Kazumi Miura

Insects have various defense responses to natural enemies, including autotomy. Detailed knowledge of autotomy patterns and frequencies in the wild is required to make reliable inferences concerning the fitness benefits and costs of the consequences of autotomy. However, few quantitative surveys have been conducted on the frequency of autotomized insects in the wild. Here, I examined data on autotomy in adult Parapodisma tanbaensis and Parapodisma subastris grasshoppers, which are sympatric, closely related species, collected over two consecutive years at three field sites in Kyoto, Japan. To investigate what traits were related to the frequency of autotomized adults, I recorded the species, sex, body size, and hind leg status after sampling adults because, according to previous research, these four parameters can be used to make predictions about the frequency of autotomized adults in the wild. There was a significant interaction effect between grasshopper sex and the sampling season on the frequency of autotomized adults and a non-linear increase in the frequency of autotomized adults as the season advanced. However, there were no significant effects caused by species or body size. Thus, a sexual difference existed in the occurrence and disappearance of autotomized adults in the wild as the season advanced. The ecological and evolutionary factors and mechanisms causing this pattern are discussed.

Summary: Persicaria perfoliata is an annual plant of Asian origin, which is a serious invader of native and orchard plant communities in the eastern USA. Based on a 2-year survey of herbivores of this plant in Japan, a suite of herbivorous insects were collected. Six species, including 1 bug, 1 aphid, 2 moths, 1 sawfly, and 1 beetle, are considered as specialists on Polygonaceae.

We examined the effects of diet mixture on the nymphal performance of a polyphagous grasshopper Parapodisma subastris Huang by developing the first-stadium nymphs with either single or various combinations of plants occurring in their natural habitat. Intrinsic quality in terms of nymphal survival differed largely across the 16 plant species. However, even combinations of the six worst quality plants (survival 10% or less in each) greatly improved nymphal survival when compared to that of superior quality plants (more than 70% survival). In contrast, the addition of either of two inferior plants (more than 10% and less than 40% survival) to the superior plant affected neither the survival nor the adult mass. Thus, diet mixture can be particularly important when only low quality plants are available. The adaptive significance of diet mixture was discussed in relation to the habitat flora and foraging habits of the grasshopper in the present study.