Spatial and temporal density dependence in a population of melon aphid, Aphis gossypii Glover (Homoptera: Aphididae), on established and sentinel taro plants

Abstract

A study carried out across 33 weeks in a patch of taro, Colocasia esculenta L., quantified demographic parameters and density-dependent processes for a population of melon aphid, Aphis gossypii Glover. Variation in relative density of aphids per cm 2 of leaf tissue between consecutive weeks declined with the initial density of aphids, indicating that density dependent processes regulate populations of A. gossypii on taro. High abundance of aphids on large leaves suggest that host attributes affect the rates of colonization or reproduction of adults. Even though the incidence of winged aphids was consistently low throughout the experiment, between plant dispersal by aphids still homogenizes their spatial distribution within an array of plants, as indicated by similar relative densities of aphids on established plants and on sentinel (initially uninfested) plants 60 days following their introduction in the patch. The proportion of aphids parasitised by Aphidius colemanii Viereck and Aphelinus spp. was low (Ͻ3%), which may be attributed to a high level (Ͼ95%) of hyperparasitism. Mortality caused by two entomopathogens, Neozygites fresenii Nowakowski and Verticillium lecanii Zimmerman, averaged 12%. The proportion of fungal infection increased with the density of aphids, both on a spatial and temporal scale. However, the population of A. gossypii on taro was most likely not regulated by entomopathogens, because the proportion of diseased aphids did not influence variations of population density between consecutive weeks. The lower proportion of fungal infection on sentinel plants than on established plants suggests a limited impact of entomopathogens on taro plants recently colonized by aphids.

Factors affecting colonization and abundance of Aphis gossypii glover (hemiptera: aphididae) on okra plantations

“…On the other hand, lower populations were recorded after leaves were colonized and winged forms of this insect for dispersal were observed, such as related by Byamukama et al (2004) and Rhainds & Messing (2005). High abundance of A. gossypii on large leaves of Colocasia esculenta (L.) Schott.…”

“…High abundance of A. gossypii on large leaves of Colocasia esculenta (L.) Schott. and okra plants suggest that host attributes affect the rates of colonization or reproduction of adults (RHAINDS & MESSING, 2005;SECHSER et al, 2002).…”

“…were the most important natural enemies for population reduction of A. gossypii on both okra plantations with more than 55% of parasitised aphids in the last plantation. The parasitoids of Braconidae family (RHAINDS & MESSING, 2005;SAMPAIO et al, 2005), spiders (MEN et al, 2004), Chrysoperla sp. (KABISSA et al, 1996), ladybird beetles (MEN et al, 2004) and Syrphidae larva (SECHSER et al, 2002) The lower aphid attack was observed in the second okra plantation, planted 50 m apart from the first, probably due to the fact that part of the Adialytus spp.…”

“…because this parasitoid presented higher percentage of parasitised aphids in the basal than in the apical leaves of okra plants. Rhainds & Messing (2005) Although no significant effects (P > 0.05) of plant age, total rainfall and median temperature on aphid population were observed, in June and October, when plants were 86 and 140 days old respectively, there was a drastic decrease in the insect population, probably due to, besides natural enemies, plant senescence and/or associated with rainy season (total rainfall = March: 189 mm, April: 25 mm, May: 0 mm, June: 24 mm, July: 0 mm, August: 0 mm, September: 32 mm, October: 125 mm and November: 509 mm). High rainfall is an important mortality factor of A. gossypii in the field (MCDONALD et al, 2003;RHAINDS & MESSING, 2005) and this insect is considered to be initial pest due to changes in plant quality as the crop gets older (MEN et al, 2004;RHAINDS & MESSING, 2005;SANTOS et al, 2003;SOGLIA et al, 2002).…”

“…Also, plant phenology such as leaf position on plant canopy, plant age, leaf areas, and trichomes besides natural enemies and weather can influence population of A. gossypii (CHAU et al, 2005;338 Ciênc. agrotec., Lavras, v. 31, n. 2, p. 337-343, mar./abr., 2007MEN et al, 2004RHAINDS & MESSING, 2005;SANTOS et al, 2003;SATAR et al, 2005;SECHSER et al, 2002;SOGLIA et al, 2002SOGLIA et al, , 2003. Since effects of such factors on okra plants are little known, the aim of the present investigation was to evaluate the effects of predators, parasitoids, leaf organic compounds, levels of N and K, leaf trichome density, canopy height, plant age, leaf areas, rainfall and temperature on attack intensity of A. gossypii on successive okra plantations under field conditions.…”