Desempenho de Thyrinteina arnobia Stoll (Lepidoptera: Geometridae) em eucalipto e goiaba: o hospedeiro nativo não é um bom hospedeiro?

Abstract

-Plants can develop mechanisms of defense that reduces the effects of herbivore attacks. In response, the herbivores evolve to breaking the defense mechanisms of plants. Herbivores may also escape from the plant defense system by migrating to other host whose defense is not effective against them. In Brazil, outbreaks of the defoliator caterpillar Thyrinteina arnobia Stoll in Eucalyptus sp. are frequently observed. However, the native host of this insect is guava, Psidium guajava where outbreaks are not registered. The absence of outbreaks in P. guajava may be related to the development of defense mechanisms in that specie of Myrtaceae, which has apparently not yet occurred on eucalyptus. Here we investigated the performance of T. arnobia reared on its origin host plant, in comparison with those reared on its exotic host, Eucalyptus sp. The intrinsic growth rate of T. arnobia was higher on eucalyptus than on P. guajava. It is possible that the defense mechanism on guava plants acts as a chemical barrier, probably reducing the digestibility of the insect, which could affect the development of the current population and the next generations.KEY WORDS: Constitutive defense, Eucalyptus cloesiana, Psidium guajava, herbivory RESUMO -As plantas podem desenvolver mecanismos de defesa que reduzem o efeito do ataque de herbívoros. Em resposta, os insetos herbívoros evoluem de forma a quebrar os mecanismos de defesa das plantas. Uma das formas que os insetos têm de escapar do sistema de defesa das plantas é migrar para outros hospedeiros cujo sistema de defesa não seja eficiente a seu ataque. No Brasil, em plantios de Eucalyptus spp., observam-se surtos freqüentes da lagarta desfolhadora Thyrinteina arnobia Stoll, cujo hospedeiro nativo é a goiaba. A não ocorrência de surtos populacionais em goiaba pode estar relacionada ao desenvolvimento de mecanismos de defesa, nessa espécie de Myrtaceae, o que aparentemente ainda não ocorreu com o eucalipto. Por isso, investigou-se neste trabalho se o desempenho de T. arnobia criada em seu hospedeiro de origem, plantas de goiaba, difere do seu desempenho em hospedeiro exótico, o eucalipto. A taxa intrínseca de crescimento populacional de T. arnobia (r m ) foi maior em eucalipto do que em plantas de goiaba. O pior desempenho de T. arnobia em plantas de goiaba possivelmente se deu por atuação do sistema de defesa constitutiva dessas plantas. Barreiras químicas das plantas de goiaba podem estar atuando principalmente na redução da digestibilidade do inseto, afetando o desenvolvimento da população atual e, por conseguinte, o das próximas gerações.

Rearing of Thyrinteina arnobia (Lepidoptera: Geometridae) on guava and Eucalyptus in laboratory

“…T. arnobia showed higher values for numbers of eggs/egg mass, total eggs/female and viability of eggs with guava than with eucalyptus leaves. This disagreed with Holtz et al (2003b) who found higher values for these parameters when T. arnobia was reared on eucalyptus after four generations on this plant or with eucalyptus leaves in laboratory. These authors considered that this adaptation period was enough for chemical compounds present in this plant to affect populations of this herbivore in the original host (guava) but not in the introduced one (eucalyptus).…”

Development and reproduction of Podisus nigrispinus (Hemiptera: Pentatomidae) fed with Thyrinteina arnobia (Lepidoptera: Geometridae) reared on guava leaves

“…Holtz et al (2007) reported that this caterpillar reared on eucalyptus leaves was not a good prey, because these leaves had a specific essence which produced secondary substances, which might affect stinkbug development. However, Holtz et al (2003) evaluated the effect of these substances on T. arnobia and found that these compounds did not affect the development of this caterpillar on eucalyptus, but others substances that come from guava could affect their development. Santos et al (2000) and Oliveira et al (2005) found that T. arnobia had better development on guava leaves, which could be considered as the best host for it, while eucalyptus leaves had poor digestibility and nutritional quality which reduced the development of this caterpillar.…”

Host plant and the predator Podisus nigrispinus: when the defense compounds of the plant affect the third trophic level

“…Thyrinteina arnobia is considered one of the main defoliator pests of eucalyptus forests, due to its periodic outbreaks and damage caused to plantations (Santos et al., ; Garlet et al., ). The development of T. arnobia was better on eucalyptus plants than on guava plants (Holtz et al., ,b). Thus, we may conclude that the poor performance of P. nigrispinus on T. arnobia from eucalyptus was not due to low nutritional quality, compared to T. arnobia from guava plants (Holtz et al., ,b).…”