Impact of the parasitoidLathrolestes ensator(Hym., Ichneumonidae, Ctenopelmatinae) as antagonist of apple sawflyHoplocampa testudinea(Hym., Tenthredinidae)

Abstract

Lathrolestes ensator (Brauns) was the only parasitoid species reared from larvae of apple sawfly Hoplocampa testudinea (Klug) collected in Dutch orchards. The life history parameters of apple sawfly and its parasitoid L. ensator were investigated in field and semi‐field experiments. Usually, the adult parasitoids emerge in synchrony with the preferred host stage, the second instar sawfly larvae. Parasitoid females carried 120–175 eggs, but never laid more than half this number. The mortality of sawfly eggs and larvae varied from 75 and 99%. The eggs and mining larvae are most vulnerable, as the older larvae survive for 90% on average. Three factors at least determine how many of the descending larvae become adult sawfly or parasitoid next spring. The failure of descending larvae to construct a cocoon varied from 7 to 31% and was highest in clay soil. Probably a similar mechanical hindrance prohibited more emerging adults, of both sawfly and L. ensator, from attaining the surface in heavier soils next spring. Relatively more sawfly prepupae than parasitoids died in the cocoon stage, from fungus disease or other causes, but more parasitoids than hosts stayed in prolonged diapause. Mainly due to this last factor, the overall result was a decrease of the parasitoid : host ratio during the first season underground. A life table based on survival rates during various life stages yields a net reproductive rate of up to 2.4 daughters per female sawfly. It indicates that 60% of the sawfly larvae need to be parasitized to stop population growth, or correspondingly less when more than 75% of the host eggs and young larvae are killed by predators or other causes.

Obuolinio pjūklelio (Hoplocampa testudinea Klug) populiacijos tankis ir žalingumas soduose Lietuvoje, įvairių veislių obelis auginant pagal dvi ūkininkavimo sistemas

“…Although potential of biological control of apple sawfly using hymenopteran parasitoids Aptesis nigrocincta (Gravenhorst, 1815) and Lathrolestes ensator (Brauns, 1898) (Hymenoptera: Ichneumonidae) has been examined (Babendreier, 1998;Zijp, Blommers, 2002), control is mostly based on synthetic or biological pesticides. In commercial integrated protection orchards sawfly control strategies rely mostly on non-selective insecticide treatments.…”

Species ratio, spring emergence, population dynamics and damage of plum sawflies Hoplocampa minuta and H. flava in plum orchard

“…This variability could be attributed mainly to biological reasons and environmental conditions during egg-laying larval development and overwintering periods. Several authors reported prolonged winter diapause in apple sawfly (H. testudinea) populations when overwintering larvae remain in the soil for two or three winters (Kuenen, van de Vrie, 1951, Zijp, Blommers, 2002. Prolonged diapause insures the apple sawfly against elimination of a year class of its host (Tauber, Tauber, 1976), when, for example, fruitlets are destroyed by late frost or other causes.…”

Apple sawfly Hoplocampa testudinea (Hym., Tenthredinidae) and its parasitoid Lathrolestes ensator in Dutch apple orchards (Hym., Ichneumonidae, Ctenopelmatinae)

“…Lathrolestes ensator (Brauns) is a both common and specific parasitoid of apple sawfly in the Netherlands (Z ijp and blommers , 1993). The aim of this study, which also includes Z ijp and B lommers (2002), was to find answers to the following questions. Is L. ensator present in sawfly infested orchards?…”

“…The orchards are encoded by two letters (table 1), if needed with a plot number added. Plantings SK88 and SK65 in Experimental Orchard De Schuilenburg, Kesteren (Gelderland), are described in Z ijp and B lommers (2002).…”

“…To determine the parasitism levels, the samples of sawfly larvae taken in 1991 were reared in soil‐filled plastic pots in an outdoor insectary until after adult emergence next spring (cf. Z ijp and B lommers 2002), and the remaining cocoons dissected. In 1992–94, parasitism was assessed directly by inspection of the sawfly larvae, as the black parasitoid eggs are readily visible through the skin.…”