Responding positively to plant defences, a candidate key trait for invasion success in the New Zealand grass grub Costelytra zealandica

Occasionally, exotic plant introductions lead to the emergence of an invasive insect within its native geographical range. Such emergence could be explained by a pre-adaptation of the insect to break through the defences of the new encountered host. We investigated the fitness responses of two New Zealand endemic scarabs (Costelytra brunneum and C. zealandica ) when given a diet of an exotic pasture species, Trifolium repens, whose defences were artificially triggered by the phytohormone jasmonic acid. We found differential fitness responses between the two species when they were exposed to a defence-induced diet. We observed a significant weight increase in the invasive species C.zealandica when it was fed with treated roots compared with untreated controls, whereas no significant weight increase was observed in the non-invasive C.brunneum compared with the control treatments. Our study suggests that C. zealandica has a pre-existing ability to tolerate the defence chemicals of its exotic host and, more interestingly, to benefit from them, which may explain why this species has become a serious pest of pasture throughout its native geographical ran

A native beetle fond of exotic plants. Characteristics that contribute to invasive success in Costelytra zealandica (Scarabaeidae: Melolonthinae)

Widespread replacement of native ecosystems by productive land sometimes results in the outbreak of a native species. In New Zealand, the introduction of exotic pastoral plants has resulted in the diet alteration of the native coleopteran species, Costelytra zealandica (White) (Scarabaeidae) such that this insect has reached the status of pest. In contrast, C. brunneum (Broun), a close congeneric species, has not developed such a relationship with these ‘new’ host plants. This study investigated the feeding preferences and fitness performance of these two closely related scarab beetles to increase fundamental knowledge about the mechanisms responsible for the development of invasive characteristics in native insects. To this end the feeding preferences of larvae of both Costelytra species were investigated under controlled conditions and the survival and larval growth of the invasive species C. zealandica were compared on native and exotic host plants. Costelytra zealandica, when sampled from exotic pastures, was unable to fully utilise its ancestral native host and showed better performance on exotic plants. In contrast, C. zealandica sampled from native grasslands did not perform significantly better on either host and showed similar feeding preferences to C. brunneum. This study suggests the possibility of strong intra-specific variation, in the ability of C. zealandica to exploit native or exotic plants, supporting the hypothesis that such ability underpins the existence of distinct host-races in this species

Number of <i>Acizzia solanicola</i> that produced a particular waveform type (n = 23 and n = 20 on eggplant and tobacco bush respectively).

<p>Number of <i>Acizzia solanicola</i> that produced a particular waveform type (n = 23 and n = 20 on eggplant and tobacco bush respectively).</p

Sequential EPG parameters of <i>Acizzia solanicola</i> on eggplant and tobacco bush (mean, n = 23 and n = 20 on eggplant and tobacco bush respectively).

<p>Sequential EPG parameters of <i>Acizzia solanicola</i> on eggplant and tobacco bush (mean, n = 23 and n = 20 on eggplant and tobacco bush respectively).</p

Boxplots representing duration of waveforms of <i>A</i>. <i>solanicola</i> (n = 23 and n = 20 on eggplants and tobacco bush respectively).

<p>Boxplots representing duration of waveforms of <i>A</i>. <i>solanicola</i> (n = 23 and n = 20 on eggplants and tobacco bush respectively).</p

Boxplots representing percentage probing spend in each waveform of <i>A</i>. <i>solanicola</i> (n = 23 and n = 20 on eggplants and tobacco bush respectively).

<p>Boxplots representing percentage probing spend in each waveform of <i>A</i>. <i>solanicola</i> (n = 23 and n = 20 on eggplants and tobacco bush respectively).</p

Number of <i>Acizzia solanicola</i> that produced a particular waveform type (n = 23 and n = 20 on eggplant and tobacco bush respectively).

<p>Number of <i>Acizzia solanicola</i> that produced a particular waveform type (n = 23 and n = 20 on eggplant and tobacco bush respectively).</p

Summary of main characteristics of <i>Acizzia solanicola</i> EPG waveforms and putative correlations of stylet tip position in plant tissue.

<p>Summary of main characteristics of <i>Acizzia solanicola</i> EPG waveforms and putative correlations of stylet tip position in plant tissue.</p

Waveforms produced by <i>Acizzia solanicola</i> on eggplant.

<p>(A) overview of 1 h recording period showing non-penetration (NP) and waveforms C and G. (B) overview of 1 h recording period showing waveforms D, E1 and E2. (C) traces of waveform C in 15 s overview. (D) traces of waveform G in 5 s overview. (E) traces of waveform D in 30 s overview. (F) traces of waveform E1 in 5 s overview. (G) traces of waveform E2 in 5 s overview. Refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178609#pone.0178609.t001" target="_blank">Table 1</a> for explanation of putative stylet tip position in plant tissue for each waveform.</p