Masters Theses

Date of Award

8-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Jerome F. Grant

Committee Members

Paris L. Lambdin, M. L. Pan

Abstract

Parasitoids can be an important part of a biological control program. The use of freezer-stored pupae has been suggested as a means to rear large numbers of parasitoids for release in biological control programs (Grant and Shepard 1987). Brachymeria ovata (Say) (Hymenoptera: Chalcididae) has been reared successfully from freezer-stored pupae of several noctuid species of lepidoptera (Grant and Shepard 1987); however, it was not known if the use of freezer-stored pupae as hosts of B. ovata had any affect on the biological characteristics of this parasitoid.

A colony of B. ovata was maintained, and all experiments were conducted, utilizing the pupae of the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). Experiments were conducted at 27±2°C and 50 to 65%RH.

The mating ability of individuals reared from freezer-stored pupae was not significantly impacted; however, a slight decrease in successful matings was observed when males were reared from freezer-stored pupae. The mean preovipositional period increased when individuals were reared from freezer-stored pupae. B. ovata generally parasitized pupae during the hours of light. The greatest number of parasitoids were produced during the first four-hour period of light and the number of progeny produced decreased throughout the day.

Unmated female B. ovata individuals not exposed to hosts generally lived longer (114.0 and 135.8 days, respectively, when reared from live and freezerstored pupae) than unmated males (approximately 100 days), and those females reared from freezer-stored pupae lived significantly longer than females reared from live pupae. Paired adults lived for shorter periods than unmated B. ovata. Longevity of paired females exposed to live pupae was significantly shorter (approximately 15 days) than the longevity of males or females not exposed to live or freezer-stored pupae (approximately 60 to 86 days, respectively).

Fecundity of B. ovata increased when females were exposed to freezerstored pupae. Those females reared on and exposed to freezer-stored pupae produced the greatest number of eggs (x =422.2). Females exposed to live pupae lived one fourth to one third as long when reared from live or freezerstored pupae, respectively, and produced an average of 91.3 and 137.2 eggs, respectively.

Progeny production was significantly decreased when females were exposed to freezer-stored pupae. Females produced an average of 83.3 and 79.1 progeny when reared from live or freezer-stored pupae, respectively, and exposed to live pupae during their entire lifetime. Females exposed to freezerstored pupae produced significantly fewer progeny (x=31.9 and 37.3, respectively, when reared from live or freezer-stored pupae) during the first 14 days of oviposition. As the fecundity of individuals exposed to freezer-stored pupae is greater than that of ones exposed to live pupae, the potential exists for greater progeny production from females exposed to freezer-stored pupae.

The acceptability of freezer-stored pupae was significantly lower than that of live pupae in terms of the percentage of pupae containing eggs (88.2% of live pupae and 71.4% of freezer-stored pupae) but the average number of eggs per pupa was not significantly different. The suitability of live and freezer-stored pupae in terms of the percentage of pupae supporting development of B. ovata to adulthood was significantly higher for live pupae (85.5%) than for freezer-stored pupae (23.0%) Higher levels of suitability were observed in other experiments utilizing freezer-stored pupae.

The suitability of different age pupae, at time of freezing, and of live pupae also, was determined to be from two to five days after pupation. Many individuals reared on older pupae were smaller than those reared on pupae two to five days old. The production of small adults was probably a result of having less food available to the larva. The development of immature stages of B. ovata in freezer-stored pupae was lengthened from two to five days in the larval stage and about one day in the pupal stage.

Overall freezer-stored pupae did not detrimentally impact upon the biological characteristics of B. ovata. With increased suitability of freezer-stored pupae as observed in some experiments conducted in this study as well as others (Grant and Shepard 1987), it should be economically advantageous to use freezer-stored pupae as a host for B. ovata.

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