Host plant variation in mortality of the leaf-folding sawfly on the arroyo willow

Abstract. 1. We tested the hypothesis that survival and sources of mortality of the leaf-folding sawfly ( Phyllocolpa sp.) varied significantly among host plants of the arroyo willow ( Salix lasiolepis Bent ham).
2. Survival of the leaf folder differed among field and potted willows in a common environment in two of three cases, and sources of mortality differed among plants in four of five cases.
3. Egg mortality differed among field plants but not among the potted willow plants.
4. Larval mortality and parasitism differed among field and potted willows in 2 years, and appeared to be compensatory mortality sources.
5. Leaf folder density among plants was not generally correlated with percentage of leaf folds with no egg (galls formed but no subsequent oviposition), percentage survival, or percentage mortality, indicating a general lack of density dependence.
6. The proportion of folds with no egg oviposited differed significantly among field and potted plants, and was only correlated with survival or sources of mortality in one of three years.
7. The data support the hypothesis that host plant genotype affects the interaction of the leaf folder with its natural enemies, and thus represents a three trophic level interaction.     

Maternal care in the red-headed spruce web-spinning sawfly,Cephalcia isshikii (Hymenoptera: Pamphiliidae)

We describe oviposition and maternal behavior in the sawfly Cephalcia isshikiiand examine the adaptive significance of this behavior. Females deposited eggs in a single but loose cluster on needles of terminal twigs of spruces, Piceaspp., and remained with the eggs usually on the underside of the twig facing toward the tip. The female attended her eggs until death without taking food but did not follow the first-instar larvae that moved from natal needles even if she survived until then. When the female was disturbed, she usually moved toward the source and attempted to bite it. Though at much lower frequencies, this aggressive behavior was also observed in gravid females and even in males. Field observations and female removal experiments indicated that the female enhanced the survival of the eggs through the reduction of arthropod prédation.     

Plant resistance, plant traits, and host plant choice of the leaf-folding sawfly on the arroyo willow

Abstract. 1. The hypotheses that genetic variation in host plant resistance of the arroyo willow affected leaf folder ( Phyllocolpa sp.) (Hymenoptera: Tenthredinidae) density and that genetic variation in shoot length and leaf length was correlated with resistance were tested.
2. Willows grown in pots and exposed to ovipojsition by the leaf folding sawfly in cages had significantly different densities among clones, indicating variation in resistance caused by genetic differences among conspecific host plants.
3. There was a general correspondence between leaf folder density on potted cuttings and on the plants in the field that were the sources of cuttings.
4. In behavioural choice experiments, susceptible clones (with highest leaf fold densities) had the highest oviposition activity of female leaf folders compared to clones that were resistant to the leaf folder.
5. Clones differed significantly in shoot length and leaf length among clones grown in pots, among clones in the field, and between shoots with galls and shoots without galls on clones in the field.
6. Leaf folder density was significantly positively correlated with mean shoot length on field clones in 1985 and 1986, but was not correlated with leaf length, although leaf length and shoot length were correlated.
7. Leaf length variation among willow clones accounted for a significant portion of the variation in resistance of potted willows, but shoot length was unimportant.     

Effects of cyanogenesis in bracken fern (Pteridium aquilinum) on associated insects

Abstract. 1. The relationship between cyanogenesis in bracken fern and the insect fauna feeding on the plant was investigated over a 3 year period. The most common insects between May and July, while cyanide levels were high, were the sawflies Strongylogaster impressata Provancher, S.multicincta Norton, Aneug-menus fzavipes (Norton), the aphid Macrosiphum euphorbiae (Thomas) and a microlepidopteran species of Monochroa .
2. Collections of insects from cyanogenic and acyanogenic fronds showed significantly fewer sawflies on the cyanogenic fronds. The aphid and the microlepidopteran were randomly distributed with respect to cyanogenicity.
3. Feeding tests for two of the sawfly species ( Simpressata and Smulticincta ) showed that larvae grew more slowly and had a higher mortality when raised on cyanogenic fronds than on acyanogenic ones.
4. Field collected cyanogenic bracken fronds were found to have sustained less damage from chewing herbivores compared with acyanogenic fronds.     

Biocontrol of the apple sawfly,Hoplocampa testudinea,with entomogenous nematodes

Four types of experiments were conducted to assess the pathogenicity of entomogenous nematodes against the apple sawfly,Hoplocampa testudinea Klug (Hymenoptera: Tenthredinidae). In Petri dish,Steinernema carpocapsae (Weiser) DD 136 strain,S. carpocapsae All strain,S. feltiae (Filipjev) andHeterorhabditis bacteriophora Poinar caused 100% larval mortality 72 h after the treatments. In semi-field conditions under dwarf apple trees, a single treatment with either 40 or 80S. carpocapsae All strain/cm² caused significant (>80%) larval mortality. No significant increase in mortality was obtained with a second application. In 1990, late treatment with 80S. carpocapsae All strain/cm² caused significant (39.1%) pupal mortality. In 50×50 cm quadrats under dwarf apple trees, treatment with 40 and 80S. carpocapsae All strain/cm² were done in spring 1989. In spring 1990, respectively 22 and 25 apple sawfly adults emerged from quadrats treated with 40 and 80S. carpocapsae All strain/cm², whereas 78 adults emerged from untreated quadrats. In a foliar application experiment, a single treatment withS. carpocapsae All strain significantly reduced the percent of fruit showing secondary damage. The possibility of using entomogenous nematodes as part of an integrated pest management in apple orchards is discussed, with particular reference to the integration of programs aimed at managing plum curculio,Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) populations.      

Production,application, and field performance of Abietiv™, the balsam fir sawfly nucleopolyhedrovirus

Beginning in the early 1990s, the balsam fir sawfly (Neodiprion abietis) became a significant defoliating insect of precommercially thinned balsam fir (Abies balsamea (L.) Mill.) stands in western Newfoundland, Canada. In 1997, a nucleopolyhedrovirus (NeabNPV) was isolated from the balsam fir sawfly and, as no control measures were then available, NeabNPV was developed for the biological control of balsam fir sawfly. In order to register NeabNPV for operational use under the Canadian Pest Control Products Act, research was carried out in a number of areas including NeabNPV field efficacy, non-target organism toxicology, balsam fir sawfly ecology and impact on balsam fir trees, and NeabNPV genome sequencing and analysis. As part of the field efficacy trials, approximately 22 500 hectares of balsam fir sawfly-infested forest were aerially treated with NeabNPV between 2000 and 2005. NeabNPV was found to be safe, efficacious, and economical for the suppression of balsam fir sawfly outbreak populations. Conditional registration for the NeabNPV-based product, Abietiv™, was received from the Pest Management Regulatory Agency (Health Canada) in April 2006. In July 2006, Abietiv was applied by spray airplanes to 15 000 ha of balsam fir sawfly-infested forest in western Newfoundland in an operational control program.      

Desiccation of Pinus foliage induced by conifer sawfly oviposition: effect on egg viability

Abstract 1. Desiccation of needles following oviposition by Neodiprion lecontei in Pinus resinosa caused high egg mortality. Eight-five per cent of pine needles into which sawflies oviposited subsequently desiccated, compared with 2.5% of needles without eggs. No larval emergence occurred from desiccated needles.
2. Within affected shoots, the probability of desiccation increased with the extent of oviposition. In paired comparisons of needles, 41.2% of needle length was occupied by eggs in desiccated needles, compared with 24.0% of needles without desiccation.
3. Both density-dependent and density-independent factors may contribute to desiccation of egg-laden needles. The likelihood that needle vasculature will be severed by ovipositing females probably increases with population density. Drought, which was high during the observations, probably increases the incidence of needle desiccation following mechanical injury caused by oviposition.     

Anti-predator defence mechanisms in sawfly larvae of Arge (Hymenoptera, Argidae)

Larvae of the sawfly Arge (Hymenoptera, Argidae) are exposed to predators such as ants. Their defence mechanisms, which have been almost unstudied, were investigated by behavioural observations coupled to a morphological approach and by testing the bioactivity of several body parts. Arge larvae raised their abdomen when contacted by Myrmica rubra workers. The ants rarely bit a larva and generally retreated immediately, sometimes without contacting it. Most of those few ants that bit a larva then showed an uncoordinated walk. Crude hemolymph from a common species, A. pagana, was a feeding deterrent towards ants. Hemolymph extracts remained active up to a concentration of 0.8 microg DW extract per microlitre solution, and were more active than integument and gut extracts. We also observed ants paralysed by extracts, especially from the gut. It is likely that this toxicity is due to a polypeptide, lophyrotomin, which is known to occur in A. pullata. Six or seven non-eversible ventro-abdominal glands occurred in all species studied (A. fuscipes, A. nigripes, A. ochropus, A. pagana, A. pullata, A. ustulata). These glands contain volatiles. We consider both types of chemicals to be important in defence, and we propose that the paralysing effect is a common feature among Arge species.     

Host plant derived feeding deterrence towards ants in the turnip sawfly Athalia rosae

Larvae of the sawfly Athalia rosae ruficornis Jakovlev (Hymenoptera: Tenthredinidae) feed on several glucosinolate-containing plants and have been shown to sequester the main glucosinolates of different hosts, namely sinalbin (p-hydroxybenzylglucosinolate) from Sinapis alba L., sinigrin (allylglucosinolate) from Brassica nigra (L.) Koch, and glucobarbarin ((S)-2-hydroxy-2-phenylethylglucosinolate) from Barbarea stricta Andrz. (Brassicaceae). These plant metabolites are stored in the haemolymph, which is readily released when larvae are attacked by predators. In a dual-choice bioassay the bio-activity of sawfly haemolymph collected from larvae reared on different host plants (S. alba, B. nigra, and B. stricta) was tested against the ant Myrmica rubra L. (Hymenoptera: Formicidae). The haemolymph had a stronger deterrence effect when the corresponding sawfly larvae were reared on S. alba than when reared on B. nigra and B. stricta. Haemolymph of caterpillars of Pieris rapae L. (Lepidoptera: Pieridae) that had fed on S. alba was not deterrent to the ants. No sinalbin could be detected in their haemolymph. The glucosinolates sinalbin and sinigrin, offered in a concentration comparable to that in the sawfly haemolymph, were deterrent to the ants, but not as strongly as the corresponding haemolymph samples. This suggests, that glucosinolates are not the only compounds involved in the chemical defence of A. rosae. However, the presence of sequestered glucosinolates is already a sufficient defence towards predators such as ants, and their effectiveness is modulated by the host plant chemistry.