Variety,mulch and stage of inoculation effects on incidence of tomato spotted wilt virus disease in cucumber (Cucumis sativus L.)

Abstract

Tomato spotted wilt virus (TSWV) vectored by thrips is one of the major diseases affecting cucumber yield. Control of thrips is an underlying factor in its management. A study was conducted to determine the effect of time of inoculation, variety and mulch on disease incidence. Four varieties were inoculated with TSWV at cotyledon, 3 – 4 leaf and flower bud stages in a RCBD experiment replicated four times in a greenhouse. In the field, a 2×8 factorial design where two cucumber varieties were raised on seven types of mulches (red, yellow, silver, clear, black, white, and straw) with unmulched plots as controls was used. Variety Marketer was more tolerant to the disease compared to other varieties. Most varieties were generally tolerant to TSWV at cotyledonous but susceptible at 3 – 4 leaf and flower bud stages. Silver and clear mulches significantly suppressed thrip populations, yield and quality under field conditions.     

Laboratory studies on extracts of Melia fruit and Neem fruit on B. brassicae,B. tabaci and their predators and parasites

Abstract

The biological effect of plant extracts on the two predators C. carnea and C. undecimpunctata was studied in the laboratory. Treated B. brassicae was offered to the newly hatched larvae of the two predators. The rate of prey consumption and duration of the larval instars of the two predators were slightly affected as a result of the treatments of the plant extracts. Adults of the aphid parasite D. Rapae and the whitefly parasite E. Mundus were exposed to the plant extracts via feeding on treated honey droplets or parasitized treated hosts. Mortality percentages of D. Rapae fed on honey contaminated with plant extracts were 50 and 80% for extracts of Melia fruits in ethanol and in petroleum ether, respectively. Mortalities in parasites developed in hosts treated with plant extracts of Neem fruits in ethanol and Melia flowers in petroleum ether in were 33.3 and 81.5%, respectively. Similar results were obtained when E. Mundus received the same treatments of the plant extracts.     

Plasticity in biochemical characteristics of cotton aphid,Aphis gossypii Glover in response to different host plants and neonicotinoid pesticides

In the present investigation an effort was made to realise the role of feeding host plants on some enzymes’ activities. The results showed that the enzymes’ activities were changed in the aphids feeding on different host plants which assist in detoxification of their host metabolites. It is important when the aphids are exposed to insecticides. The results indicated that the measured enzyme activity has significant changes depending on the host plant. It is shown in this study that there are no significant differences between different host plants on esterase activity (p = 0.446); however, there is a significant difference between GSH activity (p = 0.047) but this relationship is not significant on MFO activity (p = 0.417). Among three strains of Ag-PP, Ag-MO and Ag-FA, strain Ag-PP was the most resistant strain against neonicotinoids, and the resistance mechanism was related to metabolic increase in carboxyl esterase activity. The results showed that strain of Ag-MO was the most susceptible strain against neonicotinoids. The result of this investigation also showed that the general esterases might play an important role in conferring or contributing to neonicotinoid resistance in the cotton aphids.     

Effect of mineral oil on Potato virus Y acquisition by Rhopalosiphum padi

Seed potato crops are currently sprayed weekly with mineral oil to prevent transmission of the Potato virus Y (PVY; Potyviridae: Potyvirus), one of the most prevalent and important non‐persistent viruses affecting potato production. In spite of its wide usage as inhibitor of virus transmission, the mode of action for mineral oil is poorly known. The objective of this study was to quantify the effect of dosage and time from application of mineral oil on the inhibition of PVY acquisition. The bird cherry‐oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), known as vector of PVY, was used in all the experiments. The results indicated that mineral oil efficiently decreased PVY acquisition by 75 and 70% 1 day after application of 5 and 10 l ha^?1, respectively. The inhibition effect decreased with time from application; mineral oil inhibits acquisition for less than 4 days at 5 l ha^?1 and between 8 and 12 days at 10 l ha^?1. As mineral oil was detected in the body of fewer aphids when they fed on plants 1 day after oil application, a change in the aphid probing behaviour on mineral oil‐treated plants was deduced. These results support the hypothesis that mineral oil physically inhibits the binding of the virus at the tip of the stylets.     

When can embryos learn? A test of the timing of learning in embryonic amphibians

Learning is crucial to the survival of organisms across their life span, including during embryonic development. We set out to determine when learning becomes possible in amphibian development by exposing spotted salamander (Ambystoma maculatum) embryos to chemical stimuli from a predator (Ambystoma opacum), nonpredator (Lithobates clamitans), or control at developmental stages 16–21 or 36–38 (Harrison 1969 ). Once exposures were completed and embryos hatched, we recorded the number of movements and time spent moving of individuals in both groups and all treatments. There was no significant difference in number of movements or time spent moving among any of the treatments. The groups that were exposed to predator stimuli and a blank control at stages 36–38 were also tested to determine whether there was a difference in refuge preference or difference in survivorship when exposed to a predator (marbled salamander). There was no difference in survival or refuge preference between individuals; however, all individuals preferred vegetated over open areas regardless of treatment type. We discuss hypotheses for the absence of embryonic learning in this species and suggest it may be the result of the intensity of the predator–prey interaction between the predator, large marbled salamander larvae, and the prey, spotted salamander larvae.     

Ecological genetics of Italian peach‐potato aphid (Myzus persicae) populations in relation to geography,dispersal and insecticide resistance as studied using microsatellite and resistance markers

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Abscisic acid deficiency increases defence responses against Myzus persicae in Arabidopsis

Comparison of Arabidopsis thaliana (Arabidopsis) gene expression induced by Myzus persicae (green peach aphid) feeding, aphid saliva infiltration and abscisic acid (ABA) treatment showed a significant positive correlation. In particular, ABA‐regulated genes are over‐represented among genes that are induced by M. persicae saliva infiltration into Arabidopsis leaves. This suggests that the induction of ABA‐related gene expression could be an important component of the Arabidopsis–aphid interaction. Consistent with this hypothesis, M. persicae populations induced ABA production in wild‐type plants. Furthermore, aphid populations were smaller on Arabidopsis aba1‐1 mutants, which cannot synthesize ABA, and showed a significant preference for wild‐type plants compared with the mutant. Total free amino acids, which play an important role in aphid nutrition, were not altered in the aba1‐1 mutant line, but the levels of isoleucine (Ile) and tryptophan (Trp) were differentially affected by aphids in wild‐type and mutant plants. Recently, indole glucosinolates have been shown to promote aphid resistance in Arabidopsis. In this study, 4‐methoxyindol‐3‐ylmethylglucosinolate was more abundant in the aba1‐1 mutant than in wild‐type Arabidopsis, suggesting that the induction of ABA signals that decrease the accumulation of defence compounds may be beneficial for aphids.     

Changes in interspecies association patterns of Atlantic bottlenose dolphins,Tursiops truncatus,and Atlantic spotted dolphins,Stenella frontalis,after demographic changes related to environmental disturbance

Animal populations can be affected by environmental disturbances in many ways including demographic and behavioral changes. This can affect interspecies associations for regularly interacting sympatric species, like bottlenose and spotted dolphins in the Bahamas (observed since 1985 and interspecies associations analyzed since 1993). After two hurricanes in 2004 each species lost roughly 30% of their respective communities resulting in differing social structure and behavioral changes. During mixed species encounters (MSE) group sizes for spotted dolphins ( = 14.1 ± 9.2) were significantly larger than bottlenose dolphins ( = 6.0 ± 7.3; F = 11.74, df = 1, P < 0.001), however, t‐tests revealed no differences between aggressive vs. affiliative encounters. Sexual/aggressive behavior regularly seen previously was not observed posthurricanes and aggressive encounters were greatly reduced. Generally results were similar to prehurricane data including high resightings of spotted dolphins with male alliances prevalent (including new juvenile alliances seen only posthurricane), and individualized bottlenose participation with few male alliances. However temporal associations varied compared to prehurricane. Interspecies association and behavior patterns were altered and likely affected by the changes in intraspecies association patterns following the hurricanes. However both species still participated in MSE, suggesting this is an important component of their ability to coexist as sympatric species.     

Differences in oscillatory whistles produced by spinner (Stenella longirostris) and pantropical spotted (Stenella attenuata) dolphins

Acoustic recordings of two closely related species, spinner dolphin (Stenella longirostris) and pantropical spotted dolphin (Stenella attenuata), were investigated from four different geographic locations: two in the Central Tropical Pacific, one in the Eastern Tropical Pacific and one in the Indian Ocean. The two delphinid species occur in tropical and warm temperate waters, with overlapping ranges. They produce very similar vocalizations, but at the same time their calls exhibit a certain degree of intraspecific variation among different geographic locations as has been observed in other delphinid species. Oscillatory whistles (whistles with at least two oscillations in their frequency contours) were identified and manually extracted from the recordings. Whistles with four or more maxima (oscillations) occurred only in spinner dolphins and they were present in all geographic regions investigated. In addition, the oscillatory whistles with two and three maxima were significantly more frequent in spinner than in spotted dolphins. The differences in oscillatory whistles for these two species seem to be consistent across study areas and therefore, could be used in addition to other whistle features to help distinguish between them.