Occurrence, bionomy and harmfulness of the sawfly Pachynematus (Pikonema) scutellatus in the eastern Czech Republic

From 1998 to 2006 the sawfly Pachynematus (Pikonema) scutellatus (Hattig) was studied at 45 localities in the eastern Czech Republic. A total of 3417 adults and 248 larvae were collected using Malaise traps, yellow sticky boards, emergence traps and sweep-net. The sawfly occurs from 220 m to above 1000 m a.s.l. in the mountains. Numbers of cocoons correlated positively with forest age. A profound decrease occurred in the numbers of P. scutellatus in mature forests during the 8-year study period. Less than 10% of the sawflies had a prolonged 2-year diapause. More males than female sawflies were caught in the Malaise traps and by sweeping with nets. Equal numbers of males and females were caught in emergence traps and on yellow sticky boards. The flight period started about April 24 for both males and females and ended around May 27 for males and May 30 for females and was strongly affected by the weather, which sometimes stopped flight activity. The period of flight varied according to year and localities from 9 to 27 days in males and from 27 to 36 days in females. Most likely four instars occur in males and five in females. Larval development lasted about 5 weeks, ending at the beginning of June. Control measures already formulated for use against Pristiphora abietina (Christ) are also suitable for P. scutellatus, because their phenology is closely similar.