\title{Biological Control of Puncture Vine with Imported Weevils}
\author{C. B. Huffaker \and D. W. Ricker \and C. E. Kennett}

Puncture vine, \textit{Tribulus terrestris}, was sufficiently abundant to attract attention as a pest in California around 1912--1915. The weed became so troublesome by 1925 that a basic plan for its control was developed by the California State Department of Agriculture and was adopted in most sections of the state. Expenditures by county governments alone, from 1927 to 1930 inclusive, totalled more than half a million dollars.

Substantial sums were still being spent to control this pest in the early 1950's by county weed control officials. The Association of County Agricultural Commissioners passed a resolution in 1956 requesting research on the possibilities of biological control. Prior to this, Dr. G. W. Angalet of the U. S. Department of Agriculture had been in India exploring for parasites of the oriental fruit fly. He noted the rarity of puncture vine in India and made extensive observations on two species of weevils he found attacking it. His tests and additional research conducted at Albany (by Huffaker) and later in France and Italy by Drs. Angalet and Lloyd Andres established the safety in introduction of both the stem boring weevil, \textit{Microlarinus lypriformis}, and the seed weevil, \textit{Microlarinus lareyniei}. These insects were shown to be entirely incapable of breeding on any plants other than puncture vine and possibly its very close relative, \textit{Kallstroemia} sp. Officials of both the federal and state governments then approved introduction of these insects.

It is much too early in the research program to even guess at how well the weevils imported last summer will work to eventually control puncture vine in California. But limited samples of seed pods and stems taken to field have already indicated 30 to 50 per cent infestation on some plants at release sites in counties from San Joaquin to Riverside. Next year, if the weevils get off to a good start, it is expected that all interested counties can be supplied with initial stocks for wider distribution of the stem boring weevil, \textit{Microlarinus lypriformis}, or the seed weevil, \textit{Microlarinus lareyniei}. Both insects breed only on puncture vine.

\subsection{Importation}
Importation and establishment of these biological control agents were initiated during the summer of 1961. Because of the need to be certain that only these species would be introduced, rather small-scale importations were planned. Since positive identification of each specimen had to be made while it was alive, it was not practical to handle large numbers of the imported weevils. From 800 to 1,000 insects of each species were to be imported, with approximately half of these to be released in California.

The first shipment from Dr. Andres was received on July 11, 1961 and colonizations from this and subsequent shipments were made in July and August, 1961. Seed weevil distributions of about 100 adult insects were made in San Joaquin County near Manteca, Kern County near Bakersfield, and Los Angeles County near Castaic. Two larger colonies of 200 adults each were released near Hughson in Stanislaus County and at Riverside. Stem weevil colonies of 100 adults each were released near Clovis in Fresno County, near Woodville in Tulare County, near Moreno in Riverside County, and at Madera.

Weevils were in egg deposition when the releases were made. In general, half of each colony was released in a cage over a field stand of puncture vine and the other half released outside the cage. After about one month, at which time progeny were beginning to emerge, the cages were removed. While these cages were intended to provide protection to the beetles, they actually proved to be an impediment.

\subsection{Progress varied}
Progress of the weevil colonies has varied greatly. Multiplication from the small numbers of seed weevils released at the Hughson plot in Stanislaus County has been phenomenal. Most of the multiplication came from the first release of 100 weevils on July 13, because a later release of 100 was too late to accomplish marked reproduction. At this site adult weevils could readily be found in early September beneath the large puncture vine plants at distances of 50 to 60 yards from the exact release spot. A conservative guess is that from 25,000 to 100,000 weevils were produced during the two-month period involved, predominantly from the 50 females of the original release. While minimal developmental time was only 22 to 23 days during July and August, since the egg-laying females are long-lived, two full generations were not completed during the time involved, even though some of the population may be of the F3 generation.

\subsection{Seed weevils}
The Riverside colony of the seed weevil also progressed almost as well. But due to a much more limited supply of host plants, the total multiplication appears to have been less than at the Hughson location. However, reproduction continued approximately one generation longer at this more southern location and higher rates of pod infestation were encountered. Eight hundred weevils emerged from one large plant after it was dug up and caged. Progress of this species was also promising at the Los Angeles County site but