Laboratory screening of tropical hardwoods for natural resistance to the marine borer Limnoria quadripunctata: The role of leachable and non-leachable factors

The marine borerLimnoriaingests essential wood components including the extractives the wood contains. Some extractives may confer borer resistance on certain timbers. Feeding byLimnoriacorrelates with the rate of production of faecal pellets. The faecal pellet production rate and mortality on over 40 test timbers and non-resistantPinus sylvestrissapwood was measured over 15 days. By placing animals in leachate from wood and with wood in flowing seawater, the effects of leaching-resistant and water-soluble compounds were measured. Some previously untested timbers affectedLimnoriaas strongly as timbers reputed for durability in marine construction. Wood ofMinquartia guianensis,Nectandra rubraandBruguiera gymnorhizacaused high mortality, and pellet production on them was less than 10% of production onP. sylvestris. Suppressed feeding rates, but with no heavy mortality, were observed on known durable species such asChlorocardium rodiei,Dicorynia guianensis, Lophira alataandNauclea trillesii, but also onCynometra ananta,Distemonanthus benthamianus,Enterolobium schomburgkii,Goupia glabra,Hymenaea courabil,Mammea africana,Shoreasp. andSacoglottis guianensis. Leachate fromB. gymnorhiza,G. glabra,H. coubaril,N. rubraandShoreasp. caused high mortality. These short-term bioassays thus detected clear differences between wood species in their resistance toLimnoriathat matched findings from long-term marine trials, while indicating new species worthy of detailed testing.

Quantitative evaluation of the feeding of the carmine spider mite Tetranychus cinnabarinus (Boisd.) (Acari, Tetranychidae)

Faecal pellet production by Tetranychus cinnabarinus (Boisd.) was recorded at different temperatures (19, 24, 30, 35°C) and relative humidities (0% to 100%); at all temperatures pellet production was greater under dry than under wet conditions. A feeding index based on faecal pellet production and the proportion of adults surviving each day showed that the optimal conditions for the mite were 24°C and 38% r.h. Pellet production increased under continuous light and, under any particular set of conditions, was closely correlated with the numbers of eggs laid. It is concluded that faecal pellet production can be used as a measure of feeding within a given set of conditions provided it is supplemented and checked by other data.