Lethal and sublethal effect of heat shock on Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae).

Temperature is an important abiotic environmental factor, and is responsible for various kinds of behavioral and physiological changes in living organisms. Induced heat shock is associated with feeding behaviour, reproduction and reactive oxygen species (ROS) generation that causes oxidative damage. In this experiment, we examined the lethal and sublethal effects of heat shock on reproduction, feeding behaviour and antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and peroxidases (POD) in P. solenopsis. Results showed that males were highly susceptible to heat shock treatments than females, as LTemp50 values were 43.8 °C for males and 45.11 °C for females. Heat shock events non-significantly affected the fecundity in female only treated adults and significantly affected the both sexes heat treated adults, it increased the xylem feeding duration, percentage of xylem feeding adults and reduce the phloem feeding duration and percentage of phloem feeding adults. Similarly it alter the antioxidant enzymes activities, an increase of CAT, SOD and POD activities were noticed in response to highest intensity of heat shock while a reduction of CAT and SOD activity were noticed in response to lowest intensity of heat shock compared to control (30 °C). These results suggest that heat shock may result in loss of body water and induce oxidative stress in P. solenopsis. However, antioxidant enzymes play a significant role in overcoming the oxidative damage.

Effect of Constant and Fluctuating Temperature on the Development, Reproduction, Survival, and Sex Ratio of Phenacoccus solenopsis (Hemiptera: Pseudococcidae).

Effects of temperature on the development, survival, reproduction, longevity and sex ratio of the cotton mealybug, Phenacoccus solenopsis Tinsley, was assessed at five constant temperatures ranging from 20 to 35°C and five fluctuating temperatures ranging from 15 to 40°C under laboratory conditions. Results showed that nymphal development duration, preoviposition period, oviposition period, fecundity, and adult longevity were reduced significantly with increasing temperature until 30°C, but developmental duration of third female nymphal instar and female adult longevity was longer at 35°C than 30°C, and no males could emerge from pupae at the constant temperature 35°C. Fluctuating temperature, in general, significantly accelerated the nymphal developmental duration, prolonged preoviposition period, shortened oviposition period, reduced fecundity, lowered the survival rate of nymphs, and decreased adult longevity of males and females compared to their mean corresponding constant temperature. Overall, it is suggested that one should be prudent when applying the obtained results under constant and fluctuating temperatures under laboratory conditions.

Lethal and Sublethal Effects of Neonicotinoid Insecticides on the Adults of Phenacoccus solenopsis (Hemiptera: Pseudococcidae) on Tomato Plants.

Acetamiprid and imidacloprid are two important neonicotinoid insecticides that are widely utilized under field conditions for the management of sucking insect pests, including the solenopsis mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae). Although some information is available regarding their lethal effects, nothing is currently known about the sublethal effects of these insecticides. We, therefore, performed a series of experiments to test the lethal and sublethal effects of these chemicals on oviposition duration and fecundity. We also assessed sublethal effects on feeding behavior using the electrical penetration graph (EPG) technique. The results of this study reveal that acetamiprid toxicity is higher than imidacloprid and that both insecticides have negative effects on the oviposition, fecundity, and feeding behavior of P. solenopsis when applied at sublethal dosages. These chemicals also significantly reduce oviposition duration and fecundity and significantly prolong nonprobing duration, increase penetration problems, and reduce phloem and xylem feeding activities when compared with adults exposed to just water. No significant differences were detected in all waveform durations and events when adults previously exposed to foliage treated with each of these two insecticides were compared. The results of this study, therefore, suggest that both insecticides are capable of protecting crops from mealybug damage by not only killing these pests directly but also reducing their fecundity and inhibiting feeding behaviors when applied at sublethal dosages.