Tomatillo Resistance to Colorado Potato Beetle (Coleoptera: Chrysomelidae)

Tomatillo (Physalis ixocarpa Brot ex Hornem) resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say), was evaluated in the laboratory. In vivo assays confirmed that L. decemlineata larvae fed tomatillo leaves had lower weights and survival than larvae fed potato leaves. Larvae fed potato leaves coated with α-tomatine also had lower weights and survival than controls. Larvae were also fed potato leaves coated with tomatillo leaf extracts. These larvae exhibited lower weights but equal survival compared with the controls. Removal of trichome exudates from tomatillo leaves did not affect the detrimental effects of the leaves on larvae. These results confirm the negative effects of tomatillo leaves and α-tomatine on L. decemlineata larval survival and weight. However, HPLC and mass spectrometry results show that α-tomatine was not present in the tomatillo leaf samples we studied. These results suggest that further research is warranted to isolate compounds for further plant resistance research within tomatillo.

Why Trichogramma (Hymenoptera: Trichogrammatidae) egg parasitoids of Helicoverpa armigera (Lepidoptera: Noctuidae) fail on chickpea

Trichogramma spp. egg parasitoids are generally absent in eggs of Helicoverpa armigera (Hübner) collected from chickpea, Cicer arietinum. In this study, the plant characters responsible for the absence of egg parasitoids and the feasibility of increasing parasitism levels on chickpea by mass-releasing Trichogramma chilonis Ishii were investigated. The residence time of female T. chilonison chickpea leaves was affected by trichomes and the acidic trichome exudates secreted on all green parts of the plant. The parasitoids spent a longer time on chickpea leaves where the acidic trichome exudates had been washed off than on unwashed leaves, and longer on leaves of a glabrous chickpea mutant than on washed leaves. When placed on unwashed chickpea leaves, 6.8% of the parasitoids were trapped and killed by the exudates. In a filter paper bioassay, female T. chilonis were deterred by high concentrations of malic and oxalic acids, the major components of the trichome exudate. Acetone and hexane extracts from the surface of chickpea leaves did not elicit a response from the parasitoids in the bioassay. Similarly, the parasitoids did not respond to volatiles emitted by chickpea plants in a four-armed airflow olfactometer. No parasitized eggs were collected from a chickpea field in which T. chiloniswere released five times at a weekly interval at a rate of > 137,000 females ha–1. Sticky trap catches showed that no parasitoid population was sustained in the release field.