Refuges and host shift pathways of host-specialized aphids Aphis gossypii

Abstract

Polyphagous cotton-melon aphid populations usually comprise cotton- and cucurbit-specialized biotypes. Host-specialized aphids are prone to food shortages. Cucumber, the favourite food of cucurbit-specialized aphids, is usually absent during autumn and winter in Nanjing, China. Therefore, suboptimal host plants act as refuges and govern the population dynamics of this aphid. The species, growth stages and leaf ages of host plants that cotton- and cucurbit-specialized aphids potentially could use were explored in this study. Cotton-specialized aphids were found to use wild chrysanthemum, potato, zucchini, pumpkin and flowering cucumber besides cotton, whilst cucurbit-specialized aphids were able to utilize potato, zucchini, pumpkin and mature cotton besides cucumber. The population dynamics and genotype frequencies of aphids on hibiscus, cotton, zucchini, cucumber and pumpkin showed that cotton-melon aphids on cucumber could transfer onto mature cotton. Aphids on zucchini shared microsatellite genotypes with aphids on cotton and cucumber. The predominant genotype of aphids on cotton was found on hibiscus, but the predominant genotype on cucumber was not found on hibiscus. Host-specialized aphids clearly have refuges during food shortages. Hibiscus is an overwintering host for cotton-specialized aphids but not for cucurbit-aphids. Removing refuges or managing aphids on refuges could potentially be an effective method to control cotton-melon aphids.

The host range of Aphis gossypii is dependent on aphid genetic background and feeding experience

“…In China, A. gossypii populations on cotton could not colonize cucumber seedlings, and the populations collected from cucumber could not colonize cotton seedlings either (Liu, Zhai & Zhang, 2008; Wang et al, 2016). The populations on cucumber could not use chrysanthemum, but these on cotton could use this plant (Liu, Xu & Lei, 2017). These results indicate that A. gossypii populations have differentiated into at least two host biotypes: cotton- and cucurbit-specialized aphids.…”

“…Moreover, recent experimental data show that host specialization in A. gossypii populations is conditional. The host range expansion of host-specialized A. gossypii has been found under some specific conditions (Liu, Zhai & Zhang, 2008; Wu et al, 2013; Xu, Ma & Liu, 2014; Liu, Xu & Lei, 2017; Hu et al, 2017). Feeding experience on cowpea for one generation or on hibiscus plants for three generations extended the host range of the cucurbit-specialized biotype, and this biotype gained the ability to use both the cotton and cucumber seedlings (Liu, Zhai & Zhang, 2008; Wu et al, 2013).…”

“…When the cotton-specialized biotype was reared for five or more generations on zucchini plants, it acquired the ability to use cucumber seedlings, but consequently lost the ability to use cotton plants (Wu et al, 2013). The cucumber at the inflorescence stage and cotton at the infructescence stage acted as a refuge for the cotton- and cucumber-specialized aphid biotypes, respectively, when these aphids encountered a food deficiency (Liu, Xu & Lei, 2017). These previous studies illustrate that the host range of aphid populations varies with the population’s feeding experience, and the host specialization of aphids to a specific host plant can change over a small number of generations.…”

“…High genetic differentiation between host races was found in the pea aphid (Jaquiéry et al, 2012). The main genotypes of A. gossypii on cotton and cucurbit plants were also different (Carletto et al, 2009; Wang et al, 2016; Liu, Xu & Lei, 2017).…”

Coinfection of the secondary symbionts,Hamiltonella defensaandArsenophonussp. contribute to the performance of the major aphid pest,Aphis gossypii(Hemiptera: Aphididae)

“…The cotton-melon aphid, A. gossypii, is one of the most destructive aphids and a cosmopolitan pest damaging many agricultural crops and ornamental plants (Liu et al, 2017). It is widely distributed and damages at least 64 plant hosts such as cotton, Cucurbitaceae (e.g., cucumber, zucchini, pumpkin, and watermelon), Solanaceae (e.g., chilli and tomato) and different flowering ornamental plants (Inaizumi, 1980).…”