in turn, affected by tree phenology; but their population fluctuations in the Southeast Asian tropics have not been extensively investigated. We examined population fluctuation patterns of the 34 most dominant chrysomelid species in relation to the two supra-annual events by conducting monthly light-trapping over seven years in a lowland dipterocarp forest in Borneo. Our results showed large community variation in population fluctuation patterns and a supra-annual (between-year) variation in abundance for most of the dominant chrysomelids that was significantly larger than the annual (within-year) variation. Specifically, in response to a severe drought in 1998, chrysomelid species exhibited different population responses. These results show that population fluctuations of individual species, rather than the entire assemblage, must be analyzed to determine the effects of changes in environmental conditions on the structure of insect assemblages in the tropics, especially in regions where supra-annual environmental changes are relatively more important than seasonal changes.

Tree community structure, dynamics, and diversity partitioning in a Bornean tropical forested landscape

Human-modified forested landscapes are prevalent in the tropics, and the role of complex mosaics of diverse vegetation types in biodiversity conservation remains poorly understood. Demographic traits and the spatial pattern of biodiversity are essential information when considering proper forest management and land use strategies. We compared the tree community structure (stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and species composition) and the forest dynamics (mortality, recruitment rate, and increments of basal area, and above- and below-ground biomass) of 39–46 plots among five dominant forest types: young and old fallows, rubber plantations, and fragmented and old-growth forests in Sarawak, Malaysia. We also explored how tree diversity was distributed across different spatial scales using additive partitioning of diversity. Swidden cultivation and rubber plantations showed decreased stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and increments of above- and below-ground biomass, which affected tree mortality, dominant trees, and species composition. Little distinction in species composition was observed among young and old fallows and rubber plantations, indicating a relatively quick recovery of the tree community in the early stages. The highest diversity was found among forest types, indicating that the whole forested landscape comprises a suitable scale for tree biodiversity conservation in the region. Our results suggest that although fragmented and old-growth forests have an irreplaceable role and a high priority in conserving biodiversity and sustaining the function of the forest ecosystem, secondary forests may also have a reinforcing role in maintaining tree diversity in the region, especially under the current circumstances in which a large portion of the landscape is human-modified and faces an increasing threat from the expansion of oil palm plantations.

Consequences of a severe drought associated with an El Niño-Southern Oscillation on a light-attracted leaf-beetle (Coleoptera, Chrysomelidae) assemblage in Borneo

The El Nino-Southern Oscillation (ENSO) phenomenon occurs irregularly and supra-annually at intervals of 2–7 y (Hughen et al . 1999, McPhaden et al . 2006), and is the strongest source of supra-annual climate fluctuation (Hughen et al . 1999, Philander 1990). During ENSO, the interior of the South-East Asian tropics, which is characterized by constant high temperature and no distinct dry season, experiences severe drought (Walsh 1996).

Biological characterization of the obligate symbiosis between Acropyga sauteri Forel (Hymenoptera: Formicidae) and Eumyrmococcus smithii Silvestri (Hemiptera: Pseudococcidae: Rhizoecinae) on Okinawa Island, southern Japan

The ant Acropyga sauteri Forel has an obligate, mutualistic symbiosis with a mealybug, Eumyrmococcus smithii Silvestri, on Okinawa Island, southern Japan. The mealybugs live inside ant nests nearly all their lives, and the ants depend on them for food. Alate foundress queens carry mealybugs during their nuptial flights, using them to establish new colonies at new sites. However, important aspects of the symbiosis have not yet been elucidated. The present study characterizes the basic biology of the symbiosis and describes for the first time the morphologies of all growth stages of E. smithii. Our study suggests that E. smithii has only one nymphal stage, followed by a female pupal stage or male prepupal stage. Intensive sampling of ant nests across seasons showed that A. sauteri prefers nest sites 5–20 cm underground. Acropyga sauteri produced reproductive stages mainly in mid‐March or early April, and numbers of both ant workers and mealybugs increased from spring to summer. Experimental determination of colony identity with a method using nestmate recognition by ants suggested that each ant colony rarely has a perimeter greater than 30 cm, that the ants are monogynous, and that different ant colonies are densely aggregated along the root system of a plant, adjacent to each other but not interflowing. Both symbiotic partners were vulnerable to attacks by several common subaerial ant species following physical disturbance to their nests.

Seasonality in phytophagous scarabaeid (Melolonthinae and Rutelinae) abundances in an ‘aseasonal’ Bornean rainforest

Abstract.  1. Seasonal patterns in insect population fluctuations have rarely been examined in rainforests of the central part of Southeast Asia where the climate is aseasonal.

Effects of remnant primary forests on ant and dung beetle species diversity in a secondary forest in Sarawak, Malaysia

Tropical landscape structures have been transformed into mosaic structures consisting of small patches of primary and secondary forests, and areas of other land use. Diversity of insect assemblages is often higher in primary forests than in surrounding secondary forests. However, little is known about how the primary forests affect diversity in surrounding secondary forests in a landscape. In Sarawak, Malaysia, the typical landscape in areas from which lowland tropical rainforests had originally spread consists mainly of primary and secondary forests, with small areas of cultivation. In this study, we examined how the proportion of remnant primary forests in a landscape affects species diversity and species composition of ants and dung beetles in Macaranga-dominated secondary forests. The proportions were quantified based on remote-sensing data at various spatial scales, ranging from 100- to 5,000-m radius from each of the target forests. We found that the proportions of remnant primary forests within a 100-m radius had a significant positive effect on ant species diversity, and those within 100-, 300-, and 500-m radii significantly affected species compositions. However, the proportions of remnant primary forests had no significant relationship with dung beetle diversity, while those within 100- and 1,000-m radii had significant effects on species composition. The different responses to the remnant primary forests are likely to be related to differences in the movement and dispersal traits between the two taxa.

Inventory of the Heteroptera (Insecta: Hemiptera) in Komaba Campus of the University of Tokyo, a highly urbanized area in Japan.

Abstract Background The Heteroptera, or true bugs, forms one of the major insect groups with respect to the very diverse habitat preferences, including both aquatic and terrestrial species, as well as a variety of feeding types. The first comprehensive inventory of the Heteroptera at Komaba Campus of the University of Tokyo, or an urban green space in the center of the Tokyo Metropolis, Japan, was conducted. New information A total of 115 species in 29 families of the suborder Heteroptera were identified. The area had a high species richness compared with other urbanized and suburbanized localities in Tokyo. The campus is found to show a substantial difference in heteropteran species compositions, despite being close to the other localities surrounded by highly urbanized zones in central Tokyo.