Predators of Plutella xylostella in Nicaragua : feeding capacity and potential role in biological control

Sammanfattning: The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most destructive insect pests of Brassica crops in both temperate and tropical regions over the world. The insect is considered as a key pest of crucifers in Central America. Due to the intense use of pesticides and because the pest occurs in all development stages at any time of the year in the tropics, Plutella xylostella has easily developed resistance to at least 46 different pesticides, including DDT. Few studies have been made on the predators of P. xylostella and even less is known about their feeding rate. The maximum prey consumption and the density of the predators are basic elements in the evaluation of a predator as a possible biological control agent. Therefore a quantitative study was done to (1) identify possible predators of the diamondback moth and (2) estimate their feeding rate on P. xylostella eggs and larvae of different stages under laboratory conditions. The overall goal was to provide information that can serve as a basis for finding important biological control agents in cabbage cultivation in Nicaragua, where the investigation took place. The result showed a broad spectrum of predators eating P. xylostella. The most important predators, with respect to larval consumption in the laboratory and abundance in the field and on plants, were wolf spiders (Lycosidae). Rove beetles (Staphylinidae), jumping spiders (Salticidae) and damsel bugs (Heteroptera: Nabidae) had also high consumption rates and were frequently observed on cabbage plants or in cabbage fields. The feeding rate varied least among predator groups when they were fed 2nd instar larvae (L2) compared to when fed eggs or L3. The feeding rate of predators on L2 was also significantly higher than that on L3, for all predator groups except for Paederus sp. (Staphylinidae). No differences in feeding capacity were found between individuals of predators, belonging to the same groups, collected in field margins and in cabbage fields.