We tested the possibility that a lepidopteran leafminer, Coptotriche japoniella Puplesis and Diskus, inhibits the host plant Eurya japonica Thunberg from abscising mined leaves prematurely to increase its survivorship in immature stage. We monitored abscission patterns of mined leaves with sacrificed larvae, mined leaves with living larvae, and unmined leaves from April to July 2004 and 2005 until leafminers emerged as adults. Unmined leaves rarely abscised before July. Mined leaves with sacrificed larvae fell at a constant rate after May, abscising significantly more than unmined leaves. In contrast, mined leaves with living larvae rarely fell before adult emergence; afterward they abscised rapidly. We also examined larval/pupal survivorship and mortality sources on the ground and trees after leafminers completed larval development. Leafminers on the ground suffered a higher mortality from predation than those on trees, and thus they emerged as adults on the ground less successfully. These findings suggest that the leafminer C. japoniella prevents the host plant from abscising mined leaves prematurely until adult emergence, thereby increasing their survivorship.
We quantified differences in leaf traits between upper and lower crowns of a deciduous oak, Quercus acutissima, and examined feeding preference, consumption and performance of the Japanese oak silkmoth, Antheraea yamamai, for those leaves. Upper-crown leaves had significantly smaller area, larger dry mass per area, greater thickness, lower water content, higher nitrogen content and a higher N/C ratio than lowercrown leaves. When simultaneously offered upper-crown and lower-crown leaves, moth larvae consumed a significantly larger amount of the former. However, when fed with either upper-crown or lower-crown leaves (no choice), they consumed a significantly larger amount of the latter. Female larvae reared on uppercrown leaves had a significantly smaller fresh weight, but attained a significantly larger pupal fresh and dry weight, with a significantly higher relative growth rate than those on lower-crown leaves. Although, like female larvae, male larvae had a significantly smaller fresh weight when reared on upper-crown leaves, they had a significantly larger value only for pupal dry weight. These results suggest that: (i) larvae ingest a greater amount of lower-crown leaves to compensate for the lower nitrogen content of the foliage, resulting in having an excess of water because of the higher water content of the foliage; (ii) feeding preference for upper-crown leaves accords with better performance (with respect to dry pupal weight and relative growth rate) on the foliage; (iii) better performance is explained by a higher nitrogen content and N/C ratio of the upper-crown foliage; and (iv) the effects of leaf quality on performance differ between sexes.
There has been an argument as to whether early leaf abscission substantially affects larval mortality of leafminers because of leaf senescence. Recently, a study reported that leaf abscission considerably increased the mortality of a leafminer (Ectoedemia cerviparadisicola Sato, sp. nov.) associated with Quercus gilva (Blume) in Nara Park, central Japan, where sika deer (Cervus nippon (Temminck)) have been protected for 1,200 yr, because deer consumed many abscised leaves containing living larvae. The study, however, did not investigate the life history of the leafminer or survey the leaf-fall pattern of Q. gilva through the season, so that it failed to quantify larval mortality because of deer predation. To test whether deer have a substantial effect on larval mortality of this leafminer, we regularly collected abscised and nonabscised leaves of Q. gilva through the season, examining mines and larvae in those leaves. Over 90% of mined leaves abscised in the period of peak leaf fall, when almost all larvae had already emerged from mines to pupate. Most dead larvae in abscised leaves were judged to have already died at the time of abscission from their instars and body features. The proportion of living larvae in abscised leaves was estimated to be <1.8%. Thus, even when deer preyed upon all living larvae in abscised leaves, they would hardly contribute to the increase in larval mortality. These results indicate that the effect of leaf abscission on leafminer mortality via deer predation and other causes is limited. The leafminer was described as new to science in the Appendix.
The parasitoid assemblage associated with a lepidopteran leafminer, Coptotriche japoniella (Tischeriidae), on an evergreen tree, Eurya japonica (Theaceae), was studied in the center of Japan to explore parasitoid coexistence mechanisms. The leafminer supported 12 parasitoid species. Eight abundant or common species were classified into five guilds according to their koinobiont/idiobiont mode and host-instar utilization pattern: early larval koinobiont, mid-larval idiobiont, mid-larval-late larval idiobiont, late larval-pupal idiobiont, and pupal idiobiont. The early larval koinobiont (Orgilus kumatai) and mid-larval idiobiont (Achrysocharoides sp.) seemed to be specialized on the host, whereas the members of the other guilds had a wide host range. The mid-larval-late larval (Cirrospilus diallus and Pnigalio sp.) or late larval-pupal idiobionts (Chrysocharis albipes, Apleurotropis kumatai, and Pleurotroppopsis japonica) facultatively hyperparasitized half of spinning larvae or pupae of the early larval koinobiont. These results suggest that parasitoid coexistence in this assemblage is greatly promoted by high levels of facultative hyperparasitism by idiobionts with wide host ranges on the dominant koinobiont.
The parasitoid assemblage associated with a lepidopteran leafminer, Coptotriche japoniella (Tischeriidae), on an evergreen tree, Eurya japonica (Theaceae), was studied in the center of Japan to explore parasitoid coexistence mechanisms. The leafminer supported 12 parasitoid species. Eight abundant or common species were classified into five guilds according to their koinobiont/idiobiont mode and host-instar utilization pattern: early larval koinobiont, mid-larval idiobiont, mid-larval-late larval idiobiont, late larval-pupal idiobiont, and pupal idiobiont. The early larval koinobiont (Orgilus kumatai) and mid-larval idiobiont (Achrysocharoides sp.) seemed to be specialized on the host, whereas the members of the other guilds had a wide host range. The mid-larval-late larval (Cirrospilus diallus and Pnigalio sp.) or late larval-pupal idiobionts (Chrysocharis albipes, Apleurotropis kumatai, and Pleurotroppopsis japonica) facultatively hyperparasitized half of spinning larvae or pupae of the early larval koinobiont. These results suggest that parasitoid coexistence in this assemblage is greatly promoted by high levels of facultative hyperparasitism by idiobionts with wide host ranges on the dominant koinobiont.
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