Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues (Araneae: Lycosidae).

Some prey can distinguish between chemical cues from predators fed different diets. Here we document the first evidence of diet-based chemical discrimination of predators in a terrestrial arthropod and measure the survival value of behavioural responses to predator chemical cues. We tested activity level and avoidance behaviour of the wolf spider, Pardosa milvina, to faeces and silk associated with the predatory wolf spider, Hogna helluo, fed either P. milvina or crickets (Acheta domesticus). We then measured survival of Pardosa in the presence of Hogna when placed on blank paper or paper previously occupied by Hogna fed either crickets or Pardosa. Filter paper previously occupied by Hogna from each diet treatment or a blank control were simultaneously presented to adult female Pardosa among four treatment pairs (N=15/treatment): (1) blank paper/blank paper, (2) Hogna fed crickets/blank, (3) Hogna fed Pardosa /blank and (4) Hogna fed Pardosa / Hogna fed crickets. Cues from Hogna fed either crickets or Pardosa elicited significantly less activity relative to blank controls. Cues from Hogna fed Pardosa elicited a significantly greater reduction in activity than Hogna fed crickets. When given a choice, Pardosa initially chose the blank substrate significantly more often than either substrate with Hogna cues. Spiders survived longer in the presence of cues from either Hogna diet treatment relative to blank paper, but there was no significant effect of predator diet on survival. Results suggest diet-based predator cues elicit different levels of activity in Pardosa that reduce predation in the presence of Hogna. Copyright 2001 The Association for the Study of Animal Behaviour.

Wolf spiders show graded antipredator behavior in the presence of chemical cues from different sized predators.

The wolf spider, Pardosa milvina, displays effective antipredator behavior (reduced activity) in the presence of silk and excreta cues from adults of another cooccurring wolf spider, Hogna helluo. However, Pardosa and Hogna engage in size-structured intraguild predation, where Pardosa may be either the prey or predator of Hogna. We tested the ability of adult female Pardosa to vary antipredator responses toward kairomones produced by Hogna that vary in size. Hogna were maintained on filter paper for 24 hr. We then presented the paper to adult female Pardosa simultaneously paired with a blank sheet of paper. One treatment had two sheets of blank paper to serve as a control. The Hogna stimulus treatments were as follows (N = 15/treatment): (1) 1 Hogna half the mass of Pardosa; (2) 1 Hogna of equal mass of a Pardosa; (3) 1 adult Hogna, 30 times the mass of Pardosa; and (4) 8 Hogna each 0.25 the mass of Pardosa. Pardosa decreased activity in the presence of kairomones from Hogna of equal or larger size, but showed no change in activity in the presence of a blank control or from a single Hogna smaller than itself. Pardosa showed a reduction in activity in the presence of cues from eight small Hogna. Pardosa avoided substrates with adult Hogna cues, but showed no avoidance response to any other treatment. These results suggest that Pardosa is showing graded antipredator behavior relative to the quantity of predator kairomones present rather than directly discriminating among the different sizes of the predator.

Insectivory and social digestion in Drosophila.

It has long believed that Drosophila larvae feed almost entirely by ingesting yeast and possibly other microorganisms that are associated with fermenting fruits or other vegetable matter. However, we have discovered that the larvae of a number of Drosophila species can consume such diverse substrates as insect tissues, including the exoskeleton. Experiments reported here, which include raising sterile dechorionated eggs to adulthood on adult carcasses under axenic conditions, show that larvae can consume complex chitinous substrates directly without the assistance of microorganisms. We show that Drosophila larvae are able externally to digest amylose, cellulose, and chitin, without coming into physical contact with them. We conclude that not only do Drosophila larvae produce enzymes enabling them to digest a wide variety of substrates, but also these enzymes are egested onto the substrates so that at least some digestion, especially of large polymers, takes place externally. Finally, we suggest that the phenomenon of external digestion explains both the previously unexplained massiveness of Drosophila salivary glands and their chromosomes and the tendency of larvae to cluster, which may also be true of other dipterans.