Incorporating insect behaviour in standard tests of wood preservatives - A possible way to reduce pesticide loadings
H Hertel, R Plarre
The application of wood preservatives to protect timber against insect infestation is common practice world wide. The effectiveness of wood protecting insecticides is usually determined in various standard tests. Depending on the target pest species and the test method, larvae of different developmental stages and sizes or adult insects are exposed artificially to the insecticide-treated commodity by placing them into or on to the material. The achieved mortality usually rates the effectiveness of the tested insecticide. Detailed observations have shown, that a lot of insecticides already show repellent effects to ovipositing females, or have ovicidal effects at much lower quantities necessary for larval kill. Furthermore, if the natural chain of behavioral steps in the insect, which lead to an infestation, are correctly analyzed, an interference and manipulation of the behavior should prevent or at least minimize the risk of an infestation and thus the needs for wood preservatives. Examples for successful manipulation of mating and host finding behavior are presented in this paper, using the old house borer Hylotrupes bajulus L., as a model: In the general biology of the old house borer, males emerge slightly before females and attract the later with a sex pheromone from the future breeding site. Experiments in the laboratory and semi field situations have shown, that pine wood, offered in no-choice bioassays, was most attractive to males, more than any other given alternative. Virgin females neither accepted pine nor the alternatives. Only the presence of males on pine wood increased its attractiveness to virgin females. Females of H. bajulus, when mated, readily deposit their eggs on any material (natural or artificial) if a suitable crack is presented. However, they hesitate to deposit eggs on timber treated with certain preservatives even in no choice situations. Additionally, it was found, that certain modern insecticides show ovicidal effects, preventing the larvae from hatching, rather than larvicidal effects. The observed host selection and mating behavior, together with general considerations of energy budgeting in insects suggests, that males rather than females of the old house borer most likely select new breeding sites. Interfering with host selection biology might therefore enable alternative control strategies against this destructive pest of structural timber. These strategies include: reducing the attractiveness of breeding sites for males, repelling host seeking males, trapping mate seeking virgin females, etc. Furthermore, ovicidal effects of wood preservatives are not yet considered in standard test. More detailed knowledge of the general behavior of wood boring insects will permit new ways to preserve timber without or with reduced amounts of pesticides. The effectiveness of behavior modifying chemicals can not be evaluated in existing standard test methods. An alternative test set up is presented in this paper.
Keywords: STANDARD TEST METHODS; BEHAVIOR; WOOD PRESERVATIVES; HYLOTRUPES BAJULUS