Cohabiting With the Enemy: Comparative Population Ecology of Two Mantid Species in a Successional Old Field.

Two praying mantids, Tenodera aridifolia sinensis Saussure and Tenodera angustipennis Saussure, are commonly found in the same old-field habitats in the eastern United States and in much of temperate zone Asia. Naturally established populations of these two species were studied intensively over two consecutive years (2010 and 2011) in an old field in southeastern Virginia, to compare life history features relevant to how they coexist, or whether one or the other of them is likely to be more successful in the same habitat. Populations of both species declined about 50% from 2010 to 2011 (adults from 47 to 21 for T. a. sinensis; 37 to 20 for T. angustipennis), but T. a. sinensis oviposited 10 oothecae and T. angustipennis only one in 2011. Tenodera a. sinensis was more abundant in the study site in both years, hatched earlier, and matured and oviposited earlier than T. angustipennis. Fewer females of both species survived to maturity in 2011 than in 2010, possibly indicating a reduction in prey or habitat suitability in 2011. We suggest that T. angustipennis will always be at a disadvantage as a result of its smaller body size, because of interspecific predation (and potentially competition) from its congener, lower clutch size, and susceptibility to egg parasitism. Further, environmental variability across field habitats and years profoundly affects populations of both species in successional old fields.

Coexistence of Two Congeneric Praying Mantids: A 7-Year Field Study of Reproductive Success and Failure.

Two species of Asian praying mantids, Tenodera angustipennis (Saussure) and Tenodera aridifolia sinensis (Saussure), which have become common to old fields in the northeastern United States, share a common resource base that raises the question of how they can coexist in the same habitat. We studied the reproductive output measured by numbers of oothecae of naturally established populations of these two species in an old field during 7 yr (2009­2015) of secondary succession. During the initial herbaceous vegetation-dominated stage, T. angustipennis oothecae were more abundant than those of its congener, but numbers steadily declined, until it had nearly disappeared by 2014. In contrast, numbers of T. a. sinensis oothecae increased from 2007 until 2014, and then sharply declined in 2015. The steady increase in abundance of this species throughout most of the successional development during the study may be owing to greater diversity of plant species used for oviposition. We believe that the most likely reasons for the continuous decline in T. angustipennis were a combination of intraguild predation by the larger T. a. sinensis, and egg parasitism by the wasp Podagrion mantis, which is not able to parasitize oothecae of T. a. sinensis. The later decline in T. a. sinensis may reflect the fact that the site had become dominated by trees, and neither of these species is typically found in forest habitats.

The Ontogenetically Variable Trophic Niche of a Praying Mantid Revealed by Stable Isotope Analysis.

Praying mantids have been shown to exert strong influences on arthropod community composition. However, they may not occupy the same trophic level throughout their lives. Trophic shifting over a life cycle could explain the documented variation in results from field studies, but specific interactions of predators within food webs have been difficult to determine simply by comparing control and treatment assemblages in field experiments. We examined the trophic position of the Chinese praying mantid, Tenodera aridifolia sinensis (Saussure), using stable isotope analysis (SIA). We measured the δ(13)C and δ(15)N of field-collected arthropods, and of laboratory groups of mantids fed known diets of these arthropods chosen from the most abundant trophic guilds: herbivores (sap feeders and plant chewers), and carnivores. We also collected mantids from the field over a growing season and compared their SIA values to those of the laboratory groups. Both δ(13)C and δ(15)N of mantids fed carnivorous prey (spiders or other mantids) were higher than those fed herbivores (grasshoppers). SIA values from field-collected mantids were highly variable, and indicated that they did not take prey from trophic guilds in proportion to their abundances, i.e., were not frequency-dependent predators. Further, δ(15)N decreased from a high at egg hatch to a low at the third instar as early nymphs fed mainly on lower trophic levels, and increased steadily thereafter as they shifted to feeding on higher levels. We suggest that the community impact of generalist predators can be strongly influenced by ontogenetic shifts in diet.

First identification of a putative sex pheromone in a praying mantid.

Praying mantids are models for a wide variety of behavioral, physiological, and ecological studies, and sex pheromones have been assumed to be important components of their biology. However, no mantid pheromone has ever been identified. We collected volatiles emitted by females of the mantid, Sphodromantis lineola, via solid phase microextraction (SPME). Mass spectral analysis revealed the collected volatiles to be a mixture of pentadecanal and tetradecanal. We prepared a synthetic mixture of these compounds, and found that males were both attracted to this mixture and stimulated to exhibit typical precopulatory behavior. We then examined male antennae with scanning electron microscopy, and confirmed the presence of porous antennal sensilla typical of insect pheromone receptors, i.e., that male mantids are equipped with the appropriate morphological apparatus to receive volatile chemical signals. Pheromones, in conjunction with visual and tactile cues, are thus an important feature of the reproductive biology of this, and undoubtedly other species of mantids. In addition to adding a crucial aspect of behavioral biology to our knowledge of this group, identification and synthesis of mantid pheromones may be a first step in attracting and aggregating these generalist predators for use in pest control.