Effects of irradiation on Planococcus minor (Hemiptera: Pseudococcidae)

Quarantine Disinfestation of Papaya Mealybug, Paracoccus marginatus (Hemiptera: Pseudococcidae) Using Gamma and X-rays Irradiation

Paracoccus marginatus is a highly polyphagous invasive pest that poses a significant quarantine threat to tropical and subtropical countries. Infested commodities in international trade should undergo phytosanitary treatment, and irradiation is recommended as a viable alternative to replace methyl bromide fumigation. Dose-response tests were conducted on the 2-, 4-, and 6-day-old eggs and gravid females of P. marginatus using the X-ray radiation doses of 15-105 Gy with an interval of 15 Gy. Radiotolerance was compared using ANOVA, fiducial overlapping and lethal dose ratio (LDR) test, resulting in no significant difference among treatments, except for the overall mortality and LDR at LD90 (a dose causing 90% mortality at 95% confidence level). The estimated dose for LD99.9968 was 176.5-185.2 Gy, which was validated in the confirmatory tests. No nymphs emerged from a total of 60,386 gravid females exposed to a gamma radiation dose range of 146.8-185.0 Gy in the confirmatory tests. The largest dose in confirmatory tests should be the minimum threshold for phytosanitary treatment, consequently, a minimum dose of 185 Gy is recommended for the phytosanitary irradiation treatment of papaya mealybug-infested commodities, ensuring a treatment efficacy of ≥99.9950% at 95% confidence level.

Irradiation-induced sterility in an egg parasitoid and possible implications for the use of biological control in insect eradication

Classical biological control is a pest control tool involving the release of imported natural enemies. The Sterile Insect Technique (SIT) comprises releasing sexually sterile insects of a pest into the wild population for suppression or eradication. Both these approaches are environmentally friendly and their combination can result in a synergistic impact on pest populations and improve eradication. However, stringent regulation surrounding the introduction of biological control agents limits their use in eradication owing to the perceived risk of effects on non-target organisms. We investigated the irradiation biology of the egg parasitoid Trissolcus basalis to ascertain whether sterile parasitoids could mitigate the risk of potential sustained non-target impacts. Mated female T. basalis were gamma-irradiated at doses between 120 and 150 Gy and exposed to egg masses of their host Nezara viridula throughout their lifespans. This resulted in host mortality, despite a substantial reduction in developing parasitoid offspring, which followed a negative dose-response. There was no emergence of parasitoid offspring at 140 Gy and above. Irradiation did not affect oviposition behaviour but caused an increase in longevity. Consequently, sterile parasitoids could possibly alleviate concerns regarding the irreversibility of biological control release, which promotes further investigation of their potential role in eradication.

Effects of X-Ray Irradiation on the Eggs and Females of Dysmicoccus lepelleyi (Hemiptera: Pseudococcidae)

The mealybug of Dysmicoccus lepelleyi Betrem (Hemiptera: Pseudococcidae) attacks a wide range of fruits, vegetables, and ornamental plants and is categorized as a quarantine pest in China. Utilization of phytosanitary irradiation (PI) as a potential treatment to disinfest agricultural commodities in trade (which has expanded rapidly in the recent years) and preventing the hatch of F1 generation eggs is used as a criterion for the PI treatment of mealybugs. A RS-2000 Pro X-ray irradiator (Rad Source Technologies, Inc.) was used to treat the gravid adult females and eggs of the mealybug. The primary tests were conducted to explore the minimum dose for preventing egg-hatch from the irradiated adult females, resulted in a 1.69% of eggs hatched from 100 Gy-irradiated adult females and no crawler developed as treated at the dose of 110 and 120 Gy. To estimate the minimum dose for preventing egg-hatching, the dose-response tests were conducted for 1-, 2-, and 3-d-old eggs at the dose of 20, 40, 60, 80, 100, and 120 Gy, respectively. The results showed that the radio-tolerance increased very slowly with developmental times of eggs, and the estimated dose for 99.9968% mortality at the 95% confidence level (Probit 9) by Probit analysis is 146.2, 155.7, and 156.1 Gy for 1-, 2-, and 3-d-old eggs, respectively. Therefore, dose range between 110 and 160 Gy could be efficient to prevent the reproduction of this mealybug.

Factors affecting ionizing radiation phytosanitary treatments, and implications for research and generic treatments

Phytosanitary irradiation (PI) treatments are promising measures to overcome quarantine barriers to trade and are currently used in several countries. Although PI has advantages compared with other treatments one disadvantage bedevils research, approval, and application: organisms may remain alive after importation. Although this does not preclude their use as a phytosanitary treatment, it does leave the treatment without an independent verification of efficacy and places a greater burden for assuring quarantine security on the research supporting the treatment. This article analyses several factors that have been hypothesized to affect PI efficacy: low oxygen, pest stage, host, dose rate, and temperature. Of these factors, the first is known to affect efficacy, whereas host and dose rate probably need more research. The International Plant Protection Convention considered several PI treatments for its international standard on phytosanitary treatments and did not approve some at first because of perceived problems with the research or the presence of live adults after irradiation. Based on these concerns recommendations for research and dealing with the issue of live adults postirradiation are given. Generic PI treatments are suggested.