Combining genetic engineering and traditional breeding to provide elevated resistance in potatoes to Colorado potato beetle

The sustainable deployment of resistant crop varieties is a critical issue for the implementation of biotechnology in crop pest management. Feeding, biomass accumulation, and mortality were evaluated for susceptible, insecticide‐resistant, and Bacillus thuringiensis (Bt) Cry 3A‐selected Colorado potato beetle (Leptinotarsa decemlineata Say) (Coleoptera, Chrysomelidae) larvae fed on: cultivated potato, a Solanum chacoense line expressing leptine glycoalkaloids, a transformed line expressing Bt toxin, or the leptine line transformed to express Bt toxin. Larvae selected for resistance to Bt‐Cry3A performed better on Bt foliage, but not as well on the leptine foliage, compared to susceptible or insecticide‐resistant larvae. Neither leptine nor Bt toxin completely inhibited the feeding and growth of 3rd and 4th instars of all three strains of Colorado potato beetle. However, for all three strains of Colorado potato beetle on leptine + Bt foliage, feeding was almost zero, growth was zero or negative, and mortality was near 100%.     

Growth compensation and faster development of Colorado potato beetle (Coleoptera: Chrysomelidae) feeding on potato foliage expressing oryzacystatin I

Feeding, growth, development, and food conversion efficiency of Colorado potato beetle larvae reared on foliage from a “Kennebec” potato line expressing oryzacystatin I (OCI) at about 1% of its total soluble proteins were compared to those of larvae feeding on untransformed foliage from the same line. During stages L1 to L3, larvae feeding on OCI consumed leaf material 14% faster, gained weight 28% faster, and weighed 20% more at the end of the L3 stage, compared to controls. Continued exceptional performance on OCI during the final L4 stage was expressed as faster development than controls, an effect that persisted during pupal development and resulted in emergence of similar weight adults 1 day earlier than controls. Larvae initially maintained on control foliage and switched to OCI foliage during L4 did not overcompensate as those on OCI foliage throughout development, but performed similarly to larvae on control foliage throughout. Total azocaseinase activity in midgut extracts from these 4th instars 1 d after switching to OCI foliage was sensitive to inhibition by a recombinant form of OCI expressed in Escherichia coli, but was no longer sensitive 4 d after switching, indicating a gradual adaptation of the insect digestive protease system, based on the production of OCI insensitive proteases. Despite OCI potato foliage being consumed faster by small larvae using it for food, there was no indication that it was less efficient than untransformed foliage as food protein. Arch. Insect Biochem. Physiol. 40:69–79, 1999. © 1999 Wiley‐Liss, Inc.     

Compatibility of a natural enemy, Coleomegilla maculata lengi (Col., Coccinellidae) and four insecticides used against the Colorado potato beetle (Col., Chrysomelidae)

Abstract:   The toxicity of four insecticides used to control the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), imidacloprid (Admire^®), cryolite (Kryocide^®), cyromazine (Trigard^®), and Bacillus thuringiensis var. tenebrionis (Novodor^®), to one of its natural enemies, the 12-spotted lady beetle, Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae) was determined in the laboratory. Toxicity assays against C. maculata adults and larvae consisted of (1) topical applications and (2) exposures to treated foliage and prey, using concentrations up to 10 times the manufacturer's recommendations. Over a 6-day period, cyromazine (insect growth regulator) and B. t . var. tenebrionis (microbial insecticide) had no lethal effects on first and third instars C. maculata . For both larval and adult stages, cryolite (inorganic insecticide) caused very low predator mortality when topically applied and moderate mortality when ingested through contaminated eggs of Colorado potato beetles. Imidacloprid (systemic organic insecticide) was highly toxic to adult and larval C. maculata . Its estimated LD₅₀ at 6 days following treatment, corresponded to 0.02–0.09 times the recommended field concentration, depending on the developmental stage and mode of contamination. These results indicate that integrated pest management programmes for Colorado potato beetles using imidacloprid or, to a lesser degree, cryolite, would be detrimental to C. maculata . Cyromazine and B. t . var. tenebrionis seem to present a better compatibility with the protection of C. maculata populations.     

Mortality of Colorado potato beetle (Leptinotarsa decemlineata) after sublethal stress with the CryIIIA delta-endotoxin of Bacillus thuringiensis and subsequent exposure to Beauveria bassiana

Acute or chronic sublethal exposure of Colorado potato beetle larvae to the CryIIIA delta-endotoxin of Bacillus thuringiensis Berliner did not significantly (P > 0.05) alter their subsequent susceptibility to Beauveria bassiana (Balsamo) Vuillemin. During the period of exposure to B. bassiana there was continued mortality from previous exposure to delta-endotoxin, and B. bassiana also caused significant mortality. Acute and chronic exposure to delta-endotoxin significantly prolonged larval development. The weights of prepupae and adults were significantly reduced by exposure to delta-endotoxin, with the greatest effect being from chronic exposure. Separation of the manifestations of stress in time (feeding vs soil stages) and space (toxin damage to the insect gut vs fungal penetration of the cuticle and activity in the hemocoel) may have precluded alteration of insect susceptibility to infection by B. bassiana. Endemic populations of B. bassiana are not expected to influence the development of resistance in the Colorado potato beetle to the delta-endotoxin of B. thuringiensis.     

Host acceptance behaviour of Colorado potato beetle larvae influenced by potato glandular trichomes

ABSTRACT. In no-choice tests, larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), avoided contact with, and were less frequently observed feeding on, excised foliage of the resistant wild potato Solanum berthaultii Hawkes than on leaves of the cultivated potato, S.tuberosum L. For older larvae, reduced feeding was a consequence of less frequent contact with S.berthaultii leaves. However, first instars appeared unable to penetrate the adhesive barrier presented by glandular trichomes of S. berthaultii , and those that remained on the leaflets fed less often than did first instars on S. tuberosum. Removal of the trichome barrier by wiping leaflets with tissue paper did not attenuate the apparent repellent effect of S. berthaulti foliage, but led to increased incidence of feeding by first instars. Inhibition of larval feeding may therefore rely on a mechanical barrier provided by the glandular trichomes of S.berthaultii.     

Influence of fertilization on the Colorado potato beetle, Leptinotarsa decemlineata, in organic potato production

The abundance of the Colorado potato beetle, Leptinotarsa decemlineata (Say), in organically grown potato did not change significantly in response to increasing rates of dehydrated poultry manure. However, peaks of abundance of larvae were shifted forward in time in response to the high rate of organic fertilizer. Tests using excised foliage showed that the shift was not caused by differential larval mortality or longer developmental times. Time allocation to resting, walking, and feeding by adults was similar regardless of fertilizer rate. Adult foliage consumption was unaffected by organic fertilizer rates in no choice tests and significantly affected in few choice tests. A 22% longer larval development time on plants treated with low fertilizer rate than on plants with high rate was the most significant effect. Even though maximum plant height, canopy, biomass, and yield were significantly smaller in the organic than in conventional plots, the suitability of the plants was not affected except for reduced feeding by summer beetles. Summer adults spent less time feeding and consumed two to five times less foliage on organic potato than on inorganically fertilized and conventionally produced plants. The overall influence of fertilizer on Colorado potato beetle populations was limited and therefore can only play a secondary role in management strategies for organic potato. Avoidance of excessive organic fertilizer that promotes short larval development time and extension of the period over which large Colorado potato beetle larvae are present should be recommended.     

Pymetrozine causes a nontarget pest, the Colorado potato beetle (Coleoptera: Chrysomelidae), to leave potato plants

Pymetrozine is a selective insecticide that targets aphids. Published assessments of the effects of pymetrozine on nontarget organisms focus mainly on predatory insects, and they rarely indicate toxicity. In a laboratory bioassay, survival of Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), larvae was not affected by pymetrozine exposure. We subsequently used pymetrozine to implement low-aphid-density treatments in a field experiment that involved separate manipulations of Colorado potato beetle density. Unexpectedly, the addition of Colorado potato beetle adults and eggs did not increase the densities of Colorado potato beetle larvae in plots that were sprayed with pymetrozine (applied with water and an adjuvant). In control plots sprayed with water and adjuvant (without pymetrozine), addition of Colorado potato beetles increased densities of their larvae. Data collected on a smaller scale suggest that a behavioral mechanism underlies the population-level pattern: Colorado potato beetle larvae become more active and are less likely to remain on a host plant after exposure to pymetrozine. Thus, potato, Solanum tuberosum L., growers who use pymetrozine against aphids also might benefit in terms of Colorado potato beetle control.     

Modifications in dispersal and oviposition of Bt-resistant and Bt-susceptible Colorado potato beetles as a result of exposure to Bacillus thuringiensis subsp. tenebrionis Cry3A toxin

Laboratory strains of Colorado potato beetle, Leptinotarsa decemlineata (Say), physiologically resistant and susceptible to Bacillus thuringiensis (Berliner) subsp. tenebrionis Cry3A toxin were reared to adults on caged potato plants. Influence of three different diets (transgenic potatoes, regular potatoes, and regular potatoes followed by the transgenic potatoes) on beetle mortality, fecundity, and flight behavior were tested under laboratory conditions. A computer-linked flight mill system was used to quantify beetle flight, and dissections were performed to determine the level of flight muscle development. Susceptible beetles continuously fed on transgenic foliage suffered heavy mortality, did not develop flight muscles, and did not produce any eggs. Resistant beetles continuously fed on transgenic foliage were capable of flight and reproduction; however, it took them longer to initiate flight behavior, and their fecundity was lower than fecundity of other treatments. In both strains, detrimental effects became significantly less severe when the beetles were allowed to feed on regular foliage prior to toxin ingestion. In the resistant strain, ingestion of Cry3A toxin significantly increased flight activity, indicating that physiological resistance was probably reinforced by the behavioral escape from toxic environments. No such response was observed for susceptible beetles. When fed on regular foliage, resistant Colorado potato beetles engaged in significantly fewer flights than susceptible beetles. Behavioral differences between resistant and susceptible beetles observed in the present study are likely to affect gene flow between transgenic crops and adjacent refugia, and should be taken in consideration when designing resistance management plans for transgenic potato crops.     

Adult Colorado potato beetles, Leptinotarsa decemlineata compensate for nutritional stress on oryzacystatin I-transgenic potato plants by hypertrophic behavior and over-production of insensitive proteases

Protease inhibitors have been proposed as potential control molecules that could be engineered into potato plants for developing crops resistant to the Colorado potato beetle, Leptinotarsa decemlineata, a major pest of potato and other Solanaceae. In this study, we examined the effects of feeding young female beetles with foliage from a cultivar of the "Kennebec" potato line (K52) transformed with a gene encoding oryzacystatin I (OCI), a specific cysteine proteinase inhibitor with proven activity against cathepsin H-like enzymes of larvae and adults of the potato beetle. To evaluate the insect's performance, we collected data over a 16-d postemergence period on survival, diapause incidence, foliage consumption, weight gain, and oviposition of females. Tested individuals were fed untransformed (control) and OCI-transformed foliage at two stages of potato leaf differentiation, corresponding to "low" and "high" levels of OCI expression in leaves of K52. The OCI-expressing foliage did not affect female survival (close to 100%), incidence of diapause (15-30%), relative growth rate (RGR) during postemergence growth (5-9% d(-1)) or maximum weight reached (140-160 mg). Neither did it affect female reproductive fitness as measured by preoviposition time (8-9 d), 16-d fecundity (220-290 eggs), or egg eclosion incidence (86-91%). However, nutritional stress to females feeding on OCI foliage was evident, as reflected in their lower efficiency of conversion of ingested foliage (ECI) during postemergence growth, increased foliage consumed per egg laid (up to 119% more), and adaptation of their digestive proteolytic system to the inhibitory effect of OCI. Interestingly, beetles fed foliage expressing the highest level of OCI reacted rapidly to the presence of OCI by producing OCI-insensitive proteases, and exhibiting strong hypertrophic behavior by ingestion of 2.4-2.5 times more OCI rich foliage apparently as a compensatory response for nutritional stress due to the protease inhibitor in their diet.     

Effects of temperature on survival and preimaginal development rates of Colorado potato beetle on potato and horse-nettle: potential role in host range expansion

The effect of temperature on the ability of Colorado potato beetles (Leptinotarsa decemlineata, Say) to use horse-nettle (Solanum carolinense L.) as a host plant was determined for larvae from colonies originating from two geographically separated populations, one adapted to horse-nettle (NC) and the other unadapted to horse-nettle (MA). Survival and developmental rate on horse-nettle and potato were measured for larvae from both colonies over a range of constant temperatures (12–30 °C) and one fluctuating temperature regime (22 °C to 30 °C). The ability of Colorado potato beetles to use horse-nettle as a larval host was strongly influenced by temperature, but the effects of temperature differed greatly between beetles from the two colonies. Survival of adapted larvae on horse-nettle was highest and comparable to that on potato at the constant 30 °C and the fluctuating temperature regime. Below 30 °C, survival of adapted larvae decreased drastically but some larvae survived at all temperatures except the lowest (12 °C). In contrast, survival of unadapted larvae to adult occurred only at 30 °C, and was low (10%). At lower temperatures, all larvae died. On potato, the effect of temperature was less dramatic, and consistent across colonies. At 12 °C, survival to adult was poor (ca. 10%), but at higher temperatures, survival increased sharply and larvae from both colonies survived equally well. On potato, small but statistically significant differences in developmental rates between beetle colonies were detected at the constant but not at the fluctuating temperature regimes. Also, the developmental day degree requirements (DD) and the low temperature development threshold (T0) values for the various developmental stages did not differ between colonies on potato. On horse-nettle, development times for both colonies were always significantly longer and DD requirements were greater than on potato. At 30 °C, the only constant temperature at which larvae from the unadapted colony completed development, the development rate to adult emergence was similar to that of beetles from the adapted colony. Differences between colonies in performance on horse-nettle were not a result of host-independent, genetically based differences in the thermal requirements of the two populations. Our findings are consistent with the hypothesis that adaptation to horse-nettle by Colorado potato beetle may be facilitated by a genotype × environment interaction involving temperature. These findings have important implications for host plant utilization, host range expansion and selection of pest biotypes adapted to plant resistance traits used in crop protection.     

A freeze-dried diet to test pathogens of Colorado potato beetle

The Colorado potato beetle is an important pest on potato, eggplant, and tomato. Because Colorado potato beetles develop resistance to insecticides quickly, new methods are needed for control. Bacillus thuringiensis is the only bacterium to successfully control Colorado potato beetle. Until recently, one of the drawbacks to testing bacteria against the Colorado potato beetle has been the lack of an artificial diet for screening. Previous artificial diets will only be consumed by Colorado potato beetle larvae when fresh. To improve storage, we developed a freeze-dried diet, based on a 96-well plate, suitable to feed larvae for the duration of a bioassay. Individual diet components were tested both for their effect on insect growth and on pathogen toxicity. When the preservatives, methylparaben and sorbic acid, were removed from the diet, the average weight of second instar larvae increased from 7.9 mg to greater than 9.8 mg. The preservatives inhibited the growth of two of the bacteria tested, Photorhabdus luminescens HM and Chromobacterium sp. PRAA. The removal of these preservatives also allowed for fungal growth and reduced survival from 94 to 38%. Removing diet preservatives, that inhibited the growth of Chromobacterium sp. PRAA, increased the total mortality of the larvae as well as reducing the time needed to kill 50% of the larvae. Compared to incorporation of bacteria into molten diet, the total mortality of Colorado potato beetle fed either P. luminescens HM or Chromobacterium sp. PRAA on freeze-dried diet doubled. Preparation of freeze-dried diet need not be synchronized with the insect or the pathogen. The freeze-dried diet gave consistent results as measured by low control mortality and pathogen toxicity over time.     

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.     

The effect of mode of exposure to Beauveria bassiana on conidia acquisition and host mortality of Colorado potato beetle, Leptinotarsa decemlineata

The effects of the mode of exposure of second instar Colorado potato beetles to Beauveria bassiana on conidia acquisition and resulting mortality were investigated in laboratory studies. Larvae sprayed directly with a B. bassiana condial suspension, larvae exposed to B. bassiana-treated foliage, and larvae both sprayed and exposed to treated foliage experienced 76, 34, and 77% mortality, respectively. The total number of conidia and the proportion of germinating conidia were measured over time for four sections of the insect body: the ventral surface of the head (consisting mostly of ventral mouth parts), the ventral abdominal surface, the dorsal abdominal surface, and the legs. From observations at 24 and 36 h posttreatment, mean totals of 161.1 conidia per insect were found on sprayed larvae, 256.1 conidia on larvae exposed only to treated foliage, and 408.3 conidia on larvae both sprayed and exposed to treated foliage. On sprayed larvae, the majority of conidia were found on the dorsal abdominal surface, whereas conidia were predominantly found in the ventral abdominal surface and mouth parts on larvae exposed to treated foliage. Between 24 and 36 h postinoculation the percentage of conidia germinating on sprayed larvae increased slightly from 80 to 84%). On the treated foliage, the percentage of germinated conidia on larvae increased from 35% at 24 h to 50% at 36 h posttreatment. Conidia germination on sprayed larvae on treated foliage was 65% at 24 h and 75% at 36 h posttreatment. It is likely that the gradual acquisition of conidia derived from the continuous exposure to B. bassiana inoculum on the foliar surface was responsible for the increase in germination over time on larvae exposed to treated foliage. The density and germination of conidia were observed 0, 4, 8, 12, 16, 20, and 24 h after being sprayed with or dipped in conidia suspensions or exposing insects to contaminated foliage. Conidia germinated twice as fast on sprayed insects as with any other treatment within the first 12 h. This faster germination may be due to the pressure of the sprayer enhancing conidial lodging on cuticular surfaces.     

Bacillus thuringiensis cry3Ca1 protein is toxic to the Colorado potato beetle, Leptinotarsa decemlineata (Say)

We expressed the wild-type cry3Aa3 and cry3Ca1 Bacillus thuringiensis genes, which code for insecticidal proteins, in an Escherichia coli expression system. Highly purified preparations of the soluble delta-endotoxins were used to perform comparative bioassays with third-instar larvae of the Colorado potato beetle (CPB). Acute mortality data showed that Cry3Ca1 (LD(50) = 320.1 ng) was 2-fold more toxic than Cry3Aa3 (LD(50) = 672.9 ng). We also compared the chronic effects of sublethal doses of these toxins by measuring the consumption of untreated foliage and monitoring survival and development for 6 days after intoxication. No significant additional mortality was recorded, but we found that surviving larvae fed Cry3Ca1 consumed foliage at a slower rate than the larvae fed Cry3Aa3, suggesting more damage to their digestive epithelium. This study, the first assessment of the toxicity of cry3Ca1 in third-instar CPB, suggests cry3Ca1 will prove useful for the control of this important insect pest.     

Effect of diet and feeding history on flight of Colorado potato beetle, Leptinotarsa decemlineata

We evaluated the hypothesis that Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) flight frequency is related to diet, and that it changes with duration of food unavailability or exposure to poor quality food by exposing adult overwintered and summer CPB populations to an acceptable host plant (conventional foliage), a poor host (insect resistant transgenic foliage expressing Bacillus thuringiensis tenebrionis[Btt] Cry3a toxin) and no host. Exposure to poor host and no host treatments (with or without water) decreased mean daily flight frequencies and the overall number of overwintered CPB flying, but increased the mean daily flight frequency and number of summer population CPB that flew. Overwintered CPB did not react to an absence of plants at emergence whereas summer CPB increased mean daily flight frequencies when plants and water were not available. The flight response to insect resistant foliage was similar to that for starvation treatments in both populations indicating that flight may not be triggered by Btt toxins but by starvation brought on by feeding on poor quality food. Flight was observed in all treatments for the duration of the test with two exceptions; overwintered beetles fed insect resistant foliage ceased flying after day 17 and summer beetles starved without water ceased after day 8 of a 29‐day study.     

Bioassay determination of the distribution of imidacloprid in potato plants: implications to resistance development

Soil-applied imidacloprid exhibits exceptional efficacy as a systemic insecticide against the Colorado potato beetle, Leptinotarsa decemlineata (Say). An uneven distribution of the chemical within potato plants could result in differential concentrations, which may allow for discrimination between genotypes of varying susceptibility. In this study, susceptible and tolerant larvae were fed leaves from the lower, middle, and upper canopy of treated and untreated plants to characterize within-plant distribution of imidacloprid at 4, 6, 8, 10, 12, and 14 wk after planting. Significant differences in larval mortality and development indicated that the concentration of imidacloprid was unevenly distributed in the potato foliage during 6-14 wk after planting. The concentration of imidacloprid was lowest in the younger tissues of the upper leaves and highest in the older, lower leaves. At 6 wk, a time when the postdiapause beetles are colonizing potato fields, the lower concentration in upper leaves was toxic to susceptible larvae but did not kill a substantial portion of the tolerant larvae. Results suggest that higher concentrations of imidacloprid in the lower canopy leaves may act as a toxic barrier to colonizing susceptible beetles but may allow more tolerant individuals to reach the upper canopy with lower concentrations. Possible scenarios of how different concentrations of the systemic insecticide could influence the rate of resistance development are discussed.     

非寄主植物间套作对马铃薯甲虫种群及其天敌的影响

农田作物布局作为害虫生态调控的重要内容,一直是保护性生物防治的研究热点。为进一步明确马铃薯田块作物间套作种植模式对马铃薯甲虫种群动态的影响,探索马铃薯甲虫可持续防控的新思路与新方法,本研究在马铃薯甲虫发生期对马铃薯-玉米、马铃薯-向日葵、马铃薯单作3种作物间套作模式进行田间种群数量调查,分析比较不同种植模式下的马铃薯甲虫种群动态差异。结果表明：在马铃薯甲虫发生期,马铃薯单作第二代幼虫为害高峰期出现晚于两种间套作模式,第一代成虫为害高峰期早于两种间套作模式。第二代幼虫为害低峰期（8月26日-9月7日）时,马铃薯-玉米间套作幼虫量显著低于马铃薯单作（P<0.05）,马铃薯-玉米间套作幼虫量显著低于马铃薯-向日葵（P<0.05）,整个调查期间,马铃薯单作虫量要大于两种间套作。此外,天敌昆虫群落调查表明：间套作玉米异色瓢虫量显著高于马铃薯单作（P<0.05）,间套作向日葵的草蛉、食蚜蝇虫量高于马铃薯单作。间套作向日葵或玉米对越冬代马铃薯甲虫的扩散有影响,马铃薯播种初期间套作向日葵或玉米能在一定程度上阻隔马铃薯甲虫的定殖扩散。     

棉铃虫幼虫自相残杀习性与其龄期和食物营养的相关性（英文）

【目的】 昆虫自相残杀行为可以促进特定病原体的传播,这在利用昆虫病原体防治害虫方面有潜在的应用价值。本研究旨在探究棉铃虫 Helicoverpa armigera 幼虫自相残杀习性与其龄期及食物营养之间的相关性。【方法】 分别饲喂室内品系和野外品系的棉铃虫幼虫含不同Na⁺浓度的人工饲料,并在饲养至3龄、4龄、5龄和6龄时,将取食相同饲料的10头幼虫为一群组移入同一培养皿中,通过测定各处理幼虫存活率,评估幼虫龄期和饲料中的Na⁺含量对自相残杀行为的影响。【结果】 当以3龄和4龄为群组的起始龄期时,棉铃虫幼虫存活率显著低于起始龄期为5龄和6龄的群组。此外,取食正常人工饲料的幼虫存活率最高,取食缺钠饲料时,幼虫存活率明显下降。最后,幼虫群组起始龄期和食物Na⁺含量对幼虫化蛹率无明显影响。【结论】结果说明,棉铃虫4和5龄幼虫与3和6龄幼虫相比,自相残杀行为发生的概率更大,而Na⁺含量较低的食物在一定程度上促进自相残杀行为发生的可能性。本研究为在这一领域的进一步工作提供了基础。     

Resistance potential of colorado potato beetle (Coleoptera: Chrysomelidae) to novaluron

Novaluron (Rimon 10 EC), a novel insect growth regulator, could play an important role in future management programs for Colorado potato beetle, Leptinotarsa decemlineata (Say). Studies were conducted to determine the potential of Colorado potato beetle to develop resistance to novaluron before its widespread use in Colorado potato beetle management. Second instars of an imidacloprid-resistant Colorado potato beetle strain exhibited reduced susceptibility (2.5-fold) to novaluron. The toxicity of novaluron to this strain was synergized by S,S,S-tributyl phosphorotrithioate (DEF) but not by piperonyl butoxide (PBO), suggesting that esterase-based detoxification mechanisms were responsible for novaluron resistance. Bioassays with treated potato foliage found that a single low- or medium-rate novaluron application was highly persistent under field conditions, resulting in up to 85% mortality of second instars 5 wk after treatment. Thus, intense selection pressure for novaluron-resistant Colorado potato beetle may continue long after population densities have been reduced below an economic threshold level. In a national survey, the susceptibility of second instars to a novaluron diagnostic dose was determined for 27 different field populations collected from six Canadian provinces in summer 2003. Despite no previous exposure to novaluron, mortalities at the diagnostic dose ranged from 55 to 100%. Although novaluron has several characteristics that should delay resistance development in insect pests, these results highlight the need for judicious use of the compound in management of Colorado potato beetle.     

Response of potato aphid (Homoptera: Aphididae) to synthetic potato-derived Colorado potato beetle (Coleoptera: Chrysomelidae) attractant and natural potato odor

A recently synthesized kairomone blend, based on the volatiles produced by potato (Solanum spp.) plants, has been demonstrated to be attractive to both adult and larval stages of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). It was subsequently formulated in a viscous inert carrier for field applications and showed potential for aggregating beetles in treated areas of the field. We investigated effects of this kairomone formulation on the potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae). The response of both winged and wingless adults to natural potato foliage and synthetic kairomone was tested in a Y-tube olfactometer. Aphid response to untreated potato foliage, foliage treated with the kairomone blend, and foliage treated with blank inert carrier also was tested in petri dishes. In addition, aphid densities on field plots treated with kairomone and blank inert carrier were compared with the control plots. The untreated potato foliage was found to be attractive to wingless, but not winged, potato aphids. In the olfactometer, the foliage treated with synthetic Colorado potato beetle kairomone was not attractive to either winged or wingless aphids. In petri dishes, aphids avoided leaflets treated with both kairomone formulation and its blank carrier. There was no statistical difference between any treatments compared in the field.