Populations of Predaceous Natural Enemies Developing on Insect-Resistant and Susceptible Tomato in North Carolina

Naturally occurring populations of immature and adultGeocoris punctipes,adultColeomegilla maculataand immature coccinellids were monitored on field-grown tomato lines susceptible and resistant toManduca sextaandHelicoverpa zea. Helicoverpa zeaandHeliothis virescenseggs and small larvae that serve as prey for these predators also were monitored. MoreH. zeaandH. virescenseggs and small larvae were found on resistant than on susceptible plant lines. However, similar populations of largeH. zeaandH. virescenslarvae were found on resistant and susceptible plants. The number of adultGeocoris punctipes,adultColeomegilla maculataand immature coccinellids on resistant plants was always as high or higher than the number on susceptible plants. The data demonstrate no incompatibility of host-plant resistance with biological control provided by these predaceous insects, but indicate that the number ofG. punctipesand coccinellids required to provide effective biological control may develop too late in the season to be of practical value. Large populations of stilt bugs (Jalysus wickhami,Hemiptera: Berytidae) and spiders were observed to occur earlier in the growing season than eitherG. punctipesor coccinellids and may be a significant source of mortality forH. zeaeggs and small larvae.     

Susceptibility of larvae ofHeliothis zea,H. virescens,andH. armigera [lep.: Noctuidae] to 3 baculoviruses

The pattern of virulence (based on inclusion bodies) for 3 baculoviruses ofHeliothis, i.e. a unicapsid, nuclear polyhedrosis virus (HzSNPV); a multicapsid, nuclear polyhedrosis virus (HaMNPV); and a granulosis virus (HaGIV) was the same (HzSNPV>HaMNPV>HaGIV) for 3 species ofHeliothis. Based on numbers of nucleocapsids, however, the HaGIV was ca 2X more virulent than the HaMNPV for larvae ofH. virescens, (F.), and the HaMNPV was about 6X more virulent than the HaGIV for larvae ofH. armigera (Hübner). The fastest rate of larval mortality was obtained with HzSNPV. Although the mortality rate for HaGIV was faster than that of HaMNPV forH. virescens andH. armigera, it was slower than that of HaMNPV for larvae ofH. zea (Boddie). The pattern of susceptibility ofHeliothis species to HzSNPV and HaMNPV wasH. zea>H. virescens>H. armigera. Differences in susceptibility of the least susceptible species (H. armigera) and the most susceptible species (H. zea) to HzSNPV was ca. 1.6 X. Larvae ofH. zea, however, were ca. 4 to 6 X more susceptible to HaMNPV than were larvae ofH. virescens orH. armigera. A different pattern of susceptibility was recorded for HaGIV when larvae were challenged with HzSNPV and HaMNPV. Larvae ofH. virescens were ca. 20 and 35 X more susceptible to HaGIV than were larvae ofH. zea andH. armigera, respectively.     

A high incidence of parasitism ofHeliothis SPP. [Lep.: Noctuidae] larvae in cotton in Southeastern Arkansas

During 1981 and 1982, bollworm,Heliothis zea (Boddie), and tobacco budworm,H. virescens (F.), larvae (n=3,666) were collected from 41 cotton fields near Portland, Arkansas (USA) to assess the occurrence of parasitism. Three strategies were employed to controlHeliothis spp. in these fields: (1) release ofTrichogramma pretiosum Riley; (2) insecticidal control; or (3) inaction (check). Insecticide use in nonchemical control fields was reduced, but not eliminated.Heliothis spp. larvae collected in cotton had higher parasitism rates in 1981 (30.9%) and 1982 (50.1%) than had been reported for cotton since the advent of organochlorine insecticide usage. Four species of larval parasites and 1 species of larval-pupal parasite were recorded. The larval parasiteMicroplitis croceipes (Cresson) comprised 90.6% and 94.5% of all parasitic insects reared from field collectedHeliothis spp. in 1981 and 1982, respectively. No difference (P>0.05) in level of parasitism existed betweenH. zea andH. virescens. Differences between treatments occurred only in 1982 whenH. zea larvae were parasitized at a greater (P<0.05) rate in check fields (68.3%) than in insecticidal control fields (44.3%). Higher levels of larval parasitism in cotton fields may be a consequence of reduced insecticide usage and changes in materials applied, particularly the pyrethroids. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Field evaluation of insect resistance in a wild tomato and its effects on insect parasitoids

Populations ofHelicoverpa (=Heliothis) zea (Boddie),Heliothis virescens (F.),Manduca sexta (L.) andM. quinquemaculata (Haw.) and their egg and larval parasitoids were sampled in field plots of the: insect-resistant wild tomato,Lycopersicon hirsutum f. glabratum C. H. Mull, accession PI 134417; susceptible commercial tomato cultivar ‘Better Boy’; F₁ hybrid; and selected, moderately resistant backcross genotype. Densities ofH. zea andH. virescens eggs and small larvae were higher on resistant genotypes than on susceptible genotypes, but densities of large larvae were similar on all genotypes. Densities ofManduca spp. larvae were too low to permit similar analyses of the effects of plant genotype. Rates of egg parasitism byTrichogramma spp. andTelenomus sphingis (Ashmead) were reduced on insect-resistant genotypes. Rates of parasitism by the larval parasitoidsCampoletis sonorensis (Cameron) andCotesia congregata (Say) were reduced on resistant genotypes. No consistent effects on parasitism rates byCotesia marginiventris (Cresson) were observed and parasitism rates byCardiochiles nigriceps Viereck were unaffected.     

Structures of Monohydroperoxides Produced from Chlorophyll Sensitized Photooxidation of Methyl Linoleate

The effects on growth and mortality of larvae of pink bollworm (Pectinophora gossypiella, Saunders), bollworm (Heliothis zea, Boddie) and tobacco budworm (Heliothis virescens, F.) of adding selected C₁₀–C₁₂ fatty acid methyl esters to a standard diet were determined. The antibiotic activity of straight chain saturated esters was compared to the activity of esters with an olefinic bond either at C-2 or terminally or with a terminal acetylenic or cyclopropyl group. The ester with the greatest activity was the naturally occurring compound methyl (Z,Z)-deca-2,8-diene-4,6-diynoate (matricaria ester) which was lethal to all pink bollworm larvae at 0.01% in the diet and lethal to all bollworm and tobacco budworm larvae at 0.05%.     

Handling time, prey preference, and functional response for Chrysoperla rufilabris in the laboratory

The predaceous larvae of Chrysoperla rufilabris (Burmeister) exhibited some success-motivated searching, particularly when feeding on Heliothis virescens (F.) eggs, but handling time did not decrease with experience. Handling time for H. virescens larvae was more than twice that for eggs. H. virescens larvae were preferred to cotton aphids (Aphis gossypii (F.)) while aphids were preferred to H. virescens eggs. C. rufilabris larvae exhibited a linear functional response to the three prey types tested, over the prey densities tested.USDA, ARS, Retire. Present address: 200 Highland, College Station, TX 77840, USA     

Effects of cuticle source and concentration on germination of conidia of two isolates of Nomuraea rileyi

The effects of cuticle from larvae of Trichoplusia ni, Heliothis zea and H. virescens on rate and extent of germination of conidia of a Mississippian isolate (MS) and an Ecuadoran (EC) isolate of Nomuraea rileyi were studied. Solid substrates generally stimulated more germination than submerged substrates. There was little or no effect of cuticle source (H. zea or H. virescens) on germination of either the EC isolate or the MS isolate cultured on a solid substrate, however, differences in patterns of germination were obtained in submerged substrates. Addition of cuticle of H. zea or H. virescens generally increased the germination time for the MS isolate. Germination time for the EC isolate was significantly increased when H. virescens cuticle was used.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by U.S. Department of Agriculture.     

Role of the exoprotease InA in the pathogenicity of Bacillus thuringiensis in pupae of Hyalophora cecropia

Two geographical biotypes of Nomuraea rileyi (from Ecuador and the United States) were topically bioassayed against seven lepidopteran species, i.e., Anticarsia gemmatalis, Heliothis zea, Heliothis virescens, Heliothis subflexa, Pseudoplusia includens, Spodoptera exigua, and Trichoplusia ni. There was an average difference of 1.7-fold in mortality in how cultures of the same insect species from different sources responded to topical applications of either biotype of N. rileyi. Regression equations and LC₅₀ values were obtained for each insect species and fungal biotype combination. Larvae of S. exigua were equally susceptible to both biotypes of N. rileyi. Although larvae of A. gemmatalis were moderately susceptible to the Ecuadoran biotype, they were relatively nonsusceptible to the Mississippian biotype. Species of Heliothis (H. zea, H. virescens, and H. subflexa) were about equally susceptible to the Mississippian biotype. Larvae of H. subflexa and H. virescens, however, were significantly less susceptible than H. zea to the Ecuadoran biotype. When the integumental barrier was breached via intrahemocoelic injections, larvae of H. virescens were as susceptible as H. zea larvae to blastospores of either biotype of N. rileyi.     

Replication and infectivity of the single-embedded nuclear polyhedrosis virus, Baculovirus heliothis, in homologous cell lines

Three cell lines of Heliothis zea and one cell line of Heliothis virescens replicated the singleembedded, nuclear polyhedrosis virus (NPV) of H. Zea, (i.e., Baculovirus heliothis) with concomitant production of polyhedral inclusion bodies (PIB). Between 20 and 60% of the H. zea cells produced PIB, whereas only 3% of H. virescens cells were found to produce PIB. The H. zea cell lines produced 10 to 20 times more PIB than did the H. virescens cell line. The PIB from all cell lines produced typical symptoms of an NPV infection when bioassayed against larvae of H. zea. More than 99% of the total viral activity of the final whole culture was due to the PIB.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Susceptibility of Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) to Vip3A insecticidal protein expressed in VipCot™ cotton

Susceptibility of laboratory and field colonies of Helicoverpa zea (Boddie) and Heliothis virescens F. to Vip3A insecticidal protein was studied in diet incorporation and diet overlay assays from 2004 to 2008. Responses of field populations were compared to paired responses of University of Arkansas laboratory susceptible H. zea (LabZA) and H. virescens (LabVR) colonies. After 7 d of exposure, observations were made on number of dead larvae (M) and the number of larvae alive but remaining as first instars (L1). Regression estimates using M (LC₅₀) and M plus L1 (MIC₅₀) data were developed for laboratory and field populations. Susceptibility of laboratory and field populations exposed to Vip3A varied among different batches of protein used over the study period. Within the same batch of Vip3A protein, susceptibilities of laboratory colonies of both species (LabZA and LabVR) were similar. Field colonies were significantly more susceptible to Vip3A than the respective reference colonies of both species. Within field populations, susceptibility to Vip3A varied up to 75-fold in H. zea and 132-fold in H. virescens in LC₅₀ estimates. Variabilities in MIC₅₀s were up to 59- and 11-fold for H. zea and H. virescens, respectively.     

Microplitis croceipes teratocytes cause developmental arrest of Heliothis virescens larvae

Microplitis croceipes teratocytes placed into nonparasitized Heliothis virescens larvae survived in the absence of a parasitoid larva and caused developmental changes in the host. Expressions of these changes included delayed larval mortality, incomplete larval-pupal ecdysis, or delayed pupation. Two day old 4th stadium H. virescens larvae were more sensitive to injected teratocytes than were 5th stadium larvae. Three day old teratocytes were more effective than were 6 day old teratocytes. The degree of response was related to the number of injected teratocytes. For example, 750 three day old teratocytes (the approximate number from a single parasitoid egg) caused delayed larval mortality in 96% of the treated larvae whereas 175 three day old teratocytes caused delayed larval mortality in only 33% of the treated larvae. Even a dose of 80 teratocytes resulted in 15% incomplete larval-pupal ecdysis compared to 0% for controls. Treatment with hemocyte-and teratocyte-free hemolymph from parasitized larvae, hemocytes from nonparasitized H. virescens, unfertilized M. croceipes eggs, Cotesia congregata teratocytes, or Micrococcus lysodeikticus cells all had very little effect either on larval growth or development time.     

Phosphorus-32 bioelimination by arthropod predators fed labeled eggs ofHeliothis virescens [Lep.: Noctuidae]

Adults ofGeocoris punctipes (Say),Tropiconabis capsiformis Germar,Nabis roseipennis Reuter andColeomegilla maculata (DeGeer) were confined inside petri dishes and fed phosphorus-32 (^32p)-labeledHeliothis virescens (F.) eggs. Observations of bioelimination of^32p over a 72 h period allowed derivation of equations for predicting the number ofH. virescens eggs ingested by each species. Twenty-four to 72 h after eggs were eaten, the percentages of^32p eliminated ranged from ca. 14% forG. punctipes to 42 % forT. capsiformis. Cautious use of the results will aid researchers in assessing predation on^32p labeledHeliothis. Publication N^o 5935. Mississippi Agricultural and Forestry Experiment Station, Mississippi State, MS 39762.     

Discovery of novel trimethylalkanes in the internal hydrocarbons of developing pupae of Heliothis virescens and Helicoverpa zea

Novel trimethyl-branched alkanes which eluted with the monomethylalkanes were identified in the internal lipids of Helicoverpa zea but were not present in Heliothis virescens. Their structures were unique in that the first methyl branch occurred on carbon 2 and the 2nd and 3rd methyl branch points were separated by a single methylene. Novel trimethylalkanes identified from their chemical ionization and electron impact mass spectra were 2,18,20-trimethyltetratriacontane, 2,18,20-trimethylhexatriacontane, and 2,24,26-trimethyldotetracontane. Previous reports did not find these trimethylalkanes in the cuticular surface lipids of larvae, pupae or adults of either species. The internal pupal hydrocarbons of H. virescens and H. zea amounted to 123 μg and 304 μg per pupa, respectively. They consisted of n-alkanes (8 and 4%, respectively) and methyl-branched alkanes (88 and 94%, respectively). The n-alkanes ranged in chain length from approximately 21 to 35 carbons and the methyl-branched alkanes from approximately 26 to 55 carbons vs. methyl-branched alkanes from 28 to 37 carbons previously reported for hydrocarbons from the pupal cuticular surface. The major n-alkane was heptacosane (3.3 and 1.2%, respectively, in H. virescens and H. zea). The major methyl-branched alkanes in H. virescens were methylhentriacontane (15%), methyltritriacontane (12%) and dimethyltritriacontane (10%), and in H. zea were methylnonacosane (17%), dimethylnonacosane (9%) and methylhentriacontane (20%). Except for the novel trimethylalkanes, the methylalkane branch points were predominantly on odd-numbered carbons as has been reported for these and other species.     

Alkanes of four related moth species,Helicoverpa and Heliothis

Comparison of the presence and quantities of cuticular hydrocarbons has been used successfully for identifying sibling species and races of several groups of insects. This approach has been extended to four species of moths previously regarded as belonging to the same genus, Heliothis. Gas chromatography was used to quantify the numerous high-molecular weight alkanes found on the cuticle of two pairs of closely related species: Helicoverpa zea and Helicoverpa armigera, and Heliothis virescens and Heliothis subflexa. Both sexes of H. zea and H. armigera contained different quantities of several alkanes that could be used for unambiguous identification. Similar comparisons of H. subflexa and H. virescens showed four peak ratios that were different for each species. Sexual dimorphism was minor in H. subflexa and H. virescens.     

Epizootics of Entomophthora aulicae in lepidopterous pests of sorghum

Entomophthora aulicae caused 48–100% mortality in Heliothis zea larvae collected from sorghum August 24–September 6, 1978, in Tift County, Georgia. The same fungus also caused 74 and 95% mortality in Celama sorghiella larvae and 19 and 40% mortality in Spodoptera frugiperda larvae collected from sorghum August 30 and September 6 in the same area. Only 2 of 94 H. virescens larvae collected from a nearby patch of pigeon peas were killed by the fungus. This is the first report of epizootics caused by E. aulicae in pests of field crops in the southeastern United States.     

The surface hydrocarbons of larval Heliothis virescens and Helicoverpa zea

Third instar larvae of Heliothis virescens and Helicoverpa zea could be distinguished based on the hydrocarbons of their surface lipids. Hydrocarbons were the major components of the surface lipids and a distinctive capillary gas chromatographic profile could be obtained from a hexane extract of the surface lipids of a single larva. Analysis of hexane extracts of the surface lipids by capillary gas chromatography-mass spectrometry (CGC-MS) showed several obvious differences between the two species: (1) in their gas chromatographic profiles; (2) in the presence of a major alkene, hentriacontene, only in H. zea; (3) in H. virescens the CGC-MS peak with a KI of approximately 2860 was 2-methyloctacosane, but in H. zea it was a mixture of 4-methyloctacosane plus 9,13- and 8,12-dimethyloctacosanes; and (4) in the methyl branch positions of dimethyl-branched alkanes with carbon backbones of C₃₁, C₃₃, C₃₅, C₄₅, C₄₇, C₄₉ and C₅₁. The methyl branch points of H. virescens dimethylalkanes were separated by seven or nine methylenes, while in H. zea the methyl branch points of the dimethylalkanes were separated by three and sometimes five methylenes.     

Cuticular and non-cuticular substrate influence on expression of cuticle-degrading enzymes from conidia of an entomopathogenic fungus,Nomuraea rileyi

Larval cuticle fromTrichoplusia ni, Helicoverpa (=Heliothis)zea, andHeliothis virescens and a cellulose substrate were used to quantify release of proteolytic, chitinolytic, and lipolytic enzymes by germinating conidia of the entomopathogenic fungus,Nomuraea rileyi. There was no significant difference in conidial viability incubated withT. ni, H. zea or cellulose substrates. Conidial viability onH. virescens cuticle, however, was significantly lower (ca. 19–25%) than the other three substrates. The presence of cuticle substrates, especially cuticle ofT. ni, stimulated germination. The nature of the substrate influenced both the time and quantity of the enzymes expressed. Specific proteases (aminopeptidase, chymoelastase, trypsin) generally were expressed earlier and/or in greater quantities on cuticular than on the cellulose substrate. Although both chitinolytic enzymes (endochitinase, N-acetylglucosaminidase) were detected on all three cuticular substrates, their activity was substantially lower than that of the proteolytic enzymes. Lipase activity was only minimally present. Early concurrent release of both proteases and chitinases suggested that both may be important in the penetration of the larval integument by germinating conidia ofN. rileyi. Expression of proteases and chitinases, especially aminopeptidase and endochitinase was probably a specific response to cuticle, because little or no activity was expressed on the non-host, cellulose substrate.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by the US Department of Agriculture.     

Importance of predation by Coleomegilla maculata larvae in the natural control of the corn earworm in sweet corn

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) is a serious pest of many crops in North America, particularly sweet corn. The larvae of Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae) are the most frequently observed predators of H. zea eggs in sweet corn. Companion cropping strategies have been developed to augment densities of C. maculata in sweet corn plantings. In this study, the importance of predation by C. maculata larvae was evaluated in experiments when larval abundance was manipulated using hand removal and physical exclusion. In 2003 and 2004, sentinel H. zea eggs were exposed on corn for 48 h. Egg mortality was 13.8% greater in the treatment where C. maculata larvae were present. In 2004 and 2005 eggs were exposed on corn under the same hand removal and physical exclusion techniques and monitored at 3-h intervals for 24 h to directly observe predation on sentinel eggs. Coleomegilla maculata larvae were the most frequently observed predators of the eggs, accounting for 45.9% of 85 total observed predation events in the control. Whereas in the treatment where C. maculata larvae were reduced, egg survival was 26.13% greater and only 37 total predation events were observed. All pest eggs were eliminated from individual ears 22.1% more often when C. maculata larvae were present at natural densities indicating that predation by this predator stage lessens crop damage by H. zea. The results of this study suggest that C. maculata larvae are an irreplaceable source of natural mortality for H. zea eggs on sweet corn.     

Functional response ofChrysopa carnea [Neur: Chrysopidae] larvae feeding onHeliothis virescens [Lep.: Noctuidae] eggs on cotton in field cages

The functional response of 3rd instarChrysopa carnea (Stephens) larvae feeding on 4 densities ofHeliothis virescens (F.) eggs was determined on caged cotton (Gossypium hirsutum L.).C. carnea larvae had a mean search rate of 1.08×10⁻⁵ ha/predator-day or 0.11 row-m/predator-day.