Life history parameters and biocontrol potential of the mealybug parasitoid Coccidoxenoides peregrinus (Timberlake) (Hymenoptera: Encyrtidae): Asexuality, fecundity and ovipositional patterns

Properties relevant to the ovipositional activity and lifetime productivity of Coccidoxenoides peregrinus (Timberlake) were assessed in the laboratory, to determine the potential of this species as a biocontrol agent against the citrus mealybug, Planococcus citri (Risso). In general, this species has not performed well in orchards, except for a few localities on different continents. The mode of reproduction of C peregrinus is almost entirely thelytokous, with males produced sporadically and at low frequency. The females have both pro-ovigenic and synovigenic traits, which raises questions of the utility of this distinction. The females have a high reproductive potential with 10-20 eggs per day available within the first two days (after a short (12 h) pre-oviposition period), and 80-150 eggs per day thereafter until death at about eight days. Mean lifetime fecundity was 239.2 +/- 34.3 eggs. C peregrinus oviposits across a range of P. citri instars, but productivity relies predominantly on second instar hosts. Second stage (N2) hosts received most eggs in choice (about 52%) and no-choice (about 50%) tests. Most eggs deposited into N2 hosts (82%) reached adult stage whereas only a few of those deposited into N1 and N3 (about 5% each) developed successfully. The haemolymph of parasitised reproductive mealybugs contained granular structures and no parasitoid eggs were found 24 h after exposure to ovipositing wasps. Also, no wasps emerged from parasitised adult hosts that were kept alive. Parasitoid eggs deposited into adult hosts were presumed encapsulated and destroyed, as control mealybugs (not exposed to female wasps) had no granular structures in their haemolymph. Wasps exposed to an abundance of hosts soon started ovipositing, but only for a relatively short time each day (about 2.5 h out of a 7 h exposure). They stopped ovipositing despite eggs judged to be mature in their ovaries. The reproductive output of C peregrinus is discussed in relation to the ecological factors that could influence this output, and the implications for biocontrol are discussed. (C) 2003 Elsevier Inc. All rights reserved.

Manipulating avocado fruit ripening with 1-methylcyclopropene

Previous investigations with 1-methylcyclopropene (1-MCP) on avocado (Persea americana Mill.) fruit have focussed mainly on improving storage life by reducing the severity of disorders causing discolouration of the flesh. Development of 1-MCP and ethylene treatments, which also help control the time to reach the eating ripe stage, may confer additional practical benefits. In this context, the current study investigated the potential of 1-MCP to accurately manipulate ripening of non-stored 'Hass' avocado fruit by treatment before or after ethylene and at different times during ripening. To investigate this, 500 nL L-1 1-MCP was applied within 1 day after harvest, followed by ethylene 0-14 days after 1-MCP. In addition, fruit were treated with ethylene, then 1-MCP 0-8 days after ethylene. Treatment of fruit with 500 nL L-1 1-MCP for 18 h at 20 degreesC provided the maximum effect by increasing the days from harvest to ripe (DTR) from 8 (with no 1-MCP) to 20. Fruit treated with 500 nL L-1 1-MCP for 18 h at 20 degreesC remained insensitive to 100 muL L-1 ethylene applied between 0 and 14 days after 1-MCP for 24 h at 20 degreesC. Ripening of fruit exposed to 100 muL L-1 ethylene for 24 h at 20 degreesC could be delayed by up to 3.3 days by applying 500 nL L-1 1-MCP for 18 h at 20 degreesC up to 2 days after ethylene treatment. However, once the fruit started to soften (sprung) there was little effect of 1-MCP on DTR, compared with no 1-MCP. 1-MCP treatment was associated with increased severity of body rots (caused mainly by Colletotrichum spp.) and stem-end rots (caused mainly by Dothiorella spp.), which was likely due to the increased DTR in these treatments. Significant differences in disease severity were found between orchards (replications), with replicates with low disease severity being less affected by 1-MCP treatment. These results indicate that 1-MCP can delay ripening, but careful sourcing of fruit is required to reduce the risk of diseases in ripe fruit. There is some capacity to delay ripening using 1-MCP after ethylene. There is little potential to control ripening using ethylene after treatment with 500 nL L-1 1-1-MCP, but lower concentrations may be more effective. (C) 2004 Elsevier B.V. All rights reserved.

Between-tree variation in fruit quality and fruit mineral concentrations of Hass avocados

Inconsistent internal fruit quality in Hass avocados affects consumer confidence. To determine the influence of individual trees on fruit quality, Hass avocado fruit were harvested from adjacent trees of similar external appearance in 3 commercial orchards in 1998 and 1 orchard in 1999. The trees in each orchard were grown with similar commercial practices and in similar soil types. Within each location, there were significant (P < 0.05) differences in the mean ripe fruit quality between trees with respect to fruit body rot severity ( mainly anthracnose) with and without cold storage, internal disorders severity due to diffuse discolouration and vascular browning ( after cold storage), days to ripen, percentage dry matter, and the percentage of the skin area with purple-black colour when ripe. These effects were also noted in the same orchard in 1999. There were significant (P < 0.05) differences in fruit flesh calcium, magnesium, potassium, boron and zinc concentrations between trees. Significant (P < 0.05) correlations were observed between average fruit mineral concentrations in each tree ( particularly calcium, magnesium and potassium) and body rot severity, percentage dry matter and fruit mass. There was little conclusive evidence that characteristics such as the growth of the non-suberised roots or the degree of scion under- or overgrowth was involved in these tree effects; however, differences between trees with respect to other rootstock characteristics may be involved. The inconsistency of the correlations across sites and years suggested that other factors apart from tree influences could also affect the relationship between fruit minerals and fruit quality.