Marginal Host Research Articles

Teratocytes growth pattern reflects host suitability in a host–parasitoid assemblage

Abstract In some parasitoid species, the serosa membrane breaks apart at hatching and produces teratocyte cells that assume various functions (immunossupression, secretion and nutrition) mediating host–parasitoid relationships. Teratocyte growth pattern may thus reflect the host suitability for a parasitoid. The teratocyte growth pattern (increase in size and number of teratocytes as a function of time) is studied and used as an indirect measure of fitness to compare the development of the endoparasitoid Dinocampus coccinellae in a marginal host, the coccinellid Harmonia axyridis, and in a suitable host, Coleomegilla maculata. Indirect measures of fitness recorded in both host species confirm that C. maculata is a suitable host for D. coccinellae contrary to the marginal host H. axyridis. According to regression analysis, teratocyte numbers decrease linearly whereas teratocyte size increases linearly with time in the suitable host C. maculata (larvae or adults). In the marginal host, parasitism occurs only in the larval stage where a delay in the parasitoid larval development is observed. Increase in teratocyte size is also highly variable. The teratocyte growth pattern of the parasitoid in the marginal host does not follow the linear model found in the suitable host. Teratocyte growth pattern may be a useful criterion to evaluate host‐suitability and host range of parasitoids.

Host preference and suitability of some selected crops for two biotypes of Bemisia tabaci in Ghana

AbstractThe economic importance of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is mainly due to its wide host range, variable kinds of damage, and great intraspecific variation. The delineation of two African biotypes of this pest has been carried by molecular, ecological, and host‐affiliation approaches, with largely consistent results. However, an understanding of its intricate host–pest interaction is necessary as a basis of its sustainable integrated control. This study investigated the host preference and suitability of cassava and okra biotypes of B. tabaci, based on multiple‐choice landing and oviposition preference assays and stage‐specific survival on eight common whitefly hosts. The cassava biotype significantly preferred cassava, Manihot esculenta, for landing and oviposition, but did not oviposit on okra, Abelmoschus esculentus. The okra biotype preferred okra, oviposited on eggplant, Solanum melongena, tomato, Lycopersicon esculentum, garden egg, Solanum integrifolium, and cowpea, Vigna unguiculata, but did not oviposit on cassava. The okra biotype developed on all hosts except cassava, but only survived marginally on cabbage, Brassica oleracea, and pepper, Capsicum annum var. grosum, while the cassava biotype did not develop on okra, cabbage, or pepper. Thus the observed host acceptance of the two biotypes is wider than earlier reported by host transfer experiments and molecular genetic surveys. Mortality was highest in the first instar nymphal stage, during which total mortality occurred on non‐hosts. Development time was slightly longer on marginal hosts than on the preferred hosts. Cowpea, garden egg, and tomato are additional common hosts of the two biotypes, whose role as reservoir hosts and biotype interbreeding grounds should be investigated further.

Effects of parasitoid fecundity and host resistance on indirect interactions among hosts sharing a parasitoid

AbstractWe examine the effects of fecundity‐limited attack rates and resistance of hosts to parasitism on the dynamics of two‐host–one‐parasitoid systems. We focus primarily on the situation where one parasitoid species attacks two host species that differ in their suitability for parasitism. While all eggs allocated to suitable hosts develop into adult parasitoids, some of the eggs allocated to marginal host do not develop. Marginal hosts can therefore act as a sink for parasitoid eggs. Three‐species coexistence is favoured by low levels of parasitoid fecundity and by low levels of suitability of the marginal host. Our model also produces an indirect (+, −) interaction in which the suitable host can benefit from the presence of the marginal host, but the marginal host suffers from the presence of the suitable host. The mechanism driving the indirect (+, −) interaction is egg limitation of parasitoids incurred by allocating eggs to marginal hosts.

Two species of eriophyoid mites (Acari, Prostigmata) in wheat cultivation (Triticum aestivum L.) and associated grass community in Wielkopolska, Poland

Abstract: Quantitative characteristics of the occurrence of eriophyoid mites on wheat and associated grasses were studied. Three groups of hosts: cultivated wheat (Triticum aestivum), quackgrass (Agropyron repens) in cultivation, and quackgrass in balks were analysed. Two species of eriophyoid mites were recorded: Aceria tosichella Keifer and Abacarus hystrix (Nalepa). A. hystrix appeared more frequent [present in 65.0% of all collected samples; (95% confidence interval: 50–80)] and abundant [mean number of individuals per sample: 207.3 (94.4–351.5)] than A. tosichella (17.5%; (7.5–3.0), 13.8 (0.9–32.8), respectively). Significant differences in numbers among studied mite species populations on different host plants have been found. It is concluded that wheat is the marginal host for these two eriophyoids when compared to quackgrass.

Trade-offs in performance on different plants may not restrict the host plant range of the phytophagous mite, Tetranychus urticae.

We examined sib-mated lines of the phytophagous mite, Tetranychus urticae Koch, for trade-offs in performance on different plants. We found no significant trade-offs among 10 potential host plants examined. Trade-offs in performance were not detected in most cases, even when the variations in general performance (mean performance on all potential host plants) among the sib-mated lines were statistically adjusted, denying the possibility that this may be due to the variations in general performance among the lines. No evidence for trade-offs was obtained in an artificial selection experiment; on all tested plants, a line adapted to one marginal host plant exhibited higher performance than the control line. However, the general performance seemed to be negatively correlated with other adaptive traits of the mite, such as competition ability of adult males for their mates and overcrowding response of adult females. Such correlations may contribute to the maintenance of genetic variation in the general performance of T. urticae.

Tectonics and hydrocarbon distribution along the Brazilian South Atlantic margin

Abstract Break-up of the Brazilian margin produced a wide variety of structural styles depending on opening kinematics and thermal configuration of the lithosphere. Wide margins developed in Santos and Campos, where stretched continental crust extends for up to 600 km from the shoreline; whereas narrow margins may be only 40 km wide. The wide margins host the largest oil fields, such as those discovered in the Campos Basin. Wide margins have good hydrocarbon potential in the post-rift sequence, but narrow margins probably have the better unknown syn-rift plays which have still to be drilled in deepwater. Little is known of the narrow margins, such as the Jacuípe and Pernambuco-Cabo Basin area, as most of the prospective hydrocarbon structures lie in water depths > 1500 m. Hydrocarbons are hosted by reservoirs ranging from fractured Neocomian volcanics to Miocene turbidites, with over 80% of the reserves trapped in the Campos Basin turbidite sandstones. These sandstones occur as constrained channel-fills on the upper platform and slope, and as unconstrained lobes up to 30 km in long dimension on the mid to lower continental slope which are situated in 500+ m water depths at the present day. The wide margins will continue to be the most productive in Brazil, but deepwater production technology has advanced enough to make the deeper parts of the narrower margins attractive exploration areas.

Effects of Ovipositional Preference on Distribution of the Xylophagous Leafhopper, Homalodisca coagulata (Say)

Homalodisca coagulata (Say) is a xylem-feeding leafhopper that is the principal vector of many economically important diseases resulting from infection by Xylella fastidiosa (i.e., plum leaf scald, phony peach disease). We have previously established that high abundances and high consumption rates of H. coagulata occur on host species with high amide concentrations in the xylem fluid. Several lines of research suggest that selection of “marginal hosts” (those that typically have low abundances of leafhoppers) may be influenced by ovipositional, as well as feeding, preferences. In northern Florida, Euonymus japonica consistently has the highest densities of eggs and young nymphs, but is only a marginal host for adults. Adults caged on this host feed little and have a short longevity. In contrast, young insects (second instar) caged on the host have high survivorship rates and assimilate dietary nutrients with high efficiency. H. coagulata are abundant on Prunus germplasm in northern Florida during the month of June, but only occasionally visit Prunus after this period. In a study of 10 Prunus scion/rootstock combinations, we established that abundances of H. coagulata on Prunus during the peak period were correlated to leafhopper consumption rates. During summer, when Prunus serves as a marginal host, leafhopper abundances are tightly coupled to fecundity rates. Understanding of ovipositional preference may be central to our understanding of Xylella acquisition. These preliminary experiments suggest that leafhoppers may sample xylem fluid during ovipositional selection, as they preferentially select ovipositional sites that have proper nutrient profiles for development of young nymphs (“mother knows best”). Although consumption rates are low for marginal hosts, repeated probing for ovipositional preference may contribute to the spread of diseases caused by X. fastidiosa.

A Survey of Parasitoids of Brown Citrus Aphid (Homoptera: Aphididae) in Puerto Rico

The brown citrus aphid Toxoptera citricida (Kirkaldy) (Homoptera: Aphididae) is a pest of citrus and an efficient vector of citrus tristeza virus. Reproducing populations of this aphid were first detected in Puerto Rico in April 1992. In 1994, we surveyed citrus in Puerto Rico for the aphid and its parasitoids. The brown citrus aphid was the most abundant aphid on citrus and its populations were statistically higher in April than in July and December. Aphid populations in commercial and dooryard citrus were significantly higher than those in nurseries ( P < 0.05). Lysiphlebus testaceipes (Cresson) (Hymenoptera: Aphidiidae) was the only primary parasitoid found attacking the aphid. The parasitism rate was only 3.6% overall and was somewhat greater in April at 5.9% and December at 7.0% than in July at 2.9%. Parasitism was higher in dooryard citrus than in commercial or nursery fields ( P < 0.05). Primary parasitoid emergence rate from mummies was low at 4.0%, indicating that the brown citrus aphid was a marginal host or that conditions were not adequate. A low level of hyperparasitism by Pachyneuron sp. was also observed. We conclude that the aphid was not under good biological control by parasitoids and suggest that classical biological control efforts should be undertaken.

Cross habituation to feeding deterrents and acceptance of a marginal host plant by Pieris rapae larvae

AbstractSensitivity of the cabbage butterfly, Pieris rapae L. to feeding deterrents was compared for larvae reared on different food sources under laboratory conditions. Since cabbage‐reared larvae normally reject nasturtium, Tropaeolum majus L., the effects of previous exposure to allelochemicals on larval acceptance or rejection of this plant were also examined. When compared with cabbage‐reared larvae, nasturtium‐reared larvae were less sensitive to feeding deterrents including cymarin, erysimoside and 2‐O‐β‐D‐glucosyl cucurbitacin E. Nasturtium‐reared larvae were insensitive to chlorogenic acid, which was deterrent to cabbage‐reared larvae. Feeding by larvae reared on a wheat germ diet was not deterred by these compounds. The results indicate that dietary experience can extensively affect larval sensitivity to feeding deterrents and that cross habituation of larvae to deterrents occurs in response to certain chemical constituents of nasturtium and wheat germ diet. Digitoxin, however, proved to be an exception. Larvae reared on either nasturtium or wheat germ diet were as sensitive to digitoxin as those reared on cabbage. Previous results have shown that rejection of nasturtium by cabbage‐reared larvae is due to the presence of strong feeding deterrents in this plant. However, more than 50% of 2nd instar larvae reared from neonate on cabbage leaves treated with strophanthidin, cymarin, erysimoside, digitoxigenin and digitoxin accepted nasturtium as a food source. 2‐O‐β‐D‐glucosyl cucurbitacin E, 2‐O‐β‐D‐glucosyl cucurbitacin I and rutin were also active in causing larvae to feed on nasturtium. Thus dietary exposure to unrelated plant chemicals can profoundly affect insect acceptance of a plant that contains feeding deterrents.

Interaction between visual and olfactory stimuli during host-finding by leafhopper,Dalbulus maidis (Homoptera: Cicadellidae)

Virtually nothing is known about the role plant volatiles play in host-finding by Homoptera in the Suborder Auchenorrhyncha. In laboratory bioassays, we examined the influence of plant volatiles on orientation and postcontact behaviors of the leafhopper,Dalbulus maidis, and determined the relationship between visual and olfactory stimuli during host-finding. When compared to the number of contacts made with reflected green light in the presence of a hexane control,D. maidis made more contacts when exposed to volatile extracts from its preferred host, maize; a similar number of contacts when exposed to volatiles from a marginal host, gamagrass; and fewer contacts when exposed to volatiles from a nonhost, sorghum. There was no difference between males and females in the number of contacts made with green light when exposed to maize volatiles compared to hexane alone. More contacts were made with green light than with white light of similar intensity, both in the presence and in the absence of olfactory stimuli; however, maize volatiles acted as a Synergist by increasing the number of contacts leafhoppers made with green light. After contacting the green light, exposure of maize volatiles significantly increased, relative to hexane, the amount of stationary time, but did not influence the amount of time spent moving, the distance traveled, or the speed while moving when within the boundaries of the green light. This study provides the first evidence for an interaction between visual and olfactory stimuli during host-finding for a leafhopper and also for olfactory mediation of postcontact behaviors not associated with feeding.

Bone Regeneration under the Influence of a Bone Morphogenetic Protein (BMP) Beta Tricalcium Phosphate (TCP) Composite in Skull Trephine Defects in Dogs

Beta tricalcium phosphate (TCP) was employed as a nonimmunogenic biodegradable delivery system for bovine bone morphogenetic protein (BMP). A BMP/TCP composite was implanted in adult dogs with skull trephine defects of a critical size of 1.4 cm that would otherwise remain unhealed in the lifetime of the individual. BMP/TCP implants induced 91%-100% incorporation by deposits of new bone. In comparison, control implants of TCP impregnated with bovine serum albumin (BSA/TCP) induced 0%-8% incorporation, or only marginal host bed reactive bone formation. The retention of unabsorbed TCP in the host bone four months after implantation suggests that further research should be encouraged to obtain a formulation of sintered calcium phosphate that could be resorbed more rapidly and in the process more completely replaced by bone.

The host range ofAenetus virescens(Lepidoptera: Hepialidae) and its evolution

The utilisation status of fungal and vascular plants as hosts for larvae of Aenetus virescens is presented. Larvae are recorded from the fruiting bodies of 8 wood-inhabiting fungi. Vascular plants are placed into categories of “terminal host”, “marginal host”, and “status unknown”. The evolution of this host range is given an orthogenetic interpretation in relation to the origin and dispersal of angiosperms.