Serial Selection for Resistance to a Wild-Type and to a Genetically Modified Nucleopolyhedrovirus in Trichoplusia ni

In previous work, cabbage loopers (Trichoplusia ni) evolved 22-fold resistance to the single nucleocapsid nucleopolyhedrovirus of T. ni (TnSNPV) after 26 generations of selection with the virus. The goal of the present study was to determine if T. ni could evolve resistance to the recombinant Autographa californica multiple nucleocapsid nucleopolyhedrovirus (AcMNPV-AaIT) that expresses an insect specific neurotoxin and to determine if it was influenced by prior development of resistance to TnSNPV. To answer these questions, the T. ni line that had been exposed to TnSNPV was divided into two sublines at generation 27. One of them was serially selected for resistance to AcMNPV-AaIT (subline TnSNPV/AcMNPV-AaIT), while the other one was mock infected with distilled water (subline TnSNPV/H₂O). The same was done with the line that was used as a control from generations 1 to 26 (subline H₂O/AcMNPV-AaIT and subline H₂O/H₂O). After 17 generations of selection with AcMNPV-AaIT, T. ni that had not been previously exposed to TnSNPV evolved only twofold resistance to AcMNPV-AaIT. However, those that had been selected with TnSNPV evolved fourfold resistance to AcMNPV-AaIT. Exposure to AcMNPV-AaIT conferred cross-resistance to TnSNPV in only one subline, subline H₂O/AcMNPV-AaIT. Resistance to AcMNPV-AaIT did not affect the developmental time, pupal weight, egg production, or percentage of egg hatch of T. ni.     

The development of larval resistance to a nucleopolyhedrovirus is not accompanied by an increased virulence in the virus

Two laboratory experiments were conducted to examine the possible coevolution of cabbage loopers (Trichoplusia ni) and their S nucleopolyhedrovirus (TnSNPV). At the conclusion of Experiments 1 and 2, T. ni had respectively evolved 4.4 × and 22 × resistance to TnSNPV. The higher level of resistance achieved in Experiment 2 could be due to marginally stronger selection, possibly greater genetic variability in larval resistance to TnSNPV, or both. However, the evolution of resistance was not accompanied by an increased virulence of TnSNPV or a change in the restriction profile of the viral DNA when digested with BamHI, EcoRI, HindIII, PstI, SalI, SstI or XhoI. Little genetic variability for virulence in the initial TnSNPV stocks, low mutation rates and possibly weak selection on the virus are some factors that may have constrained the evolution of TnSNPV. We discuss our results in light of the geographic mosaic theory of coevolution and their implications for the use of TnSNPV as a biological control agent against T. ni. This revised version was published online in November 2006 with corrections to the Cover Date.     

Impact of flowering buckwheat on Lepidopteran cabbage pests and their parasitoids at two spatial scales

We assessed the potential of annual buckwheat, Fagopyrum esculentum Moench, to lead to improved parasitism of lepidopteran cabbage pests over four years. Pest, parasitism, and hyperparasitism rates were monitored in replicated cabbage plots (12 × 20 m) with or without 3 m wide buckwheat borders from 2000 to 2003. Floral borders did not significantly increase egg, larval, or pupal densities of cabbage looper, Trichoplusia ni (Hübner), imported cabbageworm, Pieris rapae (L.), or diamondback moth, Plutella xylostella (L.). Buckwheat increased parasitism rates by Voria ruralis (Fallen) on T. ni larvae and Cotesia rubecula (Marshall) on P. rapaelarvae over four years. Parasitism by Diadegma insulare (Cresson) on P. xylostella larvae was higher in buckwheat than control plots in the first year, and parasitism by Euplectrus plathypenae (Howard) on T. ni larvae was lower in buckwheat than control plots in the second year. The hyperparasitoid Conura side (Walker) attacked D. insulare all four years, but buckwheat did not affect hyperparasitism rates. The effect of spatial scale on pest densities and parasitism in 2001 was evaluated by comparing plots separated at least 67 m (nearby) versus 800 m apart (isolated). T. ni pupae and P. rapae eggs and pupae were more abundant in plots in closer proximity, whereas P. xylostella densities did not vary by the spatial separation of plots. Tachinids and Pteromalus puparum (L.) attacked more P. rapae in nearby plots. E. plathypenae responded to the treatment × scale interaction, parasitizing more in control than buckwheat when plots were isolated but not when plots were nearby.     

Genetic Resistance to Bacillus thuringiensis Alters Feeding Behaviour in the Cabbage Looper,Trichoplusia ni

Evolved resistance to xenobiotics and parasites is often associated with fitness costs when the selection pressure is absent. Resistance to the widely used microbial insecticide Bacillus thuringiensis (Bt) has evolved in several insect species through the modification of insect midgut binding sites for Bt toxins, and reports of costs associated with Bt resistance are common. Studies on the costs of Bt-resistance restrict the insect to a single artificial diet or host-plant. However, it is well documented that insects can self-select appropriate proportions of multiple nutritionally unbalanced foods to optimize life-history traits. Therefore, we examined whether Bt-resistant and susceptible cabbage loopers Trichoplusia ni differed in their nutrient intake and fitness costs when they were allowed to compose their own protein:carbohydrate diet. We found that Bt-resistant T. ni composed a higher ratio of protein to carbohydrate than susceptible T. ni. Bt-resistant males exhibited no fitness cost, while the fitness cost (reduced pupal weight) was present in resistant females. The absence of the fitness cost in resistant males was associated with increased carbohydrate consumption compared to females. We demonstrate a sex difference in a fitness cost and a new behavioural outcome associated with Bt resistance.     

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.     

Attraction of the cabbage looper to host plants and host plant odor in the laboratory

In a laboratory flight tunnel, mated female, unmated female, and male adult cabbage loopers, Trichoplusia ni (Hübner), exhibited chemically mediated anemotaxis (attraction) in response to intact potted cabbage plants (Brassica oleracea L.), leading to contact with the plant. Similar attraction responses were also observed by mated females to potted soybean (Glycine max (L.)), tomato (Lycopersicon esculentum Miller), and celery (Apium graveolens L.) plants in noncompetitive comparisons. Mated females, unmated females, and males flew to cabbage plants throughout the scotophase. Response rates for mated females were higher than for unmated females and males. Mated female cabbage loopers were attracted by odors of cabbage, soybean, tomato, or celery piped into a flight tunnel from single plants held in glass jars and not to odors of the non-host plant Setcreasea purpurea, or to humidified air. They were also attracted to water washings of cabbage at dosages of 0.4 to 2.0 gram equivalents, when presented on cotton dental wicks in the flight tunnel.     

Electrophysiological correlates of attraction in Trichoplusia ni

A quantitative comparison was made between pheromone-induced electroantennogram (EAG) potentials and the attraction of male cabbage loopers, Trichoplusia ni. For this comparison, duplicate pheromone dispensers were used in both assays. The slope of the function of evoked EAG potentials was the same as the slope of the function of percentage attraction to different amounts of pheromone, but the EAG was calculated to be about 3 × 10⁴ times less sensitive than the attraction response. Thus, the EAG of T. ni was not a reliable indicator of relative attraction to various batches of synthetic pheromone, and no difference in the evoked EAG was observed between an inhibitor of the behavioural response to the pheromone and the pheromone itself.     

Occurrence and accumulation of viruses of Trichoplusia ni in treated field plots

Concentrations of the nuclear-polyhedrous virus (T. ni NPV) and the granulosis virus (T. ni GV) of the cabbage looper, Trichoplusia ni, in soil and on foliage were monitored up to 4 years after treatment.A single application of T. ni NPV to soil in August or 5 foliar applications of the virus at 10-day intervals in August and early September maintained substantial concentrations of the virus on foliage and high concentrations of the virus accumulated in soil. With development of natural epizootics of the virus disease in populations of the host larvae in September and October, substantial concentrations of the virus accumulated in soil and on foliage in nontreated plots, eventually becoming equal in amount with the virus in virus-treated plots. The virus accumulated more slowly in plots treated with chemical insecticides or Bacillus thuringiensis because few host larvae survived to support late-season epizootics of the disease. Small quantities of T. ni NPV were detected in heads of cabbage harvested from the plots in October.Long-term studies in which nontreated plots and plots treated with T. ni NPV or T. ni GV were replanted for up to 4 years after treatment showed that concentrations of T. ni NPV in surface soil remained constant during the winter but were reduced by dilution during cultivation preparatory to planting in the spring. T. ni NPV accumulated during the late summer and autumn with development of epizootics of the disease in populations of host larvae. Increased concentrations of the virus in soil coincided with increased concentrations on leaves in each year. T. ni GV did not persist on leaves or in soil following application and only small amounts were found 2 years after application.T. ni NPV disease was prevalent in September and October in populations of host larvae in plots in which substantial residues of the virus were found. These epizootics contributed substantially to late-season control of the looper after completion of spraying.     

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.     

Sequence variation and differential splicing of the midgut cadherin gene in Trichoplusia ni

The insect midgut cadherin serves as an important receptor for the Cry toxins from Bacillus thuringiensis (Bt). Variation of the cadherin in insect populations provides a genetic potential for development of cadherin-based Bt resistance in insect populations. Sequence analysis of the cadherin from the cabbage looper, Trichoplusia ni, together with cadherins from 18 other lepidopterans showed a similar phylogenetic relationship of the cadherins to the phylogeny of Lepidoptera. The midgut cadherin in three laboratory populations of T. ni exhibited high variability, although the resistance to Bt toxin Cry1Ac in the T. ni strain is not genetically associated with cadherin gene mutations. A total of 142 single nucleotide polymorphisms (SNPs) were identified in the cadherin cDNAs from the T. ni strains, including 20 missense mutations. In addition, insertion and deletion polymorphisms (indels) were also identified in the cadherin alleles in T. ni. More interestingly, the results from this study reveal that differential splicing of mRNA also occurs in the cadherin gene expression. Therefore, variation of the midgut cadherin in insects may not only be caused by cadherin gene mutations, but could also result from alternative splicing of its mRNA regulated by factors acting in trans. Analysis of cadherin gene alleles in F2, F3 and F4 progenies from the cross between the Cry1Ac resistant and the susceptible strain after consecutive selections with Cry1Ac for three generations showed that selection with Cry1Ac did not result in an increase of frequencies of the cadherin alleles originated from the resistant strain.     

Resistance to Bacillus thuringiensis in the cabbage looper (Trichoplusia ni) increases susceptibility to a nucleopolyhedrovirus

Cabbage loopers, Trichoplusia ni, are pests in many agricultural settings including vegetable greenhouses in British Columbia (Canada), where microbial insecticides based on Bacillus thuringiensis (Bt) toxins are commonly used. Frequent use of these insecticides has led to resistance in some populations. An alternative microbial control is the multiple nucleopolyhedrovirus of the alfalfa looper (Autographa californica), AcMNPV which occurs naturally, but at low frequencies in T. ni populations. Bioassays show that T. ni resistant to Bt were twice as susceptible to AcMNPV as were individuals from the Bt-susceptible strain and AcMNPV could be complementary in a resistance management program for T. ni.     

Chitinolytic enzymes from Streptomyces albidoflavus expressed in tomato plants: effects on Trichoplusia ni

Tomato (Lycopersicon esculentum ) cultivars were transformed with genes that encode bacterial chitinolytic enzymes (i.e., endochitinase and chitobiosidase) from Streptomyces albidoflavus. Transgenic tomato plants producing these enzymes were found to have enhanced resistance to cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), consistently reducing the growth rates of larvae. Mortality was significantly increased in two of three feeding trials. Ingestion of endochitinase and chitobiosidase not only affected development of larval T. ni from neonate to ultimate instar, but they also caused mortality and decreased insect weight when exposure began during the third instar. The results of this study provide some insight into the mode of action of the chitinolytic enzymes, by supporting the hypothesis that ingested chitinolytic enzymes damage the chitin component of the peritrophic envelope, leading to increased permeability. The size of marker molecules (FITC-dextrans) that permeated the peritrophic envelopes of T. ni feeding on transgenic plants were 50% larger than those permeating the peritrophic envelopes of T. ni feeding on the control plants. Further research is needed to more clearly identify the sites and modes of action of these chitinolytic enzymes, and the potential for synergy between these enzymes and pathogens, allelochemicals, and other environmental factors.     

Control of Lepidopteran insect pests in transgenic Chinese cabbage (Brassica rapa ssp. pekinensis) transformed with a synthetic Bacillus thuringiensis cry1C gene

 A synthetic Bacillus thuringiensis cry1C gene was transferred to three Korean cultivars of Chinese cabbage via Agrobacterium tumefaciens-mediated transformation of hypocotyl explants. Hygromycin resistance served as an efficient selective marker. The transformation efficiency ranged from 5% to 9%. Transformation was confirmed by Southern blot analysis, PCR, Northern analysis, and progeny tests. Many transgenic plants of the closed-head types (lines Olympic and Samjin) flowered in vitro. Over 50 hygromycin-resistant plants were successfully transferred to soil. The transgenic plants and their progeny were resistant to diamondback moths (DBM, Plutella xylostella), the major insect pest of crucifers world-wide, as well as to cabbage loopers (Trichoplusia ni) and imported cabbage worms (Pieris rapae). Both susceptible Geneva DBM and a DBM population resistant to Cry1A protein were controlled by the Cry1C-transgenic plants. The efficient and reproducible transformation system described may be useful for the transfer of other agriculturally important genes into Chinese cabbage. Received: 12 June 2000 / Revision received: 21 August 2000 / Accepted: 22 August 2000     

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.     

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.     

Impact of non‐pathogenic bacteria on insect disease resistance: importance of ecological context

1. The aerial surface of plants is a habitat for large and diverse microbial communities; termed the phyllosphere. These microbes are unavoidably consumed by herbivores, and while the entomopathogens are well studied, the impact of non‐pathogenic bacteria on herbivore life history is less clear. 2. Previous work has suggested that consumption of non‐entomopathogenic bacteria induces a costly immune response that might decrease the risk of infection. However, we hypothesised that insect herbivores should be selective in how they respond to commonly encountered non‐pathogenic bacteria on their host plants to avoid unnecessary and costly immune responses. 3. An ecologically realistic scenario was used in which we fed cabbage looper, Trichoplusia ni Hübner, larvae on cabbage or cucumber leaves treated with the common non‐entomopathogenic phyllosphere bacteria, Pseudomonas fluorescens and P. syringae. Their constitutive immunity and resistance to a pathogenic bacterium (Bacillus thuringiensis; Bt) and a baculovirus (T. ni single nucleopolyhedrovirus) were then examined. 4. While feeding on bacteria‐treated leaves reduced the growth rate and condition of T. ni, there was no effect on immunity (haemolymph antibacterial and phenoloxidase activities and haemocyte numbers). Phyllosphere bacteria weakly affected the resistance of T. ni to Bt but the direction of this effect was concentration dependent; resistance to the virus was unaffected. Host plant had an impact, with cucumber‐fed larvae being more susceptible to Bt. 5. The lack of evidence for a costly immune response to non‐entomopathogenic bacteria suggests that T. ni are probably adapted to consuming common phyllosphere bacteria, and highlights the importance of the evolutionary history of participants in multi‐trophic interactions.     

Effect of dietary selenium supplementation on resistance to baculovirus infection

We have examined the effects of dietary selenium (Se) supplementation on larval growth and immunocompetence of the lepidopteran pest, the cabbage looper, Trichoplusia ni. Supplementation of the diet of T. ni larvae with 10–20 ppm Se resulted in a 1 day delay in pupation. The effects of the addition and/or removal of dietary Se on total Se bioaccumulation and sequestration were determined by neutron activation analysis of pupae. Early penultimate instar larvae moved from selenium containing diet to basal diet lost total pupal Se content down to the level of those fed basal diet. Conversely, larvae moved from basal diet to diet containing additional Se rapidly attained pupal Se levels comparable to larvae fed Se throughout larval development. Therefore, dietary Se is rapidly accumulated or lost during larval development, but significant amounts are sequestered from diet into pupae. Larvae were reared on diet supplemented with 5 or 10 ppm Se until the onset of the penultimate instar then infected per os with increasing concentrations of the fatal baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Larvae fed Se in the penultimate and ultimate instars were more resistant to viral infection than larvae not fed Se in the final instars. This study indicates that dietary Se levels rapidly impact Se assimilation and sequestration and that tissue Se levels are an important factor in resistance to AcMNPV infection in larval T. ni.     

Incidence of Entomophthora sp. and other natural control agents in populations of Pseudoplusia includens and Trichoplusia ni

A species of Entomophthora was observed as a mortality factor in populations of Pseudoplusia includens and Trichoplusia ni in cotton and soybean fields throughout Alabama. Resting spores appear identical to those of Tarichium gammae. The incidence of this fungus in host populations, as well as other disease agents and parasites, was determined from larval samples collected throughout the State. Entomophthora infected 8% of all loopers collected on cotton as compared to 35% on soybeans. T. ni nuclear polyhedrosis virus infected 41% of all loopers collected from cotton but no mortality attributable to virus was found in loopers collected on soybeans, which were predominantly P. includens.Studies in 1969 and 1970 on the incidence of Entomophthora sp. in a population of P. includens infesting soybeans in central Alabama have shown it to infect between 50 and 95% of all individuals present from early August through mid-September, the period of densest abundance of the caterpillars. Spicaria sp. was also present during August and September but did not contribute significantly to reduction in population levels until late in the season. Parasites accounted for less than 1% of all mortality in each year and predator populations were very small during the periods of observation.     

Leaf shape variation and herbivore consumption and performance: a case study with Ipomoea hederacea and three generalists

The effect of leaf shape variation on plant-herbivore interactions has primarily been studied from the perspective of host seeking behavior. Yet for leaf shape to affect plant-herbivore coevolution, there must be reciprocal effects of leaf shape variation on herbivore consumption and performance. We investigated whether alternative leaf morphs affected the performance of three generalist insect herbivores by taking advantage of a genetic polymorphism and developmental plasticity in leaf shape in the Ivyleaf morning glory, Ipomoea hederacea. Across four experiments, we found variable support for an effect of leaf shape genotype on insects. For cabbage loopers (Trichoplusia ni) and corn earworms (Helicoverpa zea) we found opposing, non-significant trends: T. ni gained more biomass on lobed genotypes, while H. zea gained more biomass on heart-shaped genotypes. For army beetworms (Spodoptera exigua), the effects of leaf shape genotype differed depending on the age of the plants and photoperiod of growing conditions. Caterpillars feeding on tissue from older plants (95 days) grown under long day photoperiods had significantly greater consumption, dry biomass, and digestive efficiency on lobed genotypes. In contrast, there were no significant differences between heart-shaped and lobed genotypes for caterpillars feeding on tissue from younger plants (50 days) grown under short day photoperiods. For plants grown under short days, we found that S. exigua consumed significantly less leaf area when feeding on mature leaves than juvenile leaves, regardless of leaf shape genotype. Taken together, our results suggest that the effects of leaf shape variation on insect performance are likely to vary between insect species, growth conditions of the plant, and the developmental stage and age of leaves sampled. Handling editor: May Berenbaum.     

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.