The EVect of Release Size on the Probability of Establishment of Biological Control Agents: Gorse Thrips ( Sericothrips staphylinus ) Released Against Gorse ( Ulex europaeus ) in New Zealand

Foreign exploration for Scirtothrips perseae Nakahara (Thysanoptera: Thripidae) and associated natural enemies on avocado (Persea americana Miller)

“…Third, the small numbers of pests intercepted at border inspection stations on avocado plants that are moved into the USA suggest that founding populations of pests may often be very small. Work on Sericothrips staphylinus Haliday (Thysanoptera: Thripidae) used for the biological control of Ulex europaeus (L.), a noxious weed in New Zealand, has demonstrated that 33% of carefully managed releases of just 10 adult thrips into a permissive environment can result in establishment and proliferation (Memmott et al, 1998). The greater the frequency of small introductions, the higher the likelihood of establishment in comparison with fewer introductions of larger numbers of thrips which might go extinct due to adverse chance effects (Memmott et al, 1998).…”

“…Work on Sericothrips staphylinus Haliday (Thysanoptera: Thripidae) used for the biological control of Ulex europaeus (L.), a noxious weed in New Zealand, has demonstrated that 33% of carefully managed releases of just 10 adult thrips into a permissive environment can result in establishment and proliferation (Memmott et al, 1998). The greater the frequency of small introductions, the higher the likelihood of establishment in comparison with fewer introductions of larger numbers of thrips which might go extinct due to adverse chance effects (Memmott et al, 1998). This scenario from biological control of weeds may apply to the establishment of new thrips pests outside of their home range, that is, frequent introductions of small numbers of pests may ultimately lead to establishment when founding populations encounter a permissive environment.…”

No evidence for establishment of the wasp parasitoid,Sphecophaga vesparum burra(Cresson) (Hymenoptera: Ichneumonidae) at two sites in New Zealand

“…Biological control literature is divided over whether it is a better strategy to release a large number of individuals in a few places (e.g., Beirne 1975;Cameron et al 1993;Grevstad 1999), or a small number of individuals in many places (e.g., Campbell 1976;Memmott et al 1998) to increase the overall probability of establishment. The optimum establishment strategy is likely to vary with species and environment.…”

Theoretical contributions to biological control success

“…Control organisms must be established before they can contribute to success, and all too many control organism introductions fail to establish (Heimpel and Mills 2017). Release strategies (seeking to optimize the number and size of release populations that can be made from a finite release stock) have been a fertile area for theoretical investigation for increasing rates of establishment (Grevstad 1999;Memmott et al 1996Memmott et al , 1998Shea and Possingham 2000) as recently reviewed (Heimpel and Mills 2017;McEvoy et al 2012a). Theoretical work indicates the optimal release strategy depends on the functional form of the relationship between the number of individuals released and establishment probability, and this relationship depends on the relative influences of Allee effects (reduction in population growth rate at low density) and environmental variability (stochastic variation in population growth rates) on released populations (Grevstad 1996(Grevstad , 1999.…”