Aphids-induced plant volatiles affect diel foraging behavior of a ladybird beetle Coccinella septempunctata

The ladybird beetle Coccinella septempunctata (L.) is an important biocontrol agent of pests such as various aphid species. Despite being one of the most studied coccinellid species, many aspects of its foraging behavior are still not completely understood. This study focuses on the diel foraging behavior of C. septempunctata, investigating their olfactory orientation toward aphid-infested plants, walking activity on plants and on the soil, and feeding rates. In the scotophase the ladybird beetles were significantly more attracted to the odor of aphid-infested plants, on which they also showed considerably higher walking activity then on uninfested controls. Females were more prone to utilize olfactory cues when searching for prey and fed at higher rates than males; this shows that they are better adapted to nocturnal activity, as they require higher food intake. Coccinella septempunctata have the same feeding rate during the scotophase as in the photophase. Our study shows that C. septempunctata has the potential to forage in the scotophase if prey is abundant. The results support the hypothesis that volatiles of aphid-infested plants can attract or arrest foraging adult ladybird beetles, even in the darkness, which makes a considerable contribution to efficient prey search and enhances feeding capacity

Effect of within-species plant genotype mixing on habitat preference of a polyphagous insect predator

The effects of within-species plant genotype mixing on the habitat preference of a polyphagous ladybird were studied. Plant species diversity is often claimed to positively affect habitat preferences of insect predators, but the effects of within-species genotype diversity have not been extensively studied. In a field experiment with different barley (Hordeum vulgare) genotypes in mixed and pure stands, adult seven-spot ladybird Coccinella septempunctata, a polyphagous predator, preferred a specific combination of genotypes over the single genotypes alone before aphids had arrived in the crop, and again when aphids were emigrating. In laboratory experiments on adult ladybird orientation to odour from barley, ladybirds were attracted/arrested by the mixed odour of the same barley genotype mixture that was preferred in the field. Exposure of one barley genotype to volatiles from the other also caused the odour of the exposed plants to become more attractive to ladybirds. The results support the hypothesis that plant volatiles may attract or arrest foraging adult ladybirds, contributing to the selection of favourable habitats, and they show that within-species plant genotype mixing can shape interactions within multitrophic communities

Effect of Larvae Treated with Mixed Biopesticide Bacillus thuringiensis - Abamectin on Sex Pheromone Communication System in Cotton Bollworm, Helicoverpa armigera

Third instar larvae of the cotton bollworm (Helicoverpa armigera) were reared with artificial diet containing a Bacillus thuringiensis - abamectin (BtA) biopesticide mixture that resulted in 20% mortality (LD(20)). The adult male survivors from larvae treated with BtA exhibited a higher percentage of “orientation” than control males but lower percentages of “approaching” and “landing” in wind tunnel bioassays. Adult female survivors from larvae treated with BtA produced higher sex pheromone titers and displayed a lower calling percentage than control females. The ratio of Z-11-hexadecenal (Z11–16:Ald) and Z-9-hexadecenal (Z9–16:Ald) in BtA-treated females changed and coefficients of variation (CV) of Z11–16:Ald and Z9–16:Ald were expanded compared to control females. The peak circadian calling time of BtA-treated females occurred later than that of control females. In mating choice experiment, both control males and BtA-treated males preferred to mate with control females and a portion of the Bt-A treated males did not mate whereas all control males did. Our Data support that treatment of larvae with BtA had an effect on the sex pheromone communication system in surviving H.armigera moths that may contribute to assortative mating

SCANNING ELECTRON-MICROSCOPE STUDIES ON THE WAX COVERING THE STOMATA OF HOST PLANTS PRODUCED BY TRIALEURODES-VAPORARIORUM WESTW (HOM., ALEYRODIDAE)

WOS: A1982NB18100011

Effects of three weeds on the populations of predatory coccinellids and aphids in a kohlrabi field [Auswirkungen dreier Wildkrautarten als Begleitpflanzungen in einem Kohlrabifeld auf räuberische Coccinelliden und Blattläuse]

Investigations dealing with the olfactory reactions of parasitoids and predators have become more and more important for practical entomological reserch. One aim is to observe the reactions of beneficial arthropods to kairomones of different origin, for example to adours emitted by plants. Based on results of laboratory studies with a four-armed olfactometer, the attractiveness of the weeds wormwood Artemisia vulgaris L., tansy Tanacetum vulgare L. and stinging nettle Urtica dioica L. was examined in a kohlrabi field in summer 1999. Thereby the population densities of all developmental stages of coccinellids were recorded on kohlrabi plants in the three weed plots as well as in a control. The weeds clearly maintained higher population levels of adult coccinellids on the adjacent kohlrabi plants on most of the monitoring dates as compared with the control. As a result, the population densities of the adults in the weed plots were almost three times as high. The densities of the larvae showed similar tendencies, but these differences were smaller for the eggs and pupae. However the differences between the three weed varieties were very low. Significant differences were found between the varieties and control when mean numbers of adult concinellids were compared for the whole monitoring time. Coccinella septempunctata L. was the most abundant species in all the plots, followed by Propylea quatuordecimpunctata (L.) and Adalia bipunctata (L.): The aphid population on kohlrabi plants was also clearly different between the varieties and control. The adjacent planted weeds seemed to reduce significantly the aphid population from the end of May and the beginning of July. The most important aphid species were Brevicoryne brassicae (L.) and Myzus persicae (Sulzer) (Homoptera: Aphididae). The results of this research are discussed because of their application for the biological control of pests and as a possibility for habitat manipulation in agroecosystems

LABORATORY STUDIES OF THE EFFECT OF TEMPERATURE AND HUMIDITY ON DEVELOPMENT AND FECUNDITY OF PARABEMISIA-MYRICAE (KUWANA) (HOMOPTERA, ALEYRODIDAE)

WOS: A1993LC76400003The effect of six temperatures and three relative humidities on the developmental period of immature and the fecundity of Parabemisia myricae (Kuwana) was studied, separately, in the laboratory. The developmental time from egg to adult stage was 79.7; 41.7; 24.4, and 22.0 days at 15, 20, 25, and 30-degrees-C temperatures, respectively. The developmental time at the fluctuating temperatures of 25/35-degrees-C (12/12 h) was 24.2 days. With increasing relative humidity at 25-degrees-C constant temperature, the total developmental time decreased significantly from 26.7 days at 40 % RH to 20.3 days at 90 % RH. The mortality rate was lowest at 25-degrees-C and was highest at 30-degrees-C and 25/35-degrees-C. It was also found that temperatures above 35-degrees-C were lethal, since all eggs were killed at 35-degrees-C. At the three relative humidities tested, the mortality rate of the egg stage was highest at 90 % RH (20 %) and about 44 % of the immature stages were killed at 40 % RH. The adult's (female) longevity and the reproduction changed with changes in temperature; oviposition rate increased by the increase in temperature up to 25-degrees-C then remained at the same level

Influence of leaf portion and plant species on the egg-laying behaviour of the predatory ladybird Serangium parcesetosum Sicard (Col., Coccinellidae) in the presence of a natural enemy

WOS: 000229970600010The effectiveness of natural enemies against arthropod herbivores can depend on the characteristics of the plant on which they are found. The influence of the plant on the egg-laying behaviour of the promising whitefly predator, Serangium parcesetosum Sicard (Col., Coccinellidae) was examined in order to be able to use it effectively in biological control programs. The present work investigated the possible influence of the portion of the leaf on the number of eggs laid as well as the effect of plant species on the way in which eggs are deposited by S. parcesetosum. The experiments were conducted on cucumber and cotton leaves with Bemisia tabaci (Germ.) (Hom., Aleyrodidae) as prey in the absence and presence of a natural enemy, the lacewing, Chrysoperla carnea (Stephens) (Neur., Chrysopidae) at two different temperatures. The results showed that at 18 degrees C, S. parcesetosum females significantly preferred to lay their eggs between the veins and close to the veins of cucumber leaves, mean of 10.1 and 7.5 eggs, in the absence of C. carnea, respectively, while in its presence significantly more eggs were deposited close to the veins and close to the petiole. On cotton leaves, close to the petiole, a mean of 8.4 eggs in the absence of the lacewing, as well as close to the veins, mean of 6.3 eggs in the presence of the lacewing, were found to be the most suitable leaf portions for egg-laying. At 30 degrees C, the females laid their eggs preferentially close to the veins of cucumber leaves in the absence and presence of C. carnea. On cotton leaves, S. parcesetosum females significantly preferred to lay their eggs close to the petiole, mean of 7.6 and 6.1 eggs, as well as close to the veins, mean of 6.2 and 8.7 eggs, in the absence and presence of the lacewing, respectively. At both temperatures, the ladybird females laid their eggs singly on cucumber leaves in the absence and presence of C. carnea. While on cotton leaves, the females had a tendency to deposit their eggs together in the absence and presence of the lacewing, except at 30 degrees C in its absence. Within the same plant species, significant differences were found in the total number of eggs laid by S. parcesetosum females on cotton leaves at 18 degrees C as well as on cucumber leaves at 30 degrees C in the absence and presence of the natural enemy. In addition to the effects of presence and absence of C. carnea, and where eggs were laid, some significant differences due to plant species was found at both temperatures

LABORATORY STUDIES ON DEVELOPMENT AND FECUNDITY OF CIRCULIFER-OPACIPENNIS (LETHIERRY) (HOMOPTERA, CICADELLIDAE) AN IMPORTANT VECTOR OF SPIROPLASMA-CITRI SAGLIO ET-AL IN THE MEDITERRANEAN AREA

WOS: A1991GZ43300012The development of Circulifer opacipennis (Lethierry) was strongly influenced by temperature. The egg period decreased significantly from 10,5 days at 25-degrees-C to 5,3 days at 35-degrees-C. The adult stage was reached after 22,0 days at 25-degrees-C and 12,1 days at 35-degrees-C and no differences were found between the fluctuating temperature (20/30-degrees-C) and the corresponding mean temperature (26,5-degrees-C). The 1st and 5th instar required more time to develop than the remaining three stages. Mortality rate during egg stage was only slightly influenced by temperature, ranging between 8,2% and 9,7%. On the other hand, the mortality of immature stage was strongly affected by temperature. At 30-degrees-C, only 9,5% and at all other temperatures between 24,2% and 39,5% of all nymphs died. Oviposition period and longevity was significantly shorter at 35-degrees-C, resulting 22,1 and 28,5 days, respectively, comparing to both lower temperatures. Fecundity was highest at 30-degrees-C (234 eggs/female) compared to 181,7 and 162,2 eggs/female at 25-degrees-C and 35-degrees-C. The number of eggs laid per female per day was significantly higher at 30-degrees-C (5,1 eggs/day) and 35-degrees-C (5,6 eggs/day) than at 25-degrees-C (3,9 eggs/day)