Influence of induced water stress in ponderosa pine on pine sawflies

Summary Three levels of water stress were induced on pole-size ponderosa pine (Pinus ponderosa) to determine the influence of plant moisture stress on oviposition, survival, and growth of two species of pine sawfly (Neodiprion fulviceps and N. autumnalis). It was found that water stress affected oviposition and subsequent egg survival but not larval development or survival. Stress had a negative effect on early season oviposition (N. fulviceps) and a positive effect on late season oviposition (N. autumnalis). Egg hatch was different between species and years and among treatment levels. Larval development, feeding, and survival were not affected by water stress. Overall, the effect of stress was not sufficient to explain population outbreaks of sawflies. Several hypotheses are presented as possible explanations for the observed experimental results.     

Multiple effects of temperature,photoperiod and food quality on the performance of a pine sawfly

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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.     

Development of mating disruption for control of pine sawfly populations

Mating disruption of the pine sawflyNeodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae) was strongly indicated by reduced male trap catches in pine plantations permeated with the sex phermone, (2S, 3S, 7S)-diprionly acetate. The trap catch reduction was 95 to near 100% when dispensers every 10 m were used, giving a total release of about 3 mg per hectare and day. Two mg of pheromone per cotton roll dispenser maintained low catches for the whole season (about 2 months) without any renewal of disruption dispensers. Anerythro-mixture was as effective as the pure pheromone isomer. The effects of the experiments on population density and sex ratio were not possible to investigate, due to a general collapse of the population, also outside experimental plots, the year after the experiments.     

Effects of larval age and prolonged simulated acid rain on the susceptibility of European pine sawfly to virus infection

We studied the effect of simulated acid rain treatment of host trees on the susceptibility of the European pine sawfly larvae to virus, and possible differences when larvae of two different ages were infected. Older larvae were less susceptible to virus. Most larvae treated with virus 2 days after they started feeding on experimental foliage (group A) died rapidly within 10 days after the virus treatment, and survival to the end of the larval period was only 8–25%. Larvae treated with virus 1 week later (group B) were less affected by the virus and 36–49% survived. In group A the larval survival in the pH 3 treatment was higher than in other treatments; at the end of the larval period the difference was twofold. In group B there were no clear effects of acid rain on the susceptibility of larvae to virus. The study yielded the following new information: (1) the effect of prolonged acid rain treatment on reducing the efficacy of virus on young larvae was more distinct than in a previous study with shorter exposure to acid rain, and the difference was maintained to the end of larval period; (2) the susceptibility of older larvae to virus was not affected by acid rain treatments; (3) pH inside the needles did not explain the larval mortality caused by virus.     

Geographic variation in winter freezing susceptibility in the eggs of the European pine sawfly (Neodiprion sertifer)

Abstract 1 The European pine sawfly, Neodiprion sertifer (Geoffroy) (Hymenoptera, Diprionidae), frequently defoliates Scots pine (Pinus sylvestris L.) forests in northern Europe. It overwinters as an egg. It has been proposed that the high egg mortality caused by low winter temperatures limits the occurrence of outbreaks to the southern part of Fennoscandia. 2 In this study, variation in freezing avoidance by egg supercooling between four Finnish populations (originating between latitudes 60°N and 69°N) of N. sertifer was tested by differential thermal analysis. Offspring of 20 females within each population were selected for the study. The freezing avoidance of parasitized eggs was also examined. 3 The northernmost Inari population was found to be the cold hardiest, and the southernmost (Hanko) was the least hardy population. The within‐population variation between females was greatest in the population from Inari, and the next greatest in the one from Hanko. The inland populations in Eastern Finland had the smallest within‐population variation in freezing avoidance. 4 The high variation in freezing avoidance of eggs will enable N. sertifer to adapt to the predicted climate change and to spread its distribution northwards. This may also change the risk for outbreaks in this area. Parasitized eggs froze at higher temperature than healthy eggs. This observation indicates that N. sertifer may experience reduced egg parasitism in certain winter climate conditions.     

From where are insects recruited? A new model to interpret catches of attractive traps

Abstract 1 Two new concepts describing the origin of insects caught in an attractive trap are presented. 2 Male European pine sawflies Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae) were marked and released from 50, 100, 200, 400 and 800 m in the four cardinal directions around a centrally placed pheromone trap. 3 Based on linear regression of transformed data, we calculated the seasonal sampling range (r_s) as 1040 m. 4 We estimated the previously defined ‘effective sampling area’ (α) at 4.9 ha, assuming that the insects are evenly distributed around the trap and that they are attracted from a circular area around it. This is the area from which all insects originate if the trap is 100% effective within the area but captures nothing outside of it. The effective sampling area reveals nothing about the origin of the insects caught. We defined the Cumulative Proportional Catch (CPC) that gives the proportion of the trap catch that originates from an area within a distance r from the trap. At r = r_s CPC = 1, and in our study 50% of the captured insects originated up to 450 m from the trap. Thus, for the trap used in this study, a relatively large proportion of the catch originates some distance from the trap. 5 We also defined the Catch Concentration (CC), which is the ratio of the radius of the effective sampling area (r_α) to r_s. For our data, CC = 0.12, which is intermediate to high compared to the few other studies that we have extracted information from. If r_α is considerably lower than r_s, then only a small proportion of the insects caught originate from close proximity to the trap. When r_α is close to r_s, the catch adequately mirrors the population within most of its sampling range. 6 By using these two new concepts, we will better understand why monitoring traps mirror the local population in some cases but not in others. This will help in designing more reliable monitoring programmes.     

Mating duration and Frequency in a Pine Sawfly

Newly emerged females of the European pine sawfly, Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae), were placed on pine twigs in the field and their behavior was recorded. Twenty to 25% of the females attracted wild males and mated on the day of release. One-third to one-half of these females remained and oviposited, while the rest disappeared from their twigs after mating. The mating frequency peaked at noon, and on average the mating lasted for 19 ± 13 (SD) min. Eleven to 30% of the females that remained on their twigs after mating remated, occasionally up to five times. Most released females disappeared from their twigs on the first day. Disappearances included both predation and dispersal. Only a few dispersals >5 m were recorded, because the sawflies were difficult to follow during flight. By color marking, dispersal up to 20 m was recorded.