Tibor Jermy

Host plant finding in phytophagous insects: the case of the Colorado potato beetle

A short critical review is given on the literature of host plant finding in phytophagous insects with main emphasis on the Colorado potato beetle (Leptinotarsa decemlineata Say, col.: Chrysomelidae). The literature data are compared with the results of field experiments: (1) the foraging behaviour of adults was observed in a field arena on bare ground, and (2) adults were released in closed plant stands and recaptured by potted potato plants. It is concluded that host plant finding is a chance event in this species. The observed high directionality of move must be an adaptation increasing probability of host finding. Implications on population dynamics and agricultural practice are discussed.

Predispersal Seed Predation in Leguminous Species: Seed Morphology and Bruchid Distribution

We measured and calculated seed morphological parameters [axonometric linear measures, weight, volume and minimum-maximum seed size ratio (SMIMA)] of 110 leguminous plant species occurring in Hungary. We collected seed samples, reared the predispersal seed predators from the samples, took morphological data from the bruchids (elytra length, body width, thorax length) and calculated the body size ratio (BSR). We found that SMIMA and BSR were fairly good predictors of bruchid infestation patterns at plant tribe, species and sample (locality) levels. Bruchid body length was much less variable than the parameters (e.g., volume) of seeds from which they were reared. We also found that the closer the shape of the seeds of a leguminous plant species to a sphere, or the larger the seed volume, the higher the probability of bruchid infestation. Seed morphological traits (weight, volume and SMIMA) clearly separated the hosts of the genera Bruchus and Bruchidius. For the three related bruchid genera studied, phylogenetic and ecological effects (regarding seed shape preference) were also separated. We concluded that the evolution of the seed size of plant species studied is not likely driven by bruchids or by other seed predators

Method for screening female sex pheromone extracts of the Colorado potato beetle

The presence of a female sex pheromone in the Colorado potato beetle (CPB) has been demonstrated first by de Wilde et al. (1969) who found that in a wind tunnel female odour enhanced the anemotactic behaviour of the males. Levinson et al. (1979) reported on a binary choice arena test in which the males revealed a clearcut preference for that section of the wire screen arena that was about 8 mm above a piece of filter paper treated with an n-pentane extract of female elytra, as compared with the section above male elytra extract. No copulatory behaviour has been observed. However, when dummies were impregnated with the extract, males attempted to copulate with them. The authors did not specify the dummies. In order to find a simple screening method for pheromone extracts, a series of different trials was carried out at the U S D A Yakima Agricultural Research Laboratory (Yakima, Washington, USA) in 1978/79.

Pre-dispersal seed predation and seed limitation in an annual legume

Abstract In field experiments (1993–1998) using an annual self-pollinated vetch species, Vicia angustifolia , the effects of pre-dispersal seed predators (pre-DSPs) on plant performance and demography were studied. Insect exclusion by insecticides, vegetation perturbation at the start of the experiment by removing the top soil layer, and sowing extra seeds were applied at one site (Site 1) on 32 plots, and only insect exclusion at another site (Site 2) on 14 plots, respectively, in the plants natural habitat. The number of seedlings was influenced most by perturbation at Site 1. There were 2–4 times more seedlings on bare plots in comparison with vegetation-covered plots, although significant difference was detected only in 1993, 1994 and 1997. Density of adult plants was lower on vegetation-covered plots. Dry matter, height, length of branches, and of pods were positively affected by perturbation on Site 1. The number of seeds infested by pre-DSPs was generally low, however, it was higher on unsprayed plots, regardless whether the plot was perturbed or not. Overall, seed loss to pre-DSPs was only ca. 10%. Sowing extra seeds among vegetation increased net plant recruitment demonstrating that microsites were available in the habitat. V. angustifolia is assumed to be a weak competitor and, in spite of the low percentage of seed loss to pre-DSPs, it is most likely limited by seed number. The deficit in using available microsites might be caused by post-dispersal mortality factors. Der Einfluss von Vordispersions-Samenfresser (VDSF) auf Produktivitat und Demographie der selbstbestaubenden Wickenart, Vicia angustifolia , wurde in Feldversuchen (1993–1998) untersucht. Am naturlichen Standort der Wicke wurden an 32 Quadraten folgende Varianten angelegt: Ausschluss der Insekten mit Insektiziden, Storung der Vegetation (Entfernen der oberen Bodenschicht) und Aussaat von extra Samen (Ort 1), sowie an 14 Quadraten blos Ausschluss der Insekten (Ort 2). Die Anzahl der Keimlinge war am Ort 1 am meisten durch die Storung der Vegetation beeinflusst. In den Quadraten ohne Vegetation entwickelten sich 2 bis 4-mal mehr Keimlinge, als in den kahlen Quadraten, obzwar signifikante Unterschiede nur in 1993, 1994 und 1997 gefunden wurden. Die Populationsdichte der adulten Wickenpflanzen war kleiner in den Quadraten mit Vegetation. Trockensubstanz, Hohe, Lange der Seitentriebe und der Hulsen waren am Ort 1 durch die Storung positiv beeinflusst. Die Anzahl der durch VDSF beschadigten Samen war im allgemeinen klein, sie war jedoch an insektizidbehandelten Quadraten groser, unabhangig davon, ob die Vegetation gestort wurde oder nicht. Der durch VDSF verursachte Samenverlust war durchschnittlich blos etwa 10%. Die Aussaat von Wickensamen in die naturliche Vegetation erhohte die Anzahl der Keimlinge, d.h., es waren freie Mikroorte vorhanden. V. angustifolia ist wahrscheinlich ein schwacher Kompetitor und ihre Population ist durch die Samenzahl beschrankt, namlich durch den Einfluss von Nachdispersions-Samenschadlingen.

A comparison of food-related behaviour between geographic populations of the Colorado potato beetle (Coleoptera, Chrysomelidae), on six solanaceous plant species

Some components of the food‐related behaviour (biting, feeding, walking on the plant or walking elsewhere, and resting) of two North American and three European Colorado potato beetle (CPB) populations, on six solanaceous plant species were monitored with the help of a microcomputer‐based program, testing the hypothesis whether populations showed differences at the behavioural level to alternative host plants (S. melongena, S. dulcamara, and Lycopersicon esculentum), as well as to non‐host plants occasionally encountered (S. luteum, S. nigrum). The few significant differences found were among populations of the same continent in 1) the number of activities monitored, 2) the duration of feeding periods, 3) the number of bites taken to the onset of feeding, 4) the ‘amount of behavioural plasticity’, and 5) the ‘behavioural diversity’. On the basis of two‐way ANOVA analyses, no plant‐by‐population interactions were detected indicating that the CPB populations studied did not have specific relationships with any of the plant species tested. The lack of substantial differences in food‐related behaviour was unexpected since considerable isolation in space and time exists between the populations occurring on the two continents.

Spatial and temporal organisation of the pre-dispersal seed predator guild in a perennial legume, Vicia tenuifolia

Abstract.  1. The variability of species combinations and membership assembly patterns in an insect pre‐dispersal seed predator guild were studied at various spatial and temporal resolutions using presence/absence and abundance data in null models. The guild consists of seven beetle species (four bruchids and three curculionids) and one moth species that live on a perennial vetch, Vicia tenuifolia Roth (Leguminosae).

Within field movement of overwintered Colorado potato beetle: a patch-based approach

Abstract:  After comparing the persistence of four marking techniques, a mark–release–resight study was performed to characterize mid‐season movement of the Colorado potato beetle [Leptinotarsa decemlineata (Say); Col., Chrysomelidae] simultaneously in a fallow and in a wheat field. Isolated patches of potatoes were installed in a random spatial arrangement on both fields similarly. Overwintered beetles were individually marked and released. Beetles showed limited inter‐patch movement activity (15.9% of recovery events) with an overall mean daily dispersal of 0.309 m (0.0–7 m). There was a significant difference in the insects’ movement distance between the fallow and wheat field but there was no difference between the movement distances of males and females. The distance between the patches varied between 1 and 7.81 m, and inter‐patch movement was infrequent (15.9%). Results suggest that surrounding fields by wheat rather than fallow grounds should be studied as a possible strategy to reduce the movement of overwintered beetles between potato fields.

Niche relations in Vicia-inhabiting Bruchus spp.

Several authors (Hairston et al., 1960; Strong et al., 1984; Jermy, 1985) have questioned the frequent occurrence and overall importance of interspecific competition between phytophagous insects. Recent reevaluations of such relations (Damman, 1993; Denno et al., 1995), however, once again point to the role of competition in determining the structure of phytophagous insect communities, especially of those that exploit discrete resources such as seed predators. They emphasise that besides direct competition there are more subtle types, such as resourceand natural enemy-mediated interactions. While the former considers the importance of herbivore-induced changes in the resource affecting herbivore fitness, the latter refers to apparent competition of which avoidance is possible by entering enemy-free space, hence specialisation. We analyse niche relations of a predispersal seed predator (pre-DSP) guild on the basis of distribution data gained by the examination of seed predation (SP) in pods of wild-grown Vicia spp. collected in Hungary. We think that, although interspecific competition for food is possible at a given resource level (the pod), it is incidental and it has no structuring effect on the pre-DSP guild. Intraspecific competition, however, is more likely to occur. We discuss the following questions: