Effects of aerial spray volume, coverage, and sabadilla on Scirtothrips perseae (Thysanoptera: Thripidae).

Helicopter applications using sabadilla (27-57 g [AI]/ha and 11.1-23.7 kg/ha sugar bait) in different volumes of water were made on avocado against Scirtothrips perseae Nakahara in Ventura County, CA. On small (2.8 m tall) trees, volumes of 374 and 795 liter/ha resulted in 3-18% and 19-43% spray coverage, respectively, on water-sensitive papers. On large (6.9-8.4 m tall) trees, these volumes resulted in only 1-3% and 6-11% coverage, respectively. On small trees, sabadilla in 374 liter/ha significantly reduced numbers of larvae 3 and 6 d after treatment (DAT). In contrast, on large trees, 374 liter/ha did not reduce larval numbers and was less effective than 561-1,964 liter/ha from 3-11 DAT. However, volumes of 1,543 and 1,964 liter/ha did not increase efficacy compared with 1,169 liter/ha. The results indicate that large trees require sabadilla in higher spray volumes for control of S. perseae, making applications on large trees more costly. The extra costs may not result in larval control beyond 11 d, making it especially critical to properly time applications on large trees.     

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.     

Modeling the Influence of Resource Availability on Population Densities of Oxyops vitiosa (Coleoptera: Curculionidae), a Biological Control Agent of the Invasive Tree Melaleuca quinquenervia

The Australian snout beetle, Oxyops vitiosa, was introduced to south Florida, USA, as a biological control agent of the invasive tree Melaleuca quinquenervia during the spring of 1997. As part of ongoing post-release evaluations of this weevil, we sought to quantify the population density that can be maintained by O. vitiosa larvae when fully exploiting the available melaleuca foliage. Seasonal population densities were modeled as a function of tree size distribution and density, plant phenology, quantity of acceptable foliage (suitable for larval development) and larval consumption values. Larval densities varied dramatically due to fluctuating resource availability and ranged from 830 946 larvae/ha in July–August to >4.5 million larvae/ha in January–February. The expected population density for a generalized (mixed sized) tree distribution was estimated to be 13.9 million larvae/ha. Larval densities increased to 18.8 million larvae/ha per year when large trees (>20 cm diameter at breast height) represented the dominant size class, whereas habitats dominated by medium (10–19 cm) and small (1.3–9 cm) trees were predicted to have larval densities of 11.3 and 6.3 million/year, respectively. Validation data obtained from smaller, more accessible plants suggested that the model overestimated realized yearly larval densities by 9% or 15 416 larvae/ha per year.     

Biology and control of the raspberry crown borer (Lepidoptera: Sesiidae)

This study explored the biology of raspberry crown borer, Pennisetia marginata (Harris) (Lepidoptera: Sesiidae), in Arkansas and the optimum timing for insecticide and nematode applications. The duration of P. marginata's life cycle was observed to be 1 yr in Arkansas. Insecticide trials revealed that bifenthrin, chlorpyrifos, imidacloprid, metaflumizone, and metofluthrin efficacy were comparable with that of azinphosmethyl, the only labeled insecticide for P. marginata in brambles until 2005. Applications on 23 October 2003 for plots treated with bifenthrin, chlorpyrifos, and azinphosmethyl resulted in >88% reduction in larvae per crown. Applications on 3 November 2004 of metaflumizone, metofluthrin, and bifenthrin resulted in >89% reduction in larvae per crown. Applications on 7 April 2005 for metofluthrin, imidacloprid, bifenthrin, metaflumizone, and benzoylphenyl urea resulted in >64% reduction in the number of larvae per crown. Applications on 6 May 2004 did not reduce larval numbers. The optimum timing for treatments was found to be between October and early April, before the larvae tunneled into the crowns of plants. Applying bifenthrin with as little as 468 liters water/ha (50 gal/acre) was found to be as effective against larvae as higher volumes of spray. Nematode applications were less successful than insecticides. Nematode applications of Steinernemafeltiae, Steinernema carpocapsae, and Heterorhabditis bacteriophora reduced larvae counts per plant by 46, 53, and 33%, respectively.     

Semi‐field evaluation of a granulovirus and Bacillus thuringiensis ssp. kurstaki for season‐long control of the potato tuber moth,Phthorimaea operculella

There are few insecticidal options for potato tuber moth (PTM), Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), control late in the growing season. We evaluated the PTM granulovirus (PoGV) and Bacillus thuringiensis Berliner ssp. kurstaki (Btk) for season‐long control of PTM on potato foliage in 2006 and 2007. Compared to untreated controls, 10 weekly applications of PoGV (10¹³ occlusion bodies/ha) reduced PTM populations in replicated 1‐m³ field cages by 86–96% on pre‐harvest foliage and 90–97% on tubers added to cages shortly before harvest. Infection rates of 82–95% of L4 larvae by PoGV were noted within individual larval cohorts. Equivalently timed Btk treatments (1.12 kg product/ha) were significantly less effective at population suppression, with a 36–76% reduction in larvae recovered from tubers added to cages. A PoGV/Btk alternation was significantly more effective than Btk alone and as effective as PoGV in 2007, but not in 2006. There was some evidence that reduced rate PoGV treatments (10% rate or 50% application frequency) were less effective than the standard program. There were no treatment effects on percentage of tubers growing in the ground that were infested at harvest, which remained comparatively low at ≤8.1%. Bioassays were conducted to evaluate the residual activities of foliar deposits. Early‐season applications were highly effective for the first 24 h (≥93% mortality) with a steady decline in activity over 10 days. A second application, applied later in the season, showed similar patterns, although in this case Btk was less persistent than PoGV, whereas both agents provided significant larval mortality compared with controls over 14 days. Both PoGV and Btk provide alternatives to manage field infestations of PTM prior to harvest, thus reducing the risk of tuber infestations in storage.     

Effects of aerial spray volume, coverage, and abamectin on Scirtothrips perseae (Thysanoptera: Thripidae).

Helicopter applications using abamectin in different spray volumes were made against Scirtothrips perseae Nakahara in Ventura County, CA. On small (2.2 m tall) trees, spray coverage on water-sensitive papers was 24-48% and 43-97% for 468 and 935 liter/ha volume treatments, respectively. On large (6.2-8.1 m tall) trees, spray coverage was lower and quite variable, from 1 to 28% and 10 to 70% for 468 and 935 liter/ha treatments, respectively. On small trees, 468, 701, and 935 liter/ha with a high abamectin rate (26 g [AI]/ha) were equally effective against larvae from 13 to 27 d after treatment (DAT). On medium (4.2 m tall) trees, 468 and 935 liter/ha with the high rate were equally effective from 23 to 113 DAT. On large (6.5-8.1 m tall) trees, 468 and 935 liter/ha with a low abamectin rate (13 g [AI]/ha) were ineffective in three tests. In a fourth large (6.8 m tall) tree test, 468 and 935 liter/ha with the high rate were effective at 3 and 37 DAT. In a fifth large (6.2 m tall) tree test, 468-1,403 liter/ha with the high and 935 liter/ha with the low rate were equally effective 2-22 DAT. After all effective treatments, thrips numbers were lower than in controls for 1-3 mo. However, stable and highest reductions in populations were sometimes delayed until 20-23 DAT even when coverage was high. The variability in spray coverage on the lower levels of large trees and the delayed effect may explain inconsistencies in the reporting of or in actual aerial application results.     

Potential of selective insecticides for managing Uraba lugens (Lepidoptera: Nolidae) on Eucalypts

The leaf skeletonizer Uraba lugens Walker (Lepidoptera: Nolidae), an Australian species, locally known as "gumleaf skeletonizer", is well established in New Zealand. This insect has the potential to become a serious pest of forestry and amenity eucalypts (Eucalyptus spp.) and is the focus of a long-term management program. The use of synthetic chemical or biological insecticides is one possible control method within an integrated control program. A series of dose-response trials were conducted using laboratory bioassays to test the efficacy of several insecticides against U. lugens: pyrethroids, spinosad, Bacillus thuringiensis kurstaki Berliner (Btk) and an insect growth regulator, Mimic. Pyrethroids and spinosad proved highly effective against U. lugens larvae, achieving 100% mortality after 3-6-d exposure. The performance of Btk was lower against gregarious skeletonizing larvae compared with solitary chewing larvae. When good coverage of the target foliage is achieved, >90% mortality is possible with Btk. Mimic performed poorly against U. lugens compared with other insecticides tested (<60% mortality). The Eucalyptus species on which larvae were feeding significantly altered insecticide efficacy. Treatments applied to Eucalyptus nitens (Deane & Maiden) Maiden had reduced efficacy compared with E. cinerea F. Muell. ex Benth. or E. fastigata Deane & Maiden. Cooler temperatures also reduced insecticide efficacy, presumably by decreasing movement and food consumption by U. lugens. Recommendations on spray applications to control U. lugens in New Zealand are given.     

Studies on Aedes albopictus larval mass-rearing optimization

To set up a sterile male technique program to control Aedes albopictus (Skuse) in areas in northern Italy, a pilot mass-rearing facility is under development. For this purpose, experiments were carried out to find the optimal larval density for the optimization of the rearing parameters, i.e., to obtain the fastest larval development, the highest larval and pupal survival rate, and large-sized pupae. Several different larval densities, from 40 to 2874 larvae per liter, were tested. For densities from 40 to 600 larvae per liter significant size differences were found among pupae obtained under different larval densities. The larvae raised at the lowest density tended to be smaller and to develop most slowly, i.e., longer pupation time. Also, increasing water volume and depth seemed to negatively affect the pupation success. Compared with the other larval densities tested, the larvae reared at a density of 2874 larvae per liter developed slightly faster and showed higher survival rates, indicating this density as appropriate for the development of a mass rearing, at least using the current larval diet.     

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.     

Optimizing use of codling moth granulovirus: effects of application rate and spraying frequency on control of codling moth larvae in Pacific Northwest apple orchards

New formulations of the codling moth, Cydia pomonella (L.), granulovirus (CpGV) [family Baculoviridae, genus Granulovirus] are commercially available in North America. In field tests on apple (Malus sp. 'Delicious'), we compared different application strategies for CpGV (Cyd-X, Certis USA, Clovis, CA) used in full-season programs against high pest populations. In replicated single tree plots, three rates (0.073, 0.219, and 0.438 liter ha(-1)) and application intervals (7, 10, and 14 d) killed 81-99% of larvae in fruit and reduced the number of mature larvae recovered in tree bands by 54-98%. Although the proportion of deep entries declined by 77-98%, the amount of fruit injury was not reduced compared with controls. There was a statistical trend between increasing dosage and spray frequency intervals and virus effectiveness, but no interaction between these factors. In a commercial orchard, we assessed a standard (0.219 liter ha(-1)) and two reduced rates of the virus (0.146 and 0.073 liter ha(-1)) applied in a weekly spray program in replicated 0.2-ha blocks. In the first generation, fruit injury was reduced in virus-treated compared with three untreated blocks although the decrease was only significant at the standard rate. Mortality rates of larvae (in fruit) were > or =90%, dose dependent, and comparable with rates observed from individual trees sprayed with equivalent treatments in the previous study. Rates of larval mortality declined at all dosages (81-85%) in the first part of the second generation. Most damage and proportionally less mortality occurred in the upper canopy. High pest pressures and untreated blocks contributed to significant damage and the study was terminated early. These data suggest virus programs can be tailored according to the localized pest pressure, but it may not prevent economic damage in high-pressure situations.     

Effects of a kaolin-based particle film on obliquebanded leafroller (Lepidoptera: Tortricidae)

Studies were conducted in 1997 to evaluate the effects of the kaolin-based particle film formulation M96-018 on adults, eggs, and larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris). Particle film treatments significantly reduced female longevity, mating success, and number of egg masses oviposited compared with moths on untreated apple leaves in sleeve-cage and screen-cage tests. No differences in mating success or oviposition were caused by the application rates and coverage density of M96-018 on foliage. Females avoided ovipositing on particle film-treated leaves in choice tests. Larval hatch was not affected by topical application or residual exposure to M96-018. Larval weight gain and pupal weight were significantly reduced and larval mortality increased in no-choice feeding tests with M96-018. In choice tests, larvae preferred to feed on untreated leaf surfaces. The negative effects on larval development and survivorship on M96-018-treated foliage did not differ across a fourfold difference in spray application rate. A significant reduction in the number of infested shoots was found in orchard trials when M96-018 was applied before bud break in late March compared with untreated trees. No reductions in larval densities were found compared with an untreated control following prebloom and postbloom applications.     

Effects of bud phenology and foliage chemistry of balsam fir and white spruce trees on the efficacy of Bacillus thuringiensis against the spruce budworm, Choristoneura fumiferana

Abstract 1 Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana was investigated in mixed balsam fir‐white spruce stands. Btk treatments were scheduled to coincide with early flaring of balsam fir shoots, and later with flaring of white spruce shoots. Btk efficacy on the two host trees was compared and examined according to the foliar content of nutrients and allelochemicals and the insect developmental stage at the time of spray. 2 Larvae fed white spruce foliage were less vulnerable to Btk ingestion than larvae fed balsam fir foliage. Higher larval survival on white spruce, observed 10 days after spray, was related to higher foliage content in tannins and a lower N/tannins ratio, which might have induced inactivation of Btk toxins. 3 Larval mortality due to Btk did not depend on spruce budworm larval age. 4 Foliage protection of both host trees was similar in plots treated with Btk: larval mortality due to Btk treatment reduced insect grazing pressure on balsam fir trees; meanwhile, suitability of white spruce foliage seemed to decrease very rapidly, which induced high larval mortality among spruce budworm fed on white spruce trees. Nevertheless, following Btk sprays, 50% more foliage remained on white spruce than on balsam fir trees, because of the higher white spruce foliage production. 5 Both spray timings achieved similar protection of white spruce trees, but Btk treatments had to be applied as early as possible (i.e. during the flaring of balsam fir shoots to optimally protect balsam fir trees in mixed balsam fir‐white spruce stands).     

Evaluation of a granulovirus (PoGV) and Bacillus thuringiensis subsp. kurstaki for control of the potato tuberworm (Lepidoptera: Gelechiidae) in stored tubers

Liquid suspensions and dry formulations of a granulovirus (family Baculoviridae, genus Granulovirus, PoGV) derived from infected larvae and the bacterium Bacillus thuringiensis subsp. kurstaki (Berliner) (Btk) were evaluated for control of the potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), in stored tubers. Laboratory bioassays at 25 degrees C showed that both PoGV and a wettable powder (WP) formulation of Btk incorporated with carriers (water, talc, sand, diatomaceous earth, and kaolin clay), were effective against neonate larvae. Depending on the technique, 100% larval mortality was achieved at concentrations as low as 0.025 larval equivalents (LE) PoGV per kg tuber and 150 mg Btk WP per kg tuber. However, 100% mortality was never achieved with tests on preinfested tubers, ostensibly due to the higher dosage required to kill older instars inside tubers. The most effective PoGV formulations were dipping (water) and talc, with dipping most effective for postinfestation treatments, causing up to 91.6% mortality at 0.4 LE per kg. There was no significant effect of formulation in the Btk treatments. The protective effects of residues were also evaluated under longer-term storage conditions. Batches of tubers treated with PoGV or Btk via dipping (up to 0.1 LE and 150 mg WP per kg tuber) were stored in cages containing an initial potato tuberworm infestation (10% of tubers). Although potato tuberworm populations were reduced by up to 98.4% after 2 mo at 25 degrees C, no treatments prevented the development and reproduction of the F1 generation. The sprouting of stored tubers seemed to be a limiting factor for sustained control. No significant treatment effects were detected in similar cages held at 12 degrees C for 4.5 mo. Improved strategies for the application of PoGV and Btk for long-term potato tuberworm control in tuber stores, including the use of chemical sprout suppressants, are discussed.     

Interactions among white spruce tannins, Bacillus thuringiensis subsp. kurstaki, and spruce budworm (Lepidoptera: Tortricidae), on larval survival, growth, and development

The interactions among white spruce, Picea glauca (Moench) Voss, purified acetone tannin extracts (hydrolyzable and condensed tannin), Bacillus thuringiensis subsp. kurstaki Cry1A(c) delta-endotoxin strain HD-73 (Btk), and spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) on larval survival, growth, and development were investigated over the whole larval feeding period by using artificial diet supplemented with three concentrations of Btk toxins per milliliter of diet (0, 0.021, and 1.72 microg/ml) and three concentrations of foliar tannin extract (0, 8, and 15% dry mass basis). At high Btk concentration, tannin antagonized Btk potency against spruce budworm by lowering Btk-related larval mortality from 83 to 43%. At moderate Btk concentration tannin did not affect Btk potency. Host tree tannins antagonized not only the lethal effects of Btk toxin but also sublethal Btk-related impacts in terms of larval development, pupal weight, relative consumption rate, and growth rate. When alone in the diet, tannin negatively affected larval survival, growth, and development. Maximum potency of tannins against spruce budworm larvae (60% mortality) was reached at dietary concentrations corresponding to what is found in the plant (8% dry mass). The addition of Btk toxin in food containing tannin reduced percentage of larval mortality by one-third, indicating that Btk toxin can antagonize tannin potency against the insect. Development of Btk transgenic spruce trees should consider the antagonistic effect the toxin may have on the resistance conferred by tannins that have evolved naturally in spruce trees.     

Efficacy of transgenic cotton containing a cry1Ac gene from Bacillus thuringiensis against Helicoverpa armigera (Lepidoptera: Noctuidae) in northern China

NuCOTN 33B, a Bt transgenic variety of upland cotton (Gossypium hirsutum L.) expressing the insecticidal protein Cry1Ac from Bacillus thuringiensis Berliner sp. kurstaki, was evaluated for resistance to Helicoverpa armigera (Hübner) during 1998-2000 in northern China. The results indicated that there was no significant difference in egg densities between NuCOTN 33B and three nontransgenic varieties (DP5415, Zhongmian12, and Shiyuan321) during the season, although the survival of larvae on NuCOTN 33B seemed significantly reduced. High larval densities observed on non-Bt cotton appeared in great contrast to the low larval populations observed on NuCOTN 33B plants during the seasons. In an environment without insecticide sprays, the annual ginned cotton yields in NuCOTN 33B plots, ranging from 1391.17 to 1511.35 kg/ha, were significantly higher than those in non-Bt cotton (340.34-359.58 kg/ha). These high levels of field efficacy for NuCOTN 33B against H. armigera in northern China may pave the way for reduced pesticide applications and an expansion of alternative pest-control strategies.     

Joint Insecticidal Action of Bacillus thuringiensis kurstaki with Annona squamosa L. and Prosopis juliflora Swartz DC on Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

The efficacy of methanolic seed extracts of Annona squamosa (As) and Prosopis juliflora (Pj) individually and in combination with spore-crystal mixture of Bacillus thuringiensis kurstaki (Btk) was tested against third instar larvae of Helicoverpa armigera. The combination of botanicals with Btk significantly decreased LC₅₀ values in less time as compared to individual treatments. As and Pj in combination with Btk significantly affected feeding and dietary utilization of H. armigera significantly than in individual treatments. Physiological effects found in larvae fed on Btk and botanicals included extended larval and pupal durations, decreased adult longevity and fecundity, difficulty in moulting between various instars, formation of larval–pupal intermediates and abnormal pupae. As was found to have a higher interaction with Btk than Pj. Further, Btk showed strong synergistic action with As and Pj, which are the promising candidates for development of alternative bioinsecticide in IPM programs.     

Control of Heterodera carotae,Ditylenchus dipsaci,and Meloidogyne javanica with Fumigant and Nonfumigant Nematicides

Five field trials were conducted in Italy in 1983 and 1984 to test the efficacy of isazofos and benfuracarb in controlling Heterodera carotae on carrot, Ditylenchus dipsaci on onion, and Meloidogyne javanica on tomato. Methyl isothiocyanate (MIT) was tested against H. carotae and M. javanica. Single (10 kg a.i./ha) and split (5 + 5 kg a.i./ha) applications of isazofos gave yield increases of carrot and onion similar to those obtained with DD (300 liters/ha) and aldicarb (10 kg a.i./ha). Population densities of H. carotae in carrot roots at harvest and of M. javanica in tomato roots 2 months after transplanting were also suppressed by isazofos. Benfuracarb (10 kg a.i./ha increased onion yields in a field infested with D. dipsaci, but it was not effective against H. carotae or M. javanica. The efficacy of MIT at 400 and 600 liters/ha was similar to that of MIT + DD (Di-Trapex) at 300 liters/ha. Both nematicides inhibited hatch of H. carotae eggs and decreased the soil population density of M. javanica.     

幼虫密度对草地螟食物利用率及消化酶活性的影响

为了阐明草地螟Loxostege sticticalis大发生种群幼虫取食行为特征, 在室内条件下（温度22±1℃, 相对湿度70%）对不同幼虫密度［1, 10, 30头/瓶（650 mL）］饲养草地螟幼虫的食物利用率及消化酶活性进行了研究。结果表明： 幼虫中等（或高）密度对草地螟幼虫相对中肠重量、 相对取食量、 粪便干重、 食物利用率和近似消化率及总蛋白酶和亮氨酸氨肽酶活性影响显著。幼虫相对中肠重量以10头/瓶的幼虫密度最大, 1头/瓶的幼虫密度最小。随着幼虫密度的增加, 幼虫相对取食量和粪便干重增加, 而虫体干重减轻, 幼虫食物利用率降低。幼虫密度30头/瓶的幼虫相对取食量和粪便干重显著高于1和10头/瓶的, 而30头/瓶的幼虫食物利用率显著低于1头/瓶的。幼虫近似消化率随幼虫密度的逐渐增加而显著降低。幼虫密度10头/瓶的幼虫总蛋白酶和亮氨酸氨肽酶的活性显著高于1和30头/瓶的, 而淀粉酶的活性受幼虫密度影响不显著。随幼虫密度的增加, 幼虫相对中肠重量与总蛋白酶和亮氨酸氨肽酶活性变化趋势较为一致, 消化酶活性的变化可能与相对中肠重量大小有关。因此, 幼虫密度是影响草地螟幼虫取食行为的重要因子, 这些结果为阐明草地螟大发生种群与一般种群的为害特征提供了重要理论依据。     

Efficacy of Oxamyl Against Heterodera schachtii on Cabbage

The efficacy of oxamyl in controlling Heterodera schachtii on cabbage was determined by applying various contbinations of soil drenches at 6.7 kg (a.i.)/ha and foliar sprays at 0.04 kg (a.i.)/100 liters of water to cabbage seedlings. Pretransplant drenches provided some control of H. schachtii over a 13-week period. A single foliar spray of oxamyl 1 week before transplanting apparently prevented penetration of H. schachtii larvae; post-transplant sprays were relatively ineffective. A pretransplant or transplant drench combined with a foliar application 2 weeks after transplanting provided the most effective control. The effectiveness of drenches plus post-transplant sprays is probably due to the spray augmenting the action of the drench in inhibiting the development of larvae after penelration.     

Field evaluation of a granulosis virus for control ofPieris rapae [Lep.: Pieridae] in the United Kingdom

A purified granulosis virus isolated fromPieris brassicae (L.) was tested in the field against an introduced population ofPieris rapae (L.) larvae on cabbage (cv January King) in small experimental plots at Littlehampton, Sussex. Experiments were designed to compare the relative efficacy of single and multiple applications of virus (2.1×10¹² and 3.7×10¹² or 2.1×10¹⁴ and 3.7×10¹⁴ virus capsules/ha) in reducing numbers ofP. rapae larvae. An experiment was carried out in June 1978 and repeated in August to coincide approximately with the 2 natural generations ofP. rapae in southern England. Larval populations were monitored by regularin situ assessment of plants and by destructive sampling. Within 10 days of spraying virus there was a significant reduction in the mean larval population on all virus-treated plots compared with untreated controls. Sprays of 2.1×10¹⁴ and 3.7×10¹⁴ capsules/ha reduced larval numbers more quickly than 2.1×10¹² and 3.7×10¹²/ha treatments. In the 1st experiment, three sprays of virus at either 2.1×10¹² or 2.1×10¹⁴ capsules/ha gave no increase over the final level of control achieved by a single spray. However, in the 2nd experiment, a single spray of 3.7×10¹² capsules/ha did not significantly reduce the numbers of larvae. It is likely that this failure could be accounted for by a combination of the larger “natural” population ofP. rapae recorded midway through the 2nd experiment and the rapid inactivation of virus deposits which left little infectious virus to infect these larvae. Virus inactivation was so rapid that only 7–33 % of the initial virus deposits remained 1 day after application. These results suggest that further understanding of virus formulation, persistence and dosage rates are needed before such a virus can be used in a rational manner.