Effect of neem seed extract on feeding,growth, survival,and reproduction of Diaprepes abbreviatus (Coleoptera: Curculionidae)

A commercially available neem seed extract, Neemix 4.5, containing 4.5% azadirachtin (AZA), was assessed for biological activity against the root weevil Diaprepes abbreviatus (L.), an important exotic insect pest of Florida citrus. Laboratory bioassays against neonatal and 3-wk-old larvae fed sliced carrot treated with Neemix produced dose-dependent larval mortality and reduced fresh weights among survivors of treatments. The weight response was greater than the mortality response for both larval age groups. Neonates treated with 45 mg/liter AZA weighed 60% less than those in the control after 4 wk. Three-week-old larvae treated with 45 mg/ liter AZA weighed 30% less than those in the control after 5 wk. When neonates were exposed to insect diet incorporated with Neemix, reductions in larval survival and weight were observed at concentrations as low as 4.8 mg/liter AZA after 6 wk. Larval growth was inhibited by >97% with 42.9 mg/liter AZA in the diet. A soil drench containing 30 mg/liter AZA reduced the survival and weight gain of neonates added to potted citrus and provided protection to the roots in a greenhouse experiment. A concentration of 90 mg/liter AZA was required to provide protection of citrus roots against 4-wk-old larvae. Reproductive effects were observed when adult weevils were fed foliage treated with Neemix. The numbers of larvae hatching per egg mass were reduced by 27% and 68% at 30 and 90 mg/liter AZA, respectively. These results suggest that Neemix should be further evaluated for use in integrated pest management (IPM) programs of citrus.     

Sublethal effects of chronic exposure to tebufenozide on the development, survival, and reproduction of the tufted apple bud moth (Lepidoptera: Tortricidae)

The lethal and sublethal effects of tebufenozide on the survival, development, and reproduction of a field strain of tufted apple bud moth, Platynota idaeusalis (Walker) (Lepidoptera: Tortricidae), were assessed by feeding first and third instars tebufenozide-treated diet until pupation. Larval mortality was 27.4 and 44.7% at 0.1 and 0.2 ppm for first instars and 21.9 and 57.8% at 0.2 and 0.4 ppm for third instars, respectively. Treated larvae exhibited higher pupal mortalities, lower pupal weights, and generally more deformed adults than untreated larvae. Larval development was not affected by tebufenozide when neonates were exposed, but development was accelerated slightly at 0.4 ppm for both males and females when third instars were exposed. All treatments produced sex ratios biased toward males. When paired with either treated or untreated males, females resulting from neonates treated at 0.2 ppm and from third instars treated at both 0.2 and 0.4 ppm laid from 37 to 65% fewer eggs. A reduction in fertility was only found when third instars were treated at the higher 0.4 ppm rate. These results suggest that tebufenozide can exhibit a significant effect on the population dynamics of the tufted apple bud moth.     

Positive and negative impacts of insect frass quality on soil nitrogen availability and plant growth

Frass deposition to soil is an important pathway by which herbivorous insects impact decomposition and soil nutrient availability. However, little is known about how frass quality influences ecosystem properties. Here, we examined the effects of frass quality on the decomposition process, soil nitrogen (N) availability, and plant growth, using frass of Mamestra brassicae (L.) that fed on fertilized or unfertilized Brassica rapa L. var. perviridis Bailey. The frass quality was largely dependent on the host plant quality. Frass excreted by larvae that fed on the fertilized plants had higher N than that of larvae that fed on the unfertilized plants. The decomposition rate of the frass did not differ between N-rich and N-poor frass, except during the early decomposition period. The inorganic N concentration decreased during decomposition in both frass types. However, difference in the initial inorganic N concentration led to different consequences regarding soil N availability. Furthermore, addition of frass to the soil differently influenced the growth of B. rapa plants depending on the frass quality: plant biomass was increased by N-rich frass addition but decreased by N-poor frass addition, compared to the biomass without frass addition. These results indicate that frass quality is an important factor in determining the impact of herbivorous insects on nutrient dynamics, and that frass positively or negatively influences soil N availability and plant growth, depending on its quality.     

Effects of lufenuron on Lobesia botrana (Lepidoptera: Tortricidae) egg, larval, and adult stages

The effect of the chitin synthesis inhibitor lufenuron was evaluated against different developmental stages of Lobesia botrana Den. & Schiff. (Lepidoptera: Tortricidae). Lufenuron fed to adults at 10 ppm reduced their fecundity and fertility, but it did not affect adult longevity. High activity was observed against L. botrana eggs with greater effect on 1-d-old eggs than on the other age classes and on eggs treated by direct contact rather than those laid on a previously treated surface. Eggs laid by treated adults showed the same effects during development as eggs treated by contact or those laid on a treated surface. Larvae that emerged from treated eggs could not perforate grape berries. Administered into the diet, lufenuron had a larvicidal effect, resulting in similar LC50 values for different instars: 0.07 ppm for first instars, 0.08 ppm for third instars, and 0.11 ppm for fifth instars. None of the larvae treated with sublethal concentrations throughout their life emerged as adults at the highest concentration (0.08 ppm), and only 70% emerged at the lowest concentration (0.0025 ppm).     

Effects of food quality,particularly nitrogen concentrations,of Eucalyptus blakelyi foliage on the growth of Paropsis atomaria larvae (Coleoptera: Chrysomelidae)

Five groups of E. blakelyi seedlings were differentially fertilized to obtain a range of N concentrations from 0.8–3.0% dry wt in the foliage. Groups of P. atomaria larvae were reared from eclosion to the prepupal stage on these seedlings. The effects on larval growth and development caused by foliar concentrations of N, moisture content, and tannins and leaf toughness were measured. Pupal dry weight and development time of P. atomaria did not differ between those reared on foliage with N levels of 1.7–3.0% but there was a significant decrease in pupal weight and increase in development time for individuals fed foliage with N below this level. Larvae fed foliage with an average of 0.8% N died before reaching instar III. Total dry matter consumption increased with a decrease in N concentration. Larval nitrogen utilization efficiency increased as foliar N level decreased until N reached a level somewhere between 1.7%–1.2% below which it decreased. There appeared to be an N concentration threshold above which P. atomaria larvae received adequate N by regulating consumption and nitrogen utilization efficiency but below which they could no longer accumulate enough N by compensation to maintain an optimum growth rate and development time. Effects of food quality variables on relative growth and consumption rates are presented and discussed.     

Previous herbivore attack of red alder may improve food quality for fall webworm larvae

Summary Three hypotheses of insect-plant interactions were tested by rearing fall webworm larvae in the laboratory on foliage from red alder trees with different histories of western tent caterpillar herbivory. Fall webworm larvae raised on foliage from trees which had been attacked previously for two summers by moderate densities of western tent caterpillars grew faster and attained heavier pupal weights than did those fed foliage from unattacked trees. This contradicts the hypothesis that moderate levels of previous herbivory induces the production of plant defensive chemicals in red alders. Growth of webworms, when fed foliage from unattacked trees adjacent to alders that were attacked by fall webworm larvae, was the same as when fed foliage from trees isolated by distance from attacked trees. This contradicts the hypothesis that attacked trees stimulate the production of defensive chemicals in neigh-boring trees. Young and mature alder foliage was equally good for fall webworm growth and survival, and foliage from trees heavily attacked by both fall webworm and western tent caterpillars for three years produced slow growth rates and small pupal sizes. This supports the hypothesis that continued heavy insect attack can cause the deterioration of the food quality of attacked trees.     

Recycling of nitrogen in herbivore feces: plant recovery,herbivore assimilation,soil retention,and leaching losses

Herbivores directly and indirectly affect ecosystem functioning in forests. Feces deposition is a direct effect that supplies ephemeral N pulses to soils. Herbivore-mediated changes in plant N allocation and uptake are indirect effects that can also influence soil N availability. These effects may interact if defoliation influences the ability of plants to recover fecal N, and this may affect subsequent generations of herbivores. We added ¹⁵N-enriched insect feces (frass) to a series of replicated red oak, Quercus rubra, mesocosms that had been damaged experimentally and then followed the frass N over the course of 2 years. In the first season, some frass N was mineralized in the soil and leached in organic form from the mesocosms within 1 week of deposition. Within 1 month, frass N had been acquired by the oaks and enriched the foliage; late-season herbivores assimilated the frass N within the same growing season. In the second season, herbivore damage from the previous year lowered total leaf N contents and ¹⁵N recovered in the foliage. A subsequent cohort of early-season herbivores fed on this foliage consequently derived less of their N from the previous year’s frass, and feral leaf rollers colonized fewer of these saplings. The 0- to 5-cm soil fraction was the largest N sink measured, and 42% of the frass N was recovered in the soil. The results demonstrate that: (1) some frass N can be recycled rapidly into foliage and assimilated by successive cohorts of herbivore within the same season; (2) damage can affect N allocation in the following year’s foliage, influencing N availability to and host selection by herbivores; and (3) leaching losses occur soon after deposition but are buffered by soil pools, which are the largest sinks for frass N.     

Evaluation of synergistic interactions between the Colorado potato beetle (Coleoptera: Chrysomelidae) pathogen Beauveria bassiana and the insecticides, imidacloprid, and cyromazine

Laboratory studies investigated the interaction between the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin and sublethal doses of the insecticides imidacloprid and cyromazine when applied to larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say). When second instars were fed potato leaf discs treated with sublethal doses of imidacloprid and a range of doses of B. bassiana, a synergistic action was demonstrated. Similar results were observed when larvae were sprayed directly with B. bassiana conidia and immediately fed leaf discs treated with imidacloprid. No synergistic interaction was detected when larvae were fed leaf discs treated with sublethal doses ofimidacloprid 24 h after application of B. bassiana conidia to larvae. However, a synergistic interaction was detected when larvae were fed leaf discs treated with imidacloprid and sprayed with B. bassiana conidia 24 h later. Although sublethal doses of both imidacloprid and the triazine insect growth regulator (IGR) cyromazine prolonged the duration of the second instar, only imidacloprid interacted with B. bassiana to produce a synergistic response in larval mortality. In leaf consumption studies, the highest dose of B. bassiana tested promoted feeding in inoculated second instars. Feeding was inhibited when larvae were fed foliage treated with sublethal doses of imidacloprid and significantly reduced when fed foliage treated with a sublethal dose of cyromazine. Starvation of larvae for 24 h immediately after B. bassiana treatment produced a similar result to the combined treatment of B. bassiana and imidacloprid and increased the level of mycosis when compared with B. bassiana controls. Imidacloprid treatment affected neither the rate of germination of B. bassiana conidia on the insect cuticle nor the rate at which conidia were removed from the integument after application. The statistical analysis used to detect synergism and the possible role of starvation-induced stress factors underlying the observed synergistic interactions are discussed.     

Larval feeding behaviour affects the impact of staminate flower production on the suitability of balsam fir trees for spruce budworm

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing indicated that the feeding behaviour of the larvae, which is affected by the insect population density, significantly influenced the impact of balsam fir, Abies balsamea, staminate flowering on spruce budworm biology. At low budworm density, the production of pollen in the midcrown of host trees reduced the insect development time by 5 days without affecting pupal weight, fecundity and survival. However, at high budworm density, the small amount of current-year foliage produced by flowering branches forced old larvae (sixth instar) either to feed on 1-year-old foliage (backfeeding) or to move from the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fed on old foliage, they exhibited reduced pupal weight and fecundity without losing the advange in development time that they obtained from feeding on pollen during their early stages of development. On the other hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in development time that was gained from feeding on pollen. Results from this study indicated that the production of staminate flowers by balsam fir trees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.     

Advantages of a mixed diet: feeding on several foliar age classes increases the performance of a specialist insect herbivore

Two field studies were carried out to determine the influence of Abies balsamea foliage age on the preference and performance of larvae of Neodiprion abietis, a specialist Diprionid sawfly. Preference was determined by examining N. abietis defoliation on all age classes of foliage. Performance was estimated using larval survival, cocoon weights and the percentage of adults that were females. Neodiprion abietis preference for, and performance on, current-year foliage was very low, peaked on 2 or 3-year-old foliage, and declined on older foliage. Thus, sawfly feeding preference was adaptive. However, survival and cocoon weight were highest when sawflies were allowed to feed on all age classes of foliage, demonstrating that an insect specialist may perform better when feeding on several age classes of foliage from a single host plant species. These results indicate that either different larval instars have different nutritional requirements, or that food mixing provides the best diet, permitting the herbivore to obtain needed nutrients while avoiding ingestion of toxic doses of secondary metabolites. In addition, our results suggest that limited availability of varied foliage has more negative consequences for N. abietis females than for males, as the percentage of survivors that were females decreased when juvenile mortality was high. Our results emphasize the importance of considering non-linear changes in foliar quality as leaves age on herbivore preference and performance, and demonstrate how a herbivore can use this variability to maximize its fitness.     

Japanese oak silkmoth feeding preference for and performance on upper-crown and lower-crown leaves

We quantified differences in leaf traits between upper and lower crowns of a deciduous oak, Quercus acutissima, and examined feeding preference, consumption and performance of the Japanese oak silkmoth, Antheraea yamamai, for those leaves. Upper‐crown leaves had significantly smaller area, larger dry mass per area, greater thickness, lower water content, higher nitrogen content and a higher N/C ratio than lower‐crown leaves. When simultaneously offered upper‐crown and lower‐crown leaves, moth larvae consumed a significantly larger amount of the former. However, when fed with either upper‐crown or lower‐crown leaves (no choice), they consumed a significantly larger amount of the latter. Female larvae reared on upper‐crown leaves had a significantly smaller fresh weight, but attained a significantly larger pupal fresh and dry weight, with a significantly higher relative growth rate than those on lower‐crown leaves. Although, like female larvae, male larvae had a significantly smaller fresh weight when reared on upper‐crown leaves, they had a significantly larger value only for pupal dry weight. These results suggest that: (i) larvae ingest a greater amount of lower‐crown leaves to compensate for the lower nitrogen content of the foliage, resulting in having an excess of water because of the higher water content of the foliage; (ii) feeding preference for upper‐crown leaves accords with better performance (with respect to dry pupal weight and relative growth rate) on the foliage; (iii) better performance is explained by a higher nitrogen content and N/C ratio of the upper‐crown foliage; and (iv) the effects of leaf quality on performance differ between sexes.     

Spruce budworm growth,development and food utilization on young and old balsam fir trees

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing, gravimetric analyses, a transfer experiment, and foliage chemical analyses at six dates during the period of budworm feeding activity indicated that the age of balsam fir, Abies balsamea, trees (70-year-old mature trees or 30-year-old juvenile trees) affected tree suitability for the spruce budworm via the chemical profile of the foliage. Insects reared on old trees had greater survival and pupal weight, shorter development times, and caused more defoliation than those reared on young trees. Young trees were more suitable for the development of young larvae (instars 2–5), while old trees were more suitable for the development of older, sixth-instar larvae. These results were confirmed by the laboratory transfer experiment. Young larvae fed foliage from young trees had higher relative growth rates (RGR), digestibility (AD), and efficiency of conversion of ingested foliage (ECI) than those fed foliage from old trees. These differences appeared to be related to the high N:tannins ratio, and the high contents of P present in young trees during the development of the young larvae. Old larvae fed foliage from old trees had higher relative growth rates, relative consumption rates (RCR), and digestibility of the foliage than those fed foliage from young trees. The high digestibility of the foliage of old trees was compensated for by a lower efficiency of conversion of digested food (ECD), which in turn resulted in no significant effect of tree age on the efficiency of conversion of ingested foliage by old larvae. The low relative consumption rate of old larvae fed foliage from young trees appeared to be related to the low N:tannins ratio, and the high contents of bornyl acetate, terpinolene, and °-3-carene present in young trees during the budworm sixth instar. Variations in these compounds in relation to tree age may serve as mechanisms of balsam fir resistance to spruce budworm by reducing the feeding rate of sixth instar larvae.     

Effects of field applied residues and length of exposure to tebufenozide on the obliquebanded leafroller (Lepidoptera: Tortricidae)

Studies were conducted with the obliquebanded leafroller, Choristoneura rosaceana (Harris), and tebufenozide to determine the influence of various factors on the efficacy of this insecticide under field conditions. Larvae were exposed to apple foliage collected from commercial orchards at different intervals after insecticide applications. Mortality of neonates on actively growing (terminal) and mature (spur) foliage 10 d after an airblast sprayer application of tebufenozide was 0 and 35-74%, respectively. Feeding by larvae was also assessed on collected foliage. There was significantly less feeding on tebufenozide-treated foliage than chlorpyrifos- and nontreated foliage (P < 0.05). In the second study, to determine the efficacy of tebufenozide in the absence of larval movement to terminals with sublethal residues, terminal foliage with obliquebanded leafroller larvae was collected from two commercial orchards 24 h after an airblast sprayer application of tebufenozide. After larvae were confined on this terminal foliage in the laboratory for 10 d, mortality was >90%. In the third study, to examine the effects of obliquebanded leafroller movement to foliage with sublethal residues, we designed a laboratory bioassay in which larvae were exposed to foliage treated with tebufenozide and transferred to untreated foliage after various exposure intervals. The higher the concentration of tebufenozide, the less exposure time was necessary to cause high levels of mortality of neonates. The terminal feeding behavior ofobliquebanded leafroller larvae, low residues on terminal foliage before the end of the typical 2-wk spray interval, and the length of exposure necessary for high levels of mortality may decrease the effectiveness of tebufenozide for obliquebanded leafroller control.     

Selection, egg viability, and fecundity of the sugarcane borer (Lepidoptera: Crambidae) with tebufenozide.

Two separate attempts to select the sugarcane borer, Diatraea saccharalis (F.), for resistance to tebufenozide were unsuccessful. Both selected colonies were lost after the fourth generation due to a lack of oviposition. Differences were not detected in fecundity or percent egg viability for 5-d-old third instars exposed to concentrations (EC5, EC15, and EC30) of tebufenozide for 7 d. Decreases (P < or = 0.01) in mean female pupal weights were detected in larvae exposed to EC15 and EC30 concentrations. An ovicidal impact using serial dilutions of tebufenozide (10, 100, and 200 ppm) also was detected. Percent viability was reduced from 98% for untreated eggs to 61% for eggs dipped in 10 ppm and below 6% for eggs dipped in > or = 100 ppm. Eggs treated with 200 ppm did not hatch. Though some embryonic development was observed on eggs treated with the high concentrations (100 and 200 ppm), sclerotization of head capsule was not apparent. The ovicidal property of tebufenozide may enhance its effectiveness in controlling populations of the D. saccharalis on an area-wide basis. Fecundity and egg viability were affected in later generations of selection; however, separate studies assessing individuals that were exposed to sublethal concentration (EC5, EC15, and EC30) of tebufenozide as third instars for 7 d in one generation did not detect differences.     

Phylloplane bacteria increase the negative impact of food limitation on insect fitness

1. When populations of herbivorous insects increase in density, they can alter the quantity or quality of their food. The impacts of diet‐related stressors on insect fitness have been investigated singly, but not simultaneously. 2. Foliage quantity and quality of red alder, Alnus rubra, were manipulated together with the presence of non‐entomopathogenic phylloplane bacteria to investigate their impacts, singly and in combination, on survival, pupal mass, growth rate, fecundity and egg quality of a cyclic forest insect, the western tent caterpillar, Malacosoma californicum pluviale. 3. Food limitation (half food) had strong negative impacts on all life‐history traits. When the larvae were fed continuously, however, neither ingesting phylloplane bacteria nor eating leaves from damaged branches (induced foliage) affected survival. In the half‐food treatment, ingesting bacteria further increased mortality, while feeding on induced foliage improved survival. 4. Growth rate and pupal mass of both sexes were reduced for larvae with food limitation compared with continuously fed insects and this was exacerbated when the larvae also ate bacteria‐treated leaves. A combination of bacteria and induced foliage also reduced larval growth rate by 5% in the full‐food treatment. 5. Fecundity (eggs per egg mass) was 2.7 times greater in full‐food than in food‐limited treatments but neither phylloplane bacteria nor plant induction had an effect. Insects fed induced foliage produced smaller eggs. Overall, there was no evidence of a three‐way interaction between the three stressors, although there were negative synergistic effects, primarily between food limitation and the ingestion of phylloplane bacteria.     

Additive interaction of <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> Nucleopolyhedrovirus and Azadirachtin

Mortality of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) was higher in the combined treatment of Nucleopolyhedrovirus (NPV) and Azadirachtin (AZA) and mortality was increased when AZA concentration was doubled. Larval mortality decreased as the age of the larvae increased in all the treatments. The time for 100% kill of third instar larvae was significantly reduced to 72 h when AZA (0.1 ppm) was combined with NPV (10³ PIB/ml) when compared to 168 and 120 h for the same dose NPV and AZA individual treatments, respectively. The average leaf disc consumption, consumption index (CI), relative growth rate (RGR), the efficiency of conversion of ingested (ECI) and digested (ECD) food values were drastically reduced in the combined treatment of NPV and AZA than in the individual treatments. Larval as well as pupal durations were significantly extended and the adult longevity and fecundity were significantly reduced in the combined treatment of NPV and AZA. Weight of 14 day old control larvae was 420 mg and it was reduced to 299 and 248 mg after NPV (5 × 10² PIB/ml) and AZA (0.025 ppm) treatments, respectively. The larval weight was drastically decreased to 99 mg after the combined treatment at the same dose. The additive interaction between both the treatments, AZA and NPV, was found to be in a dose dependent manner and were highly compatible in disrupting the survival, feeding and biology of H. armigera.     

Susceptibility of Diatraea saccharalis (Lepidoptera: Crambidae) to tebufenozide.

Dosage-mortality baselines were determined for first and newly molted third instars of the sugarcane borer, Diatraea saccharalis (F.), with tebufenozide incorporated into an artificial diet. Using death as an endpoint for these assays, LC50 and LC90 values were estimated to be 0.17 and 0.41 ppm for the first and 0.87 and 3.67 ppm for third instars, respectively. Developmental effects also were observed and were defined to include mortality as well as physical impairment and retarded or prolonged development with absence of feeding. Concentrations causing developmental effects in treated larvae (EC50 and EC90) were 5.8- and 3.8-fold lower than the LC50 and LC90, respectively. The critical time of exposure to tebufenozide was determined for developmentally synchronous third instars to be less than 12 h postecdysis. Mortality through adult emergence significantly decreased from 92% (treatment at 0 h postecdysis) to 30% (treatment at 12 h postecdysis), when exposed to tebufenozide at the EC50. For surviving larvae, length of development time until pupation was significantly increased and female pupal weight significantly decreased when larvae were treated at 0 h postecdysis into the third instar. In addition, to modifying the traditional ways of assessing mortality 0-3 d postapplication, this study points out the value of using other approaches to pesticide assessment, especially where insect growth regulators are involved.     

Protection of potato crop against Phthorimaea operculella (Zeller) infestation using frass extract of two noctuid insect pests under laboratory and storage simulation conditions

The oviposition deterrent effect of water extract of Spodoptera littoralis and Agrotis ipsilon larval frass on Phthorimaea operculella adult females was studied using two types of larval food “Natural host and Semi-artificial diet” under laboratory and storage simulation (semi-field) conditions. Extracted frass of fed larvae on semi-artificial diet showed complete oviposition deterrent effect at treatments with 4th, 5th and 6th instars of S. littoralis, also at treatments with 1st–3rd and 6th instars of A. ipsilon, while the same effect was observed when the larvae fed on castor oil leaves as a natural host only at treatment with frass extract of A. ipsilon 6th instar larvae. Presence of low amounts of phenols and flavonoids in water extract of A. ipsilon larval frass resulted in relatively more effect as oviposition deterrent to fertile adult females on treated oviposition sites, while the opposite effect was obtained in S. littoralis larval frass experiments. At semi-field experiments, the percentage reduction of laid eggs reached 100% after two?days at treatments with frass extracts of 4th and 5th S. littoralis larval instars and A. ipsilon 6th instar larvae fed on semi-artificial diet and/or castor oil leaves. Percentage reduction of laid eggs for untreated sacks reached 93.24 and 48.95% after 2 and 30?days, respectively, when placed between treated sacks, in comparison with the mean number of laid eggs for isolated control.     

Effect of dietary nitrogen on gypsy moth larval nutritional indices, development and lipid content

Nutritional indices, development rates, percent dry weights and total lipids were determined in gypsy moth larvae (Lymantria dispar L.) reared on a high wheat germ (HWG) diet or diets prepared from lyophilized, ball-milled oak or pine foliage as the only source of dietary nitrogen (N). With regard to both total and proteinaceous N content, HWG diet>oak diet>pine diet. All nutritional indices measured were significantly lower in second instars fed pine diet vs. oak diet. Protein supplementation of pine diet with either casein or ovalbumin to bring total N up to the level present in oak diet resulted in small increased in approximate digestibility (AD) and effciency of conversion of ingested food (ECI), but relative growth rate (RGR) remained unaffected. The low RGR of larvae fed pine diet (unsupplemented or protein supplemented), as compared to those fed HWG or oak diet, was accompanied by significantly lower larval percent dry weight and percent total lipid. In contrast, RGR, larval percent dry weight and total lipid values were comparable in second instars fed HWG or oak diet. Insects reared from the first through the final instar on oak diet exhibited lower pupal weights compared to those reared on HWG. Casein addition to oak diet generally resulted in even more extended larval development times and further reduced pupal weights, but wheat germ addition to oak diet did not alter development rates and caused an increase in pupal weights.     

Colorado potato beetle (Coleoptera: Chrysomelidae) feeding, development, and survival to adulthood after continuous exposure to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field

Colorado potato beetle, Leptinotarsa decemlineata (Say), feeding, development, and survival to adulthood were examined after continuously exposing large larvae to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field. In laboratory assays, the overall consumption and the length of period to become prepupae were determined for larvae, which began as 3rd and 4th instars, that were offered potato leaf disks with naturally declining levels of B. thuringiensis residue. In small-cage field experiments, survival to adulthood and the period to adult emergence for beetles confined to potato plants treated with B. thuringiensis beginning as 3rd and 4th instars also were examined. Third instars remaining on plants after a B. thuringiensis application were unlikely to feed and 4th instars consumed only approximately 50% as much foliage as those fed untreated foliage. Many late instars subjected to B. thuringiensis-treated foliage failed to survive to adulthood; 58-83% of these beetles died during the larval stage. Reduced feeding and poor survival of late instars suggest that counts of large larvae after application do not provide a complete picture of the efficacy of the B. thuringiensis treatment. Late instar Colorado potato beetles that were exposed continually to naturally declining levels of B. thuringiensis-treated potato foliage took an average of 1.8-4.5 d longer to become prepupae and 4-8 d longer to emerge as adults compared with those provided with untreated foliage. Delayed emergence of adults that fed on B. thuringiensis-treated potatoes as late instars indicated that development was prolonged in these insects because of ingestion of a sublethal dose of B. thuringiensis.