The feeding preferences of the herbivore Spoladea recurvalis Fabricius (Lepidoptera: Pyralidae) was determined through choice and no-choice tests in the laboratory with 12.7-mm leaf discs of the following weeds and crops: horse purslane (Trianthema portulacastrum L), common pigweed (Amaranthus dubius Mart.), botoncillo (Borreria ocymoides [Burm. F] DC), sugar beet (Beta vulgaris L.), sweet cherry pepper (Capsicum frutescens L.), tomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativus L.), and eggplant (Solanum melongena L.). Spoladea recurvalis preferred horse purslane as its primary food host plant. The pyralid larva also fed on leaf discs of common pigweed and sugar beet, the only vegetable crop serving as an alternate food plant. Larvae did not feed on the other plants studied (sweet cherry pepper, tomato, cucumber, eggplant and botoncillo), some of which were previously reported as alternate food host plants for the herbivore. This manuscript discusses the application of these findings for the biological control of horse purslane and the foraging behavior of S. recurvalis.
A field study (1998-99) was conducted at the Juana Díaz Substation (AESUPR) to determine the population dynamics of Plutella xylostella (L.) in cabbage in a monoculture and in relay-type substitutive dicultures of cabbage/tomato or cabbage/wedelia. In 1998, subplots were created by spraying half of the main plots with Bacillus thuringiensis (Bt)-based products. All treatments, except for the control monoculture, were sprayed with Bt-based products in 1999. Cotesia plutellae Kurjumov, a larval parasitoid of P. xylostella, was released augmentatively for biological control. Tomato, as a companion crop, showed a tendency for reducing P. xylostella densities in cabbage, reduced the levels of C. plutellae parasitism and competed with cabbage, causing fewer and smaller heads. Bt-based sprays reduced P. xylostella densities, but these were at damaging levels at the critical stages of cupping and head formation, thus permitting cosmetic damage to cabbage heads. Cotesia plutellae did not regulate the P. xylostella population, thus resulting in parasitism levels of 65.3 and 11.6% in the unsprayed monoculture in 1998 and 1999, respectively. The legume Crotalaria juncea L. as a border did not improve parasitism by C. plutellae. The interpretation and application of the results are discussed.
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