The response of the grape berry moth (Lobesia botrana) to a dietary phytopathogenic fungus (Botrytis cinerea): the significance of fungus sterols

A Tortricidae (Lobesia botrana) has a mutualistic relationship with the fungus (Botrytis cinerea). In this study, we investigated the growth, survival, fecundity and amount of sterols and steroids in larvae of this vineyard pest reared on artificial diets containing mycelium (3%) or purified sterols (0.01%) of the phytopathogenic fungus. Two principal questions related to the physiological and biochemical basis of this mutualistic relationship were addressed: (1) how the fungus influences growth, survival, fecundity, sterol and steroid contents of the insect and (2) are fungal sterols involved in the biochemical basis of mutualism? The presence of fungus in the diet led to a decrease of total duration of larval development (mean gain 5.1-9.4 days compared to the total duration in control of 42.9 days), an increase in survival (mean gain 50-76.3%) and fecundity (gain of 94-102%). These positive effects of the fungus on the biology and physiology of the insect were directly correlated to the presence of fungal sterols in the diet. Fungal sterols are one of the biochemical basis of the mutualistic relationship between L. botrana and B. cinerea.     

Asymmetric plant-mediated cross-effects between a herbivorous insect and a phytopathogenic fungus

• 1 Cross‐effects between a herbivorous insect and a phytopathogenic fungus on their common host plant were examined. Specifically, we addressed the questions whether (i) infection of Chinese cabbage leaves by the fungus Alternaria brassicae affects the development and host selection behaviour of the leaf beetle Phaedon cochleariae and (ii) whether herbivory influences host suitability of Chinese cabbage for A. brassicae.
• 2 Feeding on fungus‐infected leaves prolonged larval development and reduced pupal weight of P. cochleariae. Adult beetles avoided feeding and egg deposition on fungus‐infected leaves. In contrast to these local effects, no systemic effect of phytopathogenic infection on the herbivore was detected.
• 3 Herbivory did not influence fungal growth neither locally nor systemically.
• 4 Thus, our results demonstrate an asymmetric relationship between herbivore and fungus. Whereas herbivory had no visible impact on fungal growth, fungal infection of the plant induced local resistance against P. cochleariae.

     

Influence of generation and photoperiod on larval development of Lobesia botrana (Lepidoptera: Tortricidae)

The influence of generation (under field conditions) and photoperiod (under laboratory conditions) on Lobesia botrana larvae development was studied. Some larvae were collected during three annual generations in two grape-growing areas of northeastern Italy, and others were individually reared in the laboratory from egg to pupa on an artificial diet under two different photoperiod conditions (respectively, daylight 16 h/d [long day {LD}] and 14 h/d [short day {SD}]). The mandible lengths of collected larvae were measured and the data analyzed morphometrically to determine the number of larval instars. In the laboratory study, the number of larval moultings, the mandible length of each instar, the development time from hatching larva to pupa, and the pupal weight were considered. The measurement of mandible lengths of larvae collected in the field indicated the existence of five larval instars in all three annual generations, but the size of the two oldest larval instars was significantly higher for third-generation larvae than for the previous generations. Under laboratory conditions, the larvae usually exhibited five instars, but the mandible lengths of larvae and the pupa size were greater for individuals reared under SD. These also took a greater number of days to develop from hatching larvae to pupae. Because a larger size of the final larval instar occurs in individuals that produce diapausing pupae under SD in both the laboratory and the field, a positive association between larval size and the probability of surviving the winter can be inferred.     

Evaluation of the effects of biological preparations on phytopathogenic fungi Didymella applanata and Botrytis cinerea

Fungicidal and fungistatic effects of biological preparations involving bacteria of the genera Pseudomonas and Bacillus and fungi of the genus Chaetomium on phytopathogenic fungi Didymella applanata and Botrytis cinerea were evalauated. All the biological preparations under study inhibited the growth of colonies of the fungi; however, the degree of the inhibition depended on the nature of each particular microorganism and the concentration of each particular preparation. The preparation containing Bacillus subtilis at a concentration of 0.2% effected maximum suppression of B. cinerea (the diameter of the colonies decreased sevenfold). The preparations containing bacteria of the genus Pseudomonas and fungi of the genus Chaetomium were most efficient in suppressing D. applanata. The preparations containing B. subtilis and Chaetomium spp. showed promise as agents against simultaneous development of spur blight and Botrytis blight.     

A bioassay to evaluate the activity of chemical stimuli from grape berries on the oviposition of Lobesia botrana (Lepidoptera: Tortricidae)

A two-choice bioassay was developed to evaluate the role of host-plant berry compounds on the oviposition site acceptance of the generalist moth Lobesia botrana (Denis & Shiffermüller). A key feature was the lining of the bioassay arena with felt which focused oviposition on the test substrates. Initial experiments comparing substrates with different physical features indicated that smooth textures and spherical shapes with interstices favour oviposition. Artificial oviposition substrates were thus constructed with glass spheres in order to test the behavioural activity of grapevine berry extracts. Only polar extracts obtained by soaking berries in methanol or water stimulated oviposition (more eggs were laid on the extract-treated substrate than on the control substrate), whereas more apolar ones obtained with chloroform or hexane had no significant effect. The prior removal of epicuticular waxes from grape berries before extraction did not enhance the stimulatory activity of the methanol extract. The oviposition response to this extract was dose-dependent. It is concluded that polar compounds present on grape berries act as oviposition stimulants for L. botrana.     

Effects of lufenuron on Lobesia botrana (Lepidoptera: Tortricidae) egg, larval, and adult stages

The effect of the chitin synthesis inhibitor lufenuron was evaluated against different developmental stages of Lobesia botrana Den. & Schiff. (Lepidoptera: Tortricidae). Lufenuron fed to adults at 10 ppm reduced their fecundity and fertility, but it did not affect adult longevity. High activity was observed against L. botrana eggs with greater effect on 1-d-old eggs than on the other age classes and on eggs treated by direct contact rather than those laid on a previously treated surface. Eggs laid by treated adults showed the same effects during development as eggs treated by contact or those laid on a treated surface. Larvae that emerged from treated eggs could not perforate grape berries. Administered into the diet, lufenuron had a larvicidal effect, resulting in similar LC50 values for different instars: 0.07 ppm for first instars, 0.08 ppm for third instars, and 0.11 ppm for fifth instars. None of the larvae treated with sublethal concentrations throughout their life emerged as adults at the highest concentration (0.08 ppm), and only 70% emerged at the lowest concentration (0.0025 ppm).     

Factors affecting the development of Botrytis cinerea (grey mould) on linseed (Linum usitatissimum) buds, flowers and capsules

A key was produced to describe 10 stages of development of linseed buds, flowers and capsules. Botrytis cinerea conidia germinated more rapidly and germ tubes grew longer on linseed stigmas, petals and mature senescing capsules than on green leaves, sepals and immature capsules. The proportion of conidia which germinated increased and the germ tubes continued growing for longer in the presence of linseed pollen and flower petal extracts. In controlled environment and field experiments, the response of buds, flowers and capsules to inoculation with B. cinerea changed with stage of development; few pre‐flowering buds developed symptoms (brown lesions, then grey mould), but high proportions of flowering and post‐flowering buds did so. Few immature green capsules developed symptoms and the proportion of capsules which developed symptoms increased as they matured. The presence of linseed pollen decreased the incubation period from inoculation with spore suspensions to appearance of B. cinerea symptoms on buds. A disease cycle was produced to suggest the changes in susceptibility of linseed to infection by B. cinerea conidia during bud, flower and capsule development.     

Coping with an antagonist: the impact of a phytopathogenic fungus on the development and behaviour of two species of alpine leaf beetle

Herbivorous insects and phytopathogenic fungi often share their host plants. This creates a network of direct and indirect interactions, with far‐reaching consequences for the ecology and evolution of all three parties. In the Alps, the leaf beetles Oreina elongata and Oreina cacaliae (Coleoptera: Chrysomelidae), and the rust fungus Uromyces cacaliae (Uredinales: Pucciniaceae) are found on the same host plant, Adenostyles alliariae (Asterales: Asteraceae). We compare the impact of rust infection on these two closely‐related beetle species, one of which, O. cacaliae, is a specialist on A. alliariae, while the other, O. elongata, moves repeatedly between Adenostyles and an alternative host, Cirsium spinosissimum. Larval performance, feeding preference, oviposition choice and dispersal behaviour were studied in field and laboratory experiments. When reared on rust‐infected leaves, larvae of both beetle species had lower growth rates, lower maximum weights and longer development times. Larvae and adults discriminated among diets in feeding trials, showing a preference for discs cut from healthy leaves over those bearing a patch of sporulating rust, those from elsewhere on an infected leaf, and those from an upper leaf on an infected plant. Females of the two species differed in behaviour: in O. cacaliae they favoured healthy leaves for larviposition, while in O. elongata they showed no significant preference during oviposition. In the field, larvae and adults of both species dispersed more rapidly when placed on infected host plants. The results demonstrate that rust infection reduces the quality of the plant as a host for both Oreina species, and they combine the ability to detect systemic infection with the evolution of evasive behaviours. For these beetles, competition with a rust clearly increases the difficulty of survival in the harsh conditions of alpine environments, and may have a profound impact on the evolution of their life history traits and host plant use.     

Sympatric genetic differentiation of a generalist pathogenic fungus, Botrytis cinerea, on two different host plants, grapevine and bramble

Prime candidates for sympatric ecological divergence include parasites that differentiate via host shifts, because different host species exert strong disruptive selection and because both hosts and parasites are continually co-evolving. Sympatric divergence may be fostered even more strongly in phytopathogenic fungi, in particular those where sex must occur on the host, which allows adaptation alone to restrict gene flow between populations developing on different hosts. We sampled populations of Botrytis cinerea, a generalist ascomycete fungus, on sympatric grapes and brambles in six regions in France. Microsatellite data were analyzed using standard population genetics, a population graph analysis and a Bayesian approach. In addition to confirming that B. cinerea reproduces sexually, our results showed that the fungal populations on the two hosts were significantly differentiated, indicating restricted gene flow, even in sympatry. In contrast, only weak geographical differentiation could be detected. These results support the possibility of sympatric divergence associated with host use in generalist parasites.     

The effects of plant population size on the interactions between the endangered plant Scorzonera humilis, a specialised herbivore, and a phytopathogenic fungus

We studied the effects of population size on the interactions between Scorzonera humilis (Asteraceae), its specialised seed-feeding fly Heterostylodes macrurus (Anthomyidae) and its specific systemic smut fungus Ustilago scorzonerae (Ustilaginales). The number of seeds developing per plant (potential seed production) strongly increased with population size in S. humilis. However, because seed predation by the seed feeding fly H. macrurus and the negative impact of the pathogen U. scorzonerae also increased, realised seed production was not related to population size. The probability of occurrence of H. macrurus increased with the population size of its host plant and its abundance increased more than proportionally. This suggests that Allee effects reduce insect abundance in small populations of S. humilis . The probability of occurrence of the fungus U. scorzonerae also increased with plant population size. Within populations, large genets were more likely to be infected than small ones. The systemic pathogen U. scorzonerae reduces the effective population size of its host because all flowers of an infected individual are sterilised. Nevertheless, in most populations the impact of the fly on reproduction was stronger than that of the pathogen, because most genets were not infected. Both parasites were rarer than the host plant itself, supporting the trophic-level hypothesis of island biogeography. Our results suggest that habitat fragmentation may release plants from parasites and pathogens. These positive effects of isolation and small population size may mask negative effects of fragmentation on, for instance, the quantity and quality of pollination.     

Effects of grapevine bunch exposure to sunlight on berry surface temperature and Lobesia botrana (Lepidoptera: Tortricidae) egg laying,hatching and larval settlement

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Soil nutrient effects on oviposition preference,larval performance,and chemical defense of a specialist insect herbivore

This study examined the effects of increased leaf nitrogen in natural host-plants (Plantago spp.) on female oviposition preference, larval performance, and larval chemical defense of the butterfly Junonia coenia. Increased availability of soil nutrients caused the host-plant’s foliar nitrogen to increase and its chemical defense to decrease. Larval performance did not correlate with increases in foliar nitrogen. Larval growth rate and survival were equivalent across host-plant treatments. However, larvae raised on fertilized host-plants showed concomitant decreases in chemical defense as compared to larvae reared on unfertilized host-plants. Since most butterfly larvae cannot move long distances during their first few instars and are forced to feed upon the plant on which they hatched, J. coenia larval chemical defense is determined, in large part, by female oviposition choice. Female butterflies preferred host-plants with high nitrogen over host-plants with low nitrogen; however, this preference was also mediated by plant chemical defense. Female butterflies preferred more chemically defended host-plants when foliar nitrogen was equivalent between host-plants. J. coenia larvae experience intense predation in the field, especially when larvae are not chemically well defended. Any qualitative or quantitative variation in plant allelochemical defense has fitness consequences on these larvae. Thus, these results indicate that females may be making sub-optimal oviposition decisions under a nutrient-enriched regime, when predators are present. Given the recent increase in fertilizer application and nitrogen deposition on the terrestrial landscape, these interactions between female preference, larval performance, and larval chemical defense may result in long-term changes in population dynamics and persistence of specialist insects.     

Temperature and Effects of Seed-borne Botrytis cinerea or Alternaria linicola on Emergence of Linseed (Linum usitatissimum) Seedlings

Experiments were done at temperatures from 5 to 20 C to investigate the effects of infection of linseed seed (cv. Antares) by Botrytis cinerea or Alternaria linicola on seedling emergence and to study transmission of the pathogens from seed to seedlings. In one experiment with freshly harvested seed, the maximum percentage emergence decreased linearly as the incidence of B. cinerea in seed increased from 0 to 83% at 18 C day/12 C night temperatures. In another experiment, the decrease in percentage emergence of seed associated with infection by B. cinerea. the transmission of the pathogen to seedlings to produce disease symptoms on their hypocotyls and the incidence of post-emergence death all increased as temperature decreased from 20 to 5 C. However, the decrease in percentage emergence of seed associated with infection by A. linicola and the transmission of the pathogen to seedlings to produce cotyledon lesions both increased as temperature increased from 5 to 20 C. There was little effect of either pathogen on the time from sowing to 36% of maximum emergence, which decreased with increasing temperature. In a subsequent experiment at 10 C comparing seed infected with B.cinerea or A. linicola. using the same seed sources as in the previous experiments, infection by A. linicola decreased emergence more than infection by B. cinerea , even though the incidence of A. linicola in the seed was smaller. Analyses of position and parallelism suggested that regressions of maximum percentage emergence (logitransformed) against temperature were fitted best by non-parallel lines for seed infected by B. cinerea or A. linicola.     

Study of the relationship between sex pheromone trap catches of Lobesia botrana (Den. & Schiff.) (Lep., Tortricidae) and the accumulation of degree-days in Sherry vineyards (SW of Spain)

The relationship between temperature accumulations and pheromone trap captures of the males of Lobesia botrana (Den. & Schiff.) (Lep., Tortricidae) in the Sherry vineyards (SW of Spain) presents a statistically acceptable linear behaviour through conveniently transforming the variables. Data series ranging from 1990 to 1995 were used to compute the linear correlations. The reliability of the forecasts based on the resulting log-probit lines have shown to be acceptable in order to be considered as an useful tool to improve the effectiveness of the integrated pest management in the area.     

Tritrophic interactions among Bt maize,an insect pest and entomopathogens: effects on development and survival of western corn rootworm

Agricultural systems often provide a model for testing ecological hypotheses, while ecological theory can enable more effective pest management. One of the best examples of this is the interaction between host‐plant resistance and natural enemies. With the advent of crops that are genetically modified to produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt), a new form of host‐plant resistance has been introduced to agroecosystems. How Bt crops interact with natural enemies, especially insect pathogens in below‐ground systems, is not well understood, but provides a unique opportunity to study below‐ground tritrophic interactions. In this study, we used two species of entomopathogenic fungi and three species of entomopathogenic nematodes to determine how this community of soil‐borne natural enemies might interact with Bt maize (event 59122, expressing the insecticidal protein Cry34/35Ab1) to affect survival and development of western corn rootworm (Diabrotica virgifera virgifera), which is an obligate root feeder and a serious pest of maize. We ran two experiments, one in a greenhouse and one in a growth chamber. Both experiments consisted of a fully crossed design with two maize treatments (Bt maize and non‐Bt maize) and two entomopathogen treatments (present or absent). The community of entomopathogens significantly increased mortality of western corn rootworm, and Bt maize increased larval developmental time and mortality. Entomopathogens and Bt maize acted in an independent and additive manner, with both factors increasing the mortality of western corn rootworm. Results from this study suggest that entomopathogens may complement host‐plant resistance from Bt crops.     

The Galpha subunit BCG1, the phospholipase C (BcPLC1) and the calcineurin phosphatase co-ordinately regulate gene expression in the grey mould fungus Botrytis cinerea

The Gα subunit BCG1 is essential for pathogenicity of the grey mould fungus Botrytis cinerea . Several processes such as the transition from primary infection to secondary invasive growth and the production of the phytotoxin botrydial are regulated by BCG1 via a cAMP-independent pathway. Our recent finding that the botrydial biosynthesis genes belong to the group of Ca²⁺/calcineurin-dependent genes suggested for the first time a connection between this Gα subunit and the calcineurin signalling pathway. To investigate whether this co-regulation of genes by BCG1 and calcineurin is a common feature, a cDNA macroarray approach was used to compare the gene expression pattern of the wild-type and the Δ bcg1 mutant, non-treated or treated with the calcineurin inhibitor cyclosporin A. We identified three sets of genes whose expression was regulated either by both BCG1 and calcineurin, or only by one of them. Among the BCG1/calcineurin-co-regulated genes, we found a new gene cluster coding for a yet unknown polyketide secondary metabolite. Furthermore, we show for the first time in a phytopathogenic fungus that the phospholipase C (BcPLC1) is a component of the BCG1- and calcineurin-dependent signalling pathway as several BCG1- and calcineurin-dependent genes were downregulated in bcplc1 knock-down mutants.     

Play behaviour and its effects on social development of common chimpanzees (Pan troglodytes)

The aim of the study was to monitor the social development of infant and juvenile common chimpanzees (Pan troglodytes) through their play behaviour at Taronga Zoo in Sydney in order to examine the possible effects of captivity (such as limited opportunities to play) on social development. Play behaviour was observed by focal animal sampling to determine individual differences, and their relationship to age, sex, and relatedness of the subjects. Analysis revealed marked individual variations in social, solitary, and object play behaviours indicative of a relatively well-balanced social and physical environment. Subjects showed a marked preference for play-partners of a different age compared to their own, and initiated interactions with similar frequency with members of both sexes. Many social-play dyads consisted of related individuals, and familiarity with prospective play-mates was the most decisive factor in social interactions.