Chemoreceptors in the cibario-pharyngeal pump of the cabbage looper moth,Trichoplusia ni (Lepidoptera: Noctuidae)

The structure of contact chemoreceptors in the cibariopharyngeal pump of the moth Trichoplusia ni (Lepidoptera: Noctuidae) is described. Two types of receptors designated A and B are located on the floor of the pump. Two groups of 9-12 A receptors are located in the anterior part of the pump, and two groups of two B receptors are in the posterior part of the pump. Five sensory dendrites extend to the tip of each A receptor and four to each B receptors. Available evidence indicates that these receptors are contact chemoreceptors and do not serve as mechanoreceptors. The receptors are compared to those of other insects.     

Insecticidal and feeding deterrent activities of essential oils in the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae)

Ten essential oils were tested against the cabbage looper, Trichoplusia ni larvae for contact, residual and fumigant toxicities and feeding deterrent effects. Against third instar T. ni, Syzygium aromaticum (LD₅₀ = 47.8 μg/larva), Thymus vulgaris (LD₅₀ = 52.0 μg/larva) (the two positive controls) and Cinnamomum glanduliferum (LD₅₀ = 76.0 μg/larva) were the most toxic via topical application. Litsea pungens (LD₅₀ = 87.1 μg/larva), Ilex purpurea (LD₅₀ = 94.0 μg/larva), Cinnamomum cassia (LD₅₀ = 101.5 μg/larva) and Litsea cubeba (LD₅₀ = 112.4 μg/larva) oils were equitoxic. Thymus vulgaris (LC₅₀ = 4.8 mg/ml) and S. aromaticum (LC₅₀ = 6.0 mg/ml) oils were the most toxic in residual bioassays. Cymbopogon citratus (LC₅₀ = 7.7 mg/ml) and C. cassia (LC₅₀ = 8.5 mg/ml) oils were equitoxic followed by Cymbopogon nardus (LC₅₀ = 10.1 mg/ml) in this bioassay. The remaining five oils showed little or no residual effects. In a fumigation bioassay, L. cubeba (LC₅₀ = 16.5 μl/l) and I. purpurea (LC₅₀ = 22.2 μl/l) oils were the most toxic. Cinnamomum glanduliferum (LC₅₀ = 29.7 μl/l) and Sabina vulgaris (LC₅₀ = 31.2 μl/l) oils were equitoxic. Interestingly, S. aromaticum did not exhibit any fumigant toxicity. Cymbopogon citratus, C. nardus and C. cassia strongly deterred feeding by third instar T. ni (DC₅₀s = 26.9, 33.8 and 39.6 μg/cm², respectively) in a leaf disc choice bioassay. The different responses of T. ni larvae to the oils in different bioassays suggest that these essential oils exhibit different modes of action. Based on their comparable efficacy with essential oils already used as active ingredients in many commercial insecticides (i.e. clove oil and thyme oil), some of these essential oils may have potential as botanical insecticides against T. ni.     

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.     

Ultrastructure of host tissues exposed to the calyx fluid of the parasitoid,Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae)

Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) is a solitary endoparasitoid of Heliothis virescens. The lateral oviducts of the female parasitoid contain a particulate suspension called calyx fluid. The particles in calyx fluid are a polydnavirus (CsV) which, when injected into last-instar H. virescens, stimulates degeneration of the host's prothoracic glands. In order to determine if CsV-induced degeneration is specific to prothoracic glands, last-instar H. virescens larvae were injected with C. sonorensis calyx fluid. After 4 days, a variety of host tissues were dissected from both calyx fluid-injected and uninjected control larvae and fixed for transmission electron microscopy. Prothoracic glands from injected larvae were ultrastructurally degenerated by 4 days post-injection, whereas control glands remained intact. Other tissues from calyx fluid-injected larvae (tracheal epithelia, corpora allata, Malpighian tubules, fat body, skeletal muscle, and the brain) showed no signs of ultrastructural degeneration or gross abnormalities as compared with control tissues. These observations suggested that CsV-induced degeneration is specific to the host's prothoracic glands.     

Campoletis sonorensis [Hym.: Ichneumonidae] as a parasitoid ofSpodoptera frugiperda [Lep.: Noctuidae]: Host stage preference and functional response

The response of the parasitoidCampoletis sonorensis (Cameron) as a natural control agent of the fall armyworm,Spodoptera frugiperda (J. E. Smith), was evaluated at 6 host densities and 2 temperature regime. A type-II functional response was exhibited by femaleC. sonorensis in response to varying densities of all armyworn larvae at both temperatures. Significantly more larvae were parasitized at 25°C for the host densities of 60 and 75, than for the same densities at 30°C. Third instar fall armyworm larvae were found to be the preferred stage for parasitization byC. sonorensis. This research was supported by funds from HATCH project no. H-368 as allocated to the Georgia Agricultural Experiment Station.     

Secretion of Na+, K+ and fluid by the Malpighian (renal) tubule of the larval cabbage looper Trichoplusia ni (Lepidoptera: Noctuidae)

The Malpighian (renal) tubules play important roles in ionic and osmotic homeostasis in insects. In Lepidoptera, the Malpighian tubules are structurally regionalized and the concentration of Na⁺ and K⁺ in the secreted fluid varies depending on the segment of tubule analyzed. In this work, we have characterized fluid and ion (Na⁺, K⁺, H⁺) transport by tubules of the larval stage of the cabbage looper Trichoplusia ni; we have also evaluated the effects of fluid secretion inhibitors and stimulants on fluid and ion transport. Ramsay assays showed that fluid was secreted by the iliac plexus but not by the yellow and white regions of the tubule. K⁺ and Na⁺ were secreted by the distal iliac plexus (DIP) and K⁺ was reabsorbed in downstream regions. The fluid secretion rate decreased > 50% after 25 μM bafilomycin A1, 500 μM amiloride or 50 μM bumetanide was added to the bath. The concentration of K⁺ in the secreted fluid did not change, whereas the concentration of Na⁺ in the secreted fluid decreased significantly when tubules were exposed to bafilomycin A1 or amiloride. Addition of 500 μM cAMP or 1 μM 5-HT to the bath stimulated fluid secretion and resulted in a decrease in K⁺ concentration in the secreted fluid. An increase in Na⁺ concentration in the secreted fluid was observed only in cAMP-stimulated tubules. Secreted fluid pH and the transepithelial electrical potential (TEP) did not change when tubules were stimulated. Taken together, our results show that the secretion of fluid is carried out by the upper regions (DIP) in T. ni Malpighian tubules. Upper regions of the tubules secrete K⁺, whereas lower regions reabsorb it. Stimulation of fluid secretion is correlated with a decrease in the K⁺/Na⁺ ratio.     

Superparasitism behavior and host discrimination of Campoletis chlorideae (Ichneumonidae: Hymenoptera) toward Mythimna separata (Noctuidae: Lepidoptera)

The oriental army worm, Mythimna separata Walker (Lepidoptera: Noctuidae), was adopted as a host to keep Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) populations in the laboratory, because it can be mass reared. However, wasp cocoon production in this system via single parasitism was not satisfactory. To improve the rearing efficiency of C. chlorideae on M. separata, we studied the effects of superparasitism on the offspring production of C. chlorideae, as well as the host discrimination ability of the adult wasps in the laboratory. The results showed that, compared with single parasitism, both double and quintuple parasitism significantly increased C. chlorideae cocoon production in M. separata without a significant effect on emergence, weight, or sex ratio of adult wasps at the P < 0.05 level. Host selection experiments suggested that C. chlorideae preferred to lay eggs on unparasitized hosts rather than freshly parasitized hosts but could distinguish neither the 24-h postparasitization hosts from the unparasitized hosts nor the freshly self-parasitized hosts from the conspecifically parasitized hosts. No-choice behavior tests indicated that C. chlorideae took significantly longer time to accept the freshly parasitized hosts containing more than two eggs compared with the unparasitized hosts. In the end, superparasitism behavior and its application in the mass rearing of this endoparasitoid are discussed.     

Interaction of Acronicta rumicis (Lepidoptera: Noctuidae) and its larval parasitoid, Glyptapanteles liparidis (Hymenoptera: Ichneumonidae)

As a result of parasitism by Glyptapanteles liparidis in the first, second, third and fourth instar larvae of Acronicta rumicis, the mortality of each larval stage was found to be 46.67, 90, 71 and 16.67%, respectively. The mortality was highest when G. liparidis parasitized the second and third instar larvae. The difference in mortality between the parasitized group and the control group was 72.14% in the second instar larvae. With regards to the food consumption of the parasitized larvae, the first and second instar larvae consumed 6495.58 ± 646.52 mm² (leaf surface) and 7951.12 ± 4167.36 mm², respectively, while the third and fourth larvae consumed 13 826.77 ± 3396.66 mm² and 18 599.85 mm², respectively, showing that food consumption increased with instar stages of the host larvae. The clutch size of G. liparidis increased in relation to the instar stages of the host: it was 25.25 ± 7.89, 48.65 ± 53.75, 91.09 ± 44.52 and 114 individuals when they were fed with the first, second, third and the fourth instar larvae of the host, respectively.     

Plant exudates trigger leaf-trenching by cabbage loopers, Trichoplusia ni (Noctuidae)

Cabbage loopers, Trichoplusia ni, cut a narrow trench across leaves of plants that release exudate, then feed distal to the trench in an area of reduced exudation. The larvae do not normally trench plant species such as plantain, Plantago lanceolata, that lack exudate. To determine what cues elicit trenching, I reared larvae to the final instar on plantain, then applied test solutions to their mouthparts during feeding. Loopers that received latex from Lactuca serriola (Asteraceae) or phloem exudate from watermelon, Citrullus vulgaris (Cucurbitaceae), often responded by cutting a trench in plantain, even though these larvae had not previously encountered exudate nor previously trenched. Loopers that were allowed to trench and feed on L. serriola for 1 day prior to the assay subsequently cut trenches in plantain more frequently and in response to more fluids, including a viscous solution of polyethylene glycol and latex from a non-host, poinsettia (Euphorbia pulcherrima). Subsequent bioassays with larvae reared entirely on plantain tested whether bitter cucurbitacins or gelation are essential cues for trenching. Sap from non-bitter cucumber plants (Cucumis sativus) caused larvae to trench, showing that cucurbitacins are not required to induce trenching. Loopers also trenched after receiving cucumber sap that did not gel due to the addition of mercaptoethanol. An extract of sap lacking the proteins that cause gelation likewise triggered trenching. Further fractionation revealed that cucumber sap and also butternut squash sap (Cucurbita moschata) contain trenching stimulants that are small (molecular weight < 3,000) water-soluble molecules. Received: 13 January 1997 / Accepted: 6 June 1997     

Establishment of a cell line from embryos of the cabbage looper,Trichoplusia ni (hubner)

Summary A new cell line was developed from 3-d-old embryonated eggs of the cabbage looper,Trichoplusia ni, and has been designated IPLB-TN-R². It contains a variety of morphological cell types, including myoblastlike, neuroblastlike, and epithelial-like cells. Chromosome analysis revealed typical lepidopteran chromosomes. Isozyme characterization showed patterns similar to two other cabbage looper cell lines (TN-368 and IAL-TND1) in the case of five enzymes but differed from these two lines for two other enzymes. Virus infectivity tests revealed the line is highly susceptible toAutographa californica nuclear polyhedrosis virus, but no cytopathology was observed after inoculation with several other lepidopteran viruses.     

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.     

Toxicity,persistence, and efficacy of indoxacarb on cabbage looper (Lepidoptera: Noctuidae) on cabbage

Toxicity of indoxacarb was bioassayed against eggs and young (first and second instars) and older larvae (third and fourth instars) of cabbage looper, Trichoplusia ni (Hübner), on cabbage (Brassicae oleracea variety capitata L.), and persistence of field-aged leaf residues of indoxacarb was bioassayed with second and third instars of T. ni on cabbage. Efficacies of indoxacarb and several other newer insecticides to T. ni were tested under field conditions for two seasons in south Texas. LC50 and LC90 values for T. ni eggs were relatively high, indicating that indoxacarb has little ovicidal effects on T. ni eggs. Indoxacarb was highly toxic to T. ni larvae, having low LC50 and LC90 values. Bioassays of field-aged leaf residues of indoxacarb tested in the spring of 1998 (0-, 3-, 5-, and 12-d-old residues) and the fall of 2000 (0-, 3-, 5-, 7-, 9-, and 13-d-old residues) indicated that ingesting indoxacarb was highly toxic to the second and third instars of T. ni, giving 100% mortality for the second instars at 2 d after exposure, and 100% mortality for third instars at 5 d after exposure. Two trials conducted under field conditions show that indoxacarb at 0.072 g (AI) /ha rate was effective against T. ni in cabbage, providing marketable cabbage with three applications per season. In addition, indoxacarb was as effective as spinosad and chlorfenapyr and significantly more effective than tebufenozide and emamectin benzoate.     

Positive association between resistance to Bacillus thuringiensis and overwintering survival of cabbage loopers, Trichoplusia ni (Lepidoptera: Noctuidae)

Development of resistance to insecticides has generally been associated with fitness costs that may be magnified under challenging conditions. Lepidopterans which are resistant to the biopesticide Bacillus thuringiensis subsp. kurstaki (Btk) have been shown to have reduced fitness, such as lower survival when subjected to overwintering stress. Recently, resistance to Btk has been found in some populations of Trichoplusia ni Hübner in greenhouses in British Columbia. This situation provides an opportunity to investigate potential trade-offs between overwintering survival and insecticide resistance in a major pest species. Here, we assess the survival and eventual fecundity of Btk resistant and susceptible T. ni pupae exposed to cool temperatures. Contrary to our expectations, resistant T. ni had higher overwintering survival than susceptible individuals. This is the first account of a potential advantage associated with Btk resistance. Resistant and susceptible moths had reduced fecundity and smaller progeny after cold exposure compared to controls, and this may counteract the survival advantage. Nevertheless, it seems unlikely that this is sufficient to select out the resistant phenotype in the presence of strong selection for resistance and in the absence of immigration of susceptible moths. The appearance of resistance without evidence of a trade-off in overwintering survival presents a major challenge to management in production greenhouses.     

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.     

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.     

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.