Host Races of the Cotton Aphid,Aphis gossypii, in Asexual Populations from Wild Plants of Taro and Brinjal

Abstract

Worldwide, several studies have shown that adaptation to different host plants in phytophagous insects can promote speciation. The cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae: Aphidini), is a highly polyphagous species, but its populations increase by parthenogenetic reproduction alone in Indian subcontinent. This study showed that genotypes living in wild plants of taro, Colocasia esculenta var. esculenta (L.) Schott (Alismatales: Araceae), and brinjal, Solanum torvum Swartz (Solanales: Solanaceae), behave as distinct host races. Success rates of colonization after reciprocal host transfers were very poor. Clones of A. gossypii from wild taro partly survived in the first generation when transferred to wild brinjal, but nymph mortality was 100% in the second generation. In contrast, brinjal clones, when transferred to taro, could not survive even in the first generation. Significant differences between the clones from two host species were also recorded in development time, generation time, fecundity, intrinsic rate of increase, net reproductive rate, and mean relative growth rate. Morphologically, aphids of wild taro clones possessed longer proboscis and fore-femora than the aphids of the brinjal clones. The results showed that A. gossypii exists as distinct host races with different abilities of colonizing host plants, and its populations appear to have more potential of sympatic evolution than previously regarded.

Identification of Generalist and Specialist Phenotypes of the Peach-Potato Aphid <i>Myzus persicae</i> (Insecta : Hemiptera : Aphididae) in Agroecosystem of Northeast India

“…Occurrence of asexual reproduction by parthenogenesis and viviparity in spring and summer months followed by sexual reproduction during winter have made these phytophagous insects to breed profusely with wide range of adaptations to different host plants 3 . The prevalent polyphenism and plasticity in different traits in aphids have often proved difficult to correctly identify species that are morphologically similar but show different reaction norms (differences in physiological, ecological, biological, or behavioural performances) on different host plants of agroecosystems 4 .…”

“…It was predicted that the differences recorded in life colour and colonization behaviour of different asexual lineages of M. persicae on three different host environments of potato, eggplants and mustard crops in the fields of Tripura might also show differences in their ecological and biological fitness. It was tested in multiple clonal lineages of M. persicae reared on three host plants by examining their ecological (growth) and biological (developmental and reproductive) performances, the determinants of Darwinian's fitness of phytophagous insects in selection of their host plants [21][22][23] . Aphids from three crop hosts were also subjected to reciprocal host transfer experiments to record the effect of a new host environment on their performances 6,7,22,24 .…”

“…It was tested in multiple clonal lineages of M. persicae reared on three host plants by examining their ecological (growth) and biological (developmental and reproductive) performances, the determinants of Darwinian's fitness of phytophagous insects in selection of their host plants [21][22][23] . Aphids from three crop hosts were also subjected to reciprocal host transfer experiments to record the effect of a new host environment on their performances 6,7,22,24 . Three plant species were raised in open nursery till early vegetative stage (2-3 leaf stage) and then ten plants of each species were planted individually in clay pots (20 cm diameter) and were held in water trays on benches illuminated with photo-synthetically active radiation lamps in a greenhouse (temperature: 24  1C, RH: 65%, photoperiod: 16 : 8L : D).…”

“…This method allowed achieving several sister clones of mixed origins of M. persicae on each of the three plant species. Aphids on each plant were monitored by frequent observations to record the following parameters after Agarwala and Ray Choudhury 22 . For ecological performance, maximum population size representing the carrying capacity of the host plant, which is the maximum aphids that can be supported by a growing plant under a set condition (K), population growth rate denoting increase in number of aphids per day per plant (GR), and the time (T k ) taken to reach K value were determined for each clone of the three plant species.…”

“…Intrinsic rate of increase (R max ), a measure of rate of increase of a population under controlled conditions, was determined using the formula 4,22,23 0 max log ( ) , e R R G  Aphid clones of the potato, eggplants and mustard were subjected to reciprocal transfers of host plants to record the colonization success, which is the ability of individual aphid to survive and reproduce in a new food environment, on the transferred hosts 4,22 . Individual 0-12 h old nymphs were collected from the stock culture and released one per potted plant of similar age of the field host species (control) and the laboratory host species (treatment).…”