High hydrostatic pressure induces synthesis of heat-shock proteins and trehalose-6-phosphate synthase in Anastrepha ludens larvae.

The Mexican fruit fly (Anastrepha ludens) is responsible for losses of up to 25% of crops such as mango and citrus fruits in Central America and México. The larval life cycle of A. ludens comprises three stages with a duration ranging from 3 to 8 days. Because of the damage caused by A. ludens, several methods of control have been studied and implemented. High hydrostatic pressures (HHP) are currently applied to foods and it is now proposed to be employed to inactivate eggs and larvae of A. ludens. Originally HHP was designed to inactivate microorganisms, since it exerts marked effects on cell morphology, and can affect enzymatic reactions and genetic mechanisms of microbial cells, with no major changes altering the sensory or nutritional quality of the foodstuff. In this study, A. ludens in two larval stages (5- and 8-day-old) were subjected to HHP treatments. The biochemical response of the larvae of A. ludens was dependent on their stage of development. The third larval stage (L3) developed a better protection mechanism based on the synthesis of stress proteins or heat-shock proteins (HSPs) and the enzyme trehalose-6-phosphate synthase, which are linked and possibly act together to achieve greater survivability to stress caused by hydrostatic pressure.

Resistance of Mexican fruit fly to quarantine treatments of high-pressure processing combined with cold.

Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae) is one of the most important insects infesting fruits. Although high pressure has been proposed as an alternative quarantine process for this pest, conditions applied to destroy eggs and larvae can also damage the fruits. The objective of this study was to assess the biological viability of A. ludens eggs treated by high-pressure processing at 0°C, establishing whether nondestroyed eggs and larvae preserved their ability to develop and reproduce. One-, 2-, 3-, and 4-day-old eggs were pressurized at 50, 70, or 90 MPa for 0, 3, 6, or 9 min. The hatching ability of pressurized eggs and their capacity to develop larvae, pupae, and reproductive adults were evaluated. The ability of pressurized larvae to pupate was also registered. The results showed that most of the eggs that resisted the treatments were able to produce adults with capability to reproduce a new generation of A. ludens flies. Larvae were less resistant than eggs. All larvae were killed at 90 MPa for 9 min. The pressure induced the expression of heat shock proteins (HSP) in second- and third-instar larvae. The HSP showed a baroprotective effect in A. ludens larvae. These results are relevant to the industry because they show that eggs of insects infesting fruits treated by high-pressure processing were able to pupate after treatments. This indicates that efforts must be addressed to destroy all eggs because most of the surviving organisms could reach an adult stage and reproduce.