Tritrophic effects on survival and development in a Coccidophagous coccinellid.

Chilocorus nigritus is currently considered one of the most successful biological control agents of armoured scale insects. However, establishment of this beetle in crop pest situations has not always been successful and there are still gaps in our knowledge of its ecology and behaviour. The research involved an examination of tritrophic effects on the survival and development of this common diaspid predator. The effect of a forced change in host plant on the developmental time of the juvenile stages was also examined. The prey and host plants used were the armoured scales Aspidiotus nerii Bouché Homoptera: Diaspididae and Abgrallaspis cyanophylli (Signoret) Homoptera: Diaspididae, on potatoes (Solanum tuberosum L.) and Butternut squashes (Cucurbita moschata Duchesne ex Lamarck). C. nigritus eggs were incubated on four treatments of scales on potatoes or squashes for ten days, half the second instar larvae were then switched to the same scales on the other host plant. Daily observations were made during development to adult emergence. C. nigritus larvae survived and completed development on two species of diaspid scales and the two host plants examined with varying levels of success. Larvae were able to switch from feeding on A. nerii on potatoes to A. nerii on squashes or A. cyanophylli on potatoes to A. cyanophylli on squashes and vice versa with little or no deleterious effects when compared to those beetles reared on one prey and host plant throughout. There were significant differences in survival of larvae reared to the adult stage on both A. nerii and A. cyanophylli on potatoes when compared to larvae reared on these scales on squashes. Squash appears to be a less desirable and potato a more favourable host plant for survival and development. The results have implications for rearing programmes, and the release and establishment of C. nigritus, in fields and glasshouses where scale pests may be present on a variety of host plants, or may be on host plants different to those used in the insectary.

Landing responses of Anopheles gambiae elicited by oxocarboxylic acids.

A wind tunnel bioassay and video system were used to observe Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) landing on glass cylinders, heated to human skin temperature (34 degrees C) and treated with aqueous solutions of oxocarboxylic acids. Six of nine compounds tested: 2-oxobutanoic, 2-oxo-3-methylbutanoic, 2-oxopentanoic, 2-oxo-3-methylpentanoic, 2-oxo-4-methylpentanoic and 2-oxohexanoic elicited significant landing responses in comparison to a water control. Landing responses appeared to be restricted to C4-C6, 2-oxocarboxylic acids. A solution of 1 microg/microL of 2-oxopentanoic acid elicited the highest level of response that was temperature dependent: significant numbers of landings occurred only within +/-2 degrees C of human skin temperature. Chemical analysis by linked gas-liquid chromatography/mass spectrometry of methyl-oxime, trimethylsilyl derivatized samples of human sweat extracts revealed the presence of 2-oxopropanoic (pyruvic) acid and three behaviourally active, branched chain acids: 2-oxo-3-methylbutanoic, 2-oxo-3-methylpentanoic and 2-oxo-4-methylpentanoic.