Anthony R. Chittenden

The parapatric distribution and contact zone of two forms showing different male-to-male aggressiveness in a social spider mite, Stigmaeopsis miscanthi (Acari: Tetranychidae)

Two forms showing different male-to-male aggressiveness, different male morphologies and different diapause attributes are known in Stigmaeopsis miscanthi (Saito), a social spider mite infesting Chinese silver grass (Miscanthus sinensis Anderss). Reproductive isolation exists between the forms, although it is not always complete, and the details of their distributional patterns are unknown, but expected to be parapatric. We searched for the contact zone at Mt. Unzen (Nagasaki Pref., Japan) where both forms are known to occur at different altitudes. We found the two forms together in several M. sinensis stands, suggesting there is frequent contact between the forms in their boundary area. We discuss the mechanism(s) that maintain the parapatry related to their frequent contact and the pattern of reproductive isolation between them.

Function of the web box as an anti-predator barrier in the spider mite, Schizotetranychus recki

Spider mites inhabiting Sasa bamboo show considerable variation in traits believed to be the result of coevolution between predator and prey. In Schizotetranychus recki Ehara inhabiting the hairy leaves of a dwarf bamboo, Sasa senanensis, all quiescent stages, including eggs, appear within web boxes in the leaf hairs of their host plant, and this habit is thought to be a trait involved in predator avoidance. To test this hypothesis, the survival rates of S. recki eggs inside a web box and those freed of a web box were assessed in relation to six predator species that co-occur with the spider mite in the field. The results clearly show that the webbing behavior (web box) of S. recki has a function in avoiding five predator species. However, one predator species, Agistemus summersi Ehara, preyed more on eggs protected by a web box. This suggests that this predator species has a special trait to overcome the nest barriers.

Egg-depositing behavior as a predator avoidance tactic of Yezonychus sapporensis Ehara (Acari, Tetranychidae)

Abstract Spider mites are very small phytophagous organisms living on plant leaves. They possess a diverse array of life types. Such diversity in life type has been supposed to be a result of coevolution between predator and prey, although there is little concrete evidence to support this concept. In Yezonychus sapporensis inhabiting the leaves of a dwarf bamboo, Sasa senanensis, all quiescent stages including eggs appear on the tips of the host leaf hairs during the summer season, and this habit is thought to be a kind of predator avoidance trait. To confirm this, the survival rates of Y. sapporensis eggs deposited on natural sites and experimentally manipulated sites were observed for eight co-occurring predator species. The results clearly showed that the oviposition behavior of Y. sapporensis has a function in avoiding predator attack, at least under experimental conditions.

Variation in counterattack effect against a phytoseiid predator between two forms of the social spider mite, Stigmaeopsis miscanthi

In Japan, Stigmaeopsis miscanthi (Saito) occurs in two forms that are differentiated by the intensity of male-to-male aggression, i.e. there is a low aggression and a high aggression group (known as the LW and HG forms, respectively). The effects of counterattack behavior against predators were experimentally compared between the two forms. Parental males and females of both forms could achieve significant counterattack success against Typhlodromus bambusae, a specific predator, and counterattack efficiency increased significantly with parental density. Furthermore, the HG form showed a stronger tendency than the LW form to kill predator larvae. Thus, variation in counterattack success may exist between these two forms, and there is some correspondence between male-to-male belligerence and counterattack effectiveness against predators.

An overlooked side effect of nest-scattering behavior to decrease predation risk (Acari: Tetranychidae, Stigmaeidae)

The number of nests containing egg masses a female makes over her lifetime and the pattern of scattering nests vary among species in a genus of nest-weaving spider mites (Stigmaeopsis). We hypothesized that the scattered nests of small nest builders have a previously overlooked indirect effect in that the void nests created after predation take on a new role as hindering devices that effectively decrease predator searching efficiency. First, we demonstrated that the experimental design used in this study is a good reflection of the nest distribution pattern of Stigmaeopsis takahashii (an intermediate-sized nest builder) in the field. Using this species as a model, we tested how different nest-scattering patterns affect the predator to examine how scattering may indirectly provide an anti-predation strategy by increasing a predators searching time. Next, we observed how artificially arranged void nests disturb predatory behavior in both starved and fully fed predator females and showed that void nests have a strong hindering effect on predators. Thus, we concluded that the nesting behavior of this mite species not only has anti-predator effects but must also have a stabilizing effect on predator–prey interaction systems at the population level.

Counterattack success of a social spider mite against two predominant phytoseiid predator species

A survey was conducted of the predator fauna occurring in and around the nests of the two forms (LW: low male aggression and HG: high male aggression) of Stigmaeopsis miscanthi (Saito) that occur in Japan. Two phytoseiid species, Neoseiulus womersleyi (Schicha) and Typhlodromus bambusae Ehara predominated in S. miscanthi nests and their respective occurrence frequencies were the same in LW form nests as in HG form nests. We examined the counterattack success of S. miscanthi LW form males against these two phytoseiid predators. It was shown that while LW form male(s) could kill or effectively drive the larvae of both predator species out of their nests, there were no significant differences in the male counterattack success rate between 1-male and 2-male defended nests, or against the two predator species. On the other hand, there was a significant difference between the two predator species’ behavioral response to male-defended nests.

Two New Species and Four New Life Types in Tetranychidae

Abstract Two new species—Stigmaeopsis temporalis n. sp. collected in Kochi, Japan, and S. tegmentalis n. sp. collected in Fuzhou, China—both from bamboo plants, are described. In addition, four new life types (WN-p, WN-h, WN-n, and CW-g) in five species—S. temporalis, Stigmaeopsis tenuinidus Zhang et Zhang, S. tegmentalis, Neonidulus tereotus Beard et Walter, and Eotetranychus asiaticus Ehara—are documented in relation to their supposed functions.

Ambulatory migration in mites (Acari: Tetranychidae, Phytoseiidae) to new leaves of moso bamboo shoots

The migratory behaviour of two tetranychid pest species, Aponychus corpuzae and Schizotetranychus nanjingensis, and one phytoseiid, Typhlodromus bambusae, was studied in several monocultural bamboo forests in Fujian Province, China. The aim of the study was to assess how the ambulatory immigration of tetranychid and phytoseiid mites from the ground to new leaves is affected by a sticky barrier around the stem, by the age of bamboo shoots or by shoot density. The results show that while the sticky barrier is particularly effective at disrupting the ambulatory immigration from the ground to new leaves of S. nanjingensis to 1-year-old shoots and of A. corpuzae to 3-year-old shoots, it has no significant effect on the immigration of the phytoseiid mite.

A Modified Aerosol Free Vegetation Index Algorithm for Aerosol Optical Depth Retrieval Using GOSAT TANSO-CAI Data

In this paper, we introduced a new algorithm for retrieving aerosol optical depth (AOD) over land, from the Cloud and Aerosol Imager (CAI), which is one of the instruments on the Greenhouse Gases Observing Satellite (GOSAT) for detecting and correcting cloud and aerosol interference. We used the GOSAT and AErosol RObotic NETwork (AERONET) collocated data from different regions over the globe to analyze the relationship between the top-of-atmosphere (TOA) reflectance in the shortwave infrared (1.6 μm) band and the surface reflectance in the red (0.67 μm) band. Our results confirmed that the relationships between the surface reflectance at 0.67 μm and TOA reflectance at 1.6 μm are not constant for different surface conditions. Under low AOD conditions (AOD at 0.55 μm < 0.1), a Normalized Difference Vegetation Index (NDVI) based regression function for estimating the surface reflectance of 0.67 μm band from the 1.6 μm band was summarized, and it achieved good performance, proving that the reflectance relations of the 0.67 μm and 1.6 μm bands are typically vegetation dependent. Since the NDVI itself is easily affected by aerosols, we combined the advantages of the Aerosol Free Vegetation Index (AFRI), which is aerosol resistant and highly correlated with regular NDVI, with our regression function, which can preserve the various correlations of 0.67 μm and 1.6 μm bands for different surface types, and developed a new surface reflectance and aerosol-free NDVI estimation algorithm, which we named the Modified AFRI1.6 algorithm. This algorithm was applied to AOD retrieval, and the validation results for our algorithm show that the retrieved AOD has a consistent relationship with AERONET measurements, with a correlation coefficient of 0.912, and approximately 67.7% of the AOD retrieved data were within the expected error range (± 0.1 ± 0.15AOD(AERONET)).

Tactile Crypsis Against Non-Visual Predators in the Spider Mite, Aponychus corpuzae Rimando (Acari: Tetranychidae)

Crypsis is the form or behavior of an organism that makes it difficult to detect (Begon et al., 1996). By cryptically resembling its habitat background, a prey species may remain undiscovered by its predators. The sensory nature of the predatory threat an insect faces from its natural enemies will select heavily on the type of crypsis it may employ. Visual and chemical crypsis are being perhaps the best known (Cott, 1940; Croze, 1970; Edmunds, 1974, 1990; Hunter and Rosario, 1988; Eickwort, 1990; Walters and Proctor, 1999), but examples of acoustic (Rydell, 1998) and tactile (or morphological) crypsis (Bardwell and Averill, 1996) have also been documented, although considerably fewer in number. Sasa senanensis (Franchet et Savatier) (Graminaceae) is one of eleven species of dwarf bamboo found in Japan (Ohwi, 1975). It occurs in a variety of morphs, from hairless to extremely hairy, and hosts a diverse mite fauna that can include 8 herbivorous tetranychid species and 7 predaceous phytoseiid and stigmaeid species (Chittenden and Saito, 2001; Chittenden, 2002).