The Mormon cricket (MC), Anabrus simplex Haldeman, 1852 (Orthoptera: Tettigoniidae), has a long and negative history with agriculture in Utah and other western states of the USA. Most A. simplex populations migrate in large groups, and their feeding can cause significant damage to forage plants and cultivated crops. Chemical pesticides are often applied, but some settings (e.g. habitats of threatened and endangered species) call for non-chemical control measures. Studies in Africa, South America, and Australia have assessed certain isolates of Metarhizium acridum as very promising pathogens for Orthoptera: Acrididae (locust) biocontrol. In the current study, two isolates of Metarhizium robertsii, one isolate of Metarhizium brunneum, one isolate of Metarhizium guizhouense, and three isolates of M. acridum were tested for infectivity to MC nymphs and adults of either sex. Based on the speed of mortality, M. robertsii (ARSEF 23 and ARSEF 2575) and M. brunneum (ARSEF 7711) were the most virulent to instars 2 to 5 MC nymphs. M. guizhouense (ARSEF 7847) from Arizona was intermediate and the M. acridum isolates (ARSEF 324, 3341, and 3609) were the slowest killers. ARSEF 2575 was also the most virulent to instar 6 and 7 nymphs and adults of MC. All of the isolates at the conidial concentration of 1 × 107 conidia ml−1 induced approximately 100% mortality by 6 days post application of fungal conidia. In conclusion, isolates ARSEF 23, ARSEF 2575, and ARSEF 7711 acted most rapidly to kill MC under laboratory conditions. The M. acridum isolates, however, have much higher tolerance to heat and UV-B radiation, which may be critical to their successful use in field application.

Outbreaks of three orthopteran species—Tropidacris collaris (Stoll), Cornops frenatum frenatum (Marschall) and Parascopas obesus (Giglio-Tos)—occurred in three different regions of Brazil during the summers of 2012 and 2013. Insects were observed causing severe damage in commercial crops and subsistence farming areas. In this study, the three species were shown to be susceptible to infection with an oil-based formulation of the fungus Metarhizium acridum under laboratory conditions. In this article, we briefly discuss insect mortality levels for each species and behavioural response to infection. This is the first report of the pathogenicity of the entomopathogenic fungus M. acridum to P. obesus, C. f. frenatum and T. collaris.

The effect of vegetation cover (millet) on the efficacy and conidial persistence of Metarhizium acridum (Driver & Milner) J.F. Bisch., Rehner & Humber was evaluated in semi-field conditions using breeding cages (2 × 2 × 1 m). A mixed population of third- and fourth-instar desert locust larvae, Schistocerca gregaria Forsskål, was used as a target. The insects were exposed in two different vegetation cover types classified as low (about 10%) and high (about 90%). Metarhizium acridum was used at a dose of 2.5 × 1012 conidia/ha in two different application volumes: 1 and 2 l/ha. Untreated insects kept in contact with treated vegetation were monitored to evaluate the persistence of conidia. The results showed that vegetation cover did not significantly (F= 1.320; P= 0.334) affect the efficacy of M. acridum. Under the high vegetation cover, the increase in the applied volume rate to 2 l/ha significantly improved the speed of mortality. Conidia persisted 6 days after treatment with a remarkable effect on untreated larvae exposed to the treated vegetation. In addition, the results of this study showed the efficacy of M. acridum in the low vegetation cover. With an important mass of vegetation, M. acridum conidia could persist even under high temperature conditions.

The storability of five new different formulations of Metarhizium acridum (two oil, one paste, one semi-solid and one powder) was investigated under ambient and low temperatures. Fourth-instar nymphs of the desert locust Schistocerca gregaria (Forskål) were used to evaluate their virulence. Under ambient conditions (23–38°C), all the formulations maintained acceptable viability (66.1 ± 2.30 to 71.8 ± 0.88% germination) after 6 months of storage. After 10 months, only conidia from the powder formulation remained viable. In contrast, samples of the formulations kept under low temperatures ( − 1.2 to 15°C) did not show significant loss of viability after 30 months of storage despite repeated power cuts, lasting sometimes several days. During this period, M. acridum conidia remained virulent to nymphs with 100% mortality 5 to 7 days after the treatment. These results show that all the formulations have greater stability when stored under low and even fluctuant temperature changes. Under ambient conditions, the formulations could remain effective for at least 6 months of storage.