Pristiphora leucopus (Hellen, 1948)

Grearson, K. John & Liston, Andrew D., 2012, Review of seasonal polyphenism in the Symphyta (Hymenoptera), exemplified by Pristiphora leucopus (Hellén, 1948) (Tenthredinidae), Zootaxa 3502, pp. 72-88 : 77

Biology of P. leucopus

Eggs are laid singly in the leaf edge. Newly-hatched larvae were usually found, one or two on a leaf, within 4–5 days of placing the females on the plants, appearing as a tiny pale thread in a feeding notch at the edge of a leaf. The heads of the growing larvae soon assumed a blackish colour, retained until the final feeding instar about 10–14 days later when the heads became pale with a prominent parietal stripe (see figures of larvae in Grearson 2006). The body of all instars is uniformly pale green. Cocoons of summer generations were made between the leaves in plastic boxes. The cocoons were tubular with rounded ends, brown in colour and shiny, approximately 6 mm long and 2.5–3.0 mm in diameter. Adults emerged about a week later after chewing a hole near one end of the cocoon. Completion of one summer generation cycle, in captivity, thus required typically 21–26 days, from oviposition to emergence of the adult.

As clearly indicated by the rearing of five consecutive generations during a single season from individuals which had overwintered, P. leucopus is multivoltine. Although this result was achieved under artificial conditions, field observations in Germany support the conclusion that multiple generations occur in nature. Typically, the first adults of the overwintering generation in both England and Germany were found around 20 th April. The last adults were found in Germany on 21 st September. Assuming that development of a single summer generation requires slightly less than one month, it seems likely that at least five summer generations and a final overwintering generation arise in a ‘normal’ year. The number of generations can obviously however be expected to decrease at higher latitudes and in years with below average spring or summer temperatures. That the generations start to overlap with each other towards the end of summer, under natural conditions, can be inferred from the occurrence of adults and larvae on the same tree and same day, as observed in Brandenburg.