Yves Mauffette

Temperature and food quality effects on growth, consumption and post-ingestive utilization efficiencies of the forest tent caterpillar Malacosoma disstria (Lepidoptera: Lasiocampidae).

Temperature and food quality can both influence growth rates, consumption rates, utilization efficiencies and developmental time of herbivorous insects. Gravimetric analyses were conducted during two consecutive years to assess the effects of temperature and food quality on fourth instar larvae of the forest tent caterpillar Malacosoma disstria Hübner. Larvae were reared in the laboratory at three different temperatures (18, 24 and 30 degrees C) and on two types of diet; leaves of sugar maple trees Acer saccharum Marsh. located at the forest edge (sun-exposed leaves) or within the forest interior (shade-exposed leaves). In general, larvae reared at 18 degrees C had lower growth rates and lower consumption rates than larvae reared at the warmer temperatures (24 and 30 degrees C). Moreover, the duration of the instar decreased significantly with increasing temperatures. Type of diet also affected the growth rates and amount of food ingested by larvae but did not affect the duration of the instar. Larvae fed sun-exposed leaves consumed more food and gained higher biomasses. Values of approximate digestibility and efficiency of conversion of ingested food were also higher when larvae were fed sun-exposed leaves. Higher growth rates with increasing temperatures were primarily the result of the shorter stadium duration. The higher growth rates of larvae fed sun-exposed leaves were possibly the result of stimulatory feeding and consequently greater food intake and also a more efficient use of food ingested. This study suggests that the performance of M. disstria caterpillars could be enhanced by warmer temperatures and higher leaf quality.

Seasonal variation in leaf chemistry of the coast live oak Quercus agrifolia and implications for the California oak moth Phryganidia californica

SummaryThe perennial foliage of the California coast live oak (Quercus agrifolia Nee) permits herbivores to feed on this oak species throughout the year. Patterns of herbivory for a two-year period on Q. agrifolia were observed in relation to seasonal and age-related changes in the nutritional and defensive characteristics of leaves. Nitrogen and phosphorus contents were higher in new leaves compared to mature foliage. Structural compounds (e.g., cellulose) in leaves rapidly increased with age. Concentrations of tatal phenolics (Folin-Denis) and astringency were higher in new foliage, and concentrations of condensed tannins gradually increased as the leaves matured. Peaks of herbivore damage were observed in June and in September–October, and were caused by outbreaks of the California oak moth (Phryganidia californica). P. californica, a bivoltine oak specialist, exhibited feeding preferences in June for old leaves over emerging leaves, and showed no preferences for leaf classes in September. These results suggest that P. californica is adapted to survive on nutritionally poor foliage and to circumvent “quantitative defenses” such as condensed tannins.

Effects of stand age and litter removal on the regeneration of Populus tremuloides

The objective of this study was to demonstrate the regeneration by root suckering of Populus tremuloides (quak- ing aspen) along a successional sere at Lake Duparquet in NW Quebec with six sites of different ages - 46, 74, 120, 143, 167 and 230 yr since last fire. In 1990, in each of the sites, one 20 m x 20 m plot was cut. In each plot, 4-m2 plots were selected, both control and with litter removed. The number of suckers and their height were estimated for each plot in 1991, 1992 and 1993. Results showed that sucker production was not related to the number of P. tremuloides before the clearcut, but it was related to litter whereby increasing cover lowered the produc- tion. The number of suckers produced in the control plots did not show any significant difference along the successional sere for any of the three years. Scarified plots had more suckers than control plots, and this increase was more pro- nounced and significantly different for the younger stage. Regression analysis for the 1991 and 1992 data showed that sucker number in scarified plots decreased with increasing seral stage age. Mortality, after three growing seasons, was about 60 % for all plots and was not affected by seral stage and treatment. We suggest that removal of litter in scarified plots exposed the roots to higher temperatures and caused wounds, both of which may have stimulated the production of suckers in young seral stages.

Egg cannibalism by Coleomegilla maculata lengi neonates: preference even in the presence of essential prey

Abstract 1. Egg cannibalism among coccinellids has been reported widely, however reasons why this type of behaviour is observed so frequently have been neglected. This experiment was undertaken to clarify whether cannibalistic behaviour is advantageous to Coleomegilla maculata lengi Thimberlake neonates and to understand the reasons for high levels of egg cannibalism.

Variation in the Susceptibility of the Forest Tent Caterpillar (Lepidoptera: Lasiocampidae) to Bacillus thuringiensis variety kurstaki HD-1: Effect of the Host Plant

Abstract Host-mediated effect on the efficacy of Bacillus thuringiensis Berliner against larvae of the forest tent caterpillar, Malacosoma disstria Hübner, was investigated under controlled conditions. Host plants used in this study were quaking aspen, Populus tremuloides Michx., a preferred host, and sugar maple, Acer saccharum Marsh., a secondary host. Larvae were reared in the laboratory on leaves of these hosts, and upon reaching the third, fourth, and fifth instar, they were fed leaves treated with one of a range of concentrations of B. thuringiensis variety kurstaki HD-1 suspensions. Larvae were tested on the host on which they were feeding before the 4-d bioassays. The estimated LC50s were 100-fold greater on quaking aspen than on sugar maple. Also, there was a decrease in efficacy over the whole ranges of concentrations with larval age on both hosts. LC50s varied approximately two-fold between third and fifth instar. These results indicate that host-mediated effects on B. thuringiensis efficacy warrant more interest. In particular, they strongly indicate that the host plant modifies the interaction between B. thuringiensis and a target insect, and offer the opportunity to investigate the mechanism(s) that may be involved in the enhancement of B. thuringiensis toxicity.

Forest edge effects on the biological performance of the forest tent caterpillar (Lepidoptera: Lasiocampidae) in sugar maple stands

Fragmentation of forests has considerably increased the amount of edge habitats. This edge effect could have a direct influence on the dynamics of forest insects by altering the nutritional quality of foliage. In this study, we examined from 1994 to 1997 the effects of foliage from edge trees and interior trees on biological performance of the forest tent caterpillar (Malacosoma disstria Hbn.). Each year, ten mature sugar maple trees (Acer saccharum Marsh.) were selected at the forest edge and in the forest interior. Leaves were collected on branches located at 3-6 m above ground at intervals of one or two days. These leaves were immediately brought back to the laboratory for rearing of insects in Petri dishes (8 larvae/Petri dish) and for chemical analyses. Total nitrogen levels were significantly higher in leaves from edge trees as were nonsignificantly higher levels of soluble sugars and total phenolics and lower water content. Generally, performance of the forest tent caterpillar, except for larval and pupal developmental time, varied between the forest edge and the forest interior habitats. Pupal weight, egg production and pupal survivorship were greater for larvae reared on leaves from edge trees. Stepwise multiple regression analyses revealed that total nitrogen, soluble sugars and water content were closely associated with the forest tent caterpillar’s performance. These results suggest that forest edge effects, in terms of leaf nutritional quality, could have important implications for forest tent caterpillar populations in sugar maple stands.

Early survival, growth and foliar nutrients in native Ecuadorian trees planted on degraded volcanic soil

Abstract There is a growing interest for the use of native tree species for tropical plantations. However, their silvicultural requirements are generally unknown. Fifteen native tree species, seven early- and eight late-successional species, were planted on an abandoned pasture located on a degraded Hydrandept volcanic soil in Amazonian Ecuador. The objective was to study their survival, growth and foliar nutrient levels in relation to their successional status. The experiment consisted of a random block design with three replicates, each one subdivided in 15 plots with one species per plot. Half of the plots (split-plot) were fertilized with a slow-release fertilizer (16–10–10). Height and basal diameter were measured every 6 months, for 2.5 yr. Foliar nutrients were estimated from samples taken once, at 2 yr. Soil analyses indicated that the soil was poorer and denser in the plantation compared to the adjacent forest, with a large within-site heterogeneity. Early-successional species had a significantly higher survival, growth and foliar nutrient concentrations than the late-successional species. Fertilizer addition did not affect survival or growth. Among late-successional species, Caryodendron orinocense had by far the highest survival. Four early-successional species had a high survival and good growth, with low coefficients of variation in spite of soil heterogeneity: Erythrina poeppigiana, Pollalesta discolor, Heliocarpus americanus and Inga densiflora. The better growth performances of early-successional species could be related to the relatively early stage of plantation. Our results suggest that these species could be used advantageously to rapidly create a tree cover on a degraded soil. This study highlights the importance of investigating the appropriate land use of degraded volcanic soils in the humid tropics. It also underscores the high potential of some native tree species, and recommends that more studies be done on their silviculture, as well as on the selection of those best adapted to degraded volcanic soils.

Developmental, gustatory, and behavioral responses of leafroller larvae, Choristoneura rosaceana, to tannic acid and glucose

Soluble sugars are essential nutrients generally perceived as phagostimulants to most insects studied. However, tannins are known as digestibility reducers, hence deleterious to caterpillar development, and as deterrents as well. Previous work demonstrated that larvae of the polyphagous oblique-banded leafroller, Choristoneura rosaceana, performed better when reared on a control + 0.5% tannic acid diet than on the standard control diet and that larvae reared on a control + 5% glucose diet had slower development and reduced survival. This study was designed to elucidate the behavioral and neurophysiological components of the larval responses to tannic acid and glucose. C. rosaceana larvae were reared individually from the first to the sixth instar on one of four different artificial diets: (1) control; (2) control + 5% glucose; (3) control + 0.5% tannic acid; (4) control + 5% glucose + 0.5% tannic acid. After 14 days, larvae reared on the control + 5% glucose diet had not developed past the fourth instar, whereas a considerable proportion of larvae reared on the control + 0.5% tannic acid diet had already attained the pupal stage. Insects reared on the control or the control + 5% glucose + 0.5% tannic acid diet had intermediate development, with most larvae in the fifth instar. In addition, once the mid-sixth instar was reached, the feeding preferences to 25 and 300 mM glucose, 25 mM tannic acid, and 25 mM glucose + 25 mM tannic acid over water were assessed in two-choice tests. Feeding affected preference. Control-reared insects preferred feeding on treatments containing glucose and were not deterred by tannic acid. However, larvae that had been exposed to tannic acid during their development were deterred by tannic acid and their glucose discrimination was impaired. The sensitivity to glucose was also examined from neurophysiological recordings by stimulating the sugar-sensitive cell (cell 1) on the lateral styloconic sensillum of the maxillary galea with increasing concentrations of glucose (1, 10, 25, 50, 100, 200, 300, and 500 mM). We also determined whether tannic acid was phagostimulatory, since insects develop relatively quickly on a diet containing this compound, by testing 1 mM tannic acid, 1 mM tannic acid + 300 mM glucose, and 300 mM glucose on the lateral styloconic sensilla. The traces indicated that 1 mM tannic acid was not detected by any of the four chemosensory cells in these sensilla. The combination of tannic acid and glucose produced no spikes from the sugar-sensitive cell, whereas a prominent spike activity resulted with 300 mM glucose. We concluded that, although C. rosaceana larvae develop faster on a tannic acid diet, this compound is not a phagostimulant. The converse is true for glucose; i.e., it stimulates the sugar-sensitive cell in the lateral styloconica in a concentration-dependent fashion. Previous dietary experience changes the sensory and behavioral responses of C. rosaceana to glucose. Our findings imply that not all compounds that are phagostimulatory are necessarily beneficial to an insects fitness. Therefore, developmental studies should be interpreted in conjunction with behavioral and physiological data.

Elevated C02 Does not Provide Protection against Ozone Considering the Activity of Several Antioxidant Enzymes in the Leaves of Sugar Maple

Summary Seedlings of sugar maple ( Acer saccharum Marsch.) were exposed for 46 days to 700 ppm of C0 2 , 200 ppb of ozone, and 700 ppm of C0 2 + 200 ppb of ozone. A significant increase in the activity of H 2 0 2 scavenging enzymes, i.e. ascorbate peroxidase [EC 1.11.1.11] and catalase [EC 1.11.1.6], was measured due to the action of 0 3 . This increase was rather negatively affected by elevated C0 2 . A tendency of decreased activity of glutathione reductase [EC 1.6.4.2] and superoxide dismutase [EC 1.15.1.1] due to the action of 0 3 was detected. Elevated C0 2 does not provide enhanced tolerance to oxidative stress in the seedlings of sugar maple. Changes in the activity of antioxidant enzymes were more pronounced in the young leaves (developed during the experiment) than in the old leaves (developed before starting the experiment). Stimulation of chloroplastic FeSOD by elevated C0 2 was observed, indicating oxidative stress in chloroplasts evoked by elevated C0 2 level. This effect did not result in enhanced protection against the detrimental effect of ozone, most probably due to compartmentation of C0 2 and 0 3 effects within the cell.

Laboratory-Based Toxicological Assessments of New Insecticides on Mortality and Fecundity of Neoseiulus fallacis (Acari: Phytoseiidae)

ABSTRACT Neoseiulus fallacis (Garman) is one of the most abundant predatory phytoseid in deciduous fruit orchards under an integrated pest management (IPM) regimen in eastern North America. Laboratory studies using N. fallacis, and the ‘modified excised leaf disc method’ identified four insecticides out of six, that would require second-tier field studies before inclusion in an IPM program for deciduous orchards. The overall egg mortality caused by flubendiamide, chlorantraniliprole, chlothianidin, novaluron, Spinetoram, and spirotetramat ranked from 0 to 37.6%. Larval mortality caused by spirotetramat, spinetoram, novaluron, and chlothianidin ranged from 100 to 78.3%, respectively. Chlorantraniliprole and flubendiamide were virtually nontoxic to larvae. Spinetoram, chlothianidin, and spirotetramat caused 100, 61.4, and 40.2% mortality of adult N. fallacis, respectively. Spirotetramat and chlothianidin significantly reduced fecundity, whereas novaluron, flubendiamide, and chlorantraniliprole had no such adverse effect for the duration of the study (168 h). Chlorantraniliprole and flubendiamide do not require further second tier field studies and may be included in deciduous orchard IPM programs. Spirotetramat is toxic to several growth stages but it has a very short residual activity, and along with novaluron, which is toxic only to larvae, should be evaluated in second-tier field studies. Clothianidin and spinetoram should be evaluated in second-tier field studies only if alternatives are unavailable.