Population Interaction Between Stethorus punctum picipes (Coleoptera: Coccinellidae) and Tetranychus urticae (Acari: Tetranychidae) in Red Raspberries at Low Predator and Prey Densities

Abstract

Previous studies concluded that species in the coccinellid genus Stethorus Weise, although obligate predators of tetranychid mites, exhibit a strong numerical response only to high population densities of their prey. The study reported here was conducted to test the hypothesis that in western Washington red raspberries, Stethorus punctum picipes Casey is capable of detecting and attacking spider mite populations of very low density which are distributed in small, widely scattered patches during the early part of the growing season. In addition to using conventional leaf sampling methods, S. p. picipes interactions with prey were examined by observing their response to prey patches introduced into the field from laboratory cultures. Our results indicate that S. p. picipes is active at low prey densities, although undetected by conventional sampling methods, and is capable of locating rare, small prey patches. This finding suggests that dispersal and searching ability, rather than numerical response are the key components of this preypredator association. KEY WORDS Stethorus punctum picipes, spider mites, raspberry PREVIOUS STUDIES OF Stethorus Weise spp, con

Survey of natural enemies of spider mites (Acari: Tetranychidae) in citrus orchards in eastern Spain

“…Several species of Stethorus have been reported as potential biological control agents of spider mites in agricultural systems (Hull et al 1977;Rott and Ponsonby 2000;Roy et al 2005;Yang et al 1996). However, because of the low rate of natural increase of S. punctillum relative to that of its tetranychid prey (Roy et al 2003), the effectiveness of this predator as a biocontrol agent of spider mites is thought not be based on its numerical response but rather on its ability to locate prey patches and its dispersal ability (Congdon et al 1993).…”

Coccinellidae as predators of mites: Stethorini in biological control

“…Adult S. punctum were able to find eight P. ulmi-infested apple trees out of a 1-ha orchard, even though these infested trees had fewer than 1 mite/leaf (Hull et al, 1977b). Similarly, S. punctum was able to find small patches of pest mites in avocados, citrus, and raspberries (Congdon et al, 1993;McMurtry and Johnson, 1966;Haney et al, 1987). Similar low-density detection of mite prey has also been demonstrated by S. chengi in citrus orchards in China (Chen, 1993;Chen and Zhao, 1994).…”

“…Congdon et al (1993) challenged this ''high density predator" designation and asserted that high density spider mite populations have become common only since the advent of synthetic insecticides , and that the studies that support the ''high density predator" status of Stethorini ignored the spatial context of spider mite populations. While it is true that most Stethorini species do not lay eggs until mite populations are relatively high in comparison to the low mite levels maintained by some Phytoseiidae, the Stethorini have provided economically successful regulation of pest mites in several cases.…”

“…The importance of Stethorini species worldwide as biological control agents is also suggested by the over 500 references found in the course of this review. Congdon et al (1993) hypothesized that the active discovery of rare and very small prey patches by adult Stethorini was a key element in their natural interactions with spider mites over evolutionary time. Few, if any, predator eggs are laid until mite populations become high enough to support the development of larvae, a common phenomenon in coccinellids (Seagraves, 2009).…”

Food Relationships

“…When such responses are rapid and strong, ladybirds may be effective in preventing large -scale outbreaks of their prey . Field experiments reveal that small, highly localized populations of mites and aphids can be quickly discovered and reduced in size by ladybirds , Congdon et al 1993, Evans 2004. Evidence is still lacking with respect to the sensory cues employed by fl ying coccinellid adults to locate profitable patches .…”