Comparative Biology of Three Geographic Populations of Trissolcus Basalis (Hymenoptera: Scelionidae)
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Comparative Biology of Three Geographic Populations of Trissolcus basalis (Hymenoptera: Scelionidae) M. S. AWAN, L. T. WILSON,' AND M. P. HOFFMANN Department of Entomology, University of California, Davis, California 95616 Environ. Entomol. 19(2): 387-392 (1990) ABSTRACT Laboratory studies were conducted to determine if there were biological or behavioral differences among populations of Trissolcus basalis (Wollaston) (Scelionidae: Hymenoptera) collected from France, Italy, and Spain. Observations of isolated and mated females indicated little difference in fecundity, adult longevity, male and female progeny produced, length of oviposition period, and percentage of parasitism of Nezara uiridula (L.) (Heteroptera: Pentatomidae) eggs. Females from all locations showed greater fecundity and rates of parasitism during the first week after emergence. The French population showed a significantly higher emergence rate from N. uiridula eggs than those from Italy or Spain. When male T. basalis were continuously present with females, fecundity, number of male progeny, and percentage of parasitism were significantly higher than when females were isolated. Over the lifetime of T.basalis females, the sex ratio of adult progeny favored female; however, there was a progressive shift from predominantly female to male progeny as the female aged. Adult males lived longer than females. No significant differences in adult male or female longevity were detected across geographic populations. However, the Italian pop- ulation took significantly more time to complete immature development than the French or Spanish population. N. vtridula egg mortality was significantly higher when female T. basalis were continuously present than when absent, indicating that parasites may cause some mortality in addition to that resulting from parasitism. There were no significant differences in mating, egg selection, or oviposition times among the geographic populations. Females from Italy spent significantly less time in marking N. utridula eggs than those from Spain or France. The results of these studies suggest that the three populations compose a single T. basalis biotype. KEY WORDS Insecta, Trissolcus, Nezara, biotype THE SOUTHERN GREEN STINK BUG, NE" ViridUkJ based on material obtained from Australia with (L.) (Heteroptera: Pentatomidae), is a serious pest introductions into New Zealand in 1949 (Cumber of many agricultural and horticultural crops in var- 1951) and to Hawaii in 1962 (Davis 1964). Tri- ious parts of the world. It occurs in most tropical chopoda pennipes (F.) (Diptera: Tachinidae), a and subtropical regions of the world and causes parasite of adult N. viridula, was also introduced damage to a wide variety of fruit, nut, grain, and into these locations, but only proved effective in vegetable crops (Todd & Herzog 1980).N. viridula Hawaii. Reports on the results of these introduc- was first officially recorded in the Sacramento Val- tions show satisfactory to outstanding control of N. ley of California in 1986 (Hoffmann et al. 1987) viridula (Caltagirone 1981). and in the absence of effective natural enemies, is Although T. basalis occurs with N. viridula in a potentially serious threat to many crops through- the United States, it does not provide consistent out California. Since its arrival, populations have control of this pest on susceptible crops (Jones 1988). been found feeding on weeds and several crops, Several biological characteristics contribute to the particularly tomatoes (Table 1). success of a biological control agent at the popu- Trissolcus basalis (Wollaston), an egg parasite lation level. These include searching ability, fe- of N. viridula, has shown considerable promise in cundity, general dispersal ability, and, in the case its ability to regulate N.viridula populations below of biparental populations, sex ratio (Caltagirone economically damaging levels. T. basalis was in- 1985). How well an organism performs also de- troduced into Australia from Egypt in 1933 and pends on its genotype and the environment. As a provided effective control in coastal areas. A later component of a pest management program aimed introduction of T. basalis from Pakistan proved at managing pentatomid pests of tomatoes in Cal- successful in inland areas (Ratcliffe 1965). Subse- ifornia, T. basalis was obtained from France, Italy quent biological control programs were initiated and Spain by the USDA-ARS European Parasite Laboratory, Behoust, France. This paper presents the results of laboratory experiments, where we I To whom reprint requests should be sent. Current address: Department of Entomology, Texas A&M University, College Sta- quantify and compare several biological and be- tion, Tex. 77843. havioral parameters including immature devel- 0046-225X/90/0387-0392$02.00/00 1990 Entomological Society of America 388 ENVIRONMENTAL ENTOMOLOGY Vol. 19, no. 2 opmental time, fecundity, adult longevity, sex ratio Table 1. Host plant records of N. viridula in the Sac- of progeny, length of oviposition period, percent- ramento Valley of California age of host parasitism, mating, egg selection, ovi- Family Genus Common name position, and egg marking times. ~~ Amaranthaceae Amaranthus Pigweed C henopodiaceae Salsola Russian thistle Materials and Methods Chenopodium Lambsquarters Asteraceae Hebanthus Sunflower Insect Colonies. Colonies of T. basalis from Stlybum Milk thistle Convolvulaceae Ipomoea Morning glory France, Italy, and Spain were maintained in glass- Brassicaceae Brassica Broccoli topped wooden sleeve cages (46 by 46 by 76 cm) Cucurbitaceae Cucurbita Pumpkin at 27 k 2°C and a 16:8 (L:D) photoperiod; they Cucurbita Squash were provided N. viridula eggs as host material Poaceae Zea Sweet corn Fa baceae Phaseolus Beans three to four times per week. In these colonies and Malvaceae Malva C heeseweed throughout all the various studies, adult T. basalis Hibiscus Okra were provided with fresh honey droplets daily. Rosaceae Rubus Raspberry Because low relative humidity may reduce the rate Ru taceae Citrus Orange Solanaceae Solanum Egg plant of T.basalis emergence from N.viridula eggs (Orr Solanum Nightshade et al. 1985),parasitized N. viridula egg masses were L ycopersicon Tomato placed upon a moistened filter paper within a plas- tic Petri dish when within two to three days of emergence. As T.basalis emerged, they exited the of stink bug nymphs and parasite adults. Tests were Petri dish through a small hole in the cover and replicated using 10 individuals of each sex. dispersed in the sleeve cage. Mated Females Plus Males. To determine if the The N. viridula colony was maintained in sleeve continuous presence of a male influenced the re- cages and in 3.8-liter ice cream cartons with mos- productive biology of the female, a second exper- quito netting tops. Stink bugs were provided with iment was conducted, which was identical to the fresh green beans, Phaseolus vulgaris (L.),and sun- above, but a male was present at all times. This flower, Helianthus annuus (L.), seeds every two was done only with the Spanish T. basalis and is days. Paper toweling was provided as an oviposi- referred to as the Spanish I1 treatment. tion substrate and replaced daily. The N. uiridula For the female and male experiments, the con- colony was kept on a laboratory bench at 22 k 2°C tents of each capsule were examined at least 2 wk and 16:8 photoperiod. after T. basalis oviposition. For females, data re- corded included the number of nymphs, host eggs that had been cannibalized (egg contents removed by adult bugs in colony), unhatched stink bug eggs Parasite Biology (unknown cause of death), emerged male and fe- Developmental Time. Developmental times for male T. basalis, partially emerged but dead par- immature T. basalis were recorded by exposing asites, and eggs that were parasitized but from five 1- to 2-d-old N. viridula egg masses to T. which no parasites emerged. This last category was basalis females for 24 h. These egg masses were determined by removing the operculum from N. held at 27 k 1°C: and observed daily until all par- viridula eggs that appeared parasitized (black). If asites completed emergence. a parasite was observed, the data were combined Mated Females Alone. For the various experi- with the partially emerged category. All N. viri- ments, adult T. basalis were obtained by holding dula eggs from which a parasite emerged or which parasitized N. viridula egg masses in sealed Petri contained a parasite that did not emerge were in- dishes until emergence. Newly emerged parasites cluded in percentage of parasitism and fecundity were released in a sleeve cage and kept there for per female calculations. Cannibalized eggs and eggs 2 d to allow sufficient time for mating to occur. A that died from unknown causes were excluded from single female was selected and placed in a 52-ml these calculations. clear plastic vial with an 8-12-h-old N. viridula egg mass. Every 24 h the old egg mass was removed and a new egg mass added to the vial. This process Egg Mortality continued until the death of a female parasite. This To determine if N. viridula egg mortality of experiment provided the mated female longevity unknown cause was associated with the presence and fecundity information. Single mated male par- of female T.basalis, a comparison of egg mortality asites were likewise isolated to estimate longevity, in the presence or absence of females was made. but no egg masses were present. Nonvented vials T. basalis females were held with N. viridula egg were placed in chambers held at 27 k 1°C and masses and data recorded as in the above studies. 16:8 photoperiod and 85 k 10% RH. Egg masses The control treatment was identical. but without that had been exposed to T. basalis were placed parasites. The comparison was conducted until individually in gelatin capsules (size 000) and held death of the first female at day 26 with each treat- in the same chambers until emergence and death ment replicated four times. I. ," I I April 1990 AWAN ET AL.: THREE POPULATIONS OF Trissolcus basalis 389 Parasite Behavior not record the sex of adults as they emerged, male generally have relatively shorter devel- Mating Time.