Sulfhydryl-reagent alteration of soybean resistance to the cabbage looper, Trichoplusia ni

The hypothesis that the sulfhydryl reagent, N-ethylmaleimide, would function as an elicitor of alterable resistance in soybean (Glycine max) plants to Trichoplusia ni herbivory was tested experimentally under greenhouse conditions. This elicitory chemical, which allows receptor thiols to add across its carbon-carbon double bond, altered the resistance in one or more leaves of plants at one or more intervals after treatment; and thus yielded results supporting the hypothesis. Leaf dipping and soil application were both effective methods of treatment. Results support the interpretation that an elicitor may function in intact plants by altering the integrity of sulfhydryl groups in receptor macromolecules which are also involved in signaling a change in the plant's biosynthesis of characteristic defensive compounds such as phenylpropanoids including antifeedant and antibiotic flavonoids. Induced feeding non-preference by T. ni was highly correlated positively with the amount of glyceollins in the leaf.     

Surface morphology of peritrophic membrane formation in the cabbage looper,Trichoplusia ni

Summary The development of the peritrophic membrane in the cabbage looper, Trichoplusia ni, was investigated by scanning electron microscopy. The development of this membrane is characterized by a series of events suggested by the observations to be (1) secretion of material among and above the microvilli of the midgut epithelial cells, (2) maturation of this material into a randomly cross-linked fibrous matrix, and (3) aggregation of amorphous materials in and within the matrix. The membrane, possessing small discontinuities, remains intact in the midgut, but shows gross damage by the time it is passed from the insect, surrounding the feces.     

Spatial and temporal changes in genetic structure of greenhouse and field populations of cabbage looper,Trichoplusia ni

Trichoplusia ni is a subtropical moth that migrates annually from southern California to southern British Columbia, Canada where it invades vegetable greenhouses and field crops. The heated greenhouse environment has altered the natural extinction–recolonization dynamics of T. ni populations, and allows year‐round persistence in some locations. In addition, the extensive use of the biopesticide, Bacillus thuringiensis subspecies kurstaki (Bt) in some greenhouses has selected for resistance. Here we investigated the genetic structure of T. ni populations in British Columbia greenhouses and in field populations in California and British Columbia using amplified fragment length polymorphisms (AFLP) as related to patterns of Bt resistance. The majority of British Columbia field populations were similar to the California field populations, the potential source of migrants. However populations in two geographic areas with high concentrations of greenhouses showed local genetic differentiation. Some of these populations experienced severe bottlenecks over‐winter and following Bt sprays. Greenhouse populations showed a pattern of isolation by distance and a strong positive relationship between genetic differentiation and levels of Bt resistance. These patterns indicate that greenhouses that sometimes support year‐round populations of T. ni and the ensuing strong bottlenecking effects following winter cleanups and Bt application cause genetic differentiation of T. ni populations. Long distance migrants to field populations contribute to genetic homogeneity of these.     

Effects of natural and synthetic neuroactive substances on the growth and feeding of cabbage looper, Trichoplusia ni

In this study we investigated the effects of two naturally occurring beta-carboline alkaloids and two synthetic tricyclic antidepressants on the growth and food consumption of fifth instar larvae of the cabbage looper, Trichoplusia ni Hübner (Lepidoptera: Noctuidae). In artificial diets at high concentrations (3,000 ppm), harmane, amitriptyline, and imipramine reduce growth and feeding; harmane reduced feeding consistently at a lower concentration (200 ppm). In animals other than insects, beta-carboline alkaloids inhibit monoamine oxidase (MAO) activity and thus affect rates of disposition of serotonin and other monoamine neurotransmitters. Because brain serotonin levels are associated with variation in rates of carbohydrate and protein intake in insects, the effects of beta-carboline alkaloid ingestion on dietary self-selection behavior were examined. Choosing between diets lacking carbohydrate but containing protein and diets lacking protein but containing carbohydrate, larvae consumed a greater proportion of diet containing protein but lacking carbohydrate in the presence of harmane than in its absence. These results are consistent with beta-carboline alkaloid-mediated persistence of serotonin in the brain due to MAO inhibition. Alternatively, these results could reflect alkaloid-mediated peripheral inhibition of sucrose taste receptors influencing ingestive behaviors. That beta-carboline alkaloid ingestion is associated with changes in feeding behavior is consistent with a possible defensive role for these compounds in plant foliage.     

Different seasonal rearing conditions do not affect pheromone-sensitive receptor neurons of the adult cabbage looper moth, Trichoplusia ni

Abstract. In southern parts of the United States the cabbage looper moth, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), is multivoltine, and therefore successive generations experience different environmental conditions during development from larvae to adults.Since environmental conditions are thought to influence pheromone communication, we tested the effects of two different temperature and light regimes (selected to mimic those occurring in the spring and summer growing seasons in the south) during rearing on the response characteristics of the adult male olfactory receptor neurons responsible for detecting the major component of the female pheromone.The dose-response functions of receptor neurons from the warm- and cold-reared insects were similar in both their slopes and thresholds to stimulation with the major component of the female-emitted pheromone, (Z)-7, dodecen-1-ol acetate and (Z)-7, dodecen-1-ol, a behavioural inhibitor.In double pulse experiments, designed to emulate the temporal dispersion of pheromone in nature, neurons were stimulated with short pulses (200 ms) of (Z)-7, dodecen-1-ol acetate separated by varying intervals.Intervals as short as 30 ms reduced the response to a second pulse by over 50%.When the intervals between pulses were longer than 2 s, significant differences were not seen between the responses to the first and to the second pulse.These temporal response patterns were similar in both warm- and cold-reared animals.     

Hydrolysis of sex pheromone by antennal esterases of the cabbage looper, Trichoplusia ni

Esterases were isolated from chemosensory sensilla on the antennaeof Trichoplusia ni (Hübner). The disc gel electrophoreticpatterns of these esterases from males and females were similar;however, more bands were observed in the antennae than in 8other tissues examined. Most of the esterases detected in the100,000 g supernatant of the antennal preparation could be dissociatedfrom the 100,000 g membrane pellet. Esterases from both maleand female antennae hydrolyzed the sex attractant, (Z)-7-dodecen-l-olacetate, more rapidly than did the legs, fat body or Malpighiantubules. The enzymes primarily responsible for pheromone catabolismwere less sensitive to paraoxon, eserine and p-(hydroxymercuri)benzoatethan those hydrolyzing 1-napthyl acetate. This suggested thata major portion of the observed pheromone-hydrolytic activitywas due to acetylesterases. Measurement of pheromone hyrolysisin sections of disc gels that contained separated antennal orabdominal body wall esterases revealed 2 peaks of activity withboth tissues; however, the rate of pheromone hydrolysis by theabdominal esterases was slower than that of the antennae. Thesignificance of these findings is discussed in relation to thepossibility of antennal esterases having a functional role inthe olfactory process of males of T. ni.     

Behavioral responses of female adult Trichoplusia ni to volatiles from soybeans versus a preferred host, lima bean

Volatiles from different plants may have quite distinct effects on insect behaviors, i.e., attraction, repulsion or neutrality. Our study used Tenax^® to trap volatiles from plants at room temperature, and assayed female adult Trichoplusia ni's (Lepidoptera: Noctuidae) responses to such volatiles. The results showed that volatiles from PI 227687 soybean leaves were repellent to T. ni, while those from Davis soybean were attractive to the moth, and those from an unnumbered PI soybean had no significant behavioral effect. Odors from Henderson lima bean, one of the more preferred hosts of T. ni, also did not influence the insect's behavior. The HPLC, GLC and GLC-MS analyses indicated that qualitative and quantitative differences among volatiles from plant species, varieties or plant introductions account for these effects. The attractive volatiles from Davis soybean contain much more 4-hexen-1-ol acetate, 2,2-dimethyl hexanal and 2-hexenal than those of PI 227678, but do not have the repellent tetradecene and dodecene which are major components in PI 227687 soybean odors. The composition of the neutral volatiles from Henderson lima bean is more complex than that of the volatiles from soybeans.     

Monosaccharide compositions of Danaus plexippus (monarch butterfly) and Trichoplusia ni (cabbage looper) egg glycoproteins

Monosaccharide compositions of eggs from Danaus plexippus (monarch butterfly) and Trichoplusia ni (cabbage looper) were analyzed. Analyses were performed mainly with high performance anion exchange chromatography (HPAEC) using crude extracts of eggs or SDS-PAGE separated and PVDF-blotted protein bands. Man and GlcN were the major components in all cases, but low levels of Gal and Fuc were possibly present in some samples. Some T. ni egg glycoproteins even contained GalN. Although a peak comigrating with Neu5Ac could be detected with HPAEC-PAD or RP-HPLC (fluorometry) after derivatization with 1,2-diamino-4,5-methylenedioxy-benzene, the quantities were too small to be significant as an integral part of the analyzed glycoproteins. These data suggests that most of glycans on the glycoproteins are pauci-Man type N-glycans, but a small portion of N-glycan may be either hybrid type or complex type.     

Costs and stability of cabbage looper resistance to a nucleopolyhedrovirus

The goal of this study was to examine the possible costs and the stability of the resistance of cabbage loopers (Trichoplusia ni) to the single (S) nucleocapsid nucleopolyhedrovirus of T. ni (TnSNPV). Resistance to the virus did not appear to incur any measurable fitness costs under laboratory conditions. When reared in the absence of the virus, there was no difference in the number of eggs produced or egg hatch of control and selected individuals. There even was a tendency for selected cabbage loopers to develop faster and to produce heavier pupae. The difference in the pupal weight and developmental time of control and selected T. ni did not covary with the number of generations of selection. Furthermore, the offspring of hybrid crosses (control × selected moths) were as fit as those of pure pairings (control × control or selected × selected adults). Finally, the resistance of cabbage loopers to TnSNPV did not decline when exposure to the virus ceased for nine generations.     

The effect of host plant species on performance and movement behaviour of the cabbage looper Trichoplusia ni and their potential influences on infection by Autographa californica multiple nucleopolyhedrovirus

• 1 Cabbage loopers Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) are serious pests in greenhouses growing tomatoes, cucumbers and bell peppers. A potential microbial control, now in development, is the broad host‐range virus Autographa californica multiple nucleopolyhedrovirus (AcMNPV).
• 2 The relationships between the three host plants and the feeding behaviour, larval movement and performance of cabbage looper larvae that might relate to their interaction with AcMNPV applications were investigated.
• 3 Larvae reared on cucumber plants consumed approximately ten‐fold more leaf area than larvae reared on pepper plants and almost five‐fold more than larvae reared on tomato plants. This could influence the amount of AcMNPV consumed if it were used as a microbial spray because increased consumption can be associated with increased probability of infection. Survival from neonate to pupa also varied, with the greatest being on cucumber, followed by tomato and pepper plants. Larvae fed cucumber were approximately four‐fold heavier than larvae fed tomato and over 15‐fold heavier than larvae fed pepper plants.
• 4 The distribution of larvae on plants in commercial greenhouses where a single crop was being grown also varied with food plant with 73% being found on the bottom and middle portions of tomato plants and 87% occurring in the top portions of pepper plants. Larvae tended to be distributed on the middle portion of cucumber plants, the lower portion of tomato plants and the top portion of pepper plants. Larval movement did not vary between AcMNPV‐infected and uninfected controls.
• 5 It is predicted that the higher leaf area consumption and location of larvae in the middle portion of cucumber plants may make them more susceptible to viral sprays. Furthermore, given their greater survival than larvae fed tomato and pepper, there may be a greater need for virus applications.

     

Antennal neurones specific for redundant pheromone components in normal and mutant Trichoplusia ni males

Abstract Recordings were made from the pheromone-sensitive receptor cells within antennal hairs of normal and mutant male cabbage loopers, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), using a cut-sensillum technique. From sampling 136 sensilla on normal males and 123 on mutant males, cells excited by pairs of behaviourally redundant minor pheromone components were discovered: Z9–14: Ac was found to be replaceable with 12: Ac and 11–12: Ac was found to be replaceable with Z5–12: Ac. These cells were not found during previous neurophysiological investigations, but explain most of the associations between mutually replaceable (redundant) pheromone components which had been demonstrated previously to be behaviourally redundant in wind tunnel studies. Our results indicate that the mutant gene in T.ni that affects pheromone production does not affect pheromone receptors in males. Using both AC- and DC-coupled recordings from receptor cells, we found that a single minor component could apparently hyperpolarize one cell while depolarizing another cell within the same sensillum, suggesting that noise reduction and other complex signal processing by receptor cells may contribute to odour processing in the macroglomerulus of the antennal lobe.     

Oviposition preference,larval performance and adaptation of Trichoplusia ni on cabbage and cotton

Most female herbivores ensure to lay eggs where their offspring can develop successfully. The oviposition preferences of females affect strategies in pest management. In this study, the performance of two cohorts of Trichoplusia ni larvae on cabbage and cotton (after they had been transferred from their original host plants) were investigated. The preferences of female moth ovipositing and larval feeding on these two host plants were observed. The results indicated that plants significantly affected oviposition preference of the female adults and development and survival of larvae of T. ni. All females preferred to lay eggs on cabbage than cotton regardless from which host they originated. The detrimental effects of cotton on the development and survival of T. ni larvae originated from cabbage (CaTn) increased with the increase of the larval age when they were transferred. In addition, the host plant change did not significantly affect the development and survival of larvae of T. ni originating from cotton (CoTn). Larvae of CaTn preferred cabbage plants as compared to cotton plants, whereas larvae of CoTn did not show a significant choice. Although the adult females preferred laying eggs on cabbage, they did not show preferences between cotton and cabbage in a Y‐tube olfactometer test. The hypothesis of oviposition preference and performance of larvae was supported by the results of CaTn, whereas they not supported by those from CoTn. Based on these results, the strategy to manage this serious pest was discussed.     

A high‐quality chromosome‐level genome assembly of a generalist herbivore,Trichoplusia ni

The cabbage looper, Trichoplusia ni, is a globally distributed highly polyphagous herbivore and an important agricultural pest. T. ni has evolved resistance to various chemical insecticides, and is one of the only two insect species that have evolved resistance to the biopesticide Bacillus thuringiensis (Bt) in agricultural systems and has been selected for resistance to baculovirus infections. We report a 333‐Mb high‐quality T. ni genome assembly, which has N50 lengths of scaffolds and contigs of 4.6 Mb and 140 Kb, respectively, and contains 14,384 protein‐coding genes. High‐density genetic maps were constructed to anchor 305 Mb (91.7%) of the assembly to 31 chromosomes. Comparative genomic analysis of T. ni with Bombyx mori showed enrichment of tandemly duplicated genes in T. ni in families involved in detoxification and digestion, consistent with the broad host range of T. ni. High levels of genome synteny were found between T. ni and other sequenced lepidopterans. However, genome synteny analysis of T. ni and the T. ni derived cell line High Five (Hi5) indicated extensive genome rearrangements in the cell line. These results provided the first genomic evidence revealing the high instability of chromosomes in lepidopteran cell lines known from karyotypic observations. The high‐quality T. ni genome sequence provides a valuable resource for research in a broad range of areas including fundamental insect biology, insect‐plant interactions and co‐evolution, mechanisms and evolution of insect resistance to chemical and biological pesticides, and technology development for insect pest management.     

Sodium polyacrylamide polyacrylate, a gelling agent in diets for cabbage looper, omnivorous looper and western avocado leafroller

Ingredient substitutions for agar or carrageenan in artificial diets for lepidopterous larvae were evaluated. A sodium polyacrylamide polyacrylate gelling agent, Water-Lock G-400, was compared with agar for solidifying diets of the cabbage looper, Trichoplusia ni (Hübner), omnivorous looper, Sabulodes aegrotata (Gueneé), and the western avocado leafroller, Amorbia cuneana Walsingham. Water-Lock G-400 is considerably less expensive than agar or carrageenan, it does not require heating to gel, and it is made from a dependable supply of agricultural starch. Sabulodes aegrotata pupae from larvae reared on agar were significantly heavier than those reared on Water-Lock G-400. However, the remainder of the variables observed (larval survival, developmental times, fecundity, sex ratio and pupal weights for A. cuneana and T. ni) were all independent of diet. Decreasing the total amount of ingredients in a Water-Lock-G-400 diet produced fewer and smaller T. ni pupae than did an agar diet when the larvae were reared using a mass production protocol. However, these lower values were still above acceptable levels for mass production and reduced the cost of diet production by 65%.Further ingredient substitutions impaired larval development (i.e., replacing pinto beans with soy protein or combinations of soy protein and -cellulose), while others did not (i.e., excluding pinto beans and reducing water content and replacing pinto beans with -cellulose or corn cob grits). Moisture control by adding corn cob grits to diets increased the yield of pupae, while removing water from diets increased survivorship and the yield of pupae.     

Vertical transmission of TnSNPV,TnCPV, AcMNPV,and possibly recombinant NPV in Trichoplusia ni

Four viruses were tested for vertical transmission in Trichoplusia ni: T. ni nucleopolyhedrovirus (TnSNPV), T. ni cypovirus (TnCPV), Autographa californica nucleopolyhedrovirus (AcMNPV), and AcMNPV engineered to express a scorpion toxin (AcMNPV.AaIT). Fifth instars were exposed to each virus, the survivors were reared and mated, and second-generation (F(1)) insects were examined for infection. TnSNPV was transmitted to offspring at a prevalence rate of 15.4%, TnCPV at 10.2%, and AcMNPV at 10.1%. Only one of 2484 F(1) insects was infected with AcMNPV.AaIT; this experiment was repeated, and none of 4774 insects was infected. Thus, vertical transmission is unlikely to contribute to AcMNPV.AaIT contacting non-target organisms after its field release. There was evidence that TnCPV and possibly TnSNPV were activated to overt infections by ingestion of a different virus. TnCPV, but not the NPVs, routinely infected 0.3-1.7% of non-treated insects, probably indicating that it is vertically transmitted at enzootic levels.     

Managing lepidopteran pests in cabbage with herbicide-induced resistance, in combination with a pyrethroid insecticide

S-ethyldipropylthiocarbamate (EPTC) applied as a soil treatment or over-the-top spray on cabbage plants (Brassica oleracea L.) caused the leaves to turn ‘glossy’ for as long as 30 days. EPTC-induced glossy plants were damaged significantly less than untreated plants by diamondback moth,Plutella xylostella (L.), imported cabbage worm,Pieris rapae (L.), and cabbage looper,Trichoplusia ni (Hbn.). Reductions in damage were equivalent to those obtained from treatment with permethrin. When used in combination with permethrin, EPTC provided additive control of damage by these pests. Our calculations show EPTC-induced resistance to be cost-effective. This use of EPTC has several limitations, however. Younger plants (<9 leaves) were killed or injured by the herbicide. The growth of older plants was not affected, but plants did not become glossy for ca. 10 days after they were treated with EPTC. The crop must be protected with insecticides until the plants are mature enough to treat with EPTC, and until treated plants become glossy. In addition, since the glossy trait is only effective against first instar larvae, populations of later instars on glossy plants must be reduced with an application of insecticide. Finally, EPTC formulations are water-soluble and can be washed away from the plants by heavy rains and irrigation, which may make this use of EPTC impractical in some situations. Where its use is practical, and the indicated precautions are taken, EPTC-induced resistance could reduce dependence on chemical insecticides and reduce selection for insecticide resistance in diamondback moth.     

Genetic variation in fitness parameters associated with resistance to Bacillus thuringiensis in male and female Trichoplusia ni

Resistance of insects to insecticides is often associated with reduced fitness in the absence of selection. We examined fitness trade-offs associated with resistance to the microbial insecticide, Bacillus thuringiensis (Bt), across full-sib families in a resistant population of Trichoplusia ni. Significant genetic variation in and heritability of susceptibility to Bt occurred among the full-sib families. Male pupal weight was positively correlated with Bt susceptibility, indicating a potential fitness cost, but no such correlation occurred for females. Significant heritability for pupal weight was present for males but not females. A significant negative genetic correlation existed between development time and Bt susceptibility, indicating that resistant larvae developed more slowly than susceptible larvae. Selection for Bt resistance in T. ni resulted in changes in life-history traits that affected males more than females.     

Circadian changes in melatonin in the nervous system and hemolymph of the cabbage looper moth,Trichoplusia ni

Quantitative levels of melatonin and 5-hydroxytryptamine were measured over the scotophase in the protocerebrum, subesophageal ganglion, optic lobes, thoracic ganglia, and hemolymph of adult male cabbage looper moths, Trichoplusia ni, using HPLC with electrochemical detection. Melatonin levels were very low (s < 1 pmol) or undetectable during the photophase, but increased in all tissues during the dark. Lowest mean levels in the dark were observed in the optic lobes (0.3 to 0.7 pmols). Maximal mean levels in the protocerebrum (5.2 pmols) occurred in the early part of the scotophase, but in all other tissues (2.8 in the subesophageal ganglion; 9.5 in thoracic ganglia) and hemolymph (18 pg/l) maximal mean levels were observed later in the dark. Levels of 5-hydroxytryptamine in each tissue, in contrast, were higher than melatonin levels in the photophase, and in the protocerebrum and thoracic ganglia decreased during the dark, but in the optic lobes and subesophageal ganglion remained unchanged. Further, decreases in 5-hydroxytryptamine during the dark were significantly lower than the increased levels of melatonin, suggesting that active synthesis of 5-hydroxytryptamine was occurring. In a second experiment, when measured from individuals in three different photoperiods (618, 1212, 186 lightdark) maximum mean melatonin levels in the brain (protocerebral and subesophageal ganglia) peaked within the first 1.5 h of the dark and remained at measurable levels for the duration of the dark. In a third experiment, levels of melatonin in the brain and thoracic ganglia displayed rhythmicity in continuous dark conditions but not in continuous light, when compared with profiles obtained in a normal light dark regime.Abbreviations CNS Central nervous system - HPLC-ECD high performance liquid chromatography with electrochemical detection - MEL melatonin - 5HT 5-hydroxytryptamine - N-ac-SHT N-acetyl-5-hydroxytryptamine