Overwintering inside the food in the diapausing larvae of pomegranate fruit moth

Low temperatures are a major survival challenge for insects living in temperate zones. The most common features that guaranty survival in the most overwintering insects are diapause and cold hardiness. In spite of obvious advantages, damages due to diapause associated stresses such as cold shock and depletion of energy reserves make diapause a costly life history strategy. Apomyelois ceratoniae (Zeller), a major pest of pomegranate in Iran, overwinters as different larval instars. In comparison to larger counterparts, early instars of pomegranate fruit moth must have sequestered fewer energy reserves, thus they might be less tolerant to cold. By designing experiments similar to natural conditions in December, we demonstrated that overwintering inside pomegranate fruits provides opportunity for larvae to feed and compensates energy depletion. Our results also indicated that there is no significant difference between supercooling point and cold tolerance of the small and the large field collected larvae during autumn and winter, thus overwintering mortality might not be a key driver in population dynamics

Fumigant toxicity and repellency effects of essential oil of Salvia mirzayanii on Callosobruchus maculatus (Col.: Bruchidae) and Tribolium confusum (Col.: Tenebrionidae)

In an attempt to find a natural and safe method for the control of stored-product pests, insecticidal activity and repellency effect of essential oil from Salvia mirzayanii Rech. F. & Esfand. were investigated against one day old adults of Callosobruchus maculatus (F.) (Col.: Bruchidae) and Tribolium confusum J du Val. (Col.: Tenebrionidae). The essential oil was obtained by hydrodistillation method, using a modified Clevenger-type apparatus. Experiments were carried out at 27 ± 1°C and 65 ± 5% R.H. in dark condition. Results of fumigant toxicity tests showed that the mortality of C. maculatus was increased significantly with increases in concentration and exposure time. LC50 value was 2.58 µL/L air for C. maculatus. Results indicated that C. maculatus was so susceptible to S. mirzayanii oil. LT50 values for C. maculatus were 9.73, 8.52, 7.17 and 7.08 h at 37.03, 111.11, 148.14 and 185.18 µL/L air, respectively. No mortality was observed on T. confusum at highest concentration (3703.70 µL/L air). Repellency was increased significantly with increases in concentration in both of species of the insects. The essential oil was significantly more repellent to T. confusum than C. maculatus. It is concluded that S. mirzayanii essential oil can be used as a safe pesticide to control stored insect pests, especially against C. maculatus

Cold tolerance and supercooling capacity in overwintering adults of the alfalfa weevil, Hypera postica (Col.: Curculionidae)

Alfalfa weevil, Hypera postica Gyllenhal, is a key pest of alfalfa and widely distributed in alfalfa fields of Iran. In early autumn, the first adults of H. postica arrive in the fields where they steadily increase their populations during autumn and following winter. To evaluate the impact environmental factors including temperature on the survival of the weevils, this study was conducted to measure the levels of variability in supercooling point and cold hardiness in the weevils. Overwintering adults were collected monthly from alfalfa fields on the outskirts of Karaj during the autumn 2011and winter 2012. The supercooling points and survivorship were studied at sub-zero temperatures from -5 to -13 ºC for 210 minutes. The average supercooling point ranged from -14.4 ± 0.68 in October to -8.8 ± 0.80 in March. Mean supercooling points for H. postica adults were significantly lower in autumn (-13.4 ºC) comparing winter (-8.6 ºC). Insects survived after being exposed to -5 ºC in all months. The mortality of the adults increased with cold intensity. The percent mortality for adults treated at -11 ºC was approximately 89% in November and December and reached 100% in January and February. The range of LT50 values varied from -5.7 ºC (highest) to -8.6 ºC (lowest). Results showed that adults could not withstand the temperatures below the supercooling point. It is found that the cold intensity around supercooling point could cause 80% mortality. It can be concluded that as the ambient temperature in the field approaches the supercooling point, it tends to be detrimental on H. postica population

Seasonal changes in supercooling point and cold tolerance in field collected larvae of the beet moth, Scrobipalpa ocellatella (Lepidoptera: Gelechiidae) in Karaj, Iran

A part of population of the beet moth, Scrobipalpa ocellatella (Boyd) in severe winter condition overwinters as larvae. In order to study overwintering potential ofthe pest, last instar larvae were collected monthly from September 2011 to March 2012. Seasonal changes in cold hardiness indices such as supercooling point (SCP) and lower lethal temperature of the beet moth were studied. The mean supercooling points of field collected larvae varied from –15.0 ± 0.99 to –17.8 ± 0.92 °C. Samples collected in October exhibited about 50% mortality, after 24 h exposure to -12 °C. It was gradually decrease until January (no mortality was observed) in January. Lethal temperature for 50% mortality (LT50) decreased from -13.2 ºC in October to -16.4 ºC in January. Supercooling points of overwintering larvae thorough the winter did not change significantly; while during the gradual decrease in ambient temperature, cold tolerance of S. ocellatella is progressively increased

Chemical composition and fumigant toxicity of three citrus essential oils against eggs, larvae and adults of Callosobruchus maculatus (Col.: Bruchidae)

The fumigant toxicity of volatile fractions of peel essential oils of the Rutaceae species of Citrus reticulata Blanco, C. limon L. and C. aurantium L. was studied against eggs, larvae and adults of Callosobruchus maculatus (F.) at 27 ± 1 ºC and 65 ± 5% RH in darkness. The oils were extracted from the fruit peels using water steam distillation. The essential oils were characterized by a combination of GC and GC/MS analyses. Limonene was the major constituent of the three essential oils. The effect of different concentrations of the essential oil vapors on egg hatchability as well as larval and adult mortality was found to be significant. Citrus reticulata and C. aurantium oils were more toxic on egg hatchability than C. limon extract and caused higher mortality on larvae as well. There was no significant difference between essential oils in terms of adult mortality. The adult beetles were also exposed to the concentrations of 18.5, 37, 55.5 and 74 μl/l air. At the highest concentration (74 μl/l air), C. aurantium oil caused 100% mortality after a 6 h exposure, but the oils from C. reticulata and C. limon caused 38% and 62% mortality, at the identical exposure time, respectively. The results suggest that citrus peel oils can be effectively used as botanical fumigants against various life stages of Ca. maculatus

Effect of particle size of two Iranian diatomaceous earth deposits and a commercial product on Sitophilus granarius (Col.: Dryophthoridae)

Laboratory bioassays were carried out to study the insecticidal efficacy of two Iranian diatomaceous earths (DEs) and SilicoSec® formulation against Sitophilus granarius (L.). Four different particle sizes of DEs were applied at five concentrations. The mortality was counted 2, 5 and 7 days after exposure. The experiment was carried out at 27 ± 1°C and 55 ± 5% relative humidity in continuous darkness. For SilicoSec® and Mamaghan with less than 37 µm particle size, 500 ppm was sufficient to cause 100% mortality after 5 days of exposure. While in case of Maragheh deposit with the same particle size, complete mortality was recorded at 1000 ppm after 5 days. LC50 values indicated that SilicoSec® and Mamaghan with < 37 µm particle size were the most efficient DE samples against S. granarius. In most cases, the efficacy of DEs increased with decreasing particle size. The visual observation of scanning electron microscopy (SEM) images showed that SilicoSec® has more attachment to insectsâ body. However, the adhesiveness of DE particles cannot be the main indicative of their insecticidal effectiveness

Changes of supercooling point and cold tolerance in overwintering adults of Brevicoryne brassicae (Hem.: Aphididae) in Tehran, Iran

The cabbage aphid, Brevicoryne brassicae (L.), is one of the major pests of the plant family Brassicaceae that causes serious damages to cabbage and oilseed rape. The cabbage aphid is also able to build up populations on ornamental cabbage during the winter months. To determine the level of cold tolerance in its overwintering populations, adult aphids were collected on cabbages planted in the field of Faculty of Agriculture, Tarbiat Modares University in autumn 2008 and winter 2009. The supercooling points and survivorship of the adults were studied at sub-zero temperatures for 24 h. The mean supercoolig point varied from -23.9 ± 0.46ºC in November to -19.8 ± 0.34ºC in May. About 70-95% of the cabbage aphid adults could tolerate -5°C/24 h in all months. The survival rate for the treated adults at -10ºC/24 was about 55% from October through November and 87% in December. The LT80 (the temperature at which 80% of population die after 24 h exposure to cold temperatures) was at its highest(-11.32°C) in May, showing the lowest level of cold tolerance in the population. The LT80 ranged from-13.81 to -14.79 °C from December to February, showing the highest level of cold tolerance. Findings indicated that cabbage aphid populations hold a high capacity to tolerate cold temperatures in the course of winter while being active and sexually reproductive at the same time that leads to their quick grow and emergence as an economic severe pest early in the next season

Changes of cryoprotectants in overwintering larvae of beet armyworm, Spodoptera exigua (Lep.: Noctuidae)

The beet armyworm, Spodoptera exigua (Hübner), is a polyphagous pest that causes serious damages to a wide range of agricultural crops including beet, potato and cotton. In order to deepen our understanding of the biology of the pest during the winter, overwintering larvae of beet armyworm were collected from the fields from November 2008 through March 2009. Using HPLC technique, the level of cryoprotectants (antifreeze compounds) inside the body of larvae was measured and the following five compounds were detected: trehalose, glucose, myo-inositol, glycerol and sorbitol. It is found that the amount of polyols and trehalose is always higher than the other compounds and during the coldest days of the winter their level sharply increases from 0.99 mg/g fresh weight in November to 3.9 mg/g fresh weight in January. The results suggest that trehalose is the key cryoprotectant that helps overwintering larvae of beet armyworms survives during the harsh winter days

Cryoprotectants and their changes in cabbage aphid, Brevicoryne brassicae (Hem.: Aphididae)

Cabbage aphid, Brevicoryne brassicae (L.), is an important pest of cabbage, especially ornamental cabbages, due to its voracity and population build-up on these plants in wintertime. The cryoprotectants of B. brassicae and their changes were investigated during the cold seasons. Adult aphids were collected monthly on ornamental cabbages from October 2008 through May 2009. The amount of sugars and polyols were measured by high performance liquid chromatography (HPLC) and the amount of glycogen was spectrophotometrically determined. The identified compounds were as follows: glucose, mannitol, myo-inositol and trehalose. Mannitol, myo-inositol and trehalose were significantly correlated with average temperature. The total amount of these compounds increased from the lowest amount (11.90 ± 3.07 µmol/g f.w.) in October to its highest (55.8 ± 8.83 µmol/g f.w.) in the coldest month, January. There appears that these three compounds, especially mannitol, play important roles in enhancing cold tolerance of B. brassicae during cold seasons. The amount of glycogen showed no significant differences during those months and varied from 4.8 ± 0.58 mg/g f.w. in October to 3.3 ± 0.98 mg/g f.w. in December. There was no significant correlation between glycogen and the cryoprotectants