Probing and feeding characteristics of the greenhouse whitefly in association with host-plant acceptance and whitefly strains

Host-plant and whitefly strain effects and their interactions on the probing and sap feeding of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), have been investigated in this study using the DC-EPG (Electrical Penetration Graph) technique. Whiteflies generally displayed fewer but longer probes on highly acceptable cucumber than on less acceptable tomato. Both whitefly strains, the T(omato)-strain and the C(ucumber)-strain, showed a significantly lower number of phloem phases on cucumber than on tomato. However, the duration of total phloem phases achieved by either of the whitefly strains on these two host plants was not significantly different. These data indicate that a more continuous phloem feeding has occurred on cucumber plants. Indeed, the percentage of phloem feeding time after the first sustained phloem phase (longer than 15 min) was higher on cucumber for the C-strain whiteflies. When comparing these two whitefly strains, the T-strain whiteflies probed less frequently but longer than the C-strain whiteflies did on both host plants. Also, the T-strain whiteflies displayed a longer duration of total phloem phases on tomato. An interaction between the whitefly strain and plant effects was detected on a parameter, which showed that whiteflies probed significantly longer before reaching the first phloem phase on the host plants that had been previously experienced. In conclusion, both plant species and whitefly strains affect whitefly's probing and feeding behaviour, though plant effects are much stronger.     

Irreversible thelytokous reproduction in Muscidifurax uniraptor

Three encyrtid parasitoids Apoanagyrus (Epidinocarsis) diversicornis, Aenasius vexans, and Acerophagus coccois (Hymenoptera: Encyrtidae) are used to control the cassava mealybug Phenacoccus herreni Cox & Williams (Sternorrhyncha: Pseudococcidae), an important pest of cassava in South America. The influence of parasitism on the feeding behaviour of mealybugs was studied by observing honeydew secretion and by the electrical penetration graph technique (EPG, DC-system). Honeydew secretions were observed after parasitism until mummy transformation. No strong EPG parameter differences were found between parasitised and control insects. All results indicated that parasitised mealybugs keep feeding on the phloem sap after parasitism until mummy transformation. The main influence of parasitism on EPG parameters is the appearance of a new pattern resembling the E2 pattern at the extracellular level and labelled H. This pattern was also produced with control insects located on an unfavourable feeding site and could be associated with a stress response. It might be related to the still unclear E(c) pattern of aphids. The relationship of H to stylet activities is discussed.     

Effects of treatments for electrical penetration graph recordings on behaviour and biology of Aphis craccivora (Aphididae)

Abstract. Two laboratory studies were conducted to investigate effects of treatments for direct "current electrical penetration graph (DC-EPG) recordings or 'tether effect', on behaviour and reproductive performance of cowpea aphid Aphis craccivora Koch. The experiments constituted a control study in application of DC-EPGs to analyse cowpea aphid feeding behaviour and host plant resistance mechanisms. Resistant (ICV-12) and susceptible (ICV-1) cultivars of cowpea Vigna unguiculata (L.) Walp were used. EPG treatments included two groups of aphids: tethered aphids that were exposed to DC electricity via an attachment of a thin, flexible gold wire on their dorsum using a droplet of adhesive silver paint, and 'free' (untethered) aphids with a dorsal spot of silver paint only. EPGs of the tethered aphids were recorded continuously for c. ! h, whereas from the 'free' aphids recordings were done only for brief periods of 2–5 min, by temporarily contacting a gold wire to the spot of silver paint. Waveform signals generated from resistance fluctuations and electromotive forces, and representing aphid stylet penetration behaviour were recorded. A separate experiment was conducted to investigate effects of EPG treatments on aphid survivorship and population growth. Overall, EPG treatments did not significantly affect aphid stylet penetration behaviour or life-table parameters. However, effects of crop cultivar on those characteristics were significant. Waveform E2, which denotes aphid ingestion in phloem sieve elements, and non-penetration behaviour were important indicators of aphid resistance in ICV-12. Also, apart from the number of aphid generations, other life-table parameters were useful indicators of ICV-12 resistance. Thus, DC-EPGs provided a reliable technique for studying aphid stylet behaviour, and investigation of aphid resistance in cowpeas.