The Effects of Volcanic Ash from Puyehue-Caulle Range Eruption on the Survival of Dichroplus vittigerum (Orthoptera: Acrididae)

The eruption of the volcanic complex Puyehuefresh leaves of dandelion (Taraxacum officinale Caulle Range (PC) in Chile on 4 Jun 2011 disF. H. Wigg; Asterales: Asteraceae). Treatments persed about 100 million metric tons of ash on consisted of 0.5 g of volcanic ash or diatomaceous 7.5 million hectares, mainly in northern Patagoearth per container. The treatment dust spread nia [Argentina] (Gaitan et al. 2011). The general over the surface of the dish, so the grasshoppers consequences of this type of event to flora and had to always contact it, at any point in the dish, fauna in the areas affected by volcanic ash is the Control insects were placed in clean containers, loss of habitat (Arendt et al. 1999) and population Three insects were used for each treatment and decrease of susceptible insect species due to its the experiment was replicated 3 times at each insecticidal effect (Shanks & Chase 1981; Akre et humidity level. After 24 h mortality as well as al. 1981; Buteler et al. 2011). The chemical analyamount of plant material consumed was record sis of the volcanic ash from PC eruption showed ed. Categories established were; 1 for insects that that it is extremely abrasive (Informe UNCOconsumed 50% or less of the leaf area, and 2 for Neuquen 2011) and predominantly composed of insects that consumed more than 50% of the leaf glass shards (Si02) and alumina (A1203) (Buteler area. Mortality data were analyzed with ANOVA et al. 2011; Mogni et al. 2011), two substances with treatment and humidity as fixed effects and with well known insecticidal properties. replicate and number of experiment as random Inert dusts such as diatomaceous earth, kaeffects. Significantly different least square means olin, sodium carbonate, calcium carbonate, and (P < 0.05) were separated by the Tukey adjusted volcanic ash are well known for their insectioption in SAS (SAS Institute 1998). cidal properties (Allen 1972; Shanks & Chase A second dry dust application toxicity test was 1981; Golob 1997; Subramanyan & Roesli 2000). carried out to study the survival time (in days) of The mechanism of action of these insecticides is adult insects exposed to diatomaceous earth and thought to be related to abrasion and adsorption volcanic ash (both 15 g/m2). We used a total of 62 phenomena of the epicuticular waxes, leading to adults of D. vittigerum (0.26 ± 0.01 g), and in each desiccation of the insects (Kalmus 1944; Wigglesexperiment 5 or 6 individuals were introduced in worth 1944; Stadler et al. 2010). The aim of this a 15 x 30 x 8 cm plastic container (Colombraro®) work was to evaluate the toxicity of volcanic ash containing either the inert dust treatment plus from the PC and diatomaceous earth on the grassfood or only food (control). A fan (1.65 m.seg'1) was hopper, Dichroplus vittigerum (Blanchard 1851, set on the top of the plastic containers to simulate Orthoptera: Acrididae) an occasional insect pest the wind gusts that occur in the region affected by in northern Patagonia. the PC (7 km/h). This fan was turned on 4 times A first experiment consisted of exposing adults a day for one h. The dust spread over the entire of D. vittigerum (0.25 ± 0.008 g) to fine-grained container and the fan simply recirculated the dust volcanic ash (collected by Ing. Jacobacci, Rio Newithin the container. The insects were fed ad li gro, particle size < 500 p) or diatomaceous earth bitum on dandelion plants, which were renewed (Celite® 503, World Minerals, Celite Corporadaily. Temperature and humidity were controlled tion), at either a high humidity of 75% RH ± 2 (20.43 °C ± 0.01, 39.57 ± 0.09% RH). Mortality (using a saturated solution of sodium chloride; was recorded daily. Data analyses were carried out Winston & Bates 1960), or ambient humidity of with Log-Rank, Survival Analysis. Significantly 39.57 ± 0.09% RH. Each adult was placed in a different least square means (P < 0.05) were sepa plastic dish (7 x 5.5 x 8.5 cm) with 100 mm2 of rated by the Tukey test (Sigma Stat).