Phytophagous Communities Research Articles

Laetilia coccidivora feeding on two cochineal insect species, Does the prey affect the fitness of the predator?

Dactylopius opuntiae (Hemiptera: Dactylopiidae) is a key pest of the prickly pear cactus in Mexico where the plant, and its phytophagous community, are native. It is also an introduced pest in Brazil and the Mediterranean basin. Amongst the phytophagous community of prickly pear in Mexico there is also Dactylopius coccus, the cultivated cochineal. This cochineal is used to obtain carminic acid as a natural dye, but it has also been reported as an invasive pest in Ethiopia. The most feasible control option for these insects is biological control, but whether their natural enemies develop well in both species is unknown. The aim of this work was to study the biology of the predator, Laetilia coccidivora (Lepidoptera: Pyralidae), when it was fed either D. opuntiae or D. coccus in the laboratory. The predator completed its development on both species. Carminic acid was at higher concentrations in D. coccus (8–25%) than D. opuntiae (2–5%), and feeding on D. coccus had negative effects on larval duration (16.7 vs. 22.0 days), developmental time (36 vs. 43.2 days) and survival rate of the predator (42.5 vs. 92.4%). Fecundity (22.7 vs. 12.9 eggs per female), net reproductive rate (R0 = 10.1 vs. 5.8) and intrinsic rate of increase (rm = 0.064 vs 0.041) were also diminished when L. coccidivora fed on D. coccus, compared with D. opuntiae. We discuss possible reasons for variation in predator fitness when fed on each prey type.

Higher efficiency in organic than in conventional management of biological control in horticultural crops in north-eastern Italy

This research analyzes the efficiency of natural pest control in horticultural crops (Red chicory and White cabbage) within different regimes (organic and conventional). Agroecosystem food-web structure was examined in conventional and organic fields, in north-eastern Italy, considering phytophagous, parasitoid and hyperparasitoid guilds. Natural control agents were analysed, especially parasitoids of Plutella xylostella (L.) (Lepidoptera: Plutellidae), one of the most problematic pests on cabbage crops. Phytophagous communities were more diverse and more predators and parasitoids were present in organic than in conventional farms. The parasitization of P. xylostella was significantly higher and the food-web structure was also more complex in organic than in conventional fields. Even with lower spray inputs, organic fields often supported a less abundant phytophagous community than conventional fields, even though the crop damage was similar in both management systems. The present data seem to indicate that the higher presence of biological control agents (predators and parasitoids) in organic fields is effective in moderating crop pest populations.

Orchard Management Effects on the Arthropod Community on Peach with Comparison to Apple

One hundred sixty-two species were recorded as part of the arthropod community associated with peach in eastern West Virginia. The community was composed of 33% phytophages, 35% insectivores, 14% scavengers, and 18% tourists. Diversity of the anthropod community was correlated inversely with intensity of orchard management. Comparing the phytophagous community on apple (from an earlier study) with that on peach, Lepidoptera comprised 49% on apple and only 31% on peach; Hemiptera comprised 9% on apple and 19% on peach. Diversity of the phytophagous arthropod community was significantly less in peach than in apple orchards, but was more similar in commercially-managed orchards than in unmanaged orchards. It is concluded that in commercially-managed peach and apple orchards insecticide use is the dominant factor controlling community structure, whereas, in unmanaged orchards the communities in peach and apple evolve into distinctly different communities. The presence of cyanogenic glycosides in peach, extrafloral nectaries on peach, and the relatively smaller species pool available to colonize peach are considered major factors for the difference in arthropod community structure in peach and apple.

Plant hybrid zones as centers of biodiversity: the herbivore community of two endemic Tasmanian eucalypts.

We found the hybrid zone between Eucalyptus amygdalina and Eucalyptus risdonii to be a center of insect and fungal species richness and abundance. Of 40 taxa examined, 73% were significantly more abundant in the hybrid zone than in pure zones, 25% showed on significant differences, and 2% were most abundant on a pure host species. The average hybrid tree supported 53% more insect and fungal species, and relative abundances were, on average, 4 times greater on hybrids than on either eucalypt species growing in pure stands. Hybrids may act as refugia for rare species: 5 of 40 species were largely restricted to the hybrid zone. Also, 50% of the species coexisted only in the hybrid zone, making for mique species assemblages. Although hybrids support more species and greater abundances, all hybrids are not equal: 68% of the 40 taxa examined were significantly more abundant on one hybrid phenotype than another. While herbivore concentrations on F1 type intermediates were rare, concentrations were common on phenotypes resembling backcrosses either to E. amygdalina or E. risdonii. For specialist herbivores, the hybrid phenotype most heavily utilized appears to be determined by its phenotypic affinity to its host species. Generalists exhibit an overall greater abundance on hybrids, but are less likely to utilize one hybrid phenotype over another. Mechanistic explanations for these distributions are numerous and probably species specific, but are likely to include: increased genetic susceptibility of hybrids due to hybrid breakdown; increased stress in the hybrid zone resulting in greater plant susceptibility; and a greater diversity of resources in the hybrid zone which could support more species. Seed capsule production by hybrids and their parental species is negatively correlated with herbivory. However, it is difficult to determine whether herbivores cause this pattern as hybrids may have inherently lower sexual reproduction. Laws enacted to protect rare and endangered species do not include hybrids. We argue that a re-examination of our current "hybrid policy" is warranted. Plant hybrid zones are centers of plant evolution and speciation, sources of economically important plants and potential biocontrol agents, and, as our study suggests, also provide essential habitats for phytophagous communities.

Resilience of the natural arthropod community on apple to external disturbance

Abstract. A naturally evolved arthropod community in a 6‐year‐old apple orchard was treated with three applications of permethrin; a second naturally evolved community was studied as an untreated control. Disturbance to the community was measured with Shannon's index of species diversity for the phytophagous and beneficial portions of the community. Initially, there was a reduction in diversity of both phytophagous and beneficial arthropods because of the insecticide. Reduction in diversity was a result of both lower number of species and lower evenness of species abundance. Two months after the last permethrin spray, there was no difference between diversity in the phytophagous community, but the beneficial community was more diverse in the treated orchard than in the untreated control. The year after treatment there were few differences between the phytophagous communities, but the beneficial community was more diverse in the treated orchard than in the untreated orchard in May and early June; however, by September the beneficial community was less diverse in the treated orchard. Although diversity statistics of the phytophagous communities were similar 15 months after treatment, differences still remained with the treated community being dominated by more r‐selected species and the control orchard dominated by more K‐selected species. The arthropod community on apple has a high level of stability as reflected by its resilience to a severe external disturbance. This stability would allow for large, but infrequent, disturbances for pest management and still maintain long‐term ecological equilibrium in the community.