Absence Of Host Plant Research Articles

Host‐associated pre‐mating reproductive isolation between host races of Acrocercops transecta: mating site preferences and effect of host presence on mating

1. A correlation between habitat and mating site preference is crucial for reproductive isolation between populations with different ecological requirements in the absence of any other barriers to gene flow. In phytophagous insects, host‐plant preference of ovipositing females has been postulated to directly influence the extent of assortative mating. 2. Although this pleiotropic effect of host preference is commonly postulated in both theoretical and empirical studies in phytophagous insects, few studies have assessed the mating site preferences of both sexes. In herbivorous insects, it is crucial whether males have the same host preference as ovipositing females. 3. This study examines whether males and females have preferences for mating sites and assesses the effects of host presence on mating activity in a leaf‐mining moth, Acrocercops transecta Meyrick (Gracillariidae). This species consists of two host races, which are associated with Juglans ailanthifolia Carr. (Juglandaceae) and Lyonia ovalifolia (Wall.) Drude (Ericaceae). The two host races clearly differ in host preferences of ovipositing females. 4. In an experiment of mating site selection, Lyonia‐associated host race females significantly preferred Lyonia, while males of the Lyonia‐associated host race and both sexes of the Juglans‐associated host race did not show a preference for either plant. The mating activity of the Lyonia‐associated host race was not reduced in the absence of host plants. In the Juglans‐associated host race, however, the proportion of successful matings was significantly reduced when the host was absent. 5. These laboratory experiments provide empirical evidence that the different host associations in A. transecta do not directly lead to host‐induced assortative mating between the two host races as a pleiotropic effect. However, the present results suggest that the combined effects of the mating‐site preference of Lyonia‐associated females and the mating propensity of Juglans‐associated females could contribute to reproductive isolation between the two host races.

Germination and infectivity of ectomycorrhizal fungal spores in relation to their ecological traits during primary succession

The spores of ectomycorrhizal fungi (EMF) play critical roles in the population and community development of EMF. Here, the germination and infectivity of EMF spores are examined with reference to the ecological traits of the EMF species. Spores were collected from 12 EMF species, whose successional patterns have been studied in the volcanic desert on Mount Fuji, Japan. Spore germination experiments were conducted with host plants (Salix reinii), with nonhost plants (Polygonum cuspidatum), and without plants. The mycorrhizal formation ability of spores was also examined in seven EMF using spore inoculation experiments. To determine the effects of the spore preservation period, both experiments were repeated up to 1 yr after spore collection. Spore germination was very low in the absence of host plants. In the presence of hosts, even 30 d after spore collection, spore germination was significantly enhanced in all pioneer EMF (c. 20%) but less so in late-stage EMF (< 5%), except in Hebeloma species. Mycorrhizal formation from spores was also greater in pioneer EMF but was significantly reduced by 1 yr of spore preservation. High spore germination and infectivity of pioneer EMF should enable these species to colonize disturbed and isolated areas in accordance with their ecological traits.

Evidence for Abscisic Acid Biosynthesis in Cuscuta reflexa, a Parasitic Plant Lacking Neoxanthin

Abscisic acid (ABA) is a plant hormone found in all higher plants; it plays an important role in seed dormancy, embryo development, and adaptation to environmental stresses, most notably drought. The regulatory step in ABA synthesis is the cleavage reaction of a 9-cis-epoxy-carotenoid catalyzed by the 9-cis-epoxy-carotenoid dioxygenases (NCEDs). The parasitic angiosperm Cuscuta reflexa lacks neoxanthin, one of the common precursors of ABA in all higher plants. Thus, is C. reflexa capable of synthesizing ABA, or does it acquire ABA from its host plants? Stem tips of C. reflexa were cultured in vitro and found to accumulate ABA in the absence of host plants. This demonstrates that this parasitic plant is capable of synthesizing ABA. Dehydration of detached stem tips caused a big rise in ABA content. During dehydration, 18O was incorporated into ABA from 18O2, indicating that ABA was synthesized de novo in C. reflexa. Two NCED genes, CrNCED1 and CrNCED2, were cloned from C. reflexa. Expression of CrNCEDs was up-regulated significantly by dehydration. In vitro enzyme assays with recombinant CrNCED1 protein showed that the protein is able to cleave both 9-cis-violaxanthin and 9'-cis-neoxanthin to give xanthoxin. Thus, despite the absence of neoxanthin in C. reflexa, the biochemical activity of CrNCED1 is similar to that of NCEDs from other higher plants. These results provide evidence for conservation of the ABA biosynthesis pathway among members of the plant kingdom.

Combined effects of climate and biotic interactions on the elevational range of a phytophagous insect

1. The ranges of many species have expanded in cool regions but contracted at warm margins in response to recent climate warming, but the mechanisms behind such changes remain unclear. Particular debate concerns the roles of direct climatic limitation vs. the effects of interacting species in explaining the location of low latitude or low elevation range margins. 2. The mountains of the Sierra de Guadarrama (central Spain) include both cool and warm range margins for the black-veined white butterfly, Aporia crataegi, which has disappeared from low elevations since the 1970s without colonizing the highest elevations. 3. We found that the current upper elevation limit to A. crataegi's distribution coincided closely with that of its host plants, but that the species was absent from elevations below 900 m, even where host plants were present. The density of A. crataegi per host plant increased with elevation, but overall abundance of the species declined at high elevations where host plants were rare. 4. The flight period of A. crataegi was later at higher elevations, meaning that butterflies in higher populations flew at hotter times of year; nevertheless, daytime temperatures for the month of peak flight decreased by 6.2 degrees C per 1 km increase in elevation. 5. At higher elevations A. crataegi eggs were laid on the south side of host plants (expected to correspond to hotter microclimates), whereas at lower sites the (cooler) north side of plants was selected. Field transplant experiments showed that egg survival increased with elevation. 6. Climatic limitation is the most likely explanation for the low elevation range margin of A. crataegi, whereas the absence of host plants from high elevations sets the upper limit. This contrasts with the frequent assumption that biotic interactions typically determine warm range margins, and thermal limitation cool margins. 7. Studies that have modelled distribution changes in response to climate change may have underestimated declines for many specialist species, because range contractions will be exacerbated by mismatch between the future distribution of suitable climate space and the availability of resources such as host plants.

Survival of Xiphinema index in Vineyard Soil and Retention of Grapevine fanleaf virus Over Extended Time in the Absence of Host Plants

ABSTRACT Grapevine fanleaf virus (GFLV) is transmitted specifically from grapevine to grapevine by the ectoparasitic root-feeding nematode Xiphinema index. Limited information is available on the survival of X. index in vineyard soil and on the retention of GFLV by X. index over extended periods of time. We addressed these two issues by quantifying the numbers of living X. index recovered from soil samples that were collected in three naturally GFLV-infected vineyards in France and subsequently stored at 7 or 20 degrees C in the absence of host plants. Our data indicated a two- to eightfold decrease in X. index numbers but the recovery of 8 to 10 living fourth-stage juveniles (J4) and adults per kilogram of soil after 4 years of storage regardless of temperature. In addition, GFLV was detected readily in all groups of 20 isolated X. index adults and J4 (except for J4 that were kept 4 years at 20 degrees C) by reverse transcription-polymerase chain reaction using total nematode RNAs and a primer set located in conserved regions at the 3' end of viral genomic RNA 2. Our findings on the long-term survival of viruliferous X. index under adverse conditions emphasize the need for new control strategies against GFLV.

Lessons learned from the genome analysis of ralstonia solanacearum.

Ralstonia solanacearum is a devastating plant pathogen with a global distribution and an unusually wide host range. This bacterium can also be free-living as a saprophyte in water or in the soil in the absence of host plants. The availability of the complete genome sequence from strain GMI1000 provided the basis for an integrative analysis of the molecular traits determining the adaptation of the bacterium to various environmental niches and pathogenicity toward plants. This review summarizes current knowledge and speculates on some key bacterial functions, including metabolic versatility, resistance to metals, complex and extensive systems for motility and attachment to external surfaces, and multiple protein secretion systems. Genome sequence analysis provides clues about the evolution of essential virulence genes such as those encoding the Type III secretion system and related pathogenicity effectors. It also provided insights into possible mechanisms contributing to the rapid adaptation of the bacterium to its environment in general and to its interaction with plants in particular.

Responses of Ovipositing Moths (Lepidoptera: Geometridae) to Host Plant Deprivation: Life-History Aspects and Implications for Population Dynamics

For three species of geometrid moths with noneruptive population dynamics, physiological and behavioral responses of ovipositing females to larval host deprivation were recorded. Single substrate trials were used. Availability of adult food was also varied to manipulate physiological condition of the moths. Egg production rate decreased only weakly in the absence of host plant, whereas it was strongly influenced by adult feeding. The time from the beginning of the experiment to initiation of oviposition was largely determined by presence of suitable host. This variable, oviposition latency, was only weakly affected by nutritional status of the females. Oviposition rates also remained lower on unsuitable hosts after oviposition was initiated. This indicates that the effect of inferior oviposition substrate was not limited to postponing oviposition. Host deprivation and adult feeding both lead to accumulation of chorionated eggs in abdomens. However, high egg loads of the fed females did not alter their behavior in the direction predicted by optimality models. We conclude that oviposition latency was the only variable in which female responses to unsuitable hosts were sufficiently strong to have potential significance for population dynamics. Latency presumably corresponds to dispersing behavior in nature. Such a response, not having been observed in an outbreaking geometrid studied earlier, may reflect a behavioral mechanism capable of stabilizing local population dynamics. The results are discussed in the light of the gradation from capital to income breeding. In herbivorous insects, oviposition latency may serve as an index of overall sensitivity of ovipositing females to adverse environmental conditions.

Reproductive status and flight activity of the overwintered Colorado potato beetle

AbstractMating behavior of post‐diapause Colorado potato beetles, Leptinotarsa decemlineata (Say), was observed within an overwintering site, a rotated potato field, newly colonized potato plants, and under laboratory conditions. The influence of spring mating on beetle flight in the presence and in the absence of host plants was investigated using a computer‐linked flight mill system. Diapause was terminated simultaneously in male and female beetles, and the first matings were observed as early as within the first 24 h after the beetles emerged from the soil (60–90 DD accumulated). The beetles mated within the overwintering site, the potato field, and the fields rotated out of potatoes. Mating status did not affect flight behavior of overwintered beetles; however, unfed beetles displayed higher flight activity than fed beetles. Most flight activity took place soon after flight muscle regeneration, and then declined sharply by the 5th day after flight initiation. Mating in or near overwintering sites soon after diapause termination might be an important factor in providing gene flow between insecticide‐resistant and insecticide‐susceptible Colorado potato beetle populations, and should be considered in designing resistance management plans.

Effect of habitat disturbance on inoculum potential of ericoid endophytes of Western Australian heaths (Epacridaceae)

SUMMARYThe presence of host plants was found to be a key determinant of soil infectivity for endophytes of epacrids growing in south–west Australian jarrah forest carrying a sparse epacrid understorey. A comparable Banksia woodland with higher density of epacrids showed more uniform levels of infective endophytes, presumably because of closer overlap of host–supported patches of endophyte. Disturbed sites in jarrah forest, in which topsoil had been recently returned following bauxite mining, initially showed extremely low endophyte infectivity, probably due to disruption of the hyphal network, absence of host plants and/or increased competition from soil micro–organisms antagonistic to the endophytes. As the system stabilized and epacrids recruited and grew, inoculum potential of the soil re–established and by 12 yr it equalled that of adjacent undisturbed native forest. At disturbed sites with sparsely distributed adult members of the Epacridaceae, endophyte inoculum proved to be adequate only directly adjacent to the epacrids and declined steeply to negligible levels at only 40 cm radially distant from a host plant. The significance of live epacrid root systems on survival of endophyte inoculum in Banksia woodland was examined following removal of shoots of adult plants of the endemic epacrid, Leucopogon conostephioides DC, Coincident with demise of roots of the detopped plants, endophyte inoculum potential of closely adjacent soil declined by 50% during the growing season. However, the effect was short lived and infectivity rose the following year to equal that of undisturbed adjacent woodland as mycelial matrices supported by neighbouring epacrids invaded the depleted study areas.

The Ability of Plant Pathogenic Microorganisms to Survive in Soil a Summarizing Reflection

The importance of soil as inoculum source for plant pathogenic bacteria and fungi is stated. Plant parasites have developed several modes of survival in absence of host plants. For many of them the survival in soil is essential. By examples, the differences between real soil-inhabiting plant parasites and species having only randomly invaded soil are described. Parasites continuously occurring in soil and organisms with a typical soil stage in their life cycle cause the so-called soil-borne diseases. For these plant pathogens, soil is the most essential inoculum source. In 2nd part of the paper as the most important kinds of survival of parasites in soil and plant residues are mentioned: the infection of alternative host plants the commensalism in the microhabitat rhizosphere the entrance in the saprophytic way of life the production of resting cells (bacteria) or special resting organs (fungi) In this connection, the physiological abilities providing for the long survival of the resting structure of the causal agents in soil are discussed. Finally, the possibilities to influence the survival of plant pathogens in soil by agricultural measurements as an important compound of integrated plant protection are considered. Es wird die Bedeutung des Bodens als Infektionsquelle für pflanzenpathogene Bakterien und Pilze erörtert. Die Pflanzenparasiten haben verschiedene Formen der Überbrückung von wirtspflanzenfreien Perioden entwik-kelt, für viele von ihnen spielt dabei die Überdauerung im Boden eine ausschlaggebende Rolle. An Hand von Beispielen wird eingehend die Unterscheidung zwischen echten Bodenbewohnern unter den parasitischen Mikroorganismen und solchen Arten dargestellt, die nur ± zufällig in den Boden gelangen und für die der Boden als Infektionsquelle ohne Bedeutung ist. Permanent im Boden vorkommende Erregerarten und parasitische Organismen mit einer charakteristischen Bodenphase verursachen die sog. bodenbürtigen Pflanzenkrankheiten; für sie ist der Boden die wichtigste Infektionsquelle. Im 2. Teil der Arbeit werden als die wichtigsten Formen der Überdauerung von Schaderregern im Boden und in Pflanzenresten die Infektion alternativer Wirtspflanzen, der Kommensalismus im Bereich der Rhizosphäre, der Übergang in die saprophytische Lebensweise und die Bildung von Ruhezellen (bei Bakterien) bzw. speziellen Dauerorganen (bei Pilzen) behandelt. Im Mittelpunkt der Betrachtung stehen dabei die physiologischen Fähigkeiten, die die lange Lebensdauer dieser Ruhestadien bedingen. Abschließend wird auf Möglichkeiten hingewiesen, die Überdauerung von Schaderregern im Boden im Sinne eines integrierten Pflanzenschutzes gezielt zu beeinflussen.

Effects of a host plant, Brassica juncea, on calling behaviour and egg maturation in the diamondback moth, Plutella xylostella

AbstractThe influence of the presence of seedlings of a host plant, Oriental mustard, Brassica juncea (L.) Coss., on the calling behaviour and egg maturation in the diamondback moth, Plutella xylostella (L.), was investigated. In the presence of plants, females began calling at a younger age, began calling earlier in the night, and spent more time calling. Females which were kept with plants until after their first night of calling and then were isolated from plants, subsequently called less, at a level not significantly different from females which had never been exposed to plants. Of all females, both with and without plants, which were dissected at the end of the first night of calling (n = 150), 93% contained mature eggs. Heavier females were significantly more likely to have mature eggs at adult emergence, to begin calling at a younger age and to spend more time calling on their first night of calling. The number of developed eggs in calling females was not significantly different in the presence or absence of host plants on the first night of calling. However, by the second night, females in the presence of plants contained significantly more eggs, indicating that the presence of plants accelerated egg maturation, both before and after the onset of calling.

Overwintering Biology of Dalbulus Leafhoppers (Homoptera: Cicadellidae): Adult Populations and Drought Hardiness

Despite the economic importance of the corn leafhopper, Dalbulus maidis (DeLong & Wolcott), little is known about how this maize pest and its congeners survive the dry winter in Mexico. In the field, Dalbulus populations were monitored weekly with yellow sticky card traps for 18 mo at three sites in Jalisco, Mexico. The sites included a maize field, Zea maysL. ; a natural stand of a perennial teosinte, Zea diploperennis Iltis, Doebley & Guzman; and a natural population of gamagrasses, Tripsacum spp., which are maize relatives. At all sites, highest catches of Dalbulus adults occurred during the dry season between October and March. In a laboratory study to test the survival of adult Dalbulus leafhoppers without their host plants, significant differences were detected among leafhopper species. When denied all food and water (absolute drought), Dalbulus species that specialize on maize were more tolerant than those that specialize on gamagrass. Adults reared under environmental conditions that simulate the beginning of the wet season (June-reared) were less tolerant of absolute drought than adults reared under early dry-season conditions (October-reared). When provided water but no food, October-reared D. maidis lived significantly longer than June-reared D. maidis . Survival of females under water-only conditions was significantly longer than that of males. Field observations revealed that gamagrass-specializing D. gelbus DeLong and D. quinquenotatus DeLong & Nault overwinter as continuously developing populations on their hosts. In contrast, our data indicate that D. maidis overwinter as active adults that can subsist, at least in part, on free water in the absence of host plants until the summer rainy season begins. Surviving adults then migrate locally to newly planted maize fields.

Factors Facilitating the Continued Presence of Colotis evagore (Klug, 1829) in Southern Spain

Colotis evagore (Klug) is a multivoltine pierid butterfly that has repeatedly invaded the Iberian Peninsula from Africa over the last four decades. In 1983 it invaded Spain, reproducing successfully there on its foodplant, Capparis spinosa L. During the cold season this plant is not available in most areas of Spain, and the butterfly must find alternative foodplants to maintain its populations in this newly colonized territory. Our data show that C. evagore is unable to survive on alternative cruciferous hosts, and incapable of entering diapause to avoid inhospitable times of the year and the absence of host plants. The relative growth rate of larvae depends on temperature; the threshold temperature for development is 12?C, and the estimated physiological time for larval development is 162.5?d. Our observations show that C. evagore has survived continually in certain coastal sites in southern Spain since 1983. Microenvironmental conditions in these sites are particularly favourable for the foodplant. Hence, the plant is available throughout the year, allowing the caterpillars to complete successfully their life-cycle.

Long‐term survival of sclerotia of Sclerotium cepivorum and Stromatinia gladioli

In an experiment with pure‐culture sclerotia of Sclerotium cepivorum and Stromatinia gladioli a large proportion of the sclerotia survived burial for 20 years in the field in the absence of host plants. Some evidence for metabolic activity or leakage leading to the gradual erosion of the sclerotial contents was obtained with S. cepivorum. The results of other experiments suggested that, for unknown reasons, a variable proportion of sclerotia formed naturally on infected plants may decay shortly after their formation, but those which survive beyond this limited period are likely to remain viable for many years. The viability of sclerotia was also reduced by prolonged flooding, but the period for which land would have to be under water excludes this as a method of eliminating sclerotia from infested land in the UK. Treatment with the mycoparasite Teratosperma oligocladum did not affect the survival or infectivity of sclerotia of S. cepivorum or S. gladioli.

INFLUENCE OF SOIL SURFACE CONDITIONS AND HOST PLANT ON SOYBEAN NODULE FLY RIVELLIA QUARDIFASCIATA (MACQUART) (DIPTERA: PLATYSTOMATIDAE) OVIPOSITION1

Soybean nodule fly, Rivellia quadrifasciata (Macquart) eggs were oviposition in the soil and crop residue around the bases of potential larval host plants. Approximately 75% of the egg clutches observed being oviposited in cracks and crevices, in the field, were within 2 cm of the host plant stem (Phaseolus limensis Macf. L.). Most eggs were oviposited within 2 mm of the soil surface but eggs were sometimes deeper when females entered soil cracks and crevices. Oviposition from laboratory colony adults was not observed in the absence of host plants in no-chioce situations. When given a choice between closely arranged pots of soil with and without soybean plants, little oviposition occurred in soil without plants. Significantly (p = &amp;gt; 0.05) more oviposition occurred in pots containing soybean plants with loose soil than with compacted soil surfaces. The short-term responses of females to the absence of appropriate oviposition sites included egg retention and apparent increased flight activity.

Reduction of Take‐all Inoculum by Rotation with Lupins, Oats or Field Peas

AbstractThe feasibility of use of lupins, oats and field peas as alternative rotation crops to reduce inoculum of the take‐all fungus (Gaeumannomyces graminis var. tritici) (under Western Australian field conditions) and disease in following wheat was investigated with a one year field trial, the soil from which was used in two succeeding pot experiments. The possible mechanisms of reduction of inoculum and disease by these crops were examined testing the soil for pathogen and disease suppression. Rotation with lupins or oats for two seasons reduced (P &lt;0.05) inoculum of the take‐all fungus and lupins, oats or field peas reduced (P &lt;0.05) disease in following wheat. Lupins alone reduced inoculum and disease, (P &lt;0.1) after one season. No apparent suppression of the pathogen in the absence of host plants was recorded after one season of rotation, but after two seasons, lupins, oats or field peas all suppressed (P &lt;0.02) growth of the pathogen within soil. However only field pea soil suppressed take‐all in comparison with the wheat control.Although after two seasons all rotation crops were effective in reducing inoculum and disease the mechanisms of reduction appear to differ between the rotation crops used in this study.

Role of host‐plant stimuli in sexual behaviour of small ermine moths (Yponomeuta)

ABSTRACT. 1. Studies involving experiments with olfactometers and field experiments have shown that the release of sex‐pheromone by females of Yponomeuta spp. is stimulated by the presence of host plants.2. While in Y.evonymellus L. less females emitted pheromone in the absence of host plants, in Y.padellus L. the initiation of pheromone release was delayed.3. Females of Y.evonymellus, Y.cagnagellus Hüb., Y.padellus and Y.plumbellus D. &amp; S. all preferred a place with host‐plant odour to one with non‐host odours for sex‐pheromone release.4. Male preference for host‐plant odour was demonstrated in the laboratory only for Y.cagnagellus.5. Trap catches in the field indicated a reinforcement of female attractiveness by host‐plant stimuli.

GERMINATION OF BASIDIOSPORES OF MYCORRHIZAL FUNGI IN THE RHIZOSPHERE OF PINUS RADIAT A D. DON

SUMMARYA method was developed to inoculate the surfaces of young roots of Pinus radiata D. Don uniformly with basidiospores of mycorrhizal fungi. Germination of basidiospores in the rhizosphere was 46 to 69 % in different experiments with Rhizopogon luteolus Fr. and Nord and 34 and 31 % with Suillus luteus (L. ex Fr.) S. F. Gray and 5. granulatus (L. ex Fr.) O. Kuntze, respectively. This compared with 01 % germination usually obtained for all fungi on synthetic media. Using the method, single spore cultures of R. luteolus were obtained which formed mycorrhizas on P. radiata seedlings. Germination did not respond to roots of Eucalyptus globulus Labill, Medicago truncatula Gaertn., Trifolium subterraneum L. or Lolium perenne L., showing the germination response was specific to P. radiata, although other host tree species may produce a similar response. Specificity in such mycorrhizal associations may operate both at the germination and the infection stages. It is suggested that in vivo the necessity for a host plant to stimulate spore germination is a highly effective method of inoculum conservation in the absence of host plants. The viability of inoculum remained high during storage at freezing temperatures. High spore germination rates were also obtained when the method was used in unsterilized soil.

Soil Populations of Rhizobium japonicum in a Cotton-Corn-Soybean Rotation

The ability of legume root nodule bacteria to live in soil in the absence of host plants has great practical value. Since soybean [Glycine max (L.) Merrill] is extensively grown and its value is largely dependent upon effective N2 fixation, it is important to develop an understanding of the ecology of its nodule bacteria, Rhizobium japonicum. In order to determine seasonal trends in R. japonicum populations in relation to cropping and soil fertility conditions that severely limit crop production, selected treatments in a long-term field experiment were sampled at approximately 30-d intervals over a 2-yr period for R. japonicum numbers in soil of the plow layer. Soil was serially diluted and applied to surface-sterile soybean seed in growth pouches to determine most probable number (MPN). Numbers of R. japonicum in soil were maximum during the winter after the soybean crop, exceeding 106 per gram soil. Populations declined rapidly during the following summer under cotton (Gossypium hirsutum L.). Where lime, P, and K were adequate, R. japonicum numbers stabilized at 104 to 105 per gram, while in soil deficient in P or K numbers fell to 103 to 104 per gram. In acid soil (pH 4.6), R. japonicum decreased to less than 102 per gram. Minimum populations occurred about 1 October under cotton with increasing numbers into the winter, particularly where lime, P, and K were adequate. In the following year under corn (Zea mays L.), similar cycles were found where populations declined from winter to summer and then increased into fall and winter. After rye (Secale cereale L.) harvest and planting soybeans in the third year, R. japonicum numbers increased rapidly to approach 106 per gram. Vetch (Vicia dasycarpa Tenore) and crimson clover (Trifolium incarnatum L.), while influential on crop yields, had no effect on R. japonicum numbers. Similarly, fertilizer N did not affect R. japonicum populations in soil where pH was maintained by liming. Soil acidity was the most severe stress on R. japonicum, followed in order by P and K deficiencies.

L'activité reproductrice et le développement de Bruchidius atrolineatus (Pic) sur les gousses sèches de Vigna unguiculata (Walp) en zone sahélienne, mise en évidence d'une diapause imaginale

Bruchidius atrolineatus appears at the end of the rainy season when pods of its host plant Vigna unguiculata begin to mature. The eggs are deposited along the ventral suture of pods in the vicinity of the seeds. When the eggs are not attacked by Trichogrammatidae their larvae penetrate the seeds and mortality is low during the post-embryonic development. Most of the adults emerging at pod maturity have functional reproductive organs. In that case the females laid on the same mature pods and larvae develop inside the seeds during the first part of the drying season characterised by high diurnal temperature and low relative humity. If the first emerged adults have functional reproductive organs, the following (60% of the population) are in reproductive diapause. Such diapausing insects have been found during the dry season in shelters near the cultivated fields of Vigna unguiculata . Induction or termination of this reproductive diapause are not yet studied. This diapause probably allows the maintenance of populations during the dry season in absence of host plant.