Exploring Nectar Sources for Wasps That Kill Mole Crickets Identifying Nectar Sources Could Help Spread This Biological Control of Mole Crickets
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Sponsored ResearchYou Can Use Exploring Nectar Sources for Wasps That Kill Mole Crickets Identifying nectar sources could help spread this biological control of mole crickets. BY DAVID W. HELD AND C. M. ABRAHAM An adult Larra bicolor wasp feeds on the white fl owers of Pentas lanceolata. OBJECTIVES: Start Date: 2006 This creates an opportunity for golf Determine the seasonal life history course superintendents in this area to • Project Duration: Three years of Larra bicolor in the northern Gulf utilize this biological control agent. Coast. Total Funding: $29,232 This project is the fi rst empirical • Determine the suitability of fl ower- research on Larra bicolor conducted out- ing plants as nectar sources for Larra side of Florida, and it is necessary to bicolor. arra bicolor, an introduced parasitic determine the seasonal fl ight period in • Determine if incorporating wild- wasp of mole crickets, has spread the extended range of this wasp. fl owers on golf courses will facilitate L into the northern Gulf Region From 2006 to 2008, wasps were the establishment of Larra wasps on (Mississippi and Alabama) from where monitored on four sites in south those sites. it was originally introduced in Florida. Mississippi. Across all sites, wasps were 12 GREEN SECTION RECORD The wasp egg hatches in about one week, after which the wasp larva feeds externally on the host mole cricket. generally active during June through block design. Only two taxa, Pentas tiles as a way to collect specimens for October, with an additional month of and Spermacoce, were visited by L. bicolor. research or to passively monitor the activity in fall 2007. This seasonal White pentas was readily foraged upon continued spread of L. bicolor. activity of L. bicolor is similar to that by L. bicolor, and numbers of wasps Field plots containing white-fl owered reported from the Florida panhandle were comparable to Spermacoce. Among pentas have been established on four (Gadsden Co.). Wasps were observed pentas, white-fl owered pentas was sig- holes at Grand National Golf Club, on fl owers for about 13 hours (0700 to nifi cantly different from either pink- Opelika, Ala. These plants will serve 1900 h CST) in August and 9 hours or red-fl owered pentas. White and as release points for L. bicolor on that (0900 to 1700 h CST) in October. yellow are common colors, attractive course. Wasps will be collected from Sunrise, and not temperature, more to day-active insects such as these golf course sites in Mobile and Baldwin likely triggers activity. Air temperatures wasps. However, there were several Counties in Alabama and released on in August when wasps became active taxa in the garden with yellow and the fl owers at dusk. were 81-82°F, whereas wasps were lighter-colored fl owers that went active when air temperatures were unvisited by L. bicolor. Volatiles emitted SUMMARY POINTS 65°F in October. from the plants likely determine wasp • Larra bicolor have a four- to fi ve- In August, a maximum of 14 females visitation to these fl owers. month activity period in the northern and 31 males were observed at once on Attempts to trap or passively Gulf region to parasitize mole crickets. fl owers, compared to 3 and 25, respec- monitor this species previously have Wasps are active mostly during daylight tively, in October. Males were almost been unsuccessful. In fall 2008, an hours. Although the impact of insecti- always present on fl owers during the experiment was conducted using pan cides on L. bicolor have not been evalu- hourly observations. Females, however, traps of various colors as attractants. ated, turf managers wanting to con- were observed on fl owers for distinct Despite activity on adjacent fl owers, serve these biological controls should periods (3 to 9 hours) each day. Females wasps were not recorded in the traps. consider making insecticide applica- spend their time mainly hunting for In 2009, trapping studies were con- tions later in the day as numbers of hosts, only returning to fl owers for ducted using phenylacetaldehyde foraging wasps wane. nectar as needed. (PAA) and fl oral extracts of Spermacoce • In two trials, pentas, particularly In 2007 and 2008 we established a and Pentas as lures. The objective was white pentas, recruited equivalent num- replicated garden of 16 plant taxa of to verify the results of a previous study bers of L. bicolor as fl owering Spermacoce fl owering plants in 0.5m × 0.5m plots, that demonstrated that L. bicolor could verticillata. Wasps don’t appear to be arranged in a randomized complete be trapped using PAA and fl oral vola- visually attracted to fl owers, and MARCH-APRIL 2010 13 C O N N E C T I N G T H E D O T S An interview with DR. DAVID HELD regarding his research on Larra but it was nearly impossible to keep track of a dark-colored wasp bicolor, a parasitic wasp of mole crickets. at twilight. Wasps that don’t leave before dusk won’t leave the plant until morning, despite warm air temperatures. Q: Can you provide a brief history of Larra bicolor? A: In the early 1980s, wasps were collected from Puerto Rico and Q: Do both wasp sexes have similar foraging activity? What time of introduced to fi ve sites in Florida, but populations became estab- day are female wasps most likely to parasitize mole crickets? How well lished only near Ft. Lauderdale. In the late 1980s, wasps and is the parasitizing activity of L. bicolor matched to mole cricket activity parasitized mole crickets were collected from Bolivia and released in the United States on a seasonal basis? to three sites around Gainesville, Fla. This release also was A: Males and females have different fl ower feeding habits. thought to be a failure until Larra bicolor was observed attacking a Males, which don’t attack mole crickets, are found on fl owers mole cricket and feeding on Spermacoce verticillata on the almost all day long. Females come and go on fl owers. Neither sex University of Florida – Gainesville campus in 1993. is active before sunrise, and activity, regardless of the time of year, continues until near dusk. Females hunt in the morning, which is Q: Given its current expanded range since introduction, do you think likely tied to the fresh activity of the mole crickets, then hunting L. bicolor will eventually spread to all mole cricket areas in the United decreases. In the afternoon, females make more frequent returns States? to fl owers to feed on nectar or possibly rest. Activity of Larra A: I suspect the existing populations of Larra bicolor in North bicolor begins in late May or early June and continues through fall. America can be sustained in the coastal areas where mole crickets In the spring, mole crickets complete their development and large are problematic. The range of mole crickets will be larger than that nymphs and adults are available for parasitism. While the young of the wasp, but most areas where mole crickets are problems nymphs are active (July through mid-August), populations of (coastal areas) are likely to benefi t from the incidental and wasps decline slightly. By fall, there are large nymphs and Larra intentional movement of Larra bicolor. bicolor will attack them until October or later in some years. Q: Are wasps easily disturbed or could they become a nuisance for Q: Based on your work, are you recommending that southern golf golfers? courses grow pentas or other members of the Rubiaceae plant family to A: The females on the turf are particularly skittish when people attract L. bicolor? are around. However, most golfers won’t ever notice or contact A: If you know that Larra bicolor are present on the golf course, this wasp, even on sites where the wasps are abundant. planting fl owers is one way to supplement their diet and increase their longevity. I am hesitant to recommend other members of Q: Are there signifi cant differences among nectar sources with regard the Rubiaceae family because some, like Spermacoce verticillata, can to carbohydrate concentrations or nutritive value for foraging wasps? If reseed and become weedy. Ornamental annuals such as pentas so, how do pentas rank against the other plants included in your are a non-weedy alternative. Pentas also are used extensively in experiments? butterfl y gardens, and additional nectar sources adjacent to areas A: Yes, there can be variation in composition, availability, and that are perennially infested with mole crickets may bolster amount of nectar among various fl owers. Larra bicolor has specifi c L. bicolor populations. tastes in fl owers, preferring pentas and a plant called Spermacoce verticillata, or false shrubby buttonweed. The basis for this Q: What information is necessary to demonstrate that this strategy of preference is not yet known. Based on lab studies, wasp survival is using parasitizing wasps for mole cricket control is successful? Are you comparable on both species, but I don’t have data on specifi c convinced that this approach will prove successful? nectar composition of these fl owers. A: The missing piece of the puzzle is a successful fi eld test. Q: Can environmental factors such as soil and/or air temperatures be It is diffi cult to manipulate parasitism under natural conditions. used to predict wasp activity? However, based on my observations, Larra bicolor are territorial. Once you have wasps recruited to fl owers, they will come back A: We monitored air and soil temperatures during our experi- throughout the season and year after year unless the fl owers are ments and found that both of these variables were signifi cant removed or they are inadvertently killed.