Robert L. Mangan

Tolerance of grapefruit and Mexican fruit fly larvae to heated controlled atmospheres

Abstract The potential for disinfesting grapefruit (Citrus paradisi Macf.) of Mexican fruit fly by heating the fruit in a controlled atmosphere was evaluated by comparing larval mortality and fruit quality after heat treatments with or without altered levels of oxygen and carbon dioxide. The mortality of third instar, Anastrepha ludens (Loew) larvae was significantly higher when larvae were heated at 44 °C in 1% oxygen for 2 h than when larvae were heated for the same amount of time at the same temperature in air or in air enriched to 20% carbon dioxide. Reducing the concentration of oxygen to 1 from 21% (air) during a heat treatment resulted in a 30% shorter exposure time (3.5 vs. 5 h) to achieve 100% larval mortality. The concentrations of oxygen and carbon dioxide inside the grapefruit during exposure to 46 °C were significantly different when the fruit were exposed to low oxygen, air, or high carbon dioxide during heating. Inconsistent fruit quality results warrant further study to optimize controlled atmosphere conditions during heating.

Postharvest disinfestation heat treatments: response of fruit and fruit fly larvae to different heating media.

Abstract The surface heat transfer efficiency of three heating media (water, and forced air with and without a water vapor-pressure deficit) was compared using four commodities: mango, papaya, grapefruit, and orange. Forced vapor-saturated-air (VFA), and water (HW) transferred heat most efficiently to the fruit surface. Thermal stress to the fruit was greatest during heating in VFA. Thermal diffusivity of fruit corresponded to fruit density, and was highest for papaya and mango. Differences in the oxygen (O 2 ) and carbon dioxide (CO 2 ) concentration inside grapefruit were apparent among those exposed to an identical heat dose in HW, forced water vapor-pressure deficit air (MFA), or a forced, vapor-pressure deficit atmosphere of 1 kPa O 2 with 20 kPa CO 2 (MFCA). The altered atmosphere that developed inside fruit during heating in HW or MFCA was shown to enhance efficacy of heat as a disinfestation treatment. Results from this research suggest that heating in an atmosphere that inhibits fruit respiration does not in itself predispose a fruit to injury. The water vapor pressure of the atmosphere used to heat a commodity influences the thermal stress delivered to that commodity during heating. Forced, water vapor-pressure-deficit atmospheres with altered levels of O 2 and or CO 2 have commercial potential for providing quicker, less severe heat disinfestation treatments.

Multimodal Cues Drive Host-Plant Assessment in Asian Citrus Psyllid (Diaphorina citri)

ABSTRACT Asian citrus psyllid (Diaphorina citri) transmits the causal agent of Huanglongbing, a devastating disease of citrus trees. In this study we measured behavioral responses of D. citri to combinations of visual, olfactory, and gustatory stimuli in test arenas. Stimuli were presented to the psyllids in droplets or lines of an emulsified wax formulation in two different arena types in no-choice tests. First, when placed on a colored ring situated halfway between the center and perimeter of a petri dish, D. citri spent more time on yellow versus gray rings; however, this response disappeared when either gray or yellow wax droplets were applied. When the psyllids were presented with droplets scented with terpenes, the response to both scent and color was increased. The addition of a dilute (≈0.1 M) sucrose solution to the wax droplets increased the magnitude of D. citri responses. Next, groups of D. citri were placed on plastic laboratory film covering a sucrose solution, to mimic a leaf surface. Test stimuli were presented via two ‘midribs’ made from lines of emulsified wax formulation. Probing levels were measured as a function of color saturation and scent composition, and concentration. The test scents were based on qualitatively major volatiles emitted by Murraya paniculata (L.) Jack, Citrus aurantifolia (Christm.) Swingle, and C. sinensis (L.) Osbeck. The highest probing response was observed on the middle concentration (20-µl scent/10 ml wax formulation) of the C. aurantifolia-scented wax lines. Results indicate that there are interactive effects between the different sensory modalities in directing host-plant assessment behavior.

Changes in free amino acids and polyamine levels in Satsuma leaves in response to Asian citrus psyllid infestation and water stress.

The effects of biotic and abiotic stresses on changes in amino acids and polyamine levels in Satsuma orange (Citrus unshiu; cultivar Owari) leaves were investigated. Asian citrus psyllids Diaphorina citri (Kuwayama) (ACP) infestation was used to induce biotic stress while a water deficit was imposed to induce abiotic stress. Potted trees were infested by placing 50 psyllids on 3 citrus leaves enclosed in nylon mesh bags for 5 d. A parallel set of plants were kept water stressed by maintaining the soil at 20% water holding capacity for 5 d. Levels of total free amino acids were higher in water stressed and ACP infested leaves. Polyamine putrescine increased in infested leaves but not in water stressed leaves. Proline was the most abundant amino acid and its levels significantly increased by both biotic and abiotic stresses. Proline levels in infested leaves were significantly higher than the water stressed leaves. Histidine, methionine, asparagine, arginine, serine, and leucine levels also increased significantly in infested leaves, but in water stressed leaves only leucine, methionine, and threonine increased. Levels of amino acids, such as tyrosine, isoleucine, phenylalanine, glutamic acid, and alanine, declined in infested leaves. Under water stress asparagine, phenylalanine, serine, and histidine also declined compared to controls. This indicates that while proteolysis occurred under both stresses, metabolic conversion of amino acids was different under the two stresses. In ACP infested leaves some amino acids may be used as feeding material and/or converted into secondary metabolites for defense.

Age Estimation of Mexican Fruit Fly (Diptera: Tephritidae) Based on Accumulation of Pterins

Abstract A common method of aging adult flies, fluorescence spectrometry, was used to monitor the increase of overall pterine titer in head extracts of Anastrepha ludens (Loew). Accumulation of fluorescent compounds was measured as a function of chronological age of flies maintained at 17 and 27°C. Although relative fluorescence increased with age, field studies revealed that this phenomenon could not be used for accurate age estimation, as relative fluorescence did not increase predictably with age over the entire life span. Accumulation of individual pterins, deoxysepiapterin and sepiapterin, were studied in a similar manner. These two specific compounds were separated by high-pressure liquid chromatography and their accumulation was followed at 15 and 30°C in the laboratory and under caged field conditions. While titer of deoxysepiapterin increased steadily in a curvilinear fashion, sepiapterin quickly reached a maximum and then maintained a constant level for the rest of the life of the flies. Based on the physiological response of deoxysepiapterin to chronological time and ambient thermal conditions, this compound was determined to be an age specific biological parameter for the Mexican fruit fly and should allow age estimation in field-collected flies.