Effect of tomato leaf traits on the potato tuber moth and its predominant larval parasitoid: A mechanism for enemy-free space

Tomato plants are thought to provide the potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), with enemy-free space. The present study was aimed at assessing the role of plant surface factors in lowering enemy activity or efficiency on tomato plants. Specifically, we tested: (i) the compatibility of plant resistance traits and parasitoid activity in tomato; (ii) whether tomato leaf surface factors affect the main parasitoid species of PTM larvae to a larger extent than they would the host; and (iii) whether plant traits act on the parasitoid directly or indirectly, through the host. Results indicate that the settling response of PTM neonates on tomato leaves was not affected by trichome density and was similar on the three tested tomato cultivars. The parasitoid Diadegma pulchripes, however, failed to parasitize PTM larvae actively feeding in tomato leaves, whereas it successfully parasitized 46% of larvae feeding in potato leaves. Yet the parasitoid was not affected by the plants indirectly, through the hosts; both tomato- and potato-fed larvae were equally accepted by and suitable for the parasitoid when offered in the absence of the host plants. It can be concluded that factors associated with tomato leaves, such as glandular trichomes, have no effect on the larval establishment of PTM on the plant, but they do have a direct adverse effect on D. pulchripes, the primary PTM biological control agent in the system. In cultivated tomato, therefore, leaf traits which may confer resistance to generalist herbivores but not to the oligophagous PTM may not be compatible with natural enemies of these pests.