Insecticide resistance is seriously undermining efforts to eliminate malaria. In response, research on alternatives to the use of chemical insecticides against adult mosquito vectors has been increasing. Fungal entomopathogens formulated as biopesticides have received much attention and have shown considerable potential. This research has necessarily focused on relatively few fungal isolates in order to ‘prove concept’. Further, most attention has been paid to examining fungal virulence (lethality) and not the other properties of fungal infection that might also contribute to reducing transmission potential. Here, a range of fungal isolates were screened to examine variation in virulence and how this relates to additional pre-lethal reductions in feeding propensity.

BACKGROUND: Bed bugs are a public health concern, and their incidence is increasing worldwide. Bed bug infestations are notoriously difficult to eradicate, further exacerbated by widespread resistance to pyrethroid and neonicotinoid insecticides. This study evaluated the efficacy of the newly developed fungal biopesticide Aprehend™, containing Beauveria bassiana, against insecticide‐resistant bed bugs.RESULTS: Overall mortality for the Harold Harlan (insecticide‐susceptible) strain was high (98–100%) following exposure to Aprehend™ or Suspend SC (deltamethrin). The mean survival times (MSTs) for Harold Harlan bed bugs were 5.1 days for Aprehend™ and 4.8 and 3.0 days for the low and high concentrations of Suspend SC respectively. All three strains of pyrethroid‐resistant bed bugs were susceptible to infection by B. bassiana, resulting in MSTs of 94% overall mortality. Conversely, mortality of the three insecticide‐resistant strains after exposure to Suspend SC was only 16‐40%.CONCLUSION: These results demonstrate that Aprehend™ is equally effective against insecticide‐susceptible and insecticide‐resistant bed bugs and could provide pest control operators with a promising new tool for control of bed bugs and insecticide resistance management. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

New products aimed at augmenting or replacing chemical insecticides must have operational profiles that include both high efficacy in reducing vector numbers and/or blocking parasite transmission and be long lasting following application. Research aimed at developing fungal spores as a biopesticide for vector control have shown considerable potential yet have not been directly assessed for their viability after long-term storage or following application in the field. Spores from a single production run of the entomopathogenic fungi Beauveria bassiana were dried and then stored under refrigeration at 7°C. After 585 days these spores were sub-sampled and placed at either 22°C, 26°C or 32°C still sealed in packaging (closed storage) or in open beakers and exposed to the 80% relative humidity of the incubator they were kept in. Samples were subsequently taken from these treatments over a further 165 days to assess viability. Spores from the same production run were also used to test their persistence following application to three different substrates, clay, cement and wood, using a hand held sprayer. The experiments were conducted at two different institutes with one using adult female Anopheles stephensi and the other adult female Anopheles gambiae. Mosquitoes were exposed to the treated substrates for one hour before being removed and their survival monitored for the next 14 days. Assays were performed at monthly intervals over a maximum seven months. Spore storage under refrigeration resulted in no loss of spore viability over more than two years. Spore viability of those samples kept under open and closed storage was highly dependent on the incubation temperature with higher temperatures decreasing viability more rapidly than cooler temperatures. Mosquito survival following exposure was dependent on substrate type. Spore persistence on the clay substrate was greatest achieving 80% population reduction for four months against An. stephensi and for at least five months against Anopheles gambiae. Cement and wood substrates had more variable mortality with the highest spore persistence being two to three months for the two substrates respectively. Spore shelf-life under refrigeration surpassed the standard two year shelf-life expected of a mosquito control product. Removal to a variety of temperatures under either closed or open storage indicated that samples sent out from refrigeration should be deployed rapidly in control operations to avoid loss of viability. Spore persistence following application onto clay surfaces was comparable to a number of chemical insecticides in common use. Persistence on cement and wood was shorter but in one assay still comparable to some organophosphate and pyrethroid insecticides. Optimized formulations could be expected to improve spore persistence still further.

Conidia of Metarhizium flavoviride were hermetically stored at 13.7% moisture content with four constant (20, 30, 40 and 50 C) and six fluctuating temperature regimes (20:30, 20:40, 20:50, 30:40, 30:50 and 40 C:50 C, all 24 h:24 h) for up to 119 days. Survival of conidia stored at both constant and fluctuating temperatures conformed to cumulative negative normal distributions and all 10 survival curves could be constrained to a common origin. The effect of constant storage temperature on conidia longevity was quantified satisfactorily by a negative curvilinear semi-logarithmic relation developed previously, in which the estimates of the constants CH and CQ were 0.0176 (SE 0.0013) and 0.000703 (SE 0.000019), respectively. The fitted relation at constant temperatures showed that Q10 for loss in conidia viability increased the warmer the temperature regime. The effect of the cooler temperature of each fluctuating temperature regime on conidia longevity was small, since the effective temperature of each regime for loss in conidia viability was always much warmer than the mean. Conidia were also stored in two further regimes: at 30 C for 21 or 35 days before transfer to 50 C. The standard deviations of the conidia survival curves at 50 C were unaffected by the duration of previous storage at 30 C. Thus change in temperature per se had no effect on conidia survival: conidia survival curve slopes were solely dependent upon the contemporary storage environment. Approaches are developed in order to predict loss of conidia viability in fluctuating temperature storage environments, and the predictions compared against independent observations.

The biopesticide Aprehend, containing spores of the entomopathogenic fungus Beauveria bassiana, is a biological control agent for the management of the common bed bug (Cimex lectularius L.) (Hemiptera: Cimicidae). The spores are applied in strategically placed barriers, which bed bugs walk across as they search for a bloodmeal. Application of chemical insecticides by the general public and professional pest managers is common, which means that Aprehend may be sprayed on existing insecticide residues. We evaluated the effect of chemical residues, of 22 different chemical insecticides on different household surface types. We found that residues from 12 chemical pesticides significantly reduced spore viability measured 5 weeks after application in comparison to the control. However, efficacy of Aprehend, as measured by bed bug mortality and mean survival time after exposure to sprayed surfaces, seven weeks after application was not impacted detrimentally. Furthermore, in some cases, efficacy of old chemical residues was enhanced by the combination of chemical and Aprehend seven weeks after application. Surface type also played a role in the relative efficacy of all products and combinations, particularly as the residues aged.