An association between two species of pine aphid, Schizolachnus pineti and Eulachnus agilis

Abstract. 1. Two aphid species feed exclusively on pine needles, Schizolachnus pineti (Fabr.) occupying only the outer (curved) surface with Eulachnus agilis (Kalt.) showing a preference for the inner (flat) surface.
2. Despite E.agilis favouring and S.pineti avoiding senescing needles, both species show a significant tendency to share shoots and needles in the field.
3. The same association is also apparent under laboratory conditions, although E.agilis is randomly distributed between needles in the absence of S.pineti.
4. E.agilis was found to benefit through increased survival and faster growth rates, by feeding on the same shoots and needles as S.pineti.
5. It is suggested that E.agilis may be able to detect and exploit an improvement in the nutritive quality of needles brought about by the feeding activity of S.pineti colonies.     

Suitability of brachiaria grass as a trap crop for management of Chilo partellus

The cereal stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a major insect pest of sorghum (Sorghum bicolor L. Moench) and maize (Zea mays L.) in Africa. Trap cropping systems have been shown to be a valuable tool in management of this pest. To optimize trap cropping strategies, an understanding of host‐plant preference for moth oviposition and host suitability for larval survival on potential trap plants is a prerequisite. Therefore, we assessed seven brachiaria accessions (Poaceae) for preference by C. partellus moths and subsequent larval performance. In two‐choice tests with a local open‐pollinated maize variety (cv. Nyamula), significantly higher numbers of eggs were deposited on brachiaria accessions Marandu, Piata, and Xaraes than on maize, whereas fewer eggs were recorded on plants of Mulato II, Mulato I, and Cayman. There was a significant and negative correlation between the trichome density on plant leaves and C. partellus oviposition preference for brachiaria. In addition to poor larval performance on brachiaria, there was no clear ranking in the accessions regarding larval orientation, settling, arrest, and food ingestion and assimilation. First instars did not consume leaf tissues of brachiaria plants but consumed those of maize, which also suffered more stem damage than brachiaria plants. No larvae survived on brachiaria plant tissue for longer than 5 days, whereas 79.2% of the larvae survived on maize. This study highlights the preferential oviposition of C. partellus on brachiaria plants over maize and the negative effects that these accessions have on subsequent larval survival and development. Our findings support the use of brachiaria as a trap crop for management of C. partellus through a push‐pull technology.     

Effects of Ocimum basilicum and Ruta chalepensis hydrosols on Aphis gossypii and Tetranychus urticae

Hydrosols are by‐products derived during the extraction of essential oils and are produced in a high amount and at very low cost. Their effects on crop pests have been little studied, although recent studies have shown their insecticidal properties. In this work, the effects of hydrosols derived from Ocimum basilicum (sweet basil) and Ruta chalepensis (rue) were investigated on the serious crop pests Aphis gossypii and Tetranychus urticae. The main compounds of basil hydrosol were linalool (66.5%), eugenol (18.9%) and eucalyptol (7.1%), while rue's were 2‐nonanone and 2‐undecanone at 77.0% and 8.9%, respectively. The mortality and fecundity of A. gossypii and T. urticae were recorded for 7 days after application of hydrosols. Apterous adult aphids and female mites were sprayed on cucumber leaves in special structures. Both hydrosols caused significant mortality rates, which fluctuated between 46.0% and 64.0%. The negative control (deionized water) caused no mortality, while for the positive controls (synthetic pesticides) was 100%. The fecundity of A. gossypii and T. urticae was significantly reduced after the application of the hydrosols (17.1 nymphs of A. gossypii and 22.8 eggs for T. urticae had been produced per female after treated with the hydrosol of R. chalepensis and O. basilicum, in comparison with 41.6 and 49.5 in the negative controls, respectively). In conclusion, the hydrosols from both plants presented an important effect on the mortality and fecundity of both pests.     

The Xerobranching Response Represses Lateral Root Formation When Roots Are Not in Contact with Water

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Electrical penetration graphs of the damson-hop aphid, Phorodon humuli on resistant and susceptible hops (Humulus lupulus)

Electrical penetration graphs (EPG's) were used to locate resistance to Phorodon humuli (Schrank) (Homoptera, Aphididae) in hops (Humulus lupulus, Cannabinaceae). Aphids on those hops showing resistance had a much reduced E2 pattern (uptake of phloem). In addition, many aphids on the resistant plants spent time non-probing within two minutes of withdrawing from the phloem. This was not observed with aphids on susceptible hops. The results suggest that resistance is located in the phloem. The involvement of a mechanical factor such as the blocking of aphid stylets, the presence of antinutritional factors, or simply an inadequate supply of nutrients, are discussed as possible resistance mechanisms.     

Diapause termination and egg hatch in the bird cherry aphid, Rhopalosiphum padi

Conclusion TastePROBE is a convenient and flexible electronic circuit designed to record action potentials from taste sensilla of insects. It facilitates the recording of slow potentials arising in taste sensilla, improves the signal to noise ratio, and preserves spike shapes. This new amplifier design combines excellent signal to noise ratio with complete compatibility as regards existing electrophysiological equipment.DC recordings have higher information content than filtered recordings. With DC recordings, spike shapes are not modified and thus better sorting is possible. Moreover, slow variations in the transepithelial potential (i.e. less than 10 Hz) are preserved. Both aspects are of considerable importance when studying the physiology of taste receptors.     

Effect of methoxyphenols on grain aphid feeding behaviour

Methoxyphenols might be important in the resistance of cereals to aphids. Electrical penetration graph (EPG) recordings were used to determine the effect of caffeic, ferulic and sinapic acids, and scopoletin on the feeding behaviour of the grain aphidSitobion avenae (F.). Aphids on wheat seedlings treated systemically with these phenols showed reduced ingestion of phloem sap and salivation into sieve elements in most cases. The earlier pathway phases of probing were prolonged. Moreover increase in number of probes as well as reduction of total time of probing was observed. In addition, no O-demethylase activity was found in homogenates of aphids fed on moderately-resistant (phenolic rich) or susceptible (phenolic poor) wheat varieties. The significance of these results for understanding the resistance of cereals to aphids is discussed.     

Detection of the luteoviruses, beet mild yellowing virus and beet western yellows virus, in aphids caught in sugar-beet and oilseed rape crops, 1990–1993

The incidence of beet mild yellowing luteovirus (BMYV) and non-beet-infecting strains of beet western yellows luteovirus (BWYV) in individual winged aphids, caught in yellow water-traps, in sugar beet during the spring and early summer, and in oilseed rape plots in the autumn, was monitored using monoclonal antibodies in ELISA tests from 1990 to 1993. Between 0% and 8% of the Myzus persicae trapped in sugar beet each year carried BMYV, whereas 0% to 4% caught in oilseed rape in the autumn contained this virus. In 1990, 6.5% of Macrosiphum euphorbiae trapped in sugar beet contained BMYV, but in subsequent years less than 1% were carrying virus. Much higher proportions (26–67%) of the M. persicae tested from sugar beet contained BWYV, and similar proportions tested from oilseed rape (24–45%) also carried this virus in the autumn. In contrast only 3–19% of the M. euphorbiae caught in sugar beet contained BWYV, and none in oilseed rape. In 1991 and 1992 large numbers of Breuicoryne brassicae were caught in the plot of oilseed rape, of which over 50% contained BWYV; none were carrying BMYV. In transmission studies between 1990 and 1992, 1% and 27% of M. persicae transmitted BMYV and BWYV respectively to indicator plants; subsequent ELISA tests on the same aphids showed that 3% and 33% respectively contained the two viruses. One percent of M. euphorbiae transmitted BMYV, but none were found to contain BMYV using ELISA; 15% transmitted BWYV whilst only 5% were found to carry the virus. In 1992 and 1993 the incidence of BMYV-infection in the sugar-beet fields in which aphids had been trapped ranged from 1.2%, in a field which had received granular pesticide (aldicarb) at drilling plus three foliar aphicidal sprays, to 39.5% in a field which had received only one foliar spray. In 1992 in a sugar-beet crop which had received no aphicidal treatments, and where 2.8% of immigrant M. persicae and 2.5% of M. euphorbiae contained BMYV, 11.6% of plants developed BMYV infection. Lowest levels of infection were associated with the use of granular pesticides at drilling. In 1990, 80% of oilseed rape plants in a field plot were infested with a mean of seven wingless M. persicae per plant by mid-December; 37% of these plants were infected with BWYV. The studies show that M. persicae is the principal vector of BWYV, and large proportions of winged M. persicae carry the virus, in contrast to BMYV, which is consistent with the common occurrence of BWYV in brassica crops such as oilseed rape.     

Inheritance of partial resistance to the leaf aphids Macrosiphum euphorbiae and Uroleucon sonchi in lettuce

The genetics of partial resistance (PR) of lettuce to the leaf aphid species Macrosiphum euphorbiae and Uroleucon sonchi was studied in F₁ and F₂ generations of six crosses between four cultivars. Partial resistance inherited mainly additively. With M. euphorbiae the estimates of broad-sense F₂ heritability were low and non-significant in crosses between parents of the same resistance level (S x S and PR x PR), and high (0.69-0.76) in crosses between parents of different resistance level (PR x S). The level of resistance in lettuce cultivars ‘Charan’ and ‘Marbello’ led to a marked reduction in percentage of plants with colonies of M. euphorbiae in a field experiment. With U. sonchi the highest estimates of F₂ heritability were found in ‘Charan x ‘Avoncrisp’ (0.51) and ‘Charan’ x ‘Chou de Naples' (0.48). In the cross ‘Charan’ x ‘Marbello’ (PR x PR) no significant segregation for resistance to M. euphorbiae was found, indicating that these cultivars may have the same genetic constitution for resistance to M. euphorbiae.‘Charan’ has additional genes for resistance to U. sonchi, that are not, or only weakly linked to the gene(s) for resistance to M. euphorbiae. The heritability estimates for the partial resistance to M. euphorbiae and U. sonchi indicate that it is possible to effectively select for these traits in plant breeding programmes.     

Haemolymph plasma composition of the Essig''s lupine aphid, Macrosiphum albifrons Essig (homoptera: aphididae)

Haemolymph from the Essig's Lupine aphid, Macrosiphum albifrons (Essig), was analyzed for pH, osmolality, and concentrations of magnesium, calcium, potassium, sodium, chloride, phosphate and citrate. The concentration of inorganic ions and citrate was relatively low forming only 14% of the osmotic potential of the plasma (476 mOsm). The composition of the plasma resembled more the composition of phytophagous Endopterygota than Exopterygota.