Dieback and recovery in poplar and attack by the hornet clearwing moth, Sesia apiformis (Clerck) (Lepidoptera: Sesiidae)

A survey of 801 poplar trees in central east England in 1999 demonstrated a correlation between crown dieback and infestation by hornet clearwing moth (Sesia apiformis), induced by a period of drought in 1995–1996. To determine whether trees colonised by S. apiformis would subsequently deteriorate and die or whether they could recover despite infestation and damage to the stem, all trees in the original survey were re-assessed in 2001, 2003 and 2005. The repeat surveys showed that trees with 70% or less crown dieback in 1999 replaced their canopy and generally improved by 2005, irrespective of the numbers of S. apiformis in the stem, whereas trees that had 75% or more crown dieback in 1999 either died or declined further. The presence of S. apiformis did not prevent tree recovery, and there was little evidence that infestation slowed the rate of recovery. Populations of S. apiformis, measured in terms of the numbers of adult emergence holes visible in the base of the trees, decreased between 2001 and 2005 at the same time as the amount of dieback visible in the canopy of the poplars markedly decreased. However, the fall in numbers of emergence holes at this time reflected a decline in larval establishment 2–3 years earlier, and indicated that the moth population had responded to a more rapid restoration in the internal state of the trees, which was not reflected immediately by the gradual replacement of dead branches and reduction in dieback symptoms.

Survival and Mortality of Immature Mordellids (Coleoptera: Mordellidae) Inducing Stem-galls on the Japanese Mugwort

Mordellid galls were collected from stems of Japanese mugwort, Artemisia indica var. maximowiczii (Nakai) H. Hara, in early spring at three riverbeds in the Kinki district, central Japan, and reared in the laboratory. Adults of two mordellids, Mordellistena brevilineata Nomura (96.2% of the total number of individuals) and M. fuscosuturalis Nomura (3.8%), emerged from the galls. The galls were simple fusiform swellings in the stems. We could not distinguish the 2 species by gall morphology. Mortality of the immatures mostly could not be determined, but parasitoids (Eupelmus sp., Entedon sp., and braconids, etc.) accounted for about 25% of the total mortality observed. Survival of immatures tended to be higher and the concomitant parasitism lower in thicker rather than thinner galls, and the galls became thick when they were formed in larger diameter stems. Oviposition and larval establishment in thick stems appeared to be advantageous for the completion of development and avoidance of parasitoid attack.