A possible therapy by juvenile hormone I to Spodoptera littoralis (Boisd.) larvae previously treated by precocene II

An effective constant dose (55 μg) of precocene II (PII) was topically tested against the last three instars of Spodoptera littoralis (Boisd.) larvae. Application of PII induced morphogenetic abnormalities typical of juvenile hormone (JH) excess. The resultant imperfect insects included larval‐pupal mosaic and partial or severe cases of untanned pupae. The sixth‐instar larvae were more sensitive to PII administration than the two preceding instars. However, sensitivity of the last larval instar to PII varied with the timing of dose application relative to the developmental status of the larvae. Whereas the newly ecdysed (0‐day old) larvae were more sensitive, the older larvae of the same sixth‐instar showed sharp decrease in their sensitivity to PII with a concomitant increase of their age. Application of a single dose (5 μg) of JH I to PII pre‐treated larvae significantly (P < 0.001) reduced the production of imperfect insects where many PH‐treated larvae developed successfully to apparent normal pupae. Although a single dose of PII was more effective on S. littoralis larvae than repeated daily doses, the effectiveness of JHI‐therapy to PH pre‐treated larvae by repeated doses was less effective in producing perfect insects than JH‐therapy to PII pre‐treated larvae by single doses. The reversal of any of these by applied JHI is quite interesting but the mechanisms remain to be unraveled.     

Effects of nonsteroidal ecdysone agonist RH-5992 and chitin biosynthesis inhibitor lufenuron on <Emphasis Type="Italic">Spodoptera littoralis</Emphasis> (Boisduval, 1833)

Comparative studies of the effects of two compounds, tebufenozide (an ecdysone agonist) and lufenuron (an insect growth regulator inhibiting chitin synthesis), were conducted on Spodoptera littoralis (Boisduval, 1833). The compounds, orally administered, caused larval mortality proportional to the concentrations in the food source. Tebufenozide initiated precocious molting, and lufenuron, and inhibited chitin synthesis. In both cases, larvae were unable to complete the molting process and died in the old larval cuticle. Larvae contaminated by sublethal doses completed their development to adulthood. Lufenuron is more active than is tebufenozide. LD-50 for lufenuron is 0.0001ppm and for tebufenozide 0.001ppm. Topical application of the test compounds to eggs caused dose- and agedependent inhibition of embryonic development. Application of tebufenozide in the second half of embryogenesis caused precocious molting of eclosed larvae of the 1^st instar. Some morphological changes in the process of larval-pupal transformation were also observed. Tested compounds also reduced reproduction in adult individuals that had been treated by the tested compounds in the larval stage.     

Insecticidal activities of Ginkgo biloba seed coat extracts against Spodoptera exigua (Lepidoptera: Noctuidae)

The present study relates to a methanol extract of the seed coat of Ginkgo biloba, and tested particularly on the third instar larvae of Spodoptera exigua. The extract was found to have an inhibitory effect on the growth of the larvae besides bringing a change in the nutrient reserves in the body of the insect. Topical application of five different doses of the methanol extract resulted in a mortal effect to third instar larvae of S. exigua that is very much dependent on the dose as well as duration of exposure. Lower doses revealed lower mortality after 24 h of application. At doses of 1.00, 2.00, 4.00, 8.00 and 16.00 ng/larva, mortalities were 9.25, 26.07, 50.32, 56.28 and 92.44%, respectively. The dose for 50% mortality (LD₅₀) of methanol extracts by applied by a topical method with 1 µL of acetone solution was 1.92 ng/larva. Nutrient reserves like protein, glycogen and lipid are known to regulate pupation and adult emergence. These reserves have been found to be lower in treated larvae, indicating the insecticidal role of methanol extracts from G. biloba against third instar larvae of S. exigua.     

Desiccation resistance in pre-diapause, diapause and post-diapause larvae of Choristoneura fumiferana (Lepidoptera: Tortricidae)

Desiccation resistance was examined in pre-diapause, diapause and post-diapause larvae of the spruce budworm, Choristoneura fumiferana (Clemens), in terms of passive water evaporation under three desiccation conditions: freeze-drying, desiccant-drying at 2 degrees C and desiccant-drying at 18 degrees C. Diapausing second instar larvae and post-diapause non-feeding second instar larvae showed strongest desiccation resistance: a significant amount of water was retained after repeated drying under desiccating conditions, while pre-diapause first instar larvae and post-diapause feeding second instar larvae lost almost all their water content after one or two drying cycles. A hibernaculum covering had no effect on water evaporation. While dead larvae tended to lose significantly more water than their living counterparts, particularly among first instar larvae, such an impact was much weaker among diapausing second instar larvae. Desiccation resistance was lost when post-diapause second instar larvae were allowed access to water while the level of desiccation resistance was maintained or enhanced when the larvae did not have access to water. These results are discussed in the context of overwintering ecology of the species and possible mechanisms for the desiccation resistance are also discussed.     

Effect of an ecdysteroid agonist, tebufenozide, on the completion of diapause in susceptible and resistant strains of the codling moth, Cydia pomonella

Codling moth Cydia pomonella (L.) (Lepidoptera, Tortricidae) larvae kept under a short photoperiod enter a diapause which can be broken by exposure to 25°C following an extended chilling period. We investigated the effects of the ecdysteroid agonist tebufenozide on the diapause of this species, both on a laboratory strain susceptible to insecticides and two strains selected for resistance to diflubenzuron or deltamethrin. The treatment induced moulting by breaking diapause of the susceptible strain when applied at the end of the growth period, or by reducing the pre-emergence period when applied after chilling. The strains exhibiting resistance in the neonate instar were also resistant to the ecdysteroid agonist applied to diapausing larvae, indicating that mechanisms of resistance remained active during this arrest of development. High doses of tebufenozide were lethal for the most resistant insects, but neither reduced the pupation delay nor produced the larval-pupal moults which occur in the susceptible strain. As diapausing larvae of C. pomonella can be easily collected, the expression of resistance to tebufenozide both in the target instar, i.e. neonates, and during diapause may contribute to early detection of resistance to this insecticide in field populations.     

Proteins of the fat body of non-diapausing and diapausing larvae of the southwestern corn borer, Diatraea grandiosella: Effect of juvenile hormone

The proteins of the fat body of non-diapausing, pre-diapausing, and newly-diapaused larvae of the southwestern corn borer, Diatraea grandiosella, were examined. Since a low titre of juvenile hormone (JH) is present in the haemolymph throughout the final instar of non-diapausing larvae, the hormone does not appear to stimulate the pre-metamorphic synthesis of proteins. In contrast, the high titre of JH in the haemolymph during the final instar of pre-diapausing larvae appears to stimulate the synthesis of selected proteins. For example, pre-diapausing larvae store in their fat body a low molecular weight protein which has been named the ‘diapause-associated protein’. When non-diapausing larvae were treated topically with C₁₇-JH or a JH mimic, from 50 to 70% entered a diapause-like state as fully grown larvae. These hormone-treated larvae accumulated the diapause-associated protein and a high molecular weight protein in their fat bodies. Both of these proteins were shown to be released from the fat body of newly-diapaused larvae in vitro, and may function in the haemolymph during diapause. The high molecular weight protein, isolated from the haemolymph, was shown to contain neutral and polar lipids, including biochromes. Its storage in the fat body and release into the haemolymph may be essential for the transport of lipids during diapause. The fat body proteins of newly-diapaused larvae of the southern cornstalk borer, Diatraea crambidiodes, were also examined electrophoretically. They were found to contain a similar protein pattern to that of D. grandiosella, including the presence of a diapause-associated protein.     

Brain neurosecretory cell and ecdysiotropin activity of the non-diapausing,pre-diapausing and diapausing southwestern corn borer, Diatraea grandiosella Dyar

The location and number of brain neurosecretory cells were studied in the larval southwestern corn borer. One posterior, two median and two lateral groups of paraldehyde-fuchsin positive cells were found in each cerebral hemisphere.Implantation of brain parts containing different groups of neurosecretory cells revealed that the median neurosecretory cells contained higher ecdysiotropic activity than the other cell groups. In vitro culture of ecdysial gland with brain or brain-parts extract showed also that the median neurosecretory cells contained much higher ecdysiotropic activity than other neurosecretory cells. To estimate the ecdysiotropic activity of pre-diapausing 6th instar larvae, their brain or brain extract was incubated in culture medium containing an ecdysial gland from a day-4 last-instar non-diapausing larva. Data showed that the ecdysiotropic activity in the pre-diapausing larvae was far lower than in non-diapausing and diapausing larvae.     

Response of Lymantria dispar L. (Lepidoptera: Lymantriidae) to Bacillus thuringiensis subsp. kurstaki at different ingested doses and temperatures

We examined mortality and feeding inhibition response of Lymantria dispar L. (Lepidoptera: Lymantriidae) larvae to ingested doses of Bacillus thuringiensis subsp. kurstaki as a function of dose, instar and temperature. We developed generalized (logistic) linear mixed models and a mixture survival model, commonly used in medical statistics, to analyze the complex data set. We conducted bioassays of Foray 48B with larvae from the NJSS laboratory stock, using droplet imbibing or force-feeding to ensure dose ingestion. The dose causing mortality in 50% of the test population (LD₅₀) under standard test conditions (22 °C) ranged from 0.019 International Units (IU)/larva for first instar larvae (L₁) to 1.6 IU/larva for L₄. Temperature affected larval mortality in two ways. Mortality occurred sooner and progressed more rapidly with increasing temperature (13-25 °C) at each dose level and instar, while the maximum level of mortality attained by each instar decreased with increasing rearing temperature. The mechanisms underlying this effect are being investigated. Larvae that survived exposure to B. thuringiensis resumed feeding after a period that was dependent on instar, dose, and temperature. The equations describing observed mortality and feeding recovery responses were used to construct a simulation model, which was able to predict both processes, and which forms the basis for a process-oriented model that can be used as a decision support tool in aerial sprays.     

RNAi介导的HvCDA1基因沉默影响茄二十八星瓢虫存活和发育

【目的】茄二十八星瓢虫Henosepilachna vigintioctopunctata是茄科(Solanaceae)植物上的重要害虫。昆虫体内几丁质脱乙酰酶1(chitin deacetylase 1, CDA1)催化N-乙酰氨基-D-葡萄糖胺脱去乙酰基,促使几丁质转化为壳聚糖,控制昆虫体内几丁质纤维有序堆积,并维持角质层结构的完整性。抑制虫体中CDA1基因的表达会抑制壳聚糖的合成,影响昆虫表皮结构的形成,使昆虫不能正常发育而亡。【方法】利用RT-qPCR方法测定HvCDA1基因在茄二十八星瓢虫不同发育阶段(卵、1-4龄幼虫和预蛹)和4龄幼虫不同组织(表皮、脂肪体、中肠和马氏管)中的表达模式。通过饲喂茄二十八星瓢虫1龄幼虫不同浓度dsHvCDA1溶液浸泡处理1 min的茄子叶片后及直接饲喂4龄幼虫不同浓度dsHvCDA1溶液,探究沉默茄二十八星瓢虫HvCDA1基因对其幼虫存活和发育以及HvCDA1基因表达量的影响。【结果】发育表达谱结果表明,HvCDA1在茄二十八星瓢虫的各发育阶段均有表达,但在1龄末和2龄末幼虫中的表达量最高。组织表达谱结果显示,在茄二十八星瓢虫4龄幼虫的表皮中H...     

营养改变对潜蝇姬小蜂寄生行为和寄主取食行为的影响

为了研究营养状态对卵育型寄生蜂潜蝇姬小蜂Diglyphus isaea (Walker)雌蜂的寄主取食行为和产卵寄生行为及其二者行为权衡的影响, 在培养皿条件下, 比较了饥饿、加蜂蜜水和不加蜂蜜水3种营养状态的潜蝇姬小蜂雌蜂对美洲斑潜蝇Liriomyza sativae Blanchard各龄幼虫（低、中、高）的寄生、取食及致死能力。结果表明: 非选择条件下, 3种营养状态寄生蜂对高龄幼虫均具有较高的寄生率, 对中龄幼虫具有较高的取食率, 致死率和致死量之间存在显著性差异。3种状态的寄生蜂对低龄幼虫均没有表现出致死能力。有选择条件下, 饥饿状态的寄生蜂对寄主的寄生率最低（5.0%±1.6%）, 取食率最高（16.0%±2.9%）, 特别是对高龄幼虫的取食率占到了整个寄主食物取食率的91.9%; 加蜂蜜水状态下, 寄生蜂对寄主有最低的取食率（8.3%±0.9%）和致死率（17.7%±1.1%）; 不加蜂蜜水状态下, 寄生蜂对寄主有最高的寄生率（13.3%±1.1%）和致死率（28.4%±1.8%）。综合分析发现, 取食寄主的雌蜂比取食蜂蜜水的雌蜂具有更强的致死能力和活动能力。     

虫酰肼对甜菜夜蛾多巴脱羧酶和酪氨酸羟化酶的抑制作用

虫酰肼模拟昆虫蜕皮激素的作用干扰新表皮的形成。为了探讨虫酰肼对昆虫新表皮形成的影响是否与抑制表皮形成相关酶的活性有关, 本研究应用高效液相色谱-荧光检测法（HPLC-RP）, 测定了甜菜夜蛾Spodoptera exigua 5龄幼虫用虫酰肼处理不同时间（24, 48和72 h）后多巴脱羧酶和酪氨酸羟化酶的活性。结果表明： 用LC₁₁ （28.41 μmol/L）和LC₃₃ （85.23 μmol/L）两个亚致死剂量的虫酰肼处理5龄幼虫后, 多巴脱羧酶和酪氨酸羟化酶的活性均受到明显抑制, 高浓度的抑制作用大于低浓度的抑制作用。随着处理时间的延长, 同一剂量的抑制作用逐渐增强。进一步测定虫酰肼处理24, 48和72 h后5龄幼虫血淋巴、 脂肪体、 中肠、 表皮和头部的多巴脱羧酶和酪氨酸羟化酶的活性, 可看出虫酰肼对幼虫不同组织的多巴脱羧酶和酪氨酸羟化酶的活性也具有相似的抑制作用。结果提示, 虫酰肼对甜菜夜蛾幼虫多巴脱羧酶和酪氨酸羟化酶活性具有明显抑制作用, 幼虫新表皮形成受阻可能与虫酰肼抑制多巴脱羧酶和酪氨酸羟化酶的活性有关。     

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.     

Juvenile hormone changes associated with diapause induction, maintenance, and termination in the beet webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

At 22°C and under a long-day photoperiod of L:D 16:8, all the last fifth instar Loxostege sticticalis larvae undergo prepupal stage and pupate without diapause. Under a short-day photoperiod of L:D 12:12, in contrast, they all enter diapause with approximately 36 days diapause maintenance and then terminate diapause spontaneously, although only 44% of the larvae terminated diapause successfully. Changes in hemolymph juvenile hormone (JH I) titers of diapause-destined larvae across diapause induction, maintenance and termination were examined using HPLC, and were compared with those of non-diapause-destined larvae from the fifth instar through pupation. JH I titer of the earliest fifth instar diapause-destined larvae remained at a high level with a peak of 220.4 ng/ml, though it decreased continuously to a minimum of 69.0 ng/ml on day 5 in the fifth instar when the larvae stopped feeding to enter diapause. During the diapause maintenance, JH I titer of the mature larvae increased significantly and maintained a high level until day 31 in prepupae. JH I titer declined and fluctuated at low level from 5 days before pupation. In contrast, JH I titer of both the fifth instar non-diapause-destined larvae and prepupae remained and fluctuated at low level consistently, as well as decreased before pupation. These results indicate that diapause induction and maintenance in this species might be a consequence of high JH, whereas diapause termination can be attributed to low JH titer, which was in agreement with the hormonal regulation observed in many other larval-diapausing insects.     

敲减神经肽F基因(npf)对亚洲玉米螟取食、生长发育和繁殖的影响

【目的】神经肽F(neuropeptide F, NPF)是无脊椎动物特有的一类神经肽,因其C末端是苯丙氨酸(F)而命名,参与昆虫的取食、生物节律、学习记忆等多种生理功能的调控。本研究旨在明确NPF对亚洲玉米螟Ostrinia furnacalis生长发育的影响,为害虫防治提供重要依据。【方法】采用一种基于工程菌高效合成靶向昆虫基因的dsRNA的方法经济有效地敲降npf,用低浓度(0.01%)和高浓度(0.02%)dsNPF和dsGFP(对照)分别饲喂亚洲玉米螟1龄初、3龄初和5龄初幼虫直至化蛹,检测5龄幼虫平均取食量、体重、体长、存活率和化蛹率,蛹羽化率和成虫产卵量,以及幼虫各龄期、蛹发育历期和成虫寿命。【结果】从亚洲玉米螟1, 3和5龄初幼虫开始饲喂0.01%和0.02% dsNPF时,与饲喂相应浓度dsGFP的对照相比,除个别点外,5龄幼虫的取食量、体重、体长、存活率和化蛹率,蛹羽化率和成虫单雌产卵量均显著降低,幼虫各龄期、蛹发育历期均显著延长,成虫寿命显著缩短。且dsNPF处理幼虫的龄期越早对发育的影响越大。其中0.01% dsNPF处理的1龄幼虫和0.02% dsNPF处理的3龄幼虫有90%的个体在蛹期死亡,而0.02%dsNPF处理的1龄幼虫有90%的个体在幼虫期死亡。【结论】结果提示NPF对亚洲玉米螟的发育和取食具有调控作用,这为探索新型绿色的害虫防治提供了依据。     

虫酰肼对甜菜夜蛾汰选种群生长发育及生殖的影响

研究虫酰肼对甜菜夜蛾汰选种群生长发育及生殖的影响。结果显示:经虫酰肼处理后,甜菜夜蛾SS种群和RR种群卵的孵化抑制中浓度分别为179.38和160.71mg/kg,孵化幼虫的存活抑制中浓度分别为18.64和30.53mg/kg,虫酰肼对甜菜夜蛾卵的孵化率影响较小,而对孵化后幼虫的存活率影响较大。处理初孵幼虫6d后,2种群幼虫存活率及化蛹率随处理浓度的增加而降低,幼虫历期最高饲毒浓度与最低饲毒浓度相比分别延长了2.71d和6.19d,同一浓度下,RR种群幼虫历期比SS种群缩短了0.94～2.59d。处理甜菜夜蛾3龄幼虫12h后,随虫酰肼浓度的增加,2种群化蛹率逐渐降低,雌雄蛹重均有递减的趋势,雌蛹比例随浓度的增加变化较小,但SS种群雌蛹比例≤50.00%,而RR种群雌蛹比例≥50.00%,雌雄成虫羽化率总体上依次递减,处理浓度大于1.00mg/kg时虫酰肼对甜菜夜蛾成虫羽化的影响较大。     

Insect cytokine growth-blocking peptide may regulate density-dependent phase trait of cuticular melanization in the larval armyworm,Mythimna separata

Growth-blocking peptide (GBP) is a 25 amino acid insect cytokine found in lepidopteran insects that has diverse biological activities such as larval growth regulation, paralysis induction, cell proliferation and stimulation of immune cells. Density-dependent phase polyphenism is a phenomenon of phenotypic plasticity in which the expression of a variety of traits can be affected by local population density. In the present study, the armyworm Mythimna separata larvae with four rearing densities (1 larva/vial, 2 larvae/vial, 4 larvae/vial and 6 larvae/vial) were tested for cuticular melanization and body weight throughout the third-fifth instar, and the functional role of GBP in regulating the changes was investigated. The results indicated that when reared at high densities, the larvae exhibited less body weight and more degree of cuticular melanization than larvae reared at low densities. The gene expression of GBP in armyworm larvae showed an initial rise and then decline trend with increased rearing densities in the third to fifth instar. Compared with control, more degree of cuticular melanization was observed in GBP-injected larvae (500 ng/larva in volume 50 μL) than that in Ringer’s solution-injected counterparts. Furthermore, the gene expression level of dopa decarboxylase and prophenoloxidase increased significantly in GBP-injected fifth instar larvae from 6 h to 12 h after injection, suggesting the role of GBP in modulating density-dependent phase trait of armyworm cuticular melanization.     

Susceptibility of Delia radicum to steinernematid nematodes

Isolates of different Steinernema species (S. affine, S. bicornutum, S. feltiae and Steinernema C1) were used in mortality assays with third instar larvae of Delia radicum (L.) (Diptera: Anthomyiidae). The nematode isolates had been obtained by baiting soil regularly grown with cabbage. One isolate (S. feltiae) was the result of a natural infection of a D. radicum puparium. The highest mortality (77%) was obtained with an isolate of S. feltiae (DK1). The isolate DK1 was also used in tests with all larval stages of D. radicum. Mortality around 60% was observed for second and third instar larvae, while first instar larvae showed very low or no susceptibility. Maximum mortality of second and third instar larvae was reached applying only 25 nematodes per larva. Observations of larvae that pupated revealed that some of these puparia contained nematodes. Experiments with hatching puparia showed that a high proportion was infected by nematodes if the flies were prevented from leaving nematode-containing soil. In addition to mortality, the ability of the nematodes to successfully reproduce in the insects was studied. It was found that the species S. feltiae and S. bicornutum reproduced in D. radicum larvae and adults with S. feltiae being the most successful.     

Larval diapause of the European corn borer, Ostrinia nubilalis: Further experiments examining its hormonal control

The possible involvement of juvenile hormone (JH) in controlling the mature larval diapause of the European corn borer, Ostrinia nubilalis, was examined using biological and chemical assays for JH titres, topical applications of JH mimic, and injections of 20-hydroxy-ecdysone. Bioassays of extracts of larval haemolymph showed that (1) 4th instar pre-diapausing larvae had a higher JH titre (ca. 1450 Galleria Units (GU)/ml) than equivalent non-diapausing larvae (ca. 340 GU/ml), and that (2) 5th instar pre-diapausing larvae contained a JH titre of ca. 320 GU/ml, which declined to ca. 90 GU/ml in newly-diapaused larvae. Chemical assasys carried out on extracts of whole larvae showed that early diapausing larvae contained an extremely low titre of JH. In addition, the application of JH mimic or 20-hydroxy-ecdysone or both agents to diapausing larvae failed to reveal the presence of a functional JH titre during diapause. The application of JH mimic to early 5th instar non-diapausing larvae produced moribund larval-pupal intermediates rather than supernumerary larvae. Our results, therefore, suggest that although JH may control some phases of diapause induction, it is not involved in maintaining diapause.     

Effects of ultralow doses of fenoxycarb on juvenile hormone–regulated physiological parameters in the silkworm,Bombyx mori L.

Effects of fenoxycarb at ultralow doses were investigated on juvenile hormone (JH)–regulated parameters in the silkworm, B. mori. Like JH, this non-terpenoid carbamate is able to induce permanent larvae in the last larval instar. However, whereas micrograms of JH are needed to produce this effect, only a few picograms of fenoxycarb are necessary to induce the same effect. The effects of fenoxycarb observed in this study were only visible from day 4 of the last larval instar—that is, when the JH titer has dropped to undetectable levels and JH-repressed physiological parameters would naturally be expressed. We observed that the permanent larvae induced with low doses of fenoxycarb (100 pg/larva) had no 20-hydroxyecdysone (20E) peak. Their prothoracic glands (Pgs) were completely inactive and very weakly sensitive to prothoracicotropic hormone (PTTH). Fenoxycarb at doses of 1 ng/larva also significantly inhibited silk gland growth and coloration, whereas carotenoid content of the hemolymph was maintained at high levels, which could reflect an inhibition of its uptake by the silk glands. Total hemolymph protein levels in last instar larvae were also depressed at these doses. So, it seems that low doses of fenoxycarb are sufficient to maintain in a juvenilized status the physiological parameters that are normally expressed when JH titer has declined. Moreover, from an endocrinological viewpoint, we demonstrated that the corpora allata (CA) are not necessary for fenoxycarb to induce those effects and discussed its possible mode of action. Arch. Insect Biochem. Physiol. 37:178–189, 1998. © 1998 Wiley-Liss, Inc.     

Early detection of resistance to tebufenozide in field populations of Cydia pomonella L.: methods and mechanisms

Abstract: Four populations of codling moth Cydia pomonella L. were collected as overwintering larvae from apple orchards with different pesticide pressure (S. Michele, Roncafort, Revò and Vervò) in the Trento province (northern Italy). Mortality rate caused by a predetermined discriminating concentration of tebufenozide topically applied on overwintering larvae was evaluated. Neonate F1 progeny of the same populations were assayed for susceptibility to tebufenozide by feeding them on thinning apples treated with an appropriate discriminating dose of the insecticide. The activities of the main enzyme systems involved in the detoxification of insecticides were also evaluated in each population and related to their susceptibility to tebufenozide. The topical test detected a significant loss in susceptibility to tebufenozide in two populations, S. Michele and Roncafort, while all the overwintering larvae collected in the orchards of Revò and Vervò died when treated topically with the discriminating concentration. The apple‐dipping test performed on the neonate larvae showed a highly significant reduction in the susceptibility of the two populations of S. Michele and Roncafort. A less significant reduction in mortality rate was found in the Revò population; however, no statistical difference was found between the Vervò population and the susceptible reference. None of the four field populations significantly differed from the susceptible strain for Glutathione‐S‐transferase and esterase activity. A significantly higher frequency of individuals of the S. Michele and Roncafort populations exhibited a higher mixed function oxidase activity than the susceptible strain. The small resistance ratio values found for the two populations together with the low frequency of individuals exibiting enhanced enzymatic activity, reveals that the selection process was still at the early stage. Because of its efficiency in early detection of resistance to tebufenozide, topical application on diapausing larvae can thus be considered an appropriate, simple and robust tool for implementing resistance monitoring programmes for tebufenozide.