Cotesia Marginiventris Research Articles

Interspecific competition between parasitoids of the fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

Interspecific competition within larvae of the fall army worm (FAW), Spodoptera frugiperda (J. E. Smith), by the larval parasitoids, Cotesia (= Apanteles) marginiventris Cresson and Microplitis manilae Ashmead, and the egg-larval parasitoid Chelonus insularis Cresson was studied. Chelonus insularis was not able to compete successfully against Cotesia marginiventris, but was a successful competitor against Microplitis manilae. Multiple parasitization of larvae by either Cotesia marginiventris or Microplitis manilae, which as eggs were parasitized by Chelonus insularis, did not result in additional host mortality. Percentage parasitization under greenhouse conditions by Cotesia marginiventris of larvae parasitized previously by Chelonus insularis was two-fold higher in corn compared to sorghum and more than four-fold higher compared to Bermuda grass and itch grass. The host finding and behavioural sequence of oviposition of Cotesia marginiventris in FAW larvae already parasitized by Chelonus insularis consisted of nine steps. Microplitis manilae females changed their behaviour significantly by displaying a reduction of ca. fifty per cent in host examinations, 45% in ovipositor probes, and 55% in apparent ovipositions when Chelonus insularis parasitized larvae were presented. Cotesia marginiventris and Microplitis manilae exhibited no significant behavioural changes in the per cent contacts, examinations and apparent ovipositions when attacking larvae parasitized previously by either Cotesia marginiventris or Microplitis manilae.

Do Parasitoids Use Herbivore-Induced Plant Chemical Defenses to Locate Hosts?

Herbivore-induced plant chemical responses are usually considered direct defenses against the herbivorous attackers. Recent findings show that a third topic level can be involved as well. Herbivore-injured plants release relatively large amounts of volatiles that are attractive to natural enemies of the herbivores. The host-searching behavior of the generalist parasitoid Cotesia marginiventris is mediated by such plant produced volatiles. Since plant and entomophage both profit from this interaction it has been suggested that the plant responses serve to recruit the entomophages. Here we argue that induced production of plant chemicals evolved first as a direct defense against herbivores, and that the attractive function likely evolved secondarily. Results of a plant palatability experiment are given to provide preliminary support for a defensive function. Plants that were induced to release volatiles that are known to be attractive to the parasitoid became less palatable to the herbivore beet armyworm.

Spatial Density Dependence in Parasitism of Heliothis virescens (Lepidoptera: Noctuidae) by Microplitis croceipes (Hymenoptera: Braconidae) in the Field

A field experiment addressed four questions concerning the interaction between Microplitis croceipes (Cresson) and Heliothis spp.: (1) what is the relation between the proportion of hosts parasitized and host density? (2) does this relation depend on the size of the areas (spatial scale) at which it is measured? (3) what is the relation between parasitoid search rate and host density? and (4) what is the relation between parasitoid distribution and host distribution? To answer these questions a cotton field was artificially infested with various densities of Heliothis virescens (F.). M. croceipes was released uniformly across the field. At the scale of 30 by 60 m plots, the proportion of hosts parasitized by M. croceipes (adjusted for competition with other parasitoid species) increased from 0.41 ± 0.08 ( x ± SE) to 0.60 ± 0.06 as host density increased from 6,178 to 16,896 larvae/ha. The calculated search rate (area searched per parasitoid per unit time) of M. croceipes was independent of host density, and the density dependence in parasitism by M. croceipes could be explained completely by density dependence in adult female distribution. Natural populations of Cardiochiles nigriceps Viereck and Cotesia marginiventris (Cresson) parasitized 9 and 7%, respectively, of the hosts collected. At the scale of plots, parasitism by C. nigriceps increased with host density, but parasitism by C. marginiventris was independent of host density. At the scale of 1 by 2 m quadrats, parasitism by all species was independent of host density. We discuss the implications of these results for biological control of Heliothis virescens and Helicoverpa zea and for theories of parasitoid foraging and population regulation.

Reproductive Strategies of Primary Parasitoids of the Green Cloverworm (Lepidoptera: Noctuidae)

Cotesia marginiventris (Cresson), Diolcogaster facetosa (Weed), and Rogas nolophanae Ashmead, which respectively parasitize progressively older green cloverworm, Plathypena scabra (F.) larvae, produced (x ± SE) 362.7 ± 24.1, 83.2 ± 11.4, 66.3 ± 6.1 offspring, respectively, during their lifetimes. Adult female longevity at 24°C averaged lS.l ± O.S, ~3.0 ± 0.9, and 29.9 ± 2.7 d for these species, respectively. Numbers of mature eggs from dissections of 2-d-old females were 105 ± 7.1,57 ± 5.9, and 5.2 ± 0.9. Primary braconid and tachinid parasitoids of the green cloverworm exhibited decreasing observed or estimated fecundities with respect to increasing age of host larvae attacked. Decreasing fecundities of these parasitoid species may reflect increasing potential for survival until time of parasitoid emergence of the progressively older host larvae which these species attack. Other factors suggested as influencing fecundity are breadth of host range and complexity of host location, capture, and oviposition behaviors.

Larval‐damaged plants: source of volatile synomones that guide the parasitoid Cotesia marginiventris to the micro‐habitat of its hosts

Abstract Single and dual choice tests in a flight tunnel revealed that plants damaged by host larvae are the main source of the volatiles that attract females of the parasitoid Cotesia marginiventris (Cresson) to the microhabitat of its hosts. Frass and host larvae, the other two major components of a complete plant-host complex, were significantly less attractive than the damaged seedlings; frass alone was more attractive than larvae alone. However, a recombination of larvae with the damaged seedlings was significantly more attractive than the damaged leaves alone, or damaged leaves with frass. This was due to the additional feeding damage done by the larvae. The role of plants in the host-finding behaviour of parasitoids is discussed. Résumé Plantes endommagées par des chenilles: source de synomones volatiles guidant le parasitoïde Cotesia margiventris vers le micro-habitat de ses hôles L'hyménoptère C. marginiventris Cresson, parasite solitaire, est connu comme étant attiré par les odeurs liées à l'hôte émises par un complexe de chenilles consommant des feuilles. La source exacte de ces substances attractives restait encore à déterminer. Pour cela, des expériences en tunnel de vol ont été réalisées dans lesquelles différents composés du complexe plante et hôte ont été testés individuellement et en combinaisons diverses. Les 3 composés testés ont été: 1) des plantules de maïs endommagées par des chenilles de Spodoptera exigua (BAW); 2) des excréments produits par les chenilles de BAW consommant du maïs; 3) des chenilles de BAW en l'absence de plantes et d'excréments. Les plantes endommagées ont été significativement plus attractives que les excréments ou les chenilles. En expériences de choix, les excréments étaient plus attractifs que les chenilles. Différentes combinaisons de ces 3 composantes principales ont montré que l'attractivité augmentait quand les chenilles étaient associées à des feuilles endommagées. Ajouter des excréments n'augmentait pas significativement l'attractivité. Quand des chenilles étaient associées avec des feuilles endommagées, mais en présence d'écran les empêchant de consommer les feuilles, l'attractivité était celle des feuilles endommagées seules. Des feuilles de maïs n'ayant jamais été exposées aux dégâts des chenilles étaient à peine attractives. On peut en conclure que les feuilles endommagées par les chenilles sont la principale source de substances volatiles qui orientent le parasito'ide C. marginiventris vers le voisinage de ses hôtes. La consommation active par les chenilles augmente probablement la quantité de substances émises par les plantes, ce qui se traduit par une attractivité accrue. Les substances volatiles des plantes jouent un rôle dans la découverte de l'habitat de l'hôte par les parasitoïdes. De plus en plus d'éléments suggèrent qu'une interaction sophistiquée entre hôte, plante et parasitoïde sera éventuellement révélée.

Exploitation of Herbivore-Induced Plant Odors by Host-Seeking Parasitic Wasps

Corn seedlings release large amounts of terpenoid volatiles after they have been fed upon by caterpillars. Artificially damaged seedlings do not release these volatiles in significant amounts unless oral secretions from the caterpillars are applied to the damaged sites. Undamaged leaves, whether or not they are treated with oral secretions, do not release detectable amounts of the terpenoids. Females of the parasitic wasp Cotesia marginiventris (Cresson) learn to take advantage of those plant-produced volatiles to locate hosts when exposed to these volatiles in association with hosts or host by-products. The terpenoids may be produced in defense against herbivores but may also serve a secondary function in attracting the natural enemies of these herbivores.

Parasitization of Lepidopterans as Affected by Nematicide-Insecticide Use in Soybean

Larvae of green cloverworm, Plathypena scabra (F.), soybean looper, Pseudoplusta Tncludens (Walker), and corn earworm, Heltothis zea (Boddie), were sampled in soybean plots (maturity groups V and VII) treated with high rates of aldicarb, carbofuran, and fenamiphos for nematode control and with acephate for thrips control. Larval collections from both maturity groups indicated that the most abundant parasitoid of lepidopterous larvae in soybean treated with nematicide and insecticide was Cotesia margintventris (Cresson), which was responsible for > 90% of the parasitism in 1984 and 1985. Thirty-three percent of small Plathypena scabra were parasitized in 1984; 23% were parasitized in 1985. None of the treatments appeared to affect the occurrence of parasitism in Plathypena scabra larvae adversely. Soybean treated with aldicarb hosted significantly more Plathypena scabra and parasitoids than untreated plots. Soybean (maturity group V) hosted significantly higher H. zea populations in soybean treated with carbofuran (1984) or aldicarb (1985) than in untreated control plots. Heliothis nuclear polyhedrosis virus and the parasitoids Microplttis croceipes (Cresson) and Cotesia marginiventris were important in regulating H. zea populations.

Life History of the Hyperparasitoid Mesochorus discitergus (Hymenoptera: Ichneumonidae) and Tactics Used to Overcome the Defensive Behavior of the Green Cloverworm (Lepidoptera: Noctuidae)

Mesochorus discitergus (Say) is an endogenous, solitary hyperparasitoid with a broad range of hosts. Its developmental period from oviposition to adult emergence with Cotesia marginiventris (Cresson) as its host ranged from about 16 d at 27°C to about 25 d at 21°C. When hyperparasitism occurred 3 d after primary parasitism, the first two instars developed within the C. marginiventris larva, and the third instar developed within the C. marginiventris larva and pupa. Hyperparasitoid pupation occurred within the cocoon spun by the primary parasitoid. M. discitergus must overcome the defensive responses of green cloverworm larvae to oviposit in larval primary parasitoids located inside the caterpillars. Young green cloverworm larvae often drop when disturbed and hang from foliage on silken threads. To capture a young (second instar) caterpillar, the hyperparasitoid usually hangs by its hind tarsi from the edge of the leaf from which the larva is suspended and reels in the caterpillar by pulling upward on the caterpillar's silken thread. Capturing suspended third and fourth instars often requires that the parasitoid walk part or all the way down the thread toward the caterpillar. By probing briefly with the ovipositor, hyperparasitoid females distinguish between green cloverworms parasitized by C. marginiventris and those that are unparasitized. Unparasitized larvae are quickly rejected (x= 5.0 s), whereas parasitized green cloverworms are held and probed longer (x= 83.4 s).

FALL BROCCOLI PESTS AND THEIR PARASITES IN VIRGINIA

The major pests of fall broccoli in south-central Virginia between 1985/87 were Trichoplusia ni (Hübner), Hellula rogatalis (Hulst), Plutella xylostella (L.), and Heliothis zea (Boddie); minor pests included Pieris rapae (L.), Evergestis rimosalis (Gueneé), Spodoptera ornithogalli (Gueneé), Pieris protodice Boisduval and LaConte and Plathypena scabra F. Seven species of parasites were recovered, the most abundant being Diadegma insularis (Cresson) which parasitized up to 37% of the diamondback moth larvae and Cotesia marginiventris (Cresson) which parasitized up to 20% of the corn earworms. The other parasites were found in very low numbers.

Beneficial arthropod behavior mediated by airborne semiochemicals. VIII. Learning of host-related odors induced by a brief contact experience with host by-products inCotesia marginiventris (Cresson), a generalist larval parasitoid

Females of Cotesia marginiventris(Cresson), a generalist larval parasitoid, were observed to respond to host related odors in a four-arm olfactometer. The females were significantly more responsive to the odors after a brief contact experience with host-damaged leaves contaminated with host by products. During the experience, actual encounters with hosts were not required to improve subsequent responses to host-related odors. The response to odors of the plant-host complex with which parasitoids had experience was significantly higher than the response to odors of an alternative plant-host complex. This suggests that the experience effect is due, at least partly, to associative learning. We suspect that females of this generalist parasitoid, as was recently found for those of a specialist, recognize specific semiochemicals when they contact frass of suitable host larvae. The parasitoids, subsequently, associate the surrounding odors with the possible presence of hosts, and use these odors as cues in their search for more hosts. This could be an important component in the host-searching behavior of many parasitoids.

Acoustic Signals Produced during Courtship in Diachasmimorpha (=Biosteres) longicaudata (Hymenoptera: Braconidae) and Other Braconidae

Sounds produced by courting males of three species of Braconidae as they approach and then mount females differ in frequency, sound duration, and intervals between sounds. Diachasmimorpha longicaudata (Ashmead), a parasitoid of the Caribbean fruit fly, Anastrepha suspensa (Loew), has a sexually dimorphic response to broadcasts of recorded “approach song” that suggests the sound has a sexual function. Sounds directed at other males have longer pulse trains (buzzes) and shorter intervals between pulse trains than those sung to potential mates. D. longicaudata males have more oval wings than females, as is the case in some acoustically signaling Diptera. Microplitis croceipes (Cresson) and Cotesia marginiventris (Cresson) produce multiple frequency sounds that result in a warbling effect. The song of the latter species is very complex and includes two distinct forms of pulse trains.

Parasitoids and Pathogens of Green Cloverworm (Lepidoptera: Noctuidae) on an Uncultivated Spring Host (Vetch, Vicia spp.) and a Cultivated Summer Host (Soybean, Glycine max)

Parasitoids and pathogens of green cloverworm, Plathypena scabra (F.), were studied during the spring on a wild host (vetch, Vicia spp.) and during the summer on a cultivated host (soybean, Glycine max (L.) Merrill) at four locations in Louisiana during 1984 and 1985. Six species of primary parasitoids and one species of hyperparasitoid representing a total of four families were encountered during the study. Cotesia marginiventris (Cresson) was the most abundant parasitoid collected during the spring of 1984, while Rogas nolophanae Ashmead was the most common in the spring of 1985. Parasitism during the spring of 1984 and 1985 totaled 12.8 and 36.4%, respectively, whereas parasitism rates during the summer of those years were 10.4 and 6.0%, respectively. Cotesia marginiventris was the prevalant parasitoid during the summer in both years of the study. Two entomopathogens were collected from green cloverworm— Nomuraea rileyi Samson and a granulosis virus were collected in the spring, while only N. rileyi was collected during the summer.

Parasites and Disease Associated with Larvae of Beet Armyworm Spodoptera exigua (Lepidoptera: Notuidae), Infesting Processing Tomatoes in Sinaloa, Mexico

The impact of six species of parasites and a polyhedrosis virus on larvae of beet armyworm, Spodoptera exigua (Hubner), was investigated in processing tomato in the Guasave and Del Fuerte Valleys of Sinaloa, Mexico. The Polyhedrosis virus was the most important mortality factor; several epizootics occurred during the course of the study. Cotesia marginiventris (Cresson) was the most common parasite, followed by Meteorus laphygmae Viereck and Pristomerus spinator (F.). Disease and parasitization reduced beet armyworm to non-injurious levels during the seedling stage of the crop and thus should be considered as important components of the recently implemented IPM program on processing tomatoes in this area.

A new virus associated with the parasitoid Cotesia marginiventris (Hymenoptera: Braconidae): Replication in noctuid host larvae

A nonoccluded filamentous baculo-like virus occurred in scattered hypodermal and tracheal matrix cells of five species of noctuid larvae ( Spodoptera frugiperda, S. exigua, S. ornithogalli, Heliothis zea, and Trichoplusia ni) parasitized by Cotesia (= Apanteles) marginiventris. Infected cells and their nuclei were moderately hypertrophied. Infected cells contained prominent virogenic stromata, fibrous cytoplasmic inclusions, and moderate numbers of a filamentous virus. Virions were 50–98 nm in diameter, ≥865 nm in length, and straight to slightly flexuous. Nucleocapsids were 30–39 nm in diameter with a core 21–24 nm in diameter, and were enclosed by one or two envelopes. Nucleocapsids occurred in the nuclei and in the cytoplasm. Enveloped nucleocapsids were restricted to the cytoplasm.

Geographical Distributions and Parasitization Levels for Parasitoids of the Fall Armyworm, Spodoptera frugiperda

Literature citations were used to determine geographical distribution data and parasitization levels from larva colections from corn, alfalfa, three species of grass, peanut, and sorghum for the principal parasitoids of the fall armyworm, Spodoptera frugiperda (J. E. Smith). The highest parasitization levels found for corn, alfalfa, grass, peanut, and sorghum were 77, 30, 54, 37, and 20%, respectively. Chelonus insularis (Cresson) had the highest parasitization rates of all the parasitoids for North and Central America. This parasitoid was not recovered from South America or the Caribbean. Cotesia marginiventris (Cresson) had approximately the same geographical distribution as C. insularis, but attained its highest parasitization levels in grass rather than corn. None of the parasitoids exerted substantial mortality throughout any major portion of the fall armyworm's range.

Fall Armyworm (Lepidoptera: Noctuidae) Parasitoids: Differential Spring Distribution and Incidence on Corn and Sorghum in the Southern United States and Northeastern Mexico

Nineteen species of parasitoids were recovered from fall armyworm, Spodoptera frugiperda (J. E. Smith), in spring surveys conducted in Florida, Georgia, Alabama, South Carolina, Louisiana, Mississippi, south Texas, and Mexico during 1981–1983. The highest rates of parasitism were in overwintering areas of Mexico–Texas and south Florida, averaging 23.4 and 32.5%, respectively. Chelonus insularis Cresson was the most common species and represented 61.7, 59.6, and 56.1% of the parasitoids recovered from small, medium, and large larvae, respectively. In south Texas and Mexico, C. insularis was recovered from 55.6% of the parasitized small larvae while Archytas marmoratus (Townsend) was the most common species collected from medium (66.7%) and large (47.4%) larvae. A northward progression of C. insularis from overwintering areas during the spring, similar to but lagging behind the progression of fall armyworm populations, was indicated. Hence, C. insularis probably did not overwinter in Georgia or if it did, densities in the spring remained too low for detection by conventional sampling methods. In more northerly areas of the fall armyworm's distribution, C. insularis was of secondary or minor importance; A. marmoratus, Campoletis sonorensis Cameron, Cotesia marginiventris (Cresson), Rogas laphygmae Viereck, and Ophion flavidus Brulle were the most commonly occurring species, particularly in north Florida and in the other states, where rates of parasitization ranged from 9.4% in Alabama to 21.7% in Mississippi–Louisiana. Evidence of differential distribution of some species was indicated by their native scarcity or abundance in defined geographical areas within the temporal limits of the study. For example, Temelucha difficilis Dasch was an important species in south Florida but it was rarely observed in more northerly areas. Conversely, C. sonorensis was absent in collections from south Florida but was an important species elsewhere.

In vitro culture of hymenopterous larval endoparasitoids

The solitary endoparasitoids Cotesia (= Apanteles) marginiventris and Microplitis croceipes, which attack noctuid larvae, were successfully cultured from post-germband stage eggs to fully grown first-instar larvae in completely artificial (but undefined) media. However, growth rates were slower than in vivo, and while some larvae of each species attained apparent competence to moult (based upon characteristic size and form), none did so. Up to 75% of pregermband M. croceipes eggs developed and hatched when co-cultured with fat body from non-parasitized larvae of the habitual host, Heliothis zea. Heat-treated haemolymph plasma from a non-permissive host, Manduca sexta, also fostered development by ca. 40% of newly laid M. croceipes eggs, but plasma from H. zea larvae was not beneficial. Growth rates of C. marginiventris and M. croceipes larvae were not improved by haemolymph plasma from their habitual hosts ( Spodoptera frugiperda and H. zea, respectively). Heat-treated foetal bovine serum was growth-promoting for post-germband eggs and larvae of both parasitoids. Treatment of foetal bovine serum by charcoal adsorption (to remove sterols and peptide hormones) diminished its value as a supplement. Two major proteins of the serum, foetuin and albumin, also promoted survival and growth for both parasitoid species. The potential relevance of these findings to in vitro rearing of endoparasitoids is discussed.

PARASITOIDS AND PATHOGENS OF THE SOYBEAN LOOPER, PSEUDOPLUSIA INCLUDENS (WALKER), IN SOUTH GEORGIA SOYBEAN

Larvae of the soybean looper (SBL), Pseudoplusia includens (Walker), were collected from soybean fields in south Georgia during the 1982, 1983, and 1984 growing seasons. Larvae were reared in the laboratory to determine levels of parasitism and disease incidence. Twelve parasitoid species including one hyperparasitoid were reared from SBL larvae. The three most common parasitoid species were Copidosoma truncatellum (Dalman), Meteorus autographae Muesebeck, and Cotesia marginiventris (Cresson). The most abundant pathogen was the fungus Entomophthora gammae Weiser, but the fungus Nomuraea rileyi (Farlow) Samson and a nuclear polyhedrosis virus also were present. Peak SBL densities were 73.5 larvae per rowmeter in 1982, 30.9 in 1983, and 19.8 in 1984. Total mortality of larvae collected from different locales due to parasitism and disease ranged from 36.5 to 77.6% during 1982, from 4.8 to 73.2% during 1983, and from 0 to 93.9% during 1984.

Effects of a Nonoccluded Virus of Spodoptera frugiperda (Lepidoptera: Noctuidae) on the Development of a Parasitoid, Cotesia marginiventris (Hymenoptera: Braconidae)

A nonoccluded virus (identified as an Ascovirus ), isolated from fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), was tested to determine its compatability with the parasitoid Cotesia marginiventris (Cresson). Adult C. marginiventris readily transmitted the virus from infected to noninfected FAW larvae. However, the progeny of the parasitoids failed to complete development in host larvae inoculated with the virus before or during parasitization. Fewer parasitoids completed development in host larvae inoculated 4 days after parasitization than in larvae inoculated 5 days after parasitization and in parasitized controls. Mortality was not due to the virus killing the host before the parasitoids could complete development, since the virus-infected larvae lived longer than the parasitized controls. Fewer and smaller parasitoid larvae were found in virus-infected hosts than in parasitized controls when host larvae were dissected 6 days after parasitization.

Role of host-produced stimuli and learning in host selection behavior ofCotesia (=Apanteles) marginiventris (Cresson)

The study was conducted to determine how various factors, including learning, influence the host-selection behavior of the larval parasitoid Cotesia (=Apanteles)marginiventris (Cresson). Frass, silk, and feeding damage fromSpodoptera frugiperda (J.E. Smith) larvae elicited visits and antennal examinations by females of the parasitoid. Learning played a role in the effective response to these stimuli in that previous contact experience with hosts and/or chewed leaves, exuviae, frass, or hemolymph significantly enhanced the response of the parasitoid. Previous contact with host plants alone did not improve the responses. Experienced parasitoids were more active and spent less time at rest than inexperienced parasitoids. Previous experience was also found to be of significant importance in the ability of the parasitoid to discriminate between parasitized and unparasitized host larvae.