The Louisa Richards’ (London School of Hygiene & Tropical Medicine) study we’d heard so much of, a study of resident bed bug service requests to pest control teams in London from 2000 to 2006, has been published. The study found an average 28.5% yearly increase in calls about bed bugs to seven boroughs in London (24.7% annual increase in the proportion of bed bug calls relative to other pests).
Further, and most interesting, the study found evidence of ‘cyclic peaks’ of 12, 6 and 2 months. Also, the greatest number of calls were made in August and September:
The results indicate 2, 6 and 12 month periodic cycles for the number of call enquiries for bed bugs. The 12 month cycle peaked in August-September and reflects data from other studies showing the number of bed bug calls increasing during the summer and declining in the winter (Cornwell, 1974; Cleary & Buchanan, 2004; Doggett et al., 2004; Ryan et al., 2004; Kilpinen et al., 2008). The 12 month cycle increased in amplitude for later years, which may suggest greater bed bug dispersal during the summer months, and greater optimal conditions for survival and reproduction (Omori, 1941). The 6 and 2 month cycles appear, however, to be specific to this study.
There is evidence that suggests that some first and second time treatments may be ineffective (Ryan et al., 2004; Hwang et al., 2005). The 6 and 2 month cycles may reflect call back periods from members of the public to pest control services after initial treatment has failed, because the data did not differentiate between first time callers and subsequent calls received from the same household. Further studies would be necessary to confirm these findings.
Fascinating. Consider this additional area of inquiry. The authors also collected and tested additional statistics for this period: temperature, numbers of overseas visitors, and number of UK residents traveling abroad:
There was evidence for only one borough to suggest that outdoor temperature had an impact on the increase in calls concerning bed bugs. [...]
In addition, although the effect of people’s movements has been previously hypothesised to contribute to the cyclic numbers of bed bug infestations (Cornwell, 1974; Kilpinen et al., 2008), human movement only had a significant contribution in one borough. More evidence would be required to determine whether human movement influenced the number of bed bug infestations.
Emphasis added.
Richards, L., Boase, C.J., Gezan, S., Cameron, M.M. (2009) Are bed bug infestations on the increase within Greater London? Journal of Environmental Health Research 9:1 17-22. PDF available.
These pages may be of related interest:
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