|Harbison, Jacque - TEXAS A&M EXPT STATION|
|Fabritius, Stephanie - SW UNIV., GEORGETOWN, TX|
|Saldana, Robert - TEXAS A&M UNIV EXP STAT.|
|Legaspi, JR., Benjamin - TEXAS A&M UNIV EXP STAT.|
|Enkegaard, A - DANISH INST. AG SCI DENMK|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2000
Publication Date: February 1, 2001
Interpretive Summary: The Mexican rice borer (MRB), Eoreuma loftini is a major insect pest of sugarcane causing an estimated loss of $10-20 million annually in south Texas. Since the MRB tunnels inside the sugarcane stalk, chemical insecticides have not been an effective control method. Biological control (use of insect parasites) is currently one of the main tactics used to control the MRB. We studied the biology of an important parasite o the MRB, Allorhogas pyralophagus. We examined the effects of parasite age and numbers of MRB available, on the attack rates and reproduction of A. pyralophagus. Different numbers of fifth-stage larvae of MRB were exposed to female parasites ranging in age from 5 to 12 days old. Parasites were allowed 24 hrs to attack the MRB after which they were removed. The numbers of newly laid egg parasites, numbers and sex of the parasites that emerged, and numbers of MRB attacked were recorded. We found that parasite age and dnumbers of MRB available, affected the attack rates of A pyralophagus. The attack rate declined with the increasing age of the parasite and numbers of MRB. The percentages of parasite eggs that hatched and female parasite adults that emerged were not affected by parasite age, remaining to be mostly females. The numbers of eggs laid and the attack rates of A. pyralophagus are highest in young adult females (about 6 days old). Although young females laid about 20 eggs daily, maximal attack rate was only approximately two MRB larvae per day, suggesting that the parasite may be ineffective as a control agent unless very high numbers are used and may require other complementary insect pest suppression techniques.
Technical Abstract: Laboratory studies were conducted to determine the effects of parasitoid age and numbers of hosts available on selected attributes of parasitoid reproduction. Newly-emerged mated females of the gregarious parasitoid Allorhogas pyralophagus Marsh (Hymenoptera: Braconidae) were divided into groups ranging in age from 5 to 12 d. For each age class, individual females were exposed to 1, 2, 4, and 8 hosts of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Pyralidae) over a 24-h period. For each age class, numbers of eggs laid and hosts attacked were fitted to nonlinear oviposition models and Type II functional response curves, respectively. Numbers of eggs laid per female per day was highest at about 20 eggs per day in 6-d old females, declining to about 5 per day in 12-d old females. The functional response curves showed declining attack rates with time, from about 2.0 hosts per day in 5-d old females, to about 1.0 in n12-d old parasitoids. Percentage progeny emergence was not affected by either parasitoid age or numbers of hosts available. Percentage of female progeny also was not affected by parasitoid age, remaining female-biased.