W. Joe Lewis

Role of Plant Volatiles in Host Location by the Specialist Parasitoid Microplitis croceipes Cresson (Braconidae: Hymenoptera)

A study was conducted to determine the primary source of volatile cues within the plant-host complex used by hostseeking freeflying female Microplitis cro-ceipesCresson in flight tunnel bioassays. In single-source and two-choice tests, using wasps given an oviposition experience on either cotton (Gossypium hirsutum)or cowpea (Vigna unguiculata)seedlings damaged by corn earworm (CEW; Helicoverpa zeaBoddie), the damaged seedlings were significantly more attractive than the CEW frass, which was in turn more attractive than the larvae themselves. In a series of two-choice wind-tunnel tests, the discriminatory ability of the wasps was examined, following various oviposition experiences. Significantly more wasps flew to plants with “old” damage than to plants with “fresh” damage, regardless of whether they had experience on fresh or old damage. In a comparison of plant species, wasps with only one experience on either hostdamaged cotton or host-damaged cowpea were unable to distinguish between them, and showed no preference for either plant, whereas wasps with multiple experiences on a particular plant preferentially flew to that plant in the choice test. In comparing hosts with nonhosts, wasps successfully learned to distinguish CEW from beet armyworm (BAW; Spodoptera exigua)on cotton but were unable to distinguish CEW from either BAW or cabbage looper (Trichoplusia ni)on cowpea. The results show the important role played by plant volatiles in the location of hosts by M. croceipesand indicate the wasps’ limitations in discriminating among the various odors. The ecological advantages and disadvantages of this behavior are discussed.

Beneficial arthropod behavior mediated by airborne semiochemicals. VIII. Learning of host-related odors induced by a brief contact experience with host by-products in Cotesia 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.

Management of the Beet Armyworm (Lepidoptera: Noctuidae) in Cotton: Role of Natural Enemies

The beet armyworm, Spodoptera exigua (Hubner), has recently become a persistent and explosive pest of cotton in the southeastern United States. It is, however, attacked by a large and diverse complex of beneficial arthropods and pathogens that appear capable of maintaining beet armyworm populations below economically-damaging levels. Disruption of this complex contributes to outbreaks of S. exigua. It can also exacerbate problems with other pests because the complex of beneficial organisms attacking the beet armyworm is comprised of generalist species that also suppress other pests in the cotton production system. Management of the beet armyworm through conservation of its natural enemies, therefore, provides multiple benefits to growers by managing other pests as well.

Kairomones and their use for management of entomophagous insects: X. Laboratory studies on manipulation of host-finding behavior ofTrichogramma pretiosum riley1 with a kairomone extracted fromHeliothis zea (boddie) moth scales

The behavioral response ofTrichogramma pretiosum Riley females to the kairomone found inHeliothis zea (Boddie) moth scales is examined.

Kairomones and their use for management of entomophagous insects. IX. Investigations of various kairomone-treatment patterns for Trichogramma spp.

A kairomone from adultHeliothis zea (Boddie) scales is an important factor in the host selection process ofTrichogrammapretiosum Riley. If the host density is sufficiently high (i.e., 1 egg/500 cm2) and higher), a complete coverage or solid treatment of kairomone spray may be the optimum for increasing parasitization rates, but this is not the case at lower host densities (e.g., 1 egg/2000 cm2). At the lower densities, the kairomone must be distributed in such a way as to retain the parasitoids in the target area without inhibiting their movement from one ovi-position site to the next. Simulated moth scale particles appear to fill this need since their density can be regulated to provide the optimum frequency of parasitoid stimulation and thus maximum rates of parasitization at prevailing host densities.

Kairomones and their use for management of entomophagous insects VIII. Effect of diet on the kairomonal activity of frass fromHeliothis zea (Boddie) larvae forMicroplitis croceipes (Cresson)

Heliothis zea (Boddie) larvae were reared on fresh plant material (cowpea cotyledons) or on an artificial laboratory diet. Effect of these two diets on the kairomonal activity of the frass and cuticle from the larvae, as well as the kairomonal activity of the diets themselves, forMicroplitis croceipes (Cresson) was determined. Diet was found to significantly affect the kairomonal activity of the frass although the diets themselves were not active.

Comparative virogenesis of filamentous virus and polydnavirus in the female reproductive tract of Cotesia marginibentris (Hymenoptera: Braconidae)

Abstract A nonoccluded filamentous virus (CmFV) was found in the reproductive tract of females in two of five laboratory colonies of Cotesia marginiventris established from parasitized lepidopteran larvae collected in the southeastern United States. Nucleocapsids of CmFV were 35–39 nm in diameter and had electron-dense cores 21–24 nm in diameter. CmFV virions with a single envelope measured 60–70 nm in diameter; doubly enveloped virions were approximately 90 nm in diameter. The unit length was not determined. CmFV replicated in epithelial cells of the common and lateral oviducts and rarely in small nests of cells in the calyx. CmFV was also transmitted to larvae of the fall armyworm, Spodoptera frugiperda , during parasitization. The ability of C. marginiventris to transmit CmFV increased from Day 1 to Days 3–4 postemergence. A polydnavirus (PV) containing multiple nucleocapsids per envelope occurred in the reproductive tract of females in all five colonies of C. marginiventris . PV replication was limited to the portion of the calyx adjacent to the ovarioles.

Comparison of detection ability of learned odors between males and females in the larval parasitoid Microplitis croceipes

Although female parasitic wasps are known to learn to associate odors with hosts and food, the ability of males to learn and detect odors has been neglected. We conducted laboratory experiments to compare the detection ability of learned odors between males and females in the larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). We first conditioned males and females to associate sucrose water with methyl benzoate, 3‐octanone, or cyclohexanone, and then observed their behavior toward various concentrations (40 ng l−1−4 mg l−1) of the trained odors. Conditioned male wasps responded as well as female wasps to various concentrations of the three odors. Response times by wasps to these three odors were not significantly different between sexes. For the three odors, response times of both sexes were longer at the intermediate concentrations (40–400 µg l−1) than the higher or lower concentrations. The present study suggests that M. croceipes males can learn and respond to the three chemicals tested as well as the females, and conditioned males are as sensitive to learned odors as conditioned females. By using their sensitive learning and odor‐detection capabilities, M. croceipes males could search for food sources as efficiently as females under natural conditions.

Conditioned Microplitis croceipes Cresson (Hymenoptera: Braconidae) detect and respond to 2,4-DNT: development of a biological sensor.

We examined the ability of M. croceipes to learn, detect, and respond to 2,4-DNT, which is a volatile discriminator of trinitrotoluene (TNT). The percentage of conditioned wasps to detect and respond to the various concentrations of 2,4-DNT for > or = 15 sec was measured. Significantly more of the conditioned wasps responded to the concentration of 2,4-DNT used for conditioning than other concentrations examined. Accordingly, percent conditioned wasps to respond > or = 15 sec could be used as a suitable measure to screen air samples and distinguish between samples with or without the target odorant. The data recorded in this study indicate the measured behavior could be used to estimate the concentration of target odorants. Data in this study indicate M. croceipes can detect and respond to this compound, which provide further support for its development as a biological sensor.

Employment of parasitoids and predators for fall armyworm control.

Although fall armyworm, Spodoptera frugiperda (J. E. Smith), has numerous natural enemies attacking it, the insect remains an important pest of many annual row crops and pasturage. Attempts to use natural enemies to control this pest must take into consideration the characteristics of the annual row crop agroecosystem. Several approaches including importation of new species, propagation and release, and resource management are suggested and the qualities of each are discussed.